Fred Bove, MD, PhD

Because of the changes in medical practice, new medications, a better understanding of the spectrum of asthma, and the growing awareness that many divers have some form of asthma and are diving safely, the Undersea and Hyperbaric Medical Society held a workshop on diving with asthma in June of 1995. The proceedings and conclusions of the workshop have now been published, and they provide important new guidelines for managing the individual with asthma who wants to dive.

Several surveys have shown that 4-7% of active divers in the United States have asthma. Data collected by the Divers Alert Network has also shown that diving accidents are not markedly increased in individuals with asthma. The DAN data on asthma suggested that active asthmatics (someone who is short of breath and actively wheezing) may have a small increase in diving accident risk (either decompression sickness-DCS or arterial gas embolism-AGE), but the increase is small and does not reach statistical significance. The only conclusion which can be drawn from the information is that there may be a slight increase in risk for a diver who has active asthma.

Both the DAN data and the data from a British sport diving survey failed to show a risk for pulmonary barotrauma in asthmatics. Indeed when reviewing the few cases of asthmatics who died while diving, it was apparent that failure to swim to safety on the surface was a major problem with these individuals.

The new guidelines take into account the need to have normal exercise capacity when diving. The consensus was that lung function must be normal before an asthmatic can undertake diving. If treatment results in normal lung function, the risk of a problem is eliminated, and the individual can dive. The workshop provides information on the measurements needed to determine that lung function is normal.

Obviously the asthmatic who is acutely ill, with difficulty breathing, wheezing, cough, or fever should not dive. The acute illness must be resolved and breathing function restored to normal before considering diving. Full recovery however would allow return to diving, again based on evidence that the breathing test is normal. Individuals who have permanent lung damage from long standing asthma, with chronic emphysema should not dive. It is also important to avoid smoking tobacco if you are asthmatic, as the smoke will sometimes aggravate the asthma.

A copy of the workshop on Asthma and diving entitled "Are Asthmatics Fit to Dive?" can be obtained from the Undersea and Hyperbaric Medical Society, 10531 Metropolitan Ave., Kensington, Md. 20895. The cost is $20.00 plus $2.50 additional for postage and handling.


Davies MJ, Fisher LH, Chegini S, Craig TJ. Asthma and the diver. Clin Rev Allergy Immunol. 2005;29:131-138

Neuman, T.S., Bove, A.A., O'Connor, R.D., Kelsen, S.G.:  Asthma and Diving.  Ann. Allergy. 1994;73: 344-350 Reviewed 7/15/07


Fred Bove, MD, PhD

Commercial divers who experience long exposures to increased pressure have an increased risk of getting bone injuries (osteonecrosis), and damage to a joint to the point of disability. Pressurized tunnel and caisson workers, and divers exposed to saturation dives of long duration were thought to be at risk, and air divers who frequently missed decompression from long dives were found to have an increased risk of osteonecrosis. The data were compelling enough that a specific name: dysbaric osteonecrosis (DON), was given to bone disease which arose from diving or hyperbaric exposures.

The common pattern found in divers who get DON is a history of long but relatively shallow dives. Exposures to depths of 60-100 feet for several hours, with dives of this type being done for many days in a row, seems to be the typical exposure which leads to DON. DON has been found in the shafts of long bones, and near the joints. The joint injury causes problems for divers, even though injury to shaft and joint can be found by x-ray. There is some concern that technical divers who do repeated deep dives may be at risk for DON.

Reviewed 4/11/10


Fred Bove, MD, PhD

Every year, hundreds of people die from Carbon Monoxide poisoning due to exposure to fires, and faulty heating systems. I received a letter from a diver who asked about headaches and nausea during a dive. The circumstances before the dive were typical of events which can result in carbon monoxide poisoning. Several divers were in the cabin of a dive boat closed because of cold weather, when the captain lit an alcohol stove to heat some coffee. The divers noted alcohol fumes, but didn't think much of them at the time. Following their first dive, they all had headaches, and nausea which prevented any more diving that day. The diver's story was typical for CO poisoning, and illustrates the insidiousness of poisoning by CO. The incomplete combustion from a flame burning in a closed space produces carbon monoxide, an odorless, colorless gas which forms when there is incomplete combustion of fuels. Everything we burn for fuel (wood, coal, oil, gas, alcohol, etc.) contains carbon, and the process of burning combines the carbon with oxygen to form one of two combinations. The complete combustion of carbon fuels produces carbon dioxide (C02) and releases energy. The combination of oxygen with carbon is one of the fundamental energy producing chemical reactions known in biology. Animals use this reaction to produce metabolic energy, and any time we burn fuel, this reaction occurs to produce energy. Incidentally, the carbon dioxide must be recycled. If it wasn't removed from the air, we would by now, have an atmosphere laden with carbon dioxide. Excess carbon dioxide in the air traps heat and causes the temperature of the earth to rise. Many scientists are concerned that the earth's temperature is slowly rising because of the excess CO2 which is accumulating from the combustion of carbon based fuels. We are saved by the trees and plants which use the energy of the sun to convert carbon dioxide back to carbon and oxygen. The carbon becomes part of the plant structure, and the oxygen is released into the atmosphere.

When there is insufficient oxygen to completely burn the carbon in fuel, then a different product is formed-Carbon Monoxide (CO). Note that only one oxygen atom is combined with one carbon atom. This small difference from C02 converts the gas from a relatively harmless gas (carbon dioxide is not entirely harmless, but it is much less toxic than carbon monoxide) to a deadly, silent killer. The body produces minuscule amounts of CO from its own metabolic processes, but this amount has no measurable effects on body functions.

In the same way that we burn carbon based fuels to produce heat, the body burns carbon based fuels (carbohydrates and fats) to produce energy and CO2. The process is the basis for all energy production in the body. Oxygen enters the body through the lungs, and is carried by hemoglobin in the red corpuscles to the cells of the body. In the cells are small particles called mitochondria which are the energy factories of the body. The mitochondria go through a complex process to convert fuels and oxygen into energy which is then distributed within the cells for their metabolic needs. Carbon monoxide has devastating effects on two components of the energy pathway. The first effect is to block the hemoglobin in the red corpuscles from carrying oxygen. This lowers the oxygen capacity of the blood and reduces the delivery of oxygen to the cells. The second effect is to block several of the critical enzymes which convert oxygen and fuel to energy in the mitochondria. Both effects combine to cause a severe lack of energy to individual cells, and the cells often die. The cells and tissues essentially "suffocate" from lack of oxygen. Brain and heart cells are two important cells which are damaged by CO, and the poisoning may be fatal or leave serious and permanent injury. The heart cannot function very long without oxygen, and in severe CO poisoning, death may be due to cardiac arrest. Before the heart stops, the brain becomes oxygen starved, and unconsciousness develops. In severe CO poisoning (for example in a house fire), the victim is unlikely to survive after unconsciousness occurs unless rescue efforts are successful.

Unlike carbon dioxide, which is the waste product of energy production in the cells of the body, and is handled by normal body processes, carbon monoxide adheres tightly to the hemoglobin in the blood. When the blood vessels of the brain sense the lack of oxygen, they dilate to allow more blood flow to the brain. This reaction causes the headache known to occur with early CO poisoning. It is likely that the nausea comes from abnormal sensations originating from areas of the brain that are sensing the lack of oxygen. As divers, we should be concerned with CO contamination of our breathing air. Drawing exhaust fumes from an internal combustion engine into an air compressor is a classic example of how diving air can become contaminated. After several bad experiences early in sport diving, the compressor problem is nearly gone. CO present in compressed breathing air acts very quickly because of the increased partial pressure. Divers breathing contaminated air at depth will rapidly become unconsciousness when the CO content exceeds 3000 parts per million. Although CO levels in work environments should not exceed 20 parts per million, levels of CO in breathing air should not exceed 10 parts per million. In some cases of CO poisoning while at depth, the high partial pressure of oxygen prevents symptoms from occurring until reaching the surface. Occasionally, a diver using a hookah air supply develops CO poisoning when exhaust fumes from the engine which powers the air compressor are drawn into the compressor. CO poisoning can come from other sources. Faulty stoves, heaters, or furnaces can cause CO poisoning; burning a gas or charcoal stove or a catalytic heater in a closed space will consume the oxygen to the point that incomplete combustion will produce carbon monoxide. Car exhaust is heavily laden with carbon monoxide, and situations which have cause prolonged exposure to engine exhaust have also caused people to die. Cigarette smoke contains about 400 parts per million of CO, and is a common source of CO for both the smoker, and the non-smokers who breathe the cigarette smoke. If you are exposed to CO, the chances are you won't know; many unsuspecting victims died in their sleep because they could not smell, taste or see the gas.

Treatment of CO poisoning first requires removal from the source. You should get the victim to fresh air as soon as possible. Use of 100% oxygen on the surface accelerates the rate of elimination of CO from the body. We now use hyperbaric oxygen administered in a pressure chamber to rapidly remove the CO from the body and restore function to tissues and organs. Permanent brain injury is a real concern after CO exposure. Evidence of brain injury can be delayed for days to weeks after the exposure. Repeated hyperbaric oxygen treatments may be beneficial in treating the delayed brain injury.

To avoiding CO poisoning, be sure of your air supply, be sure stoves or furnaces are properly vented, do not use stoves, heaters or fires in closed spaces where you share the air supply with the fire, avoid prolonged exposure to auto exhaust, and stay out of burning buildings. You might also give up smoking cigarettes; the most common cause of elevated blood CO is smoking cigarettes. The exposure is not severe, and the CO does not usually reach levels which impair normal body functions.

Knowledge about carbon monoxide sources, effects, and avoidance is a necessary part of diving training. Learn as much as you can about carbon monoxide so that you can avoid this deadly gas.

Reviewed 4/11/10


Fred Bove, MD, PhD

At the present time, the most likely reason for a diver over the age of 40 to die suddenly while diving is a heart attack with an accompanying fatal heart rhythm. The same cause for sudden death is found in almost all other sports related sudden death in this age group. In that sense, diving is not unique. If a person with undetected heart disease jogs, plays tennis, swims, dives or engages in any other strenuous sport, he or she is at risk for sudden cardiac death. The common factor is exertion which causes the heart to work beyond its capacity to obtain oxygen. The lack of oxygen (ischemia) causes the heart to malfunction, and a fatal heart attack may occur.

If you smoke cigarettes, are overweight, with elevated blood cholesterol, have high blood pressure, don't exercise, or use cocaine, you are likely to have a heart attack while still in your 20's. Accumulating all of the risks can rapidly accelerate atherosclerosis, and age your arteries rapidly. You can greatly reduce your risk of artery damage by removing the risk factors. The most common risk is cigarette smoking. The other important risk factor is your blood lipids. Total blood cholesterol below 200 units, and LDL-cholesterol below 100 are considered to be safe. If your cholesterol is above 200, or your LDL is above 100, your risk for a heart attack is increased considerably. High blood pressure is also a risk that is avoidable because of the excellent medications we have for controlling blood pressure. Avoiding use of cocaine is a simple means of protecting your arteries from the damage that it can induce, and exercising regularly will add a positive factor to the health of your arteries.

A stress test is the best way to be sure diving will be safe from the standpoint of heart disease. By producing work loads similar to or greater that the workloads encountered in diving, we can determine if the heart can handle the usual exercise requirements of diving. If you are physically active, have positive risk factors, and are over the age of 40, you should have a periodic stress test to be sure that exercise is safe. A normal exercise test to your maximum capacity, although not a lifetime guarantee against coronary disease, does indicate that you can withstand the exercise and other stresses involved with diving. An abnormal test suggests that you could be at risk for a heart problem while diving, and further evaluation should be done before you dive.

Prevention is still your most important choice for long term health, and diving. You should have your blood lipids (cholesterol, triglycerides, HDL, LDL) measured. Cholesterol should be less than 200, triglycerides should be less than 120, LDL should be less than 100, and HDL, the good cholesterol, should be above 40 in men, and above 50 in women. If your blood lipids are not in these ranges, you should lose weight, reduce your saturated fat intake, reduce your alcohol intake, and exercise to improve these measurements. If all else fails, there are several medications that will reduce your blood lipids to acceptable levels. If you smoke cigarettes, stop. The most serious risk factor is cigarette smoking. If you do nothing else, getting rid of cigarettes will significantly reduce your heart attack risk. Exercise moderately. There is compelling evidence that exercise contributes to lowered risk for heart attack. Be sure your blood pressure is normal. If pressure is elevated, you should be treated.

Most people with coronary heart disease should not dive. Usually, there are blocked arteries to the heart which limit oxygen delivery to the heart muscle during exercise. This will increase risk for a heart attack or sudden death while diving. Exceptions to this rule can be made in some cases. If you have had extensive heart muscle damage from a heart attack, you should not dive because the heart may not be able to meet the pumping requirements of increased exercise while diving.

In summary, if you have an increased risk for coronary disease, if you are over 40 years old and have not exercised regularly, or if you have been treated for heart disease, you should be evaluated for exercise tolerance before diving. If your heart is limited by blocked arteries or damaged muscle, diving is not the time to discover the problem. A careful medical evaluation before diving will prevent a serious complication from heart disease.

Reviewed 4/11/10




Fred Bove, MD, PhD

Although diving for diabetics using insulin has been considered dangerous, recent analysis of diabetic divers indicates that some diabetics can dive safely. Two major issues raise concern in diabetic divers. The first is that hypoglycemia (low blood sugar) might result in loss of consciousness or poor judgment in the water. As a result the diabetic diver must have good control of his or her blood sugar, a good understanding of the relationship between exercise and blood sugar levels, and be able to recognize and treat the early signs of low blood sugar. The second concern is the increased incidence of heart disease in people who have had diabetes for many years and the risks they face of heart attacks while diving.

There are many diabetics who are not dependent on Insulin. These individuals may be able to control their diabetes by diet alone, or with use of an oral medication which helps to control blood sugar. In the case of diet or oral medication control of diabetes, there is minimal risk of hypoglycemia, and the diver will not be at risk for a serious underwater accident. Diabetics who are dependent on Insulin also represent a spectrum of illness, one end of which will not interfere with diving or increase risk enough to exclude diving. It is clear that diabetics who have lost the ability to develop a normal defense reaction against hypoglycemia are at high risk for hypoglycemia when diving. Loss of this safety system usually occurs in long standing diabetes. The portable machines to test blood sugar from a single drop of blood, and newer Insulin preparations make management of diabetes simpler for the active young person interested in sports of any kind. The new methods for testing and regulating blood sugar can be used at the dive site to be certain that risk of hypoglycemia is eliminated. A proper physical examination, and exercise testing when indicated can reduce the risk for a heart problem while diving.

Advances in medicine have allowed a diabetic to avoid risk when diving. These new techniques coupled with a careful medical examination will provide the basis for some insulin dependent diabetics to dive.

Reviewed 4/11/10


Fred Bove, MD, PhD

At 45 feet depth, after swimming around a large rock which is part of a formation called the Indians in the BVI, I looked back for my buddy Jim and found no one there. At the same time, Andy, our dive guide flashed his white plastic writing board which said in clear letters, "return to the boat, a diver is missing." These events took place in less than a minute, and I reached the boat in about two more minutes, a bit ahead of the other 6 divers in our group. Andy was already returning along our path to look for Jim, and I left my tank and weights, put on my snorkel, and started a surface swim around the rock in the other direction. We met halfway with no sign of Jim, and both agreed that we did not like this situation. Five minutes had already gone by, and my thought was that a lost diver would be having trouble after 5 minutes, we better keep looking. Just then, our other guide, Randy signaled from the boat with a large OK sign, we both sighed a large sigh of relief, and swam the 200 yards back to the boat to find Jim revelling in the great video he had just captured while wandering away from the group. (Beware, even the best can slip: my dive buddy Jim has been a sport diver for over 40 years!).

As I was swimming back with Andy, I began to realize the responsibility, and the continuous pressure that the dive guides experience as they lead a group of divers on what to us appears to be a routine and fairly easy dive. Later on that day, after we were on shore, the boats were secured, and all the tanks had been transferred for the next day's fill, I had the opportunity to talk about a day's work with our dive guides. Although the job appears exciting, with diving every day, experiencing daily what others experience for only a few weeks a year, the reality is that the job is difficult, carries considerable responsibility, and requires a gamut of skills from caring for an injured diver to reciting the names of every living creature on the reefs to cleaning boats and filling tanks. Obviously this is not all the glamour it first appears to be, and adding a lost diver to a day's work can ruin the day. The guide must be able to assess each divers capability, sense when a diver is getting into trouble, prevent problems, catch them early so that catastrophe is avoided, and initiate rescue proceedings when a diver is in trouble. At the same time, divers want the freedom to go where they wish, and resist being "herded" by the guide. A good guide follows a fine line between control for safety, and freedom for enjoyment by the divers under his or her responsibility.

The continuous exposure of dive guides to compressed air goes well beyond the exposures that sport divers get, because of the multiple dives over 5 or 6 days a week. This work puts the exposure to compressed air in a class with other commercial divers, and raises the question of short and long term consequences of these diving exposures. Resort guides may do 4-6 dives a day during their working week of 5 days, and then dive again for recreation on their days off from work. There have been concerns for long term effects of exposure to compressed air and other problems which might occur with frequent exposure to diving. The Japanese have the most experience with prolonged exposures, though their experience is with surface supplied diving at deeper depths. Many of the Japanese divers who worked at the time when tables were not used, developed injury to bones (dysbaric osteonecrosis). When the bone injury involves a joint, loss of function of the joint follows, and the diver becomes disabled. To date dysbaric osteonecrosis has not been a problem in sport diving, but the frequent exposure of dive guides puts them in a different category than the usual sport diver. Reduction of risk for bone necrosis probably is best done by reducing overall nitrogen loading, but this relationship has not been well established. Experience to date suggests that divers with more exposure to compressed air are more likely to develop a bone problem, but it is not necessary to experience an episode of decompression sickness. Nitrogen exposure is best controlled by reducing both pressure and dive time, but job requirements are not likely to allow these to be minimized. Nevertheless, a dive guide probably accrues less risk by remaining shallow during dives. This can be done by staying a bit above the average depth of the escorted group. Should dive guides get bone x-rays? This is an unanswerable question at present. In commercial diving, bone x-rays are required in some types of diving. Dive guides could be considered commercial divers, but to date there are no requirements for guides to obtain x-rays. Even if a dive guide elected to obtain x-rays, these studies are expensive, and should be done by a radiologist who is familiar with the findings of osteonecrosis.

I have also encountered guides who developed skin sensitivity to organisms in the sea, and developed a chronic dermatitis from allergy to the organisms. These skin injuries can be severe enough to stop a guide from working for the time needed to allow the skin to heal. Chronic skin allergies will cause severe skin damage if left untreated. The organisms in the sea which cause these skin problems (sea lice for example) are not well defined. In one experience, the problem was caused by the larvae of a form of sea nettle. Treatment of these skin problems usually takes the form of skin creams containing cortisone. However if chronic allergy develops, the dive guide may need to give up the prolonged exposures to diving. Fortunately, exposure to most other nematocyst containing animals is usually left to the sport divers who are underdressed for the dive, or who have buoyancy problems, and contact such things as fire coral.

Medical requirements for dive guides should follow standards applied to commercial or scientific divers. Chronic medical disorders which might be acceptable for sport diving may not be safe for a dive guide. Health and safety issues should be evaluated frequently by individuals who work as guides. Laws and regulations vary among different countries from very stringent to nonexistent. Attention to general health, fitness total diving exposure each week, contact with marine organisms which cause skin injury and training in rescue techniques will contribute to a successful career as a dive guide that is free from medical complications of the job.

Reviewed 4/11/10


Fred Bove, MD, PhD

One of the wonders of our time is the large number of medicines that have allowed people with chronic diseases to function normally and lead full and productive lives. Many of these medications have minimized the effects of disorders which in the past would have been disabling or even fatal. The use of medications by divers raises concerns for the interactions with medicines and the diving environment. Concerns for changes in drug action under pressure, effects of exercise, heat, cold, nitrogen narcosis on drugs all should be understood when a diver is taking medications. In this article, I will review some of the commonly used drugs, and the interaction of these medications with the diving environment.

Categories of Medications

Commonly used medications are listed in the table at the end of this article, based on the class of drug and their use. The right column has examples of drugs in each category by their brand name. Aspirin and Penicillin are not brand names but are familiar to most people by those names. The drugs mentioned are examples of each class of medication. There are many other drugs in each category, but all have similar effects.


The common pain killers are used frequently for minor joint and muscle pains, for headaches, and pain from injuries. They also lower temperature, and are used to reduce a fever. There are no interactions of note for these drugs with the diving environment. Aspirin and Advil can cause stomach upset, and even bleeding from the stomach. Excess use of aspirin or Advil for example can cause bleeding which would not be welcome on a diving vacation. These drugs are helpful for treating minor pains, and one of them should be carried in your luggage for treating an occasional headache, and for reducing a fever if you develop a cold. Aspirin and the Advil class of medications can cause excess bleeding when cut or injured. This is due to their effects on the blood platelets.


Many people take mild tranquilizers or anti anxiety medications to relieve the stresses of a busy life. They are not routinely recommended for this use, but many people obtain relief from stress with these drugs. The all cause some level of sedation, and physicians usually recommend against driving a car while using these drugs. The same effect can cause lack of judgment, and blunted reflexes when diving. There is also concern for an additive effects with nitrogen narcosis. These drugs should be avoided when diving. Hopefully, a diving trip will provide the relief from stress that we all seek, and drugs will not be needed. Hoewever, to date there are no reports of problems in divers who use mild tranquilizers.

Decongestants and Antihistamines

Probably the most common drug that divers use is some form of decongestant. Ear equalization is the most common problem we all have when diving. If allergies or a cold have been present, the upper airways, the Eustachian tube and sinus openings may be swollen. A decongestant, cautiously used, can make a dive trip successful by preventing ear or sinus squeeze. These medications often contain several drugs which have differing actions on the membranes of the nose and throat. They usually contain an antihistamine, and a drug from the adrenaline family. Both types of drug shrink the swollen membranes of the nose and throat, and allow better ear and sinus clearing while diving. The antihistamines can cause sedation, and patients are usually advised to avoid driving a car while taking these drugs, because of the risk of falling asleep at the wheel, or losing proper judgment and reflexes. Similar concerns are present when diving. Sedation can blunt judgment, and mistakes which compromise safety are more likely. As with the tranquilizers, there may be an additive effect with nitrogen, and narcosis may be more severe.

The adrenaline family of drugs may cause an increase in heart rate, and elevated blood pressure, but these effects are usually mild and produce no problem with diving.

Antacids and H2 blockers

The stresses encountered in a busy life also affect the stomach. Many people have burning or other discomfort which is due to excess acid release in the Stomach, often stimulated by stress. Antacid medications such as Maalox® may be used in liquid or tablet forms, and will provide relief for the occasional stomach upset that accompanies the stress of travel, jet lag, or eating foods that irritate the stomach. These medications usually have no associated problems, however excess use may sometimes cause diarrhea. There is no problem with these drugs and diving.

The medications which are referred to as the H2 blockers, reduce the acid secretion by the stomach, by blocking one of the actions of Histamine which involves regulation of stomach acid. These are also classed as antihistamines, but they do not shrink membranes in the nose, rather, they act on another aspect of histamine action. These drug have revolutionized the way we treat ulcers of the stomach and intestine. They prevent excess acid release, and eliminate the irritation of the stomach lining caused by excess acid. Many people obtain relief from stomach problems with these drugs, and they are commonly used. They pose no problem with diving.

Motion Sickness Drugs

The antihistamine drugs which are used as decongestants also have effects in preventing motion sickness. Sedation, loss of judgment, and aggravation of nitrogen narcosis are possible with the antihistamine type of motion sickness medications. Dramamine is an example of this class of medication.

The patch used by divers to prevent motion sickness contains the drug scopolamine. This drug has excellent antimotion sickness action, and is not an antihistamine. It acts on the area of the brain which senses the motion stimulus, and prevents the stomach from responding to the confusion of motion signals that cause motion sickness. Scopolamine has several important side effects which can affect diving. The drug causes dilation of the pupil of the eye. If you touch the patch, then rub your eye, the pupil will dilate, and vision will become blurred for several hours. This problem can be avoided by careful attention to your hands and fingers. The drug also can produce severe disorientation, and when provided in high doses, may result in a diver with disorientation and bizarre behavior. This effect has been noted when the patch is placed on children. The dose in the patch is set for an average size adult. Use of the patch in a small person, or a child, may cause a problem. There is no other problem with the patch and diving. If you are planning to use the Transderm Scop® patch, try wearing the patch at home for a few days to determine your reaction to the drug. Most people feel no adverse effects of the patch except for a dry mouth, which is a bit annoying, but nothing else.

Drugs for Hypertension

High blood pressure (hypertension) is a common disorder which affects over 15 million people in the United States. Chronic high blood pressure is associated with injury to the heart and kidneys, and a high incidence of stroke. The reduction of stroke, kidney and heart disease from use of antihypertensives is another success story for medications. Many people take antihypertensive medications to protect themselves from the serious illnesses which result from uncontrolled high blood pressure. Many divers take these medications, and a common question is whether it is safe to dive while under treatment for hypertension. There are many classes of drugs used for treatment. The most common of these drugs will be discussed.

Calcium blockers

There are a variety of drugs in this class. They all act by relaxing the blood vessel walls, and reducing the resistance to blood flow, thereby lowering blood pressure. These medications have few serious side effects, and can be taken safely by many people. In moderate doses, they may cause excessively low blood pressure, particularly when changing position to the vertical from sitting or lying down. The relaxed blood vessels cannot respond quickly enough to the postural change, and blood pressure will fall precipitously. This effect is found with larger doses of the medication, usual doses for moderate blood pressure elevation will not be a problem. The postural blood pressure effect can be a problem with diving. The sudden drop of blood pressure can cause dizzyness or even a black-out. This would not be appreciated on a dive boat, where one episode of a diver passing out on the boat can ruin the day for everyone. If you are taking a calcium blocker for hypertension, you should be aware of this postural effect. If you feel dizzy when getting up quickly, tell your physician, and have the dose adjusted. You should not dive if this reaction occurs. A common question I am asked is why continue taking medication for hypertension if the blood pressure reaches normal levels. Many times, the normal blood pressure is the result of the medication, and when the drug is stopped, blood pressure rises again. After a year or more of therapy, it may be reasonable to test the blood pressure without medication. If it rises again, medicine is still needed. The calcium blockers have no other interactions with diving.

Beta Blockers

These drugs are also commonly used for treatment of hypertension. they act by blocking one of the actions of adrenaline (the beta effect). Beta blockade slows the heart rate, and reduces the strength of the heart muscle. These effects lower the blood pressure. The drugs also prevent the overexcitement that results from too much adrenaline. Musicians have used beta blockers to avoid the shakiness that accompanies high adrenaline levels. The beta blocker drugs reduce exercise capacity, but in a normal subject being treated for hypertension, this effect is not perceived. High performance athletes notice the effects of beta blockers because their maximum performance is limited. Moderate exercise performance is not limited. The exercise tolerance needed for diving is not affected by these drugs, and there is no direct interaction with diving. Beta blockers can sometimes cause excess constriction of blood vessels in the hands when exposed to cold. Some divers have complained of cold sensitivity of the hands when taking beta blockers. If you dive in warm water, this will not be a problem. Beta blockers also can aggravate asthma. A diver with a past history of asthma, who is now free of this disorder, may develop wheezing when on a beta blocker. Physicians should inquire about past asthma history before prescribing a beta blocker. Other side effects of beta blockers which are not a problem with diving are a slight dulling of mental function, and impotence in men. Patients taking these medications are usually instructed to watch for these side effects and inform their physician if they occur.

ACE inhibitors

These medications are relatively new, and have quickly found their place in treatment of hypertension and heart disease. They act by blocking an enzyme (Angiotensin Converting Enzyme) which produces a potent blood vessel constrictor. By lowering the amount of this constrictor in the blood stream, blood vessels are relaxed, and blood pressure falls. The ACE inhibitors have little effect on exercise capacity, and are excellent medicines for treating hypertension in individuals who are active and wish to exercise. They have no problems with diving. the most important side effect of these drugs is the development of a cough, and swelling of the airways. When a cough occurs after these drugs are started, we usually change to another type of blood pressure medication. ACE inhibitors are avoided in patients with kidney disease. A related family of medications, called ARB (angiotensin receptor blocker) have similar properties to the ACE inhibitors and are also safe to take when diving.


These drugs are used to eliminate water and excess salt (sodium) from the body. They act by allowing more water to pass through the kidneys to form urine. Reduced water and sodium will lower blood pressure, so these drugs are often part of the treatment for hypertension, and they are often used to prevent swelling due to water retention in the body. Divers will have little effect from the diuretics. In hot environments, where fluid can be lost from sweating, the diuretics can cause excess water loss. If you are exposed to heat and are sweating, the diuretic may not be needed. Diuretics will also cause loss of potassium, an important mineral in the body. Excess loss of potassium will cause muscle weakness, and can affect the heart. It is best to skip your diuretic on a diving day.


These medicines are used to prevent inflammation. They are part of the family of hormones that are released by the adrenal gland. They are necessary for the stable state of the heart and circulation, for proper fluid balance, mineral balance, and the ability of the body to withstand stress. The steroid preparations are often used on the skin for treatment of allergic rashes, they are useful for treatment of fire coral and sea nettle reactions, they will stop an asthma attack, and can be used to stop or prevent severe allergic reactions. Steroids have no direct effects on diving, although in some animal studies, they made oxygen toxicity more likely. Long term use of steroids is usually avoided because of the side effects of this treatment. Short term use (days to a few weeks) has little consequence. Steroid creams used for treatment of skin disorders have no effects on diving. People taking steroids for many months will develop diabetes, weak bones, obesity and other problems.


These drugs are used to prevent or maintain a normal rhythm of the heart. There are several different classes of drugs used to control abnormal heart rhythms. These include beta blockers and calcium blockers which have the same effects as when they are used for treatment of hypertension. Drugs such as Procan® and Mexitil® have no adverse effects in the diving environment. Procan may occasionally cause muscle and joint pains, and Mexitil in high doses can cause tremulousness, nervousness, and upset stomach. These effects can be avoided by lowering the dose of the drugs. These drugs should be properly adjusted to avoid adverse reactions before undertaking diving. Lanoxin is commonly used to prevent rapid heart beat (tachycardia). There are no effects of diving on Lanoxin. Cordarone® is a potent antiarrhythmic drug that is sometimes used to prevent atrial fibrillation, a heart rhythm which results in a rapid heart beat. The drug has several side effects which can affect diving. Patients taking Cordarone are sensitive to the sun. They will develop severe sunburn if exposed to sunlight without proper skin protection or sunscreen. Divers taking Cordarone must avoid excess exposure to sun, otherwise a severe sunburn will result. Night vision may be affected by this drug. Bright lights produce a halo effect which may inhibit proper vision. Other than the sunburn risk, there is no direct interaction with the diving environment.


There are many classes of antibiotics, each of which has a specific use for a particular organism. Commonly used antibiotics for divers would be taken by mouth, and would be used for common infections, such as ear and sinus infections, tonsillitis, sore throat, gastrointestinal infections, skin infections, bronchitis. Although antibiotics are often prescribed for colds and the flu, they have no effect on the viruses which cause these diseases. Antibiotics work against bacterial and fungal infections. Their use in colds and flu is usually to prevent a bacterial infection as a complication of the viral infection. Penicillin is still commonly used even though it is one of the first antibiotics to be discovered. There are no adverse effects of penicillin related to diving. Many people are allergic to Penicillin, and must avoid its use. Antibiotics of the Tetracycline family sensitize the skin to the sun. Their use will cause a severe sunburn when the skin is exposed. Because there are good alternatives to Tetracycline drugs, you should not use these drugs if you expect to be exposed to sunlight. Many antibiotics upset the stomach and cause diarrhea. If you bring antibiotics on a dive trip, be sure to know the effects of these drugs. Many times, a person will go for days with nausea, not realizing it is caused by the drug. Diarrhea caused by antibiotics taken on a dive trip can cause havoc with your dive schedule. Remember that the majority of colds and flu are caused by viruses that will not respond to antibiotics. Taking these medications for a cold will not shorten the illness, but may add a side effect which will make you feel worse.

Because of the many drugs that divers use to maintain their health, concern for the effects of diving on these drugs is appropriate. There are many drugs not mentioned in this short review, and you should consult the physician who prescribed the medication for questions about side effects, and interactions with diving. You should receive a briefing by your physician on the effects of any new drug. You should ask about the effects of the medications you are taking so that you can detect adverse effects early, and provide information so that the dose can be adjusted to fit your response. Most drugs used for treatment of mild chronic illness have no effect on diving.

Musculoskeletal pain  analgesic
 Anxiety  tranquilizer
 Congestion  decongestant
 Allergy  Antihistamine
 Gastric upset
H2 blocker
 Motion sickness  Antimotion Sickness



Calcium blocker
Beta Blocker
ACE inhibitor	
 Fluid retention  Diuretics
 Skin rashes  Steroids  Hydrocortisone


Heart problems



Reviewed 4/11/10


Fred Bove, MD, PhD

Dizzyness can describe a feeling of lightheadedness, or a sensation of spinning (vertigo). The feeling of lightheadedness is usually associated with conditions which lower the blood pressure. If blood pressure falls to low enough values, the blood flow to the brain is reduced and a feeling of dizzyness will occur. Breathing oxygen-poor gas mixtures or carbon monoxide, and not breathing at all can cause dizzyness. Vertigo is causes by abnormal stimulation of the balance mechanism located in the inner ear. Dizziness that occurs while diving can be dangerous. When dizzyness is caused by a lack of oxygen or blood flow to the brain, a diver may blackout or have brief periods of disorientation. Either of these consequences can result in an accident, and an accident happening underwater is likely to cause a fatality. There are many causes of dizziness, but in diving, a few need special consideration.

The hyperventilating diver may be unaware of his or her condition, but the profuse cloud of bubbles rising from the regulator is a telltale sign. Dizziness, shortness of breath, numbness in the fingers and toes, and spasms of the hands and feet can occur from hyperventilation. Severe hyperventilation can cause a blackout.

Preventing hyperventilation depends on awareness. Consciously lowering the rate and depth of breathing , even if you feel short of breath, usually solves the problem. The new diver with hyperventilation problems often can overcome them by diving with an experienced and confident partner who can provide advice during the first few dives.

The balance organs can be stimulated by several events encountered in diving. On ascent, when the middle ear is decompressing, pressures can be different in the two middle ears. This situation is called Alternobaric Vertigo. Both dizziness and vertigo, can occur when the vestibular, or balance organs on the two sides are stimulated unevenly. The sensation of vertigo occurs on ascent. It can be stopped by slowing your ascent and assuring that both ears are equalizing properly. Uneven cold stimulation to the ears will produce the same sensation of vertigo. If you are diving in cold water and lift one side of your hood, cold water will reach one ear while the other remains warm. The difference in temperature stimulates the balance mechanism unevenly and results in dizzyness or vertigo. Be prepared for a vertigo spell if you dive in cold water with a wet suit. A dry suit should not cause the problem. A viral infection can involve the balance mechanism. The infection (labrynthitis) causes severe vertigo, and vomiting as though you had motion sickness. The illness usually lasts a few days, but will prevent all diving.

Although rare, when no other cause is evident, we must consider the possibility that an abnormal cardiac rhythm is causing dizziness. If the heart beats too rapidly (tachycardia), its pumping function is diminished, blood pressure will fall, and dizziness will occur. A severe slowing of the heart beat (bradycardia) also produces dizziness. There are some people who develop very slow heart beats when immersed in water. This is a rare condition, and would cause a blackout at the beginning of a dive. Excessively high or low blood pressure can cause dizziness. People who take blood pressure medicine may experience dizziness from low blood pressure. Identifying the cause of dizziness requires a thorough evaluation. The most common cause of dizziness on ascent in a healthy diver is Alternobaric Vertigo. The effect is usually brief, and with more diving experience, methods of equalizing the middle ear on ascent can be developed to avoid the problem. Another cause of dizzyness during descent is round window rupture - barotrauma to the inner ear. You can find more on this problem in the topic list on the left under ear problems.

Reviewed 4/11/10


Fred Bove, M.D., PhD.

There are several parts of the ear, each of which has a unique set of diving related disorders. The external ear includes the ear itself, and the external canal leading to the ear drum. The ear drum separates the external from the middle and inner ear.


The ear structure can be injured by trauma. Feeding fish underwater sometimes invites a nip on the ear by a dissatisfied "customer." Occasionally, a fish bite becomes severe enough to require treatment.

Swimmer's Ear

External ear canal infections, sometimes called "swimmer's ear", occur when water accumulates in the external ear canal, and remains long enough to allow bacteria and fungus to grow. Prevention of external infections is best done by using Otic Domeboro solution. A few drops in each ear before and after water exposure are adequate. Excess wax in the ear canal can also cause water retention and lead to an infection.


The middle ear includes the chamber situated behind the ear drum, which contains the small bones of the ear that transmit sound to the hearing organ. Connected into the middle ear is the Eustachian tube from the throat which is necessary for pressure equalization, and the mastoid cells which are spaces in the bone of the skull. The middle ear is easily injured by barotrauma (squeeze), and is susceptible to infection. The diagram shows the structures of the ear.

Ear Squeeze

Ear squeeze with injury to the ear drum, is the most common diving related illness. To avoid ear squeeze, be sure there is no congestion in your nose or throat when you dive. Begin clearing your ears on the surface before you descend, and continue to clear every foot or two as you go down. Waiting for ear pain to occur before you try to equalize is a bad habit. Usually you cannot clear the blocked ear at this stage.

Besides causing direct injury to the ear drum, middle ear squeeze produces swelling of the lining of the middle ear and Eustachian tube. Often fluid will persist in the middle ear until the swelling has subsided and normal Eustachian tube function returns. When a squeeze occurs, there is some damage to the ear drum, and occasionally the eardrum will rupture. If the damage is severe, and ear problems persist for several days after diving, medical attention should be sought. Most middle ear squeeze can be successfully treated with medication, but you should not return to diving until the ear is completely clear.


The inner ear consists of the hearing(Auditory) and balance (Vestibular) organs, and their nerve connections to the brain. The inner ear is connected to the spinal fluid space, and when injured, can allow infection to spread into the brain. The inner ear is separated from the middle ear by the round and oval windows. Injuries to the middle ear include round window rupture, inner ear decompression sickness and vestibular decompression sickness. Scroll up to see a diagram of the ear.

Round window rupture

A more serious barotrauma injury related to diving is rupture of the round window (RWR). You can cause RWR by forcefully trying to equalize during descent. By doing a Valsalva maneuver to equalize, you raise the pressure in the inner ear above ambient pressure. If the Eustachian tube is blocked, the middle ear pressure will be below ambient, and the large pressure difference can blow out the round window. When the round window tears, fluid from the inner ear leaks into the middle ear. When fluid is lost, hearing is lost, Vertigo occurs, and hissing or buzzing is heard constantly. The tear in the RW can heal itself, but often surgery is needed to correct the problem.

Inner ear Decompression Sickness (DCS)

Rarely DCS can occur in the inner ear and cause permanent hearing loss or permanent abnormalities in balance. This injury is characterized by sudden total hearing loss in one ear following a dive. Inner ear DCS usually occurs in commercial divers after deep saturation diving. One case of suspected inner ear DCS was recounted in a sport diver, but considering the larger number of sport divers and the questionable diagnosis, there should be no concern for inner ear DCS in sport diving. If other symptoms, such as hearing loss, vertigo, dizziness, or loud roaring or ringing noises are present, you should seek prompt consultation with an ENT specialist.


You should learn the various ways to clear your ears. If you still have trouble after using the correct method of clearing, have an ear, nose and throat exam by a doctor who knows diving medicine. Protection of your ears during diving requires careful attention to the health of your nose and throat, and to your techniques of descent and ascent.

Reviewed 4/11/10


Fred Bove, MD, PhD

The most serious problem is caused by narrowing of the coronary arteries (CORONARY ARTERY DISEASE), caused by atherosclerosis. Atherosclerosis is a disease that is accelerated by cigarette smoking, high cholesterol, hypertension, diabetes, and lack of exercise; and progresses with age. The diver who is most prone to a heart problem therefore is a male over 40 years old who is a long term smoker, has hypertension, is overweight, has a high cholesterol, and does not exercise.

Coronary disease is the most common form of heart disease, however, other forms of heart disease may also cause problems with diving. Abnormalities of the heart valves, inherited abnormalities, disease of the heart muscle, and heart rhythm problems all raise questions about diving. Many of these disorders are already known and the patient has adjusted to the problem. Whatever the disorder of the heart, a thorough understanding of the impact of exercise and diving on the disorder must be established both by the patient and the physician, in order to make an informed decision about diving.


The increasing incidence of sudden death among divers has prompted a more vigorous effort to detect and treat heart problems before a serious event occurs. This approach also prevents heart muscle damage which eventually causes the heart to fail, and the person to become permanently disabled. Atherosclerosis accounts for about 75% of heart problems. The best protection from the consequences of atherosclerosis is to avoid the disease. Prevention begins with reducing risk factors for artery disease. These include cigarette smoking, high blood pressure, high cholesterol, lack of exercise and high stress levels. High blood pressure and high cholesterol can be modified by proper diet, but in some cases medication may also be needed to attain normal levels. Blood cholesterol should be below a level of about 200, and blood pressure should be normal at 120/80. Increases in normal levels occur with age.


A heart evaluation begins with a thorough physical examination and a careful medical history taken by your physician. Since risk is related to the factors mentioned above, individuals below the age of forty with no risk factors are unlikely to have coronary artery disease. A careful history is most important in being sure that a younger individual has no evidence of other heart problems. In the absence of symptoms and risk factors, and with no history of heart disease, there is little likelihood that a man or woman below the age of forty has a risk for a heart complication while diving. There remains a small population of young individuals who have undetected heart problems other than coronary disease. These individuals may have an abnormality of the heart muscle itself (cardiomyopathy). This disease can cause sudden death because of abnormal rhythms of the heart induced by exercise. Detection and prevention of this disease is difficult. Individuals suspected of the disorder should not dive. Screening is usually completed by use of an exercise stress test. This test puts the subject under an exercise stress that equals or exceeds the stress of diving, and allows careful monitoring of the Electrocardiogram and blood pressure to search for abnormalities during exercise. Abnormalities require further evaluation and treatment to be certain that diving is safe.


Diagnosis of a heart disorder does not mean that diving is prohibited. Each case must be evaluated individually based on the specific disorder, the general health of the diver, and the potential for complications while diving. Many heart disorders are benign, and will not complicate diving in any way. Others will cause excess risk for a complication and must be treated, or the diver should be advised to give up diving. Many can be treated to restore the ability to dive.

Reviewed 4/11/10








Fred Bove, MD, PhD

Lung collapse occurs when the airtight integrity of the lining of the chest cavity is broken. The chest cavity is filled with the lungs, heart and the major blood vessels of the circulation. The lungs remain in the expanded state because they are held against the inside of the chest by a vacuum created in a thin layer of fluid between the lining of the chest, and the lining of the lung. Because the pressure within the chest cavity is negative, damage to either of the linings will cause air to leak into the chest cavity outside of the lungs and break the vacuum which holds the lungs in an expanded state. This condition is called a Pneumothorax. The collapsed lung does not allow air to be exchanged and a feeling of shortness of breath follows. Fortunately, the chest is separated into two pleural spaces separated by the heart and blood vessels, so when damage to one side occurs, collapse of only one lung is likely. Complete collapse of both lungs is usually fatal if not rapidly corrected.

The lining of the lung can be damaged when the lung is subjected to overpressure from pulmonary barotrauma, and may be weakened by disease. People with emphysema have a weakened lung lining, and are prone to pneumothorax, and some patients who had pneumonia may be prone to pneumothorax. Penetrating injuries to the chest can also injure the lung lining.

Spontaneous pneumothorax

This is an inherited disease which leaves some individuals with weak areas of the pleural lining of the lung. These may take the form of small blisters or outpouchings of the lung called blebs, which are weaker than the normal lining of the lung, and which can occasionally break and cause air to leak from the lung to the chest cavity, resulting in a pneumothorax. The disorder is called spontaneous because the lung collapse can occur without provocation, with no warning that a pneumothorax is going to happen. Often the individual is exercising, straining while lifting, or performing some other physical task, but many times the individual is doing nothing out of the ordinary. Presence of blebs and smoking seem to be risk factors for spontaneous pneumothorax. If one spontaneous pneumothorax has occurred, there is a 30% chance that another will occur within 2-3 years.

When a lung collapses while diving, the air in the chest cavity is at the ambient pressure of the dive depth. When the diver ascends, the air in the chest cavity expands, and further compresses the lung. Most divers and dive boats are not prepared to provide first aid to a diver with pneumothorax. In the diving environment, a spontaneous pneumothorax can cause a life threatening situation. Thus the proscription to diving in persons with a history of spontaneous pneumothorax. If the pressure within the chest cavity increases due to expanding gas on ascent, air may find its way into the tissues of the neck, and subcutaneous emphysema will accompany the pneumothorax. In some cases, the air surrounds the larynx (the voice box) in the neck and causes abnormal function of the vocal cords resulting in a change in the voice. A voice change following a dive should raise special concern because there may be a small pneumothorax which in itself is not harmful, but which will cause a serious problem if the diver does another dive.

As noted above, 30% of people with one pneumothorax will have another in 2-3 years, and a further 30% will have a recurrence after 3 years. There is a 60% long term risk for another pneumothorax. These statistics are related to the finding that a person who has pleural blebs usually has more than one, and all of the blebs are prone to leak at one time or another. The person with a spontaneous pneumothorax therefore is likely to have another, and the pressures on the lung caused by diving are likely to stimulate a bleb to rupture and leak air into the chest cavity. Because of the risk of another event while diving, and the concern for a severe pneumothorax if gas expands in the chest on ascent, the current consensus is that individuals with spontaneous pneumothorax should not dive.

When there is a large pneumothorax, the air must be removed from the chest, and the leak must be sealed. This is done by inserting a tube into the chest cavity through a small incision between the ribs. The tube is usually connected to a vacuum system or a water seal system which allows air to leave the chest but not enter. Eventually all the air is removed, the leak seals, the lung expands and the tube can be removed. In situations where the leak will not stop, a surgeon must repair the leak directly or with a procedure using a special scope inserted into the chest

At present, diving trained physicians will not recommend diving in anyone who has had a spontaneous pneumothorax. Advances in surgical therapy may provide the opportunity to change this standard, but at present, diving is not recommended.

Reviewed 4/11/10







Fred Bove, MD, PhD

To understand the nature of MVP, we must look inside the heart at the valves which direct blood flow through the heart . The valve that lies between the left ventricle, the main pumping chamber of the heart, and the left atrium, the priming pump for the left ventricle is called the Mitral Valve. It is so named because it consists of two crescent-shaped leaflets which resemble a Miter or Bishop's hat. The ability of the mitral valve to prevent blood from flowing backward into the left atrium was well understood as early as the first century AD. This valve allows blood to flow in one direction, but closes when blood attempts to flow in the reverse direction. The valve itself is made of thin, but tough tissue, and is supported by fine sinewy cords which attach to the heart muscle that makes up the walls of the left ventricle. Because the pressure in the left ventricle reaches levels that exceed the strength of the valve leaflets, the leaflets are supported by the cords which prevent the valve leaflets from turning backward under the pressures generated by the beating heart. The valve snaps shut every time the heart beats, and produces one of the characteristic sounds of the heartbeat.

There are a number of diseases that affect the mitral valve. Rheumatic Fever can damage the valve, and produce a lifelong disability because of narrowing (stenosis), or leakage (regurgitation) of the valve. Because of antibiotics, this disease is rare in the United States. Infections can damage the valve, and cause it to leak, occasionally severe chest trauma, that might occur in a head-on auto collision, can tear the valve due to a sudden intense surge of blood against the valve, and the valve can function abnormally when a heart attack injures the heart muscle which holds the cords that support the valve. Abnormal narrowing or leakage of the mitral valve always produces a murmur. It is usually possible to diagnose an abnormality of the mitral valve by examining the heart with a stethoscope.

The mitral valve varies in its size, and in some people, the valve leaflets are a bit too big for the heart they are in. When this occurs, there is some redundancy of the valve tissue, and the valve can balloon into the left atrium when the pressure in the left ventricle is high. It is this ballooning backward of the mitral valve which has redundant leaflet tissue that is called Mitral Valve Prolapse. When the valve leaflet balloons into the left atrium, it makes a clicking sound which can be heard with the stethoscope. Mitral Valve Prolapse was, for many years, a diagnosis made by listening to the heart. The significance of the clicks heard with the stethoscope were first understood in 1961, but a real understanding of the motion of the mitral valve did not develop until the early 1970's, when the prolapsing valve was viewed in the living person with ultrasound. Since then, ultrasound imaging of the heart (echocardiography) has advanced to the point where a clear picture of the mitral valve leaflets can be observed continuously as the heart beats, using a small sound probe that is placed on the front of the chest. Abnormalities of motion, including prolapse, can be observed directly. With the use of ultrasound to visualize the mitral valve, it became apparent that MVP could be found in normal healthy people. Current data indicate that 2-4% of all people have MVP, and the great majority of these people have no evidence of heart disease. If MVP can be found frequently in normal people, why do physicians tell people that this is a serious disease which can affect health? Actually MVP by itself cannot be called a disease. It is merely a variation of the normal mitral valve which is found in a portion of the normal population. However, there are a number of heart related symptoms that may occur randomly in people with MVP.

The table below shows the more common problems that are known to occur in people with normal hearts. Surveys of normal people indicate that these problems are as frequent in people without MVP as they are in people with MVP. When they are found with MVP, some people feel that they are related to the MVP.

 Heart disorders that may be related to Mitral Valve Prolapse
 palpitations  chest pains
 rapid heart beat  heart murmur

Palpitations are the result of extra heartbeats which occur out of rhythm with the normal heartbeat. They are sometimes produced by exercise, or stress, and may be related to increased adrenaline levels in the blood causing stimulation of the heart. They are also caused by stimulants like caffeine. When palpitations become bothersome, treatment can be provided with a variety of medications. A common treatment is with a beta blocker drug such as Attenolol. Occasionally, a person with MVP may have a period of rapid heart beat (tachycardia). Many people without MVP also have this problem, and treatment with medication is usually successful in either case. Chest pains occur in many people without heart disease, some have MVP. The cause of the pain is not known, but it is not related to angina from blockage of an artery to the heart. Both palpitations and chest pain can be treated with a medication like Atenolol.

About half of those with MVP have a leak of the mitral valve. The leak is usually minuscule, and has no effects on the heart. Occasionally, the leak progresses to the point where the mitral valve must be repaired or replaced. This occurs in a very small percent of people with MVP. We usually advise people with a leaking valve to take antibiotics when having dental work to eliminate the risk of an infection of the valve. There is no need to follow this rule if there is no leak of the valve. Similar advice is given to patients with leaks of other heart valves.

MVP is diagnosed by listening to the heart with a stethoscope. The diagnosis is usually confirmed by an echocardiogram which shows the heart chambers and valves using an ultrasound beam transmitted through the chest. This study is easy, noninvasive, and quick (about 30 minutes). It gives a definite diagnosis when used by an experienced cardiologist trained in echocardiography. Leaks of the valve can also be detected using ultrasound measurements. Sometimes an incorrect diagnosis is made with ultrasound so be sure the physician you consult is experienced with this test.

Diving with Mitral Valve Prolapse

A common question is whether it is safe to dive with MVP. Remember that MVP alone is not a problem; there is no reason to be limited in any activity including diving. Accompanying problems however can limit diving. If there are frequent bouts of rapid heartbeat, diving should not be done. If treatment eliminates the rapid beat, and there are no abnormalities of heart rhythm with exercise, diving can be done safely. When in doubt, we recommend an exercise test with electrocardiographic monitoring to detect abnormal heart rhythms induced by exercise. Chest pains are often transient, and can be treated with drugs like Atenolol. If treatment is successful, then diving can be considered. The majority of people with MVP and leaking valves have very small leaks which do not affect the heart or limit exercise capacity. A leaking Mitral valve, when severe will compromise heart function and limit exercise capacity, but this is rare. If heart function is normal, then diving can be done safely even with a mild leak. Some divers have returned to diving after having a leaking valve repaired. When a valve is replaced by an artificial valve, the patient must take anticoagulants to prevent blood clots from forming on the artificial valve. Diving is usually not recommended in this case, but there are divers with artificial mitral valves who dive successfully.

Prolapse of the Mitral valve is a common enough finding in normal people that it cannot be considered a disease, and it is not a contraindication to diving. In some people, accompanying heart problems can limit diving, but most of the associated problems can be treated with medication, and diving can be done safely.

Reviewed 4/11/10



Fred Bove, MD, PhD


Among the questions about diving and the heart that cross my desk, the most frequent seems to be the problem of Atrial Fibrillation. Among the abnormal heart rhythms, this one seems to be increasing in frequency. When Atrial Fibrillation occurs, the upper chambers of the heart (the Atria) begin beating in an irregular rapid rhythm which may reach rates of 600 per minute. Fortunately, the main pumping chambers of the heart (the ventricles) are protected from this rapid beating by a slowing of the signal from the atria so that every fourth or fifth beat of the atria reaches the ventricles. The resulting pulse rate is then a fraction of the atrial rate, and will be in the range of 120-150 beats per minute. When the heart develops this rhythm, the individual will feel an irregular heart beat, and in most cases the heart rate is rapid. Some people do not tolerate the rapid heart rate, experience a drop in blood pressure, and feel light headed, fatigued or short of breath. Some patients with coronary disease will develop chest pain with the rapid heart rate. Exercise becomes difficult, and ability to dive is compromised by fatigue and shortness of breath.

Atrial Fibrillation is caused by either abnormalities of the heart itself, by excess stimulation of the heart by adrenaline-like medications, too much alcohol, an overactive thyroid, and occasionally by excess of acetylcholine, a hormone which acts to slow the heart and stimulate the atrium. Atrial Fibrillation may be related to high blood pressure, or to coronary artery disease, and there is an increased incidence of Atrial Fibrillation with age. People with abnormalities of heart valves, or of the heart muscle, and people with inherited abnormalities of the heart also develop atrial fibrillation. In many cases, there is no identified stimulus, and the heart is normal when Atrial Fibrillation develops. The relation of Atrial Fibrillation to alcohol is well known, and has been labeled the "Holiday Heart Syndrome." Excess caffeine is also thought to provoke Atrial Fibrillation. Atrial Fibrillation may be sporadic, occurring unpredictably, or with exercise, diving, or alcohol ingestion, or it may be continuous. Many people have chronic, continuous Atrial Fibrillation, and with proper medication have no symptoms even during exercise. When treating Atrial Fibrillation, we try to return the heart rhythm to normal with drugs, or with a brief electric shock. In some cases the atria do not return to a regular rhythm and individuals must live with chronic atrial fibrillation.

Our greatest concern with Atrial Fibrillation is the risk of a stroke caused by a blood clot forming in the poorly contracting atria. In people over 60 years old, the risk of a stroke appears to be about 4.5% for each year that Atrial Fibrillation is present. This risk can be reduced to about 1% per year if anticoagulation is used. Aspirin can reduce the risk of a stroke from Atrial Fibrillation as well, but the protection is not as great. When a person requires anticoagulation, there is a risk of bleeding. By carefully monitoring the degree of anticoagulation, bleeding can be prevented, and the high risk of a stroke can be reduced. Some individuals will gain adequate protection from a stroke using only aspirin. These individuals are usually younger and have no other heart problems. When a heart problem is the cause of atrial fibrillation, treatment with an anticoagulant is usually prescribed to prevent blood clots from forming in the atria. There are many divers who take Coumadin, the most commonly prescribed anticoagulant which is used for a variety of disorders, including atrial fibrillation.

Diving with Atrial Fibrillation

For divers who are prone to atrial fibrillation, but who only develop the rhythm sporadically, diving can be one of the stimuli. When divers are submerged, there is a shift of blood into the upper body from the legs. The added blood in the heart stretches the atria and makes them prone to fibrillation. Some divers will experience transient heart rhythm abnormalities due to these fluid shifts. Individuals known to have easily provoked Atrial Fibrillation are usually advised to take a medication to prevent the abnormal rhythm, and to keep the heart rate slow in the event that Atrial Fibrillation occurs. With adequate treatment, a rapid heart rate will not occur, and the presence of Atrial Fibrillation will not compromise heart function. Under these circumstances, a diver will not be limited by the abnormal rhythm, and can dive safely. On one extreme is the diver who needs medication only before diving, as there seemed to be little evidence of Atrial Fibrillation at other times. At the other extreme is the diver who has continuous Atrial Fibrillation. This individual needs medication to control the heart rate, and also needs anticoagulation. The concern with anticoagulation is the concern for bleeding. With any injury (cuts, bruises, broken bones), bleeding can be excessive, and will need special attention to be sure blood loss is minimal. One concern is for excess bleeding from injury caused by an ear or sinus squeeze. Bleeding into the middle ear from an ear squeeze can cause a severe middle ear infection due to trapped blood. Bleeding from a sinus squeeze may continue for prolonged periods, and lead to a severe sinus infection. Fortunately, with good diving technique, squeeze can be prevented, and for those using anticoagulants, it is essential that ear and sinus squeeze be prevented. This may require judicious use of decongestants, not diving when you are congested, and taking care during descent to allow continuous equalization of ears and sinuses with the ambient pressure.

Atrial fibrillation does not mean the end of a sport diving career. In the absence of severe heart problems, use of medication to control heart rate, and use of anticoagulation when indicated will not prevent diving, but caution is needed to dive safely.

Reviewed 4/11/10






Fred Bove, MD, PhD


There are a number of divers who take the anticoagulant Coumadin and others who are taking the platelet inhibitor Plavix (see below). Coumadin provides a benefit to patients by allowing the blood to clot more slowly, thereby protecting the person from clots which may form in the veins or in the heart. Clots forming inside the blood vessels or heart will travel to vital organs to cause damage and abnormal function. Although the ability of the blood to clot is one of the most important defenses against blood loss when injured, there are certain conditions where reducing the ability of the blood to clot is beneficial to the health of an individual. Coumadin is used when there is a risk of blood clotting due to illness, artificial heart valves, certain abnormal heart rhythms or disease of the veins (phlebitis). There are many thousands of people taking Coumadin to prevent blood clotting. All people taking Coumadin must go through an initial period of adjustment where blood clotting tests must be done every few days or weeks, and must have a blood test periodically (usually monthly) to determine that the level of anticoagulation is properly maintained. Decisions about the proper amount of the medication are made by a physician who must monitor the blood clotting time and adjust the dose accordingly. The physician uses a measured blood clotting time called the International Normalized Ratio (INR). This ratio compares the clotting time of an individual's blood to a standard. The normal ratio is one. Ratios of 2-2.5 are used in some cases of vein disease or abnormal heart rhythms while in the case of heart valves, the ratio is maintained at 2.5-3.5 to minimize risk of blood clotting. People taking Coumadin get into a routine of having a blood test once a month, and checking with their physician to determine if the dose of Coumadin is to be changed.

Coumadin reduces the ability of the blood to clot by blocking the effects of vitamin K. This vitamin is important in producing one of the clotting factors (prothrombin) needed for blood to clot. Blood clotting requires the action of a large number of chemical interactions in the blood, and absence of any one of the clotting factors will reduce the ability of the blood to clot. By lowering the amount of prothrombin, clotting time is prolonged. Since vitamin K requires activity of bacteria in the intestine, certain antibiotics can cause a reduction in bacterial activity, loss of production of vitamin K, and an increase in the effects of Coumadin. Drugs, illness or dietary change can also affect the level of blood clotting when taking Coumadin. Some people have an inherited abnormality in coumadin metabolism. Newer genetic tests can identify individuals who need special dose considerations. When the blood is too thin, spontaneous bleeding occurs. This often is first noticed in the skin, nose or mouth. Physicians and pharmacists should be aware of drug interactions, and avoid or adjust for medications which can alter the effect of Coumadin on clotting time. Education about dietary and drug effects is important if you are taking Coumadin. Aspirin is usually not recommended when taking Coumadin because aspirin blocks a backup clotting mechanism which depends on the blood platelets, and leaves no protection against bleeding. However, many patients do take a low dose of aspirin with coumadin.

Divers who must take Coumadin carry a risk of bleeding from injury, ear and sinus squeeze and pulmonary barotrauma. Since blood clots more slowly when taking Coumadin, a cut will bleed longer, and may require compression bandages to control the bleeding, and an ear or sinus squeeze will cause excess bleeding if the squeeze is severe enough to cause damage to blood vessels in the middle ear or in the sinuses. In spite of the risk of bleeding, many otherwise healthy people get along for many years using anticoagulants, and have minimal complications. Contact sports are discouraged because of the risk of injury, but many other sport and recreational activities including diving can be done safely with carefully monitored blood clotting time. We have encountered divers with artificial heart valves who are diving safely, individuals with atrial fibrillation, an abnormal heart rhythm, who dive safely and a few divers who had phlebitis (clotting in the veins) take Coumadin and dive without incident. The secret of safe use of Coumadin is careful attention to the INR, with monthly blood tests, and continued surveillance by the physician. With good control of blood thinning, the risk of a bleeding complication is quite low.


Plavix is a blood thinner that blocks the effects of blood platelets on clotting, and makes the blood less prone to clot. Divers who take Plavix are prone to bleeding in much the same way as those who take coumadin, and the comments above regarding coumadin and diving can be applied to Plavix. Divers who have had a stent implanted in their coronary artery for a blockage can return to diving, but are required to take Plavix.

For divers, the most important question is whether the condition which requires the use of Coumadin or Plavix prohibits diving. In many cases, the illness is over, or chronic but well adjusted, and does not interfere with safe recreational diving. Safe diving with Coumadin or Plavix depends on the absence of illness which would limit diving, careful control of clotting time, avoiding ear or sinus squeeze, and a thorough education on drugs and foods which cause changes in the effects of Coumadin. There are many divers using Coumadin and Plavix safely, but a special effort must be made to understand how to avoid problems of excess or not enough anticoagulation.

Reviewed 4/11/10



Fred Bove, MD, PhD

I was running along a favorite trail recently, when I came upon a long time friend running in the opposite direction. After a bit of negotiating, he reversed direction and we ran together to catch up on events. During our conversation, the subject fell to nutrition for sports and athletics, and nutrition to maintain good health. He was trying to sort out a large amount of information that he had researched about diets. These are often described for specific goals (body building, lowering cholesterol, weight loss), often by advocates of a specific diet method, with little information upon which to base an informed decision about what and how much to eat. I realized that in trying to learn about healthy eating, he became more and more confused by conflicting information from many different sources. I note similar confusion among my patients when they ask about a new diet, vitamin or food supplement that is discussed in the press. For my patients, I try to provide nutritional guidelines which can be used on a long term basis, not for a short term specific goal like rapid weight reduction. Reasonable nutritional goals can be achieved without going to extremes with food resources or nutritional supplements.
To start on a good nutrition program, the basic structure and calorie value of foods need to be understood. We usually refer to the energy value of foods in calories. Physics texts define a calorie as the amount of energy needed to raise a gram of water one degree centigrade, and a kilocalorie as the amount of energy needed to raise a kilogram of water one degree centigrade. In food science, the kilocalorie is referred to as one Calorie (with a capital C). Energy requirements for a day's worth of activity depend on the amount of work you do, your age, body size, and metabolic rate. An average man doing a day's work in an office uses about 30 Calories per kilogram (13.6 Calories per pound) of body weight, and an average women uses about 25 Calories per kilogram (11.4 Calories per pound) of body weight per day. Individuals who have jobs requiring physical exertion have higher energy demands. Most dietitians recommend a balance of 20% protein, 30% fat and 50% carbohydrate (CHO) for daily energy needs. The table below shows the distribution of calories for a 160 pound man and a 110 pound woman, both leading sedentary lives.


 Weight lbs

 Total Calories

 Fat -30%













The amount of each nutrient in grams is provided for the same calorie distribution in the second table (below). If you want to reduce the amount of fat in your diet, you need to replace the calories with another food type. In most low fat foods, the substitute is carbohydrate in the form of sugar, but the proportions often leave you with the same or a greater number of calories. It is ironic that a high carbohydrate diet can cause an elevation of triglycerides (fats) in the blood, and can have an effect opposite to what is expected from the diet change.


 Weight lbs

 Total Calories

 Fat -gms













If you are contemplating a special diet, you should determine whether there is adequate information to justify a large deviation from the recommended balance of foods. Although requirements for essential fatty acids (the building blocks of fat) are only 1-2% of total caloric intake, a very low fat diet may deprive you of these essential fatty acids, and cause a loss of normal nutritional requirements. If you are concerned about blood fats and the risk for atherosclerosis, a modest reduction of saturated fat (animal fats, and tropical oils like coconut and palm) in the diet might be reasonable, but in some individuals, excess carbohydrates and excess fats can raise blood lipid levels. A long distance runner training daily will require a high calorie intake which is usually made up of increased carbohydrates. If you reduce total food intake below your daily energy needs, you will lose weight. This might be the best way to improve your health and reduce fats in the blood, as many overweight individuals have elevated blood lipid levels. Maintaining an ideal body weight by moderation in total food intake, while following the recommended balance of food components, is still the best and safest means of achieving a healthy life style. When you perform a greater amount of work, you can compensate by increasing food intake to obtain additional energy. To be ready for the demands of diving, you should add an exercise program to your nutritional program. A rough rule of thumb is that a mile travelled on foot consumes about 100 calories of energy regardless of the time it takes. A cup of dry cereal, or a cup of 1% milk is equivalent to 100 calories. So a two mile walk will account for most of the calories in your breakfast. If you are aware of your usual daily dietary needs, and add as your activity dictates, you should maintain a stable weight, and be ready for the physical demands of diving.

Reviewed 4/11/10





Fred Bove, MD, PhD

Although much of the commercial diving in the world is done under conditions of poor or no visibility, in sport diving the visual panorama is probably the most compelling reason to dive. Besides the enjoyment provided by seeing the underwater environment, having clear vision when diving is an important safety measure. Poor vision can decrease appreciation of the underwater environment and compromise safety.
Vision Correction
A common method for correcting underwater vision is to incorporate a correcting lens into a dive mask. Since a standard dive mask provides 25-30% magnification due to the refraction across the water to air boundary, mildly nearsighted individuals do not usually require optical correction underwater. Moderate to high amounts of refractive error are not compensated for by magnification and corrective lenses are usually needed.
Lenses can be bonded to the face plate of your mask or a bracket can be inserted on the upper portion of the face plate to attach a spectacle frame. Another option is to have a face plate optically ground to your prescription. If you use lenses in the mask, choose a low volume mask to bring the face plate close to your eyes.
Near vision should not be overlooked. Reading gauges or a decompression computer is as important as viewing colorful fish. Divers over age 40 who need eyeglasses for reading, may benefit from a corrective lens for reading gauges and viewing small objects.
Contact Lenses
There are many considerations in deciding between contact lenses and spectacle mask correction. A contact lens wearer will have normal vision during diving and when out of the water. Mask correction requires the diver with poor vision to carry a pair of glasses on the dive to see properly when not in the water.
For many years, it was thought that contact lenses were unsuitable for diving. There were concerns for the eyes getting adequate oxygen, bubble formation under the lens, and the risk of losing a lens. In order for the cornea (the front part of the eye) to be transparent, it must be free of blood vessels. It receives oxygen from the air and the tear film that covers the eye. When a contact lens is placed on the cornea, the amount of oxygen getting to the cornea is reduced. The decrease varies depending on the type of contact lens. Since the air in the mask will have a higher oxygen partial pressure while diving, the cornea receives more oxygen through the contact lens while diving then it would under normal conditions on the surface.
The tear film which is present between the contact lens and the cornea will take up nitrogen and other inert gases as partial pressure rises. Gas bubbles can form between the cornea and contact lens and will enlarge during ascent. These bubbles trapped between the contact lens and the cornea may cause blurred vision. After a dive, the bubbles may require 15 to 20 minutes to disperse and the blurred vision to clear. Removing, and rewetting the lenses will minimize the duration of blurred vision. Blinking is an important factor in washing away these bubbles. Pay careful attention to make sure you blink frequently, thereby rewetting the lenses to avoid difficulties.
A rigid gas permeable contact lens, which is smaller and much harder than a soft lens, is seldom lost underwater when properly fitted. Only exposure to strong turbulence can cause this type of lens to pop out. Soft lenses fit the eye differently and can be lost more easily. If you become separated from your mask either above or below the surface, a good rule of thumb to prevent the lenses from popping out, is to open your eyes only partially. Clearing a flooded mask is easily accomplished by keeping your eyes closed until most of the water has been cleared.
Soft, disposable contact lenses are intended to be discarded after use, so a lost lens is not a concern. Disposable lenses dispensed in a pack containing several lenses can be used just for diving. Extra lenses can be kept in your dive bag in case a lens is lost during a dive.
Frequent Questions
Is it safe to dive after receiving an artificial lens? These are inserted surgically inside the eye to replace a damaged natural lens. Once the eye has healed, it is possible to return to diving. A waiting time of 3-4 months is usually recommended.
Can I dive with Glaucoma? This is a disease which causes increased pressure inside the eye. If untreated, it will lead to blindness. The increased pressure is always relative to ambient pressure, so diving does not increase the effective pressure in the eye. If Glaucoma is treated and pressure inside the eye is normal, it is safe to dive.
Can I dive after cataract surgery? This surgery is done to remove a cloudy lens. It is a common procedure, and restores vision in many people who otherwise would be unable to see clearly. An artificial lens is usually inserted in place of the cloudy lens. Once the surgery is healed (3-4 months), diving can be done safely.
If you have concerns about your eyes, you should have an eye examination, including a check of your vision and measurement of the pressure inside the eye. Proper advice about corrective lenses, and identification of problems inside the eyes are important parts of maintaining good health.

Reviewed 4/11/10





Fred Bove, MD, PhD

These four divers each have a different reason for a headache. One has no cause even with extensive medical testing. In most cases a headache is of no consequence. Headaches that occur with diving may be an important symptom of contaminated breathing gas, ear or sinus problems, hypertension, CO2 intoxication or events related to circulation in the brain such as migraine or cluster headaches. One-time events are usually of no concern but a pattern of repeated headaches requires attention by a physician_FB

Q. I have been diving for the past 5 years. For the past year I have noticed a headache while diving. The headache usually begins about 15 minutes into the dive, and persists for about 30 minutes after surfacing. Can you give me some advice on how to avoid this problem?
A. There are several possibilities for headaches during diving. The most likely is a blocked sinus. There are several sinuses that can cause the headache. Often the obvious ones (maxillary or frontal) are not involved. There is also a sphenoid sinus which when blocked can cause a headache. To solve this problem, you should consult an ear-nose and throat specialist who can determine if you have one or more blocked sinuses. There is a possibility that you have an abnormality inside your head. This would best be evaluated by a neurologist who should do a MRI or CT scan to be sure you have no problems inside your head. There are rare occasions where air leaks into the spinal fluid and causes headaches. A third cause is carbon monoxide poisoning. Headache is a common problem with carbon monoxide, and you should check your air source to be sure it is not contaminated. You can also get a headache from excess carbon dioxide. This would occur if you were skip breathing or not breathing adequately while diving. There are some people who have a high tolerance for Carbon Dioxide, and allow CO2 levels to rise in the blood. This would also cause a headache. If you have an insensitivity to Carbon Dioxide, you would need to be tested by a pulmonary specialist. Finally, diving can occasionally trigger migraine headaches. The neurologist would also be able to help with that diagnosis. [We subsequently heard from this diver that he was "skip breathing". This pattern of periodic breathing while diving can increase CO2 levels and cause a headache.]

Q. I recently noticed a severe headache over the left eye and forehead during descent. The pain begins at about 8 feet below the surface, then becomes severe as I descend. The headache disappears about 20 minutes into the dive. What is the best way to avoid this problem?
A. The headache you describe is usually due to a blocked frontal sinus. This sinus is in the bone of the skull above the eye, and connects to the throat through a small orifice. Obstruction of the orifice prevents equalization of the sinus as you descend. Pressure in the sinus causes pain above the eye on descent. You should have a thorough evaluation by an Ear, Nose and Throat specialist to be sure you have open sinuses. A similar pain can be caused by a migraine headache. If your sinuses are normal, I suggest that you have an evaluation by a neurologist to determine if you have migraine or another form of "vascular" headache.

Q. Over the past year, I began to notice headaches, and sought medical attention. After extensive testing, including MRI scan of the brain, no cause for the headaches was found. I can relieve the headaches with a small amount of pain medication. Is there any risk of diving with these headaches?
A. There is no specific problem in diving with a history of headaches. I am concerned that the headaches developed in the recent past, even though no specific cause for them could be found. If you continue to have the headaches, I suggest that you have a re-evaluation in several months to be sure that there is no specific cause for the headaches. If there is no cause identified for the headaches after a careful medical evaluation, there is no specific problem that can be related to diving. You might find that the headaches are aggravated by diving because of the exertion involved. If they are triggered by diving, then you might need to avoid diving, or use a mild pain medication before diving. Common causes of headache are tension, high blood pressure, and migraine. Hypertension can be evaluated by repeated blood pressure measurements, and migraine can be treated with specific medications that prevent the headaches.

Q. I have a history of migraine headaches for many years and recently completed a scuba certification program. My instructor was concerned about diving with my migraine headache history. Is there any problem with diving with this condition?
A. Migraine is known to be triggered by diving, some physicians think it only occurs as a form of decompression sickness. If your migraine is well controlled with medication, and is not triggered by diving, then there is no particular reason to give up diving. Recent data suggest that a Patent Foramen Ovale may contribute to migraine headaches, however the data are not specific enough to recommend closing this defect in the heart
I have seen divers who develop severe migraines from diving without evidence of decompression sickness. In some cases of migraine, transient neurologic abnormalities can occur. If these are part of a migraine problem, and the migraine is triggered by diving, these individuals would be advised to give up diving. If your migraine is not triggered by diving, and you do not develop neurologic abnormalities during the headache, there should be no problem with diving.

Reviewed 4/11/10







Fred Bove, MD, PhD

A question is often posed on whether a free diver could develop decompression sickness. The question has been studied in several countries, but the best information comes from the natives of the Tuamotu Archipelago in Polynesia where free divers in the past made 40-60 dives a day to depths of 100 to 140 feet to retrieve pearls. Their descent was assisted by a lead weight , and they ascend by pulling themselves up a rope tethered to their collection basket. An assistant then raised the basket to retrieve the shells gathered on the bottom. Descent times were 30-50 seconds, total dive time about 100 seconds, and surface interval between dives was 4-6 minutes. Many of these divers developed severe illness which was called Taravana to describe the abnormal behavior associated with falling that the divers manifest when they are affected. The symptoms of Taravana are similar to those of decompression sickness. After ascent, divers would develop paralysis, visual changes, hearing loss, dizziness, and some divers died. Many divers who survived had permanent brain and spinal cord injuries. Although Taravana is likely to be decompression sickness, there are some features which do not fit the picture of decompression sickness and other causes such as hypoxia have been proposed.
The mechanism whereby free divers can develop decompression sickness was studied by Dr. P. Paulev in Denmark. Dr. Paulev studied free divers in a submarine escape training tower where free divers accompanied trainees as they performed the free ascents required to qualify for naval submarine duty. Dr. Paulev described the development of decompression sickness in a Danish Naval Medical officer. He states "The author has intimate knowledge of the event, because the medical officer happens to be himself." He performed about 60 dives to 100 feet with a two minute bottom time, and surface intervals of 1-2 minutes. After about 5 hours of free diving, he noticed pain, paralysis of the legs, nausea, visual changes and weakness of the right arm. He was treated with recompression, and following a full treatment table, all abnormalities disappeared.
Dr. Paulev calculated the nitrogen in his tissues after the repetitive breath-hold dives. He determined that the short surface intervals did not allow tissue nitrogen to be eliminated, and the tissue nitrogen was equivalent to that resulting from a continuous dive. Further studies by Dr. E. Lanphier indicated that the ratio of dive time to surface time, and the rate of ascent were important factors in the development of decompression sickness from free diving. He calculated that a ratio of surface interval to dive time of one gave a depth exposure equivalent to about 50% of the actual depth of the dive. Thus a dive to 100 feet with a 90 second dive and a 90 second surface interval would be equivalent to a continuous dive to about 50 feet. If ascent rate was rapid, the equivalent depth was about 65% of actual depth (65 feet). These relations explain why a free diver doing many repetitive free dives in the 100 -140 foot range will eventually develop decompression sickness. Divers who perform free dives for 3-5 hours will greatly exceed the no-decompression times for their equivalent depths, and are very prone to developing severe neurologic decompression sickness. The Taravana syndrome, and the experience of free divers in submarine escape training provide adequate data that this is a real phenomenon. For the average free diver Taravana is not a problem, but if you want to dive for pearls doing 130 foot dives every two minutes for 5 hours, you will get decompression sickness. By increasing the ratio of surface time to dive time to two (e.g. 90 second dive, 180 second surface interval), equivalent depth would be about 30 feet when free diving to 100 feet, and no risk of decompression sickness would occur. The information on Taravana was published in 1965 in a book entitled: Breathhold Diving and The AMA of Japan, Edited by H. Rahn and T. Yokoyama. It is publication number 1341 of the National Research Council, Washington, DC.
One other concern that has not been studied is the situation where you make a series of free dives after completing a series of scuba dives. There are several stories of divers getting decompression sickness doing free dives after scuba diving. This could occur if you are free diving during a surface interval between scuba dives. A surface interval with free diving is not really a surface interval, and the calculation of decompression will not be correct. The best advice is to avoid free diving during surface intervals between scuba dives. If you want to snorkel stay on the surface.

Reviewed 4/1/10





Fred Bove, MD, PhD

Breathing above or below the sea is done to supply oxygen to the body, and to remove the carbon dioxide that is created as the cells of the body burn fuel in the presence of oxygen. Nearly all of the energy-producing reactions that we are familiar with in our daily lives involve the combination of a fuel with oxygen to produce energy. These include burning gasoline in a car engine, heating a room with a wood stove, or burning fuel oil in a furnace to heat a building. We need oxygen to burn the fuels in the body (carbohydrates and fats), otherwise the body would cease to function in a very short time. And so we must carry an oxygen supply underwater to maintain the body energy processes. Many non-divers think we carry oxygen in our dive tanks, and one could ask why not use pure oxygen for diving rather than a mixture of nitrogen or helium or some other inert gas with the oxygen. The problem lies in the fact that as essential as oxygen is for life, too much oxygen is a poison that causes the brain to malfunction, and the lungs to be injured. The inert gas is a necessary diluent to keep the oxygen partial pressure at a safe level.

Oxygen Toxicity
Oxygen can be toxic to the body in two ways. Prolonged breathing of oxygen even on the surface (1 ATA) will eventually cause lung injury, and reduce the ability of the lungs to transport oxygen to the blood. The oxygen-induced injury to the lungs blocks the transport of oxygen into the blood, and ultimately causes a severe lack of oxygen to the body. Lung oxygen toxicity is not a problem with sport divers because the effects usually take many hours to occur, and even with extreme oxygen partial pressures, lung injury is not common in divers.
The more important toxicity of oxygen for divers is on the brain. Too much oxygen will cause a seizure. When a seizure occurs underwater, the risk for drowning is high. Avoidance of oxygen seizures is an essential part of diving. To understand the toxicity of oxygen, we need to understand the relation between depth, gas mix and oxygen partial pressure. For example when breathing air (21% oxygen) at 99 feet (4 atmospheres absolute, ATA), the partial pressure of oxygen is 4 x 0.21 = 0.84 ATA. If 50% oxygen is breathed at 99 feet, the partial pressure of oxygen would be 4 x .5 = 2 ATA. From many years of study and experimentation, and experience with oxygen, the partial pressure limits of oxygen for save diving have been established. As usual, there are several standards for exposure to increased oxygen partial pressure. Two of the standards are provided by the U.S. Navy and by the National Oceanographic and Atmospheric Administration (NOAA). The table below provides limits for oxygen partial pressure and the amount of time that a diver can be exposed to the increased partial pressure.

 O2 PP - ATA

 Time - min (NOAA)

 Time - min (USN)


















*These exposures are considered exceptional, to be used only in emergencies

Although there are differences between the two standards, both provide similar exposure times in the 1.3 to 1.6 ATA range. The USN standards were developed for surface supplied mixed gas diving, and considers 1.3 ATA a safe exposure for long durations. NOAA standards were developed for open and closed circuit scuba diving with Nitrox. Both were designed for use in working dives. If you want to use a gas mixture other than air (usually 32% nitrox) you must calculate the partial pressure of oxygen at the depth you expect to reach to be sure you do not enter the toxic range of oxygen. If we accept a safe oxygen limit of 1.4 ATA (recommended in some standards for safety) the maximum depth allowed for air would be: 1.4/0.21 = 6.67 ATA or about 187 feet (subtract one atmosphere for the surface pressure). Most air diving is done at depths shallower that 187 feet, so oxygen toxicity is very unlikely when diving with air. If you use a 32% nitrox mixture, with a safety limit of 1.4 ATA, the depth would be 1.4/0.32 = 4.37 ATA or about 112 feet. Based on the NOAA and Navy standards, a diver with 32% nitrox should be able to dive safely to 112 feet as long as the time is kept under 50 minutes. However, there are other factors involved because divers have experienced oxygen seizures at 1.4 ATA. The reasons are varied. Excess work at depth can reduce the threshold for oxygen seizures, and elevated carbon dioxide levels in the blood will do the same. It is easy to "skip breath" with nitrox because of the increased oxygen partial pressure, but the consequence will be retention of carbon dioxide and risk of an oxygen seizure. Remember, that the rate of breathing is driven by the need to remove carbon dioxide, and no matter how much oxygen is in the breathing gas, you need to breath the same amount of any gas to remove carbon dioxide. A tank of gas with increased partial pressure of oxygen will not last longer that a tank of air because the breathing rate must be maintained to eliminate carbon dioxide. To take advantage of mixed gas diving, a rebreather is needed to preserve the volume of inert gas, and allow only the oxygen to be consumed. With a rebreather, the carbon dioxide is absorbed by special chemicals in the device and the inert gas is rebreathed. Oxygen supply in a rebreather can last over 5 hours in some units.
If you plan to use mixed gas scuba, a thorough understanding of oxygen toxicity, and the ability to calculate oxygen partial pressure are essential for safe diving. Setting oxygen limits for safe diving is also essential, and a maximum of 1.3-1.4 is recommended. Limits for oxygen exposure are from the US Navy Diving Manual of 1993, and from the NOAA Diving Manual of 1975.

Reviewed 4/11/10





Fred Bove, MD, PhD


We have received a number of queries about diving after having a balloon angioplasty with stents implanted in the coronary arteries. These questions arise because of the large number of people who develop coronary disease, and the newer methods of correcting the problem, often without the need for heart surgery. The coronary arteries are the arteries that supply blood to the heart muscle and allow the heart to beat continuously without getting fatigued. Because it must beat continuously to support life, the heart has adapted to avoid muscle fatigue, but an important part of this adaptation is the need for uninterrupted blood flow to supply the oxygen needs of this continuously working muscle.
Coronary Disease
Coronary disease caused by blockage of the coronary arteries, affects about 700,000 people annually, and about 250,000 die suddenly often with no warning that they have coronary disease. The disease that causes the coronary artery blockage is called coronary atherosclerosis. For unknown reasons, the process of atherosclerosis seems to attack the coronary arteries of the heart more frequently that other arteries of the body. We know that atherosclerosis can start early in life with the progressive buildup of cholesterol and other fats in the blood vessel wall that causes a plaque to form within the artery wall. As it grows, the plaque narrows the artery and limits blood flow to the heart muscle, causing angina or chest pain with activity. This plaque becomes unstable, and eventually ruptures. When a plaque ruptures, the artery narrows further. If the artery totally occludes, a heart attack usually occurs. This process is considered to be one of the major causes of sudden death while diving. We have learned to diagnose the presence of a narrowing before total occlusion occurs using the clinical examination, evaluation of risk factors, stress test, and cardiac catheterization. Once a diagnosis of a coronary blockage is confirmed then the decision to fix the blockage must be made.
Risk Factors
We know that age, life style and inheritance can affect the risk for coronary artery disease. Cigarette smoking, diabetes, high blood pressure and elevated blood cholesterol all increase the risk for coronary disease. Age is an unavoidable risk factor, and if your family has a strong history of coronary heart disease, there is added risk. Smoking can be avoided, avoiding obesity can prevent most diabetes, and high blood pressure can be treated. There are excellent medications for lowering blood cholesterol, and if diet doesn't work to lower cholesterol, these medications should be used. By paying attention to your risk factors, you can reduce your chances of getting coronary disease and blockage of a coronary artery. Prevention is the best way to avoid questions about diving after angioplasty and stent implantation.
Because the diving population is getting older (we started teaching sport diving in the 1950's), and the incidence of coronary disease increases with age, it is inevitable that divers will be asking about returning to diving after having an angioplasty or a stent. If prevention fails, there are several ways to correct a partially blocked artery. They include medication, coronary bypass surgery, balloon angioplasty with or without implantation of a stent, cutting devices that remove the plaque (atherectomy), and even on occasion, the vaporizing of a plaque using laser energy delivered through the catheter. The choice of treatment should be made by a cardiologist who is familiar with all of the treatments and their short - and long-term outcomes, their complications, and the skills of the various cardiology laboratories in performing the procedures.
Balloon angioplasty and stents
Physicians realized in the 1960's that blockages in the coronary arteries could be opened using a long tube (a catheter) threaded into the artery to push the plaque out of the way, and allow more blood to flow through the artery. Then a small balloon mounted on the end of a catheter was positioned in the narrowing and inflated to push the plaque out of the way and open the artery. From these early beginnings, an entire field of medicine has evolved with new devices, improved skills and training, and the ability to open a blocked artery without chest surgery, and without requiring the patient to spend more than 1 or 2 days in the hospital. Rapid advances in technology have made the procedure less complicated, improved the outcome of the procedure from about an 80% immediate success rate to a 93-95% immediate success rate, and improved the 1 year success rate from about 60% to about 90%. Improvement in the immediate and long term outcomes came from the addition of a device called a stent. A stent is a fine wire mesh tube (2-3 mm in diameter, 1-2 cm in length) that is placed in the artery with a catheter, and expanded in the narrowed area of the coronary artery after opening the narrowed area with balloon angioplasty. Newer stents are coated with a medication to prevent growth of scar tissue in the stent, and thereby reduce the likelihood of renarrowing.

The stent holds the artery open, and is eventually overgrown with tissue so that it becomes a permanent implant in the coronary artery. People with blockages in the arteries that are amenable to treatment with angioplasty and a stent require short hospital stays, and can return to their usual activity in a few days. We usually advise patients who received an angioplasty and a stent that they should refrain from extreme exercise for about 4 weeks to be sure the site of insertion of the catheter (usually an artery in the groin) is well healed an not likely to bleed from excess activity.

Diving after coronary stent implantation
If you are a diver who has developed coronary diseased, and has undergone angioplasty with or without a stent, important questions are "Can I return to diving?, under what circumstances?, and when?" Stresses from diving include exercise and cold exposure. We usually provide recommendations for exercise based on a stress test done 6-8 weeks after the procedure. Based on the stress test, we can determine if the stent is open, and whether other coronary arteries are supplying adequate blood flow. We also determine your level of physical fitness and provide advice about exercise programs to improve conditioning. Because there is a risk of renarrowing in the stent, and most renarrowing occurs within the first 6 months after the procedure, I usually advise divers to wait for 6 months, get in good physical condition through a supervised exercise program, then have an exercise stress test to be sure the heart is getting adequate blood flow. For safe diving I recommend an exercise capacity of about 13 mets (a measure of work load) , or 12 minutes on a standard stress test. It is also wise to avoid extremes of cold, and heavy work on the surfaced or underwater. Smoking cessation and treatment of high blood pressure, diabetes, and elevated blood cholesterol will lower the risk of a subsequent blockage. If you participate in any recreation that requires exercise, including diving after angioplasty and stent implantation, you should have periodic stress tests (annual or biannual) to be sure exercise is safe.

Drug Eluting Stents

Stents with medication coating are called drug eluting stents (DES). These stents reduce the risk of renarrowing considerably, and are used commonly to open narrowed coronary arteries. A problem was identified with DES in 2006 when it was found that individuals who failed to take their antiplatelet medication (Plavix) had an increased risk of occlusion of the stent. Because of this finding, we recommend that anyone with a DES continue to take Plavix for at least one year. Plavix will not interfere with diving, but like aspirin, can cause easy bruising or excess bleeding form a wound. If you have a stent without a medication, called a bare metal stent, the recommendation is to take Plavix for about 6 months after the stent is implanted. You can read more about Plavix effects on blood clotting under the Blood Thinner topic on the left.

Reviewed 4/11/10







Fred Bove, MD, PhD

For the past 10 years or so we have been aware of an interesting and worrisome problem that occurs in some divers while they are under water. The problem is the rapid development of severe shortness of breath caused by fluid leaking from the bloodstream into the air spaces in the lungs and impairing the flow of oxygen into the blood. In medicine we call this pulmonary edema. It is somewhat akin to drowning but the fluid comes from the body and not from the outside environment. One diver describes the sensation:

"I went down to the bottom, knelt in the sand and remained still so as not to disturb the fish. I was in about 25-30 ft. of water for about 10 minutes or so when I started coughing into my regulator. I noticed my breathing was a little fast for someone who was inactive. I was just kneeling there watching the fish. There was a minimal current. Over the next 5 min or so, my coughing became more and more frequent. At first, I didn't feel short of breath or that my regulator wasn't working properly. I started to become a little concerned and signaled to my buddy that I was going up. Now I started swimming up and back to the boat. By the time I surfaced I was very short of breath. I swam to the stern of the boat and just hung on to the ladder. My buddy had to take off my fins and help me climb into the boat. I kept coughing and coughing and coughing. While I waited for the rest of the people, I kept coughing up a lot of secretions. I was having coughing fits. By the time we got back to the dock, my coughing slowed up. The shortness of breath cleared up after I was inactive and sitting on the boat for a few minutes. It was about 5 or 6 hours before I felt totally normal. If I had to put a label on what I was experiencing, it would be that of pulmonary edema. This episode was the third and worst yet"

This problem was described in 1990 at a scientific meeting of diving medical physicians. The syndrome occurred in divers who were wearing wetsuits in cold water. In the first report they were all over 50 years old and it was thought that these individuals had hearts problems that occurred for the first time while diving. However subsequent reports were published that included younger divers in warm water with no medical history of any serious disease. Some of these individuals were taken to hospitals and were found to have fluid scattered throughout the air spaces of the lungs and inadequate oxygen in the blood.
This problem, called pulmonary edema, usually occurs because the heart is injured or damaged, or because a process has occurred in the lung to allow fluid to leak from the bloodstream and fill the air spaces with plasma. The most serious and discomforting symptom is the rapid onset of severe shortness of breath and coughing while diving. The diver describes this well in the letter, which is a typical description. It is interesting that we do not understand the cause for this problem. Divers with heart disease can develop pulmonary edema while diving, but the cases reported so far are in individuals with no history of heart disease, and extensive evaluation including cardiac catheterization and other measures of heart function all show the heart to be normal. Subsequent studies of the lung after recovery show no abnormality of the lung. Although pulmonary edema is usual considered a serious and dangerous disease, this form of pulmonary edema is rapidly reversed with a diuretic medication.
A number of clinical scientists have considered possible causes for immersion pulmonary edema. These include intrinsic abnormality of the lungs, contaminants in the breathing air, abnormal blood pressure reactions to cold water, shifts of fluid into the lungs as a result of water immersion, and breathing against excess resistance in the regulator. To date none of these causes have been proven. Among the possibilities, breathing through a regulator with resistance to inhalation is one that is preventable. It is well-known in the medical literature particularly in anesthesia, that a partial obstruction of the airways, or of a breathing supply will cause a large negative pressure in the airways during inspiration. The negative pressure breathing can cause pulmonary edema within three or four breaths. In anesthesia, it is easy to produce negative pressure breathing and specific effort is made to avoid this situation when patients are supported with artificial respiration while under anesthesia. The results of the negative pressure pulmonary edema are identical to those of immersion pulmonary edema. There are many opportunities when diving to develop a negative pressure in the airways. It would only require a few breaths from a poorly functioning regulator to develop pulmonary edema. Although immersion pulmonary edema is rare, it is certainly not trivial and can cause significant problems with divers. The mechanism for immersion pulmonary edema is not well understood, but some precautions are worthwhile stating:

· Be sure your regulator is breathing normally. If there is resistance to inspiration, have the regulator checked and adjusted. A malfunctioning regulator that does not supply adequate air will cause negative pressure breathing and may induce pulmonary edema.
· Don't dive if you have high blood pressure. Be sure your blood pressure is treated and normal before diving as an elevated blood pressure can contribute to the problem.
· Be careful with excess fluid intake. There have been a few documented instances when divers were given large amounts of fluid just prior to diving and developed immersion pulmonary edema.
· If you have a heart problem, be sure you discuss diving with your physician and avoid diving unless your heart problem is stable and well controlled with medication. Most divers who experience immersion pulmonary edema are found to have normal hearts.

Although the cause for immersion pulmonary edema is unknown, these precautions can provide some protection. If you develop severe shortness of breath underwater, ascend at a normal rate to avoid lung overpressure. If your symptoms persist on the surface, breathe 100% oxygen if it is available. Consult your physician to be certain that your health is normal before returning to diving.

Reviewed 4/11/10












Fred Bove, MD, PhD


Although the greatest marine injury concern among divers is usually directed toward attacks from sharks, and killer whales, encounters with large marine animals are extremely rare, but contact with things that sting or stab are very common. Knowledge about nettle stings, urchin spine perforations, stonefish injuries and other contact injuries is needed to avoid mistreatment.

Stings and punctures are almost always caused by a stationary marine creature that the diver makes contact with. If you want to "blame" someone or something for an injury, don't blame the creatures, they are usually anchored to the bottom (fire coral), quite sessile (stonefish, sea urchins), or at least slow-moving enough that the diver should be able to avoid contact (sea nettles). It is often the uninformed diver who fails to recognize a stinging creature and sustains an injury. This is often the case with fire coral, which in many areas of the tropics is abundant enough that everyone will contact it and develop a rash.

Cnidarians (Coelenterates) contain some of the most venomous animals known to man, but most are harmless. These animals include true corals, soft corals, fire coral, jellyfish and sea anemones. These animals are characterized by having tentacles with stinging cells called nematocysts that deliver the venom. Some can penetrate human skin while others cannot. Coelenterate stings can be avoided by covering the skin. A full body suit with hood, gloves and boots will prevent stings, and is necessary when there are dangerous stinging animals in the water.
Fire coral, the Portuguese-Man of War, and "stinging seaweed" are actually carnivorous animals that look like innocent plants. Stings from these animals produce symptoms that range from a mild itching sensation to a severe painful sting. They produce a redness of the skin, rash and blisters.
True jellyfish are classified into mild, moderate to severe, and severe to highly dangerous stingers. Nematocysts are located along the tentacles. Symptoms range from a mild prickly sensation, itching to burning, throbbing, and shooting pain. The skin becomes red, swollen, has a rash, may blister, hemorrhage and undergo damage through its full thickness. In the more severe cases a victim may develop muscle cramps, difficulty breathing, lung congestion (pulmonary edema) loss of consciousness or even death. The most dangerous jellyfish is the box jellyfish, sometimes called the Sea Wasp found in Australian waters, and a close relative, the Irukandji, is also a dangerous jellyfish found in the same areas. Treatment of jellyfish stings includes the use of household white vinegar, which prevent the nematocysts from firing. Removing tentacles from the victim's skin may be dangerous, always wear gloves and then wash off the gloves thoroughly. Pain relief may be obtained by rubbing ice on the wound site after applying vinegar, and in mild cases giving aspirin. More severe cases may require full resuscitation, morphine and eventually a hospital respirator. The four aims of treatment are to relieve the pain, deactivate the toxin, keep the victim breathing and control any shock-like symptoms.
The third group of Cnidarians that cause trouble for the unprepared diver are the stony corals and sea anemones. In general this is a colorful harmless group of animals. If you do receive a coral cut, wash it with warm soapy water and apply antiseptic cream to the area.

Mollusks include the Cone Shells that contain a venom sac and a small poisonous dart capable of penetrating an ungloved human hand. These creatures feed on other mollusks, marine worms and fish. Consequently, they have developed a highly effective venom apparatus. If stung, the victim usually experiences immediate intense pain or a sharp stinging sensation, followed by burning, then numbness around the wound site. This may spread eventually over the entire body producing a muscle paralysis. Resuscitation, respiratory support and treatment for shock may be required. This envenomation is easily avoided by picking up any unknown shellfish with wet suit gloves.
Another mollusk that is known to have killed an individual through an envenomation is the blue-ringed octopus. The symptoms following the bite of this octopus include weakness, dizziness, tingling around the mouth, lips, tongue and throat, increased salivation, vomiting (severe and frequent) slow heart rate, breathing difficulty and shock. In general all the members of the octopus family are shy and not inclined to bite. The only time people have been bitten is when they handle them.

This group of animals includes starfish, sea urchins and sea cucumbers. These are marine bottom-dwellers with external skeletons, protruding spines and radial symmetry. Sea urchins have spines that are hollow and brittle. They can penetrate the skin, break off and become irritating. Crushing the spines in the skin may fragment them and help in the absorption process. Do not remove them surgically. Some sea urchins have a special venom apparatus called a pedicellaria that can inject venom causing pain, swelling and joint stiffness. The Crown of Thorns starfish has stout poisonous spines. Wounds from these spines are extremely painful.

Venomous Fish
Venomous fish include the stingray, weever, scorpion and stonefish. They all produce similar symptoms. When the spines from these animals perforate the skin there is an immediate, intense pain that may become excruciating over the next hour. The pain may persist for six to ten hours before diminishing. There will be swelling and redness around the injury site. The victim may experience dizziness, weakness, heart palpitations, anxiety, sweating, muscle weakness, cramps, nausea and vomiting. To treat a victim of fish envenomation, remove the injured diver from the water and immobilize the affected limb. Place the wounded limb into hot (not boiling) water. The ideal temperature is somewhere around 50°C or 122°F. Marine venoms are heat-labile proteins that are deactivated by immersing the injured area in hot water.

Sea Snakes
Another group of venomous marine animals are the sea snakes. Aquatic inhabitants of the tropical Pacific and Indian Ocean, these reptiles have bodies flattened posteriorly, with paddle shaped tails. Sea snake bites are often inconspicuous, sometimes painless and without swelling. Symptoms usually begin mildly and become progressively worse. The victim may experience a mild anxiety, drowsiness or even euphoria. Swallowing may become difficult as the patient's tongue swells. Muscle weakness may progress to paralysis. Antivenoms are available. Wrapping the injured limb with a tight dressing is thought to slow venom absorption, and allow the toxins to be deactivated by the body. Many consider the sea snake as a docile animal, reluctant to bite, but all are poisonous and potentially lethal.

The secret to avoiding marine animal injuries is to recognize the venomous animals, and avoid contact. Knowledge of first aid treatment is important since many of the injuries can be managed with simple first aid. More serious injuries may require hospital treatment, life support and antivenins. Before going to a tropical area to dive, learn about the venomous animals that you might encounter, and the treatment of their injuries. An occasional scrape against fire coral is not likely to cause a serious problem, but other injuries can be more serious and require medical assistance than can end a diving vacation.

Reviewed 4/11/10









Fred Bove, MD, PhD


Answers to questions about heart surgery vary because of the many types of heart surgery that are possible. Surgery on the valves of the heart dates back to the early 1960's when surgeons learned to replace valves of the heart damaged from Rheumatic fever. To replace a damaged valve, the heart had to be stopped, and its pumping function taken over by a mechanical pump while the surgeon worked inside the heart to replace a damage valve. This technique was perfected with use of the heart-lung bypass machine. The development of this machine that oxygenates the blood and then pumps the blood through the body, allows the blood to bypass the heart and lungs, so that the surgeon can work in a clear operating field without blood inside the heart. Once this technology was developed, replacement of heart valves became a routine part of the care of patients with heart valve disease. At the same time, people with abnormally developed hearts from congenital heart disease could now have their hearts repaired, and eventually were able to expect a reasonably healthy life, where in the past, with severe congenital heart problems, life expectancy was considerably shortened.

Coronary artery bypass surgery was started about 1968. This procedure was performed to insert new blood vessels to bypass blocked arteries to the heart, and restore the blood flow to the heart muscle. Initially, veins from the legs were used for the bypasses, but improved techniques allowed the surgeons to connect arteries from the chest and abdomen into the heart, and to use arteries removed from the forearm. We found that arteries used for bypass had a longer life than veins. Improvements in instruments and surgeons' skill now allow coronary bypass surgery to be done without the heart-lung machine, and sometimes using small incisions in the chest. Mechanical valves are sometimes replaced by tissue valves from animals or human cadavers, and the science of post operative care has advanced to the point that some heart surgery patients can leave the hospital in 3-4 days.

With over 4 million sport divers in the United States, it is inevitable that some divers will need heart surgery for replacement or repair of a heart valve, correction of a congenital abnormality of the heart, or for bypass of blocked coronary arteries, and will want to return to diving.

Issues that must be understood after heart surgery include: the effects of opening the chest on risk for lung barotrauma, the time needed for healing of the surgical incisions, diving with a mechanical heart valve and the associated blood thinners, and the question of whether the heart can handle the increased physical activity with new blood vessels to supply the heart muscle. Read about blood thinners by clicking on that subject in the menu.

Most of the queries involve return to diving after coronary bypass surgery or heart valve surgery as these are common procedures that affect many sport divers. The surgical incision and opening of the chest do not appear to cause a problem with diving. There are many divers who have had heart surgery. They have not reported an increase in the incidence of pneumothorax, or lung barotrauma. Most heart surgery is done through an incision through the sternum (breastbone), and the scar is in the middle of the chest. When surgery is done in this fashion, the pleural space may be preserved, and risk for barotrauma or pneumothorax is minimal. Healing of the surgical incisions, including the sternum requires 3-4 months so I usually advise divers not to return to diving for 6 months, and to be sure they have been exercising during that time. It is good practice to perform a stress test before returning to diving to be sure the diver can exercise adequately. Divers should be able to reach 13 mets of exercise when being tested.

If you are a sport diver and have had coronary bypass surgery, you must be sure that the bypass grafts are all working well, and blood supply to the heart muscle is adequate during exercise. The status of coronary grafts can be determined by exercise testing accompanied by blood flow imaging (thallium stress test). This should be done about 6 months after surgery, and should be normal for return to diving. Divers who have heart valve surgery should also have a stress test to determine if the heart is functioning well enough to handle the exercise needed for diving. Some patients have damage of the heart muscle itself either from heart attacks or from the overload caused by a narrowed or leaking heart valve. Congenital heart disease damages the heart muscle by causing overload from leaks inside the heart. After surgery, the heart may recover, but in many cases, the heart muscle remains weak and unable to withstand the workload caused by exercise.

If you have recovered for 6 months, and have a normal stress test with peak exercise capacity of 13 mets of exercise intensity (40 ml/kg/min), you should be able to dive safely. If you are an active diver, you should have an annual exercise test to be sure your heart is functioning normally. If you had bypass surgery for arteries clogged by atherosclerosis, you need a lipid management program to avoid a recurrence of the disease in the grafts, and in the normal coronary arteries that were not bypassed. If you were a smoker before your heart surgery, the surgical and hospital experience should be an excellent incentive to stop smoking, since further damage to the arteries, and more surgery will result from continued smoking.

Each case of a diver who wants to return to sport diving after heart surgery needs to be reviewed individually. Examination of the images of the coronary arteries to determine the extent of disease, the bypass grafts that were placed, valves that were replaced or repaired, the status of the heart muscle before and after the surgery, exercise capacity after surgery, all need to be considered before a decision to return to diving can be made. If you are diving after heart surgery, you need an annual medical examination to be sure your health and your heart are up to the stresses produced by diving.

Reviewed 4/11/10