scuba-diving-blog

Pre Dive Safety Check

2009-10-22T09:37:00.000-07:00

A pre dive safety check is perhaps one of the most effective solutions to avoid equipment related problems while scuba diving.
Speaking with dive instructors from the "good old school" (or at least that is the term that some of them use to describe the teaching techniques they used in the past)I got lots of information on how scuba diving used to be taught 20-30 years ago.

One of them told me that he used to ask his students to start descending with their tanks closed and breathing the air contained in the hoses of the regulator. At a given depth, and depending on the diver´s descending rate, he would run out of air. Then he had to reach out to this tank valve and open it to reestablish the air flow.

His rationale was that, maybe some day on a dive boat the divemaster in charge of the dive logistics may forget to open he divers tanks. It may happen to anybody, we must admit, but, is there a safer way to verify the correct functioning of our dive gear prior to enter the water?.

Luckily, today´s divers do not need to "practice" an out of air emergency using the technique described above. Divers now can rely on a very important pre immersion step known as the "Pre Dive Safety Check".

Before entering the water, your dive buddy shall verify that each part of your scuba gear works and fits properly, and you will do the same for him/her. That includes checking releases, gauges, tanks and weight belt.

The Professional Association of Dive Instructors (PADI)suggests all their entry level students to use a very efficient method to perform a predive safety check among dive buddies. They use the phrase "Begin With Review and Friend" and the acronym "BWRAF" to help divers to perform an efficient predive check.

B= BCD: Verify proper inflation so the diver is able to float in waters too deep to stand up, low pressure inflator connector, and that the tank is firmly secured to the harness.
W= Weight system: Whether if wore in a belt or a BCD integrated system, it is important that the weight system has a one hand quick release mechanism to ditch it in case of emergency.
R=Releases: Make sure every release works properly, and double check the weight belt´s quick release mechanism.
A=Air. Verify that the tank has enough air for the dive by checking the submersible pressure gauge and (critical step)making sure the tank is open.
F=Final OK: Once a pre dive safety check has been completed, it is time to enter the water.

Performing a pre dive safety check before each dive is perhaps the most efficient way to avoid common problems such as running out of air, tank loss and other equipment related problems

Scuba Diving in Cancun

Nitrogen Narcosis

2009-07-16T09:07:00.000-07:00

Besides the risk of decompression illness and other pressure related injuries, deep diving can bring divers in contact with another issue related to nitrogen: nitrogen narcosis, an euphoric, anesthetic effect. Although not a life-threatening condition, divers under the effect of nitrogen narcosis can fail in making good decisions based on good judgment.

Nitrogen Narcosis effects are frequently compared to alcoholic effects. "Martini´s law" is a tongue-in-cheek reference that says that 30 mts/100 feet has the potential of one martini, with each 15 mts/50 feet thereafter equal to an added martini.

When breathing air, nitrogen narcosis develops with an increase in nitrogen partial pressure, typically at approximately 30 mts/100 feet.

The exact mechanism surrounding narcosis is not fully understood, but almost any gas can cause anesthesia under high partial pressures. Theory suggests that nitrogen becomes dissolved in the lipids in neurons (nerve cells), which interferes with signal transmission from neuron to neuron.

Narcosis may cause a diver to feel drowsy, sleepy and may affect memory of the dive. The diver may feel falsely secure, exercise poor judgment and become uncoordinated. Some divers have reported hallucinations and giddiness.

The effects of nitrogen narcosis recede quickly upon reaching shallower depths, with no after effects. The best way to prevent it is to avoid deep dives.

Individuals vary vary in their susceptibility to narcosis just as they vary in their susceptibility to any form of drug intoxication. At a given depth, some divers will be more impaired than others.

Source: Padi Encyclopedia of Recreational Diving pp 2-38, 2-39.

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Selecting a BCD (Buoyancy Control Device)

2009-07-14T08:17:00.000-07:00

A Buoyancy Control Device (BCD) is an essential part of dive equipment because it controls the three states of buoyancy while you dive: positive while at the surface, negative as you descend, and neutral while you explore the underwater realm.

Controlling the three states of buoyancy is important, specially positive and neutral.
Positive buoyancy will help you float effortlessly while at the surface, and neutral buoyancy will help you move freely without crushing or damaging the delicate marine life.

What types of BCDs are there available?

There are three styles of BCD: front mounted, back mounted and jacket style, being this last one the most commonly used nowadays.

Features to consider when purchasing a BCD

A good BCD must be capable to hold enough air to provide you with ample buoyancy at the surface. Also, it must have a large enough inflation / deflation hose that you can operate easily. Other important features include an over pressure release valve to prevent it from bursting when over inflated, and most important, it must include at least one emergency deflation valve to quickly release all the air in case of emergency.

How to maintain a BCD

BCD´s, as well as any other part of dive gear should be rinsed with fresh water after each use. Still, there are other two additional maintenance considerations: First, you should also rinse the inside of the bcd, and second, you should always store your BCD partially inflated.

As with every piece of your dive gear, BCD´s should be serviced at least once every year (or more often if you use it frequently) by a qualified technician.

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How to avoid Decompression Illness

2009-07-13T11:01:00.000-07:00

Decompression illness, or DCI, is a term used to describe an illness that results from a reduction in the ambient pressure surrounding a body. There are two types of DCI: Decompression sickness, which is the result from bubbles growing in tissue causing local damage, and Arterial Gas Embolism, which results from bubbles entering the lung circulation, traveling through the arteries and causing tissue damage at a distance by blocking blood flow at the small vessel level.

What causes a diver to get DCI?

There are several reasons why a diver may get DCI, but among the most important ones we can list: rapid ascents, exceeding no decompression limits underwater, flying immediately after diving, being dehydrated, diving after an illness or fracture, deep diving etc.

Who can get DCI

Although every diver is susceptible to get DCI, there are some factors that increase the risk. Obesity and age are two of the most important ones. Divers with those characteristics should always dive under the supervision of their doctors.

How to avoid DCI?

1) Avoid deep dives. If you are a recreational diver the maximum recommended depth is 30 mts / 100 feet.
2) Ascent at a rate that does not exceed 18 mts / 60 feet per minute
3) Make a safety stop at the end of every dive
4) Do not make decompression dives without the proper training and equipment.
5) Understand your dive tables and /or computer and never dive beyond their limits.
6) Drink plenty of non-alcoholic fluids before, after and in between dives.
7) If you are taking prescription medications, seek your physician advice before diving.
8) Wait at least 24 hours before flying.

In conclusion, understanding DCI is the best way to prevent it. Should you have any questions, ask your doctor, dive shop or instructor.

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How to buy a dive mask

2009-03-20T08:45:00.000-07:00

When buying any equipment for scuba, your two most important selection factors are fit and comfort. This is particularly true for your mask, because a mask that does not fit well will leak and/or irritate you and take the fun out of the dive.

To test a mask for proper fit, use the "sniff" test. Place it gently against your face without using the strap and inhale through your nose. A properly fitting mask will pull into place by suction and stay as you inhale. If you have to push or twist the mask to make it seal, try a different one. After finding some that fit, try pinching your nose with each on to see which is easiest.

If you need visual correction, some masks accept prescription lenses. You´ll want to think about this when buying a mask, because not all masks do this readily.

Manufacturers coat new masks with a protective chemical that you need to scrub off or you won`t be able to defog the mask. To remove the film, use a soft cloth to gently scour the glass inside with a non-gel toothpaste or other low abrasion cleaner with fine grit that can remove the film without scratching the glass. Be sure to do this before using the mask for the first time.

Next, adjust the mask strap for a comfortable fit across the crown of your head. The strap should be snug, but not tight, and make sure to close the locking device (they differ a bit from one mask to another) so it does not slip.

Source: PADI Open Water Diver Manual pp 30-31

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Cardiovascular Fitness and Diving

2009-03-07T10:04:00.000-08:00

By JAMES L. CARUSO, M.D.

Hypertension

Hypertension, or high blood pressure, is one of the most common medical conditions seen in the diving population - no surprise, really, since it is a common medical condition in the general population. Strict criteria for hypertension can vary depending on the reference cited, but normal blood pressure is generally accepted to be a systolic pressure below 140 and a diastolic pressure below 90 mm Hg, depending on age (cited as systolic first and diastolic second - e.g. "120 over 80," by your doctor). A thorough medical evaluation should be performed to find a treatable cause for hypertension; in most cases, however, none will be found.

Basically, two different sets of complications face a person with hypertension: short-term and long-term. Short-term complications are generally due to extremely high blood pressure; the most significant is the risk of a stroke due to rupture of blood vessels in the brain (called a cerebrovascular accident). Long-term detrimental effects are more common: they include coronary artery disease, kidney disease, congestive heart failure, eye problems and cerebrovascular disease.

Fitness and Diving Issue: As long as the individual's blood pressure is under control, the main concerns should be the side effects of medication(s) and evidence of end-organ damage. Divers who have demonstrated adequate control of blood pressure with no significant decrease in performance in the water due to the side effects of drugs, should be able to dive safely.

A recent report in a diving medical journal citing several episodes of acute pulmonary edema (i.e., lungs congested with fluid) in individuals with uncontrolled hypertension while they were diving. Regular physical examinations and appropriate screening for the long-term consequences of hypertension such as coronary artery disease are necessary.

Medication Used in Treatment: Mild hypertension may be controlled with diet and exercise; however, medication is often necessary. Many classes of drugs are used to treat hypertension, with varying side effects. Some individuals must change medications after one drug appears to be or becomes ineffective. Others might require more than one drug taken at the same time to keep the blood pressure under control.

Classes of drugs known as beta-blockers often cause a decrease in maximum exercise tolerance and may also have some effect on the airways. This normally poses no problem for the average diver. ACE (angiotensin converting enzyme) inhibitors are the preferred class of drugs for treating hypertensive divers; a persistent cough is a possible side effect.

Calcium channel blockers are another choice, but lightheadedness when going from a sitting or supine position to standing may be a significant side effect.

Diuretics are also frequently used to treat hypertension. This requires careful attention to hydration and electrolyte status. Most anti-hypertensive medications are compatible with diving as long as the side effects experienced by the diver are minimal and their performance in the water is not significantly compromised. Any diver with long-standing high blood pressure should be monitored for secondary effects on the heart and kidneys.

Coronary Artery Disease

Description of Condition: Coronary atherosclerosis is commonly described as "hardening of the arteries." It's the result of the deposition of cholesterol and other material along the walls of the arteries of the heart. The walls of the arteries, in response to the deposition of this material, also thicken. The end result is a progressively increasing blockage to blood flow through the vessel. Many factors contribute to the development of coronary atherosclerosis: a diet high in fat and cholesterol, smoking, hypertension, increasing age and family history. Women of reproductive age are generally at a lower risk due to the protective effects of estrogen. In the United States and other industrialized countries, coronary artery disease is the leading cause of death.

Fitness and Diving Issue: Symptomatic coronary artery disease is a contraindication to safe diving: don't dive with it. Coronary artery disease results in a decreased delivery of blood - and therefore, oxygen - to the muscular tissue of the heart. Exercise increases the heart's need for oxygen. Depriving myocardial tissue of oxygen can lead to abnormal heart rhythms and / or myocardial infarction, or heart attack.

The classic symptom of coronary artery disease is chest pain, especially when it follows exertion. Unfortunately, many people have no symptoms before they experience a heart attack. Cardiovascular disease is a significant cause of death among divers. Older divers and those with significant risk factors for coronary artery disease should have regular medical evaluations and appropriate studies (e.g., treadmill stress test).

Medication Used in Treatment: Medications typically used in the treatment of this disease include nitroglycerin, calcium channel blockers and beta-blockers. At some point, someone with coronary artery disease may need a revascularization procedure, or the re-establishment of blood supply, through bypass surgery or angioplasty. If the procedure is successful, the individual may be able to return to diving after a period of healing and a thorough cardiovascular evaluation (see "Coronary Artery Bypass Grafting," below).

Myocardial Infarction

Description of Condition: Myocardial infarction (MI), or heart attack, occurs when damage to the heart muscle cells results from interrupted blood flow to the tissue. Risk factors for heart attack are the same as those for coronary artery disease.

Most commonly, a myocardial infarction is the direct consequence of coronary atherosclerosis, or hardening of the arteries. The blocked arteries stop blood flow to the heart tissue and deprive the cells of necessary oxygen. Small areas of heart muscle may sustain damage, resulting in a scar; this may even occur without the individual experiencing significant symptoms. If larger areas of the heart are deprived of oxygen or if the cells that conduct the primary electrical impulses are within an area where blood flow is decreased, the heart may beat irregularly or even stop beating altogether. It is not unusual for sudden cardiac death to be the first symptom of coronary artery disease.

Fitness and Diving Issue: Cardiovascular events cause 20 to 30 percent of all deaths that occur while scuba diving. For many people, the real problem is that the first sign of coronary artery disease is a heart attack. The only realistic approach is to recommend appropriate measures to prevent the development of coronary atherosclerosis and to encourage regular medical evaluations for those individuals at risk.

Prudent diet and regular exercise should be habitual for divers. Older individuals and divers who have a family history of myocardial infarctions, especially at an early age, should receive appropriate evaluations to detect early signs of coronary artery disease.

Individuals who have experienced previous heart attacks are at risk for additional cardiac events in the future, and damaged heart tissue may have compromised cardiac function. The damaged left ventricle may not be able to pump blood as efficiently as it could prior to the MI.

Regardless of whether an individual has had a revascularization procedure (see "Coronary Artery Bypass Grafting"), strict criteria must be met prior to an individual's safe return to diving. After a period of healing - six to 12 months is recommended - an individual should undergo a thorough cardiovascular evaluation, which includes an exercise stress test. The individual should perform at a level of 13 mets (stage 4 on Bruce protocol). This is a fairly brisk level of exercise, equating to progressively running faster until the patient reaches a pace that is slightly faster than running an 8-minue mile (for a very brief period of time). Performance at that level without symptoms or EKG changes indicates normal exercise tolerance.

Coronary Artery Bypass Graft

Description of Condition: Fortunately, for both patients and thoracic surgeons coronary artery disease affects the first part, or proximal end, of the artery much more frequently and severely than the downstream portion of the artery. This allows for a surgical procedure that uses a portion of a vein or another artery to direct blood around the blockage. Doctors perform this procedure hundreds of times daily around the country - more than 500,000 times annually. If the bypass is successful, the individual should become free of the symptoms of coronary artery disease, and the heart muscle should receive normal blood flow and oxygen.

A less invasive procedure, coronary angioplasty, consists of placing a catheter with a balloon on its tip into the area of the blockage and inflating the balloon to open the artery. This procedure does not require opening the chest and can be performed in an outpatient setting.

Fitness and Diving Issue: An individual who has undergone coronary artery bypass grafting or angioplasty may have suffered significant cardiac damage prior to having the surgery. The post-operative cardiac function of individuals dictates their fitness for diving.

Anyone who has had open-chest surgery needs appropriate medical evaluation prior to scuba diving. After a period of stabilization and healing (6-12 months is usually recommended), the individual should have a thorough cardiovascular evaluation prior to being cleared to dive. He or she should be free of chest pain and have normal exercise tolerance, as evidenced by a normal stress EKG test (13 mets or stage 4 of the Bruce protocol - defined at the end of previous section on MI). If there is any doubt about the success of the procedure or how open the coronary arteries are, the individual should refrain from diving.

Mitral Valve Prolapse

Description of Condition: Mitral valve prolapse (MVP - called "click-murmur" syndrome, floppy-valve syndrome) is a common condition, especially in women. The problem arises from some excess tissue and loose connective tissue in the structure of the mitral valve in the heart: part of the valve protrudes down into the left ventricle during contraction of the heart.

An individual with MVP may have absolutely no symptoms, or the symptoms may vary from occasional palpitations, or unusual feeling in the chest arising from the heart beating, to atypical chest pain and a myocardial infarction. There is also a slightly increased risk of a small stroke or transient loss of consciousness.

Fitness and Diving Issue: Frequently mitral valve prolapse will not cause any symptoms or result in any changes in blood flow that would prevent an individual from diving safely. A diver with known mitral valve prolapse who has no symptoms and takes no medications for the problem should be able to safely participate in diving. The individual should require no medications and should be free from chest pain, any alteration in consciousness, palpitations and abnormal heartbeats. Individuals with abnormal cardiac rhythm, which can produce palpitations, should not dive unless these palpitations can be controlled with low doses of anti-arrhythmic medications.

Medication Used in Treatment: Beta-blockers are occasionally prescribed for mitral valve prolapse. These often cause a decrease in maximum exercise tolerance and may also have some effect on the airways. This normally poses no problem for the average diver, but it may be important in emergency situations.

Dysrhythmias

Description of Condition: The term "dysrhythmia" means abnormal heartbeat and is used to describe a wide range of conditions ranging from benign, non-pathologic conditions to severe, life-threatening rhythm disturbances. More familiar to many people is the term "arrhythmia," which literally means "no heartbeat."

The normal heart beats 60 to 100 times each minute. In well-trained athletes or even in select non-athletic individuals completely at rest, the heart may beat as slowly as 40 to 50 times each minute. Entirely healthy, normal individuals have occasional extra beats or minor changes in rhythm. These can be caused by drugs (caffeine), stress, or for no apparent reason. Dysrhythmias become serious only when they are prolonged or when they do not result in the desired mechanical contraction of the heart.

Physiologically significant extra heartbeats may originate in the upper chambers of the heart (supraventricular tachycardia or atrial dysrhythmia) or in the lower chambers of the heart (ventricular tachycardia). The cause may be due to a short-circuit or an extra conduction pathway for the impulse or secondary to some other cardiac pathology. People who have episodes or periods of rapid heartbeat are at risk for losing consciousness during these events. There are also conditions where the person has a fairly stable dysrhythmia (e.g., fixed atrial fibrillation), but they usually have additional cardiovascular and other health problems that coincide with their rhythm disturbance. A slow heart rate or heart block may cause symptoms, too.

Fitness and Diving Issue: The more serious dysrhythmias, like ventricular tachycardia and many types of atrial rhythm disturbances, are incompatible with diving. The risk for any person developing a dysrhythmia during a dive is, of course, losing consciousness while underwater. Supraventricular tachycardias are unpredictable in onset and are often triggered by immersing the face in cold water. Someone who has had more than one episode of this type of dysrhythmia should not dive.

An individual with any cardiac dysrhythmia needs a complete medical evaluation by a cardiologist prior to engaging in scuba diving. In some cases, thorough conduction (electrophysiologic) studies can identify an abnormal conduction pathway and the problem can be corrected. Recently, doctors and researchers have determined that people with some dysrhythmias (e.g., certain types of Wolff-Parkinson-White Syndrome) may safely participate in diving after a thorough evaluation by a cardiologist. Also, in select cases, some people with stable atrial dysrhythmias (e.g., uncomplicated atrial fibrillation) may dive safely if a cardiologist determines that there are no other significant health problems.

Medication Used in Treatment: Most dysrhythmias that require medication are medically disqualifying for safe diving. Exceptions may be made on a case-by-case basis in consultation with a cardiologist and diving medical officer.

Murmurs

Description of Condition: A heart murmur is an extra sound that can be heard during chest examination with a stethoscope. The opening and closing of the heart valves produce expected and predictable sounds in individuals with normal heartbeats. Murmurs represent extra sounds caused by turbulent or abnormal flow of blood past a heart valve, in the heart itself or in great vessels (i.e., aorta, pulmonary arteries).

Some murmurs occur strictly from increased flow. For example, pregnant women often have a functional murmur due to a greater blood volume and hyperdynamic metabolism; these are benign. Other murmurs are due to damaged heart valves and represent significant pathology. Damaged valves may either restrict blood flow (stenotic lesions) or allow blood to flow back into the chamber of the heart from which it had just exited (regurgitant lesions). Heart valves can be damaged due to infection, trauma, heart muscle damage (myocardial infarction), or an individual may be born with a structurally abnormal heart valve.

Fitness and Diving Issue: Stenotic lesions, such as aortic and mitral stenosis, restrict efficient blood flow and may have serious consequences during exercise. Significant aortic stenosis places an individual at greater risk for sudden cardiac death while exercising; it is a contraindication for diving. Mitral stenosis also limits the response to exercise and, over a period of time, can result in congestive heart failure.

Regurgitant lesions pose somewhat less of a risk during diving. Over a period of years, the heart will be taxed by the extra work necessary to pump blood, and heart failure may be the long-term result. Divers with these types of heart valve problems may safely participate in diving if they have no symptoms and have normal left ventricular structure and function, as evidenced by an echocardiogram.

Atrial And Ventricular Septal Defects

Description of Condition: An atrial septal defect (ASD) results from the incomplete closing of the wall that separates the right and left atria (the two upper chambers of the heart) during embryonic development. This is not an uncommon phenomenon in the general population, and, if the hole is small enough, the average person will experience minimal physiologic consequences. Women are affected more commonly than men.

Surgical correction of the defect may be undertaken, especially if the person is experiencing symptoms secondary to blood flowing from the normally higher pressure left atrium to the right atrium. Early in life, symptoms may be few, but over a period of years, complications, such as abnormal heart beats and shunting (bypassing) of blood from left to right may occur.

On examination, the person with an ASD may have a significant murmur. A ventricular septal defect (VSD) is a communication, or opening, between the right and left ventricles, the lower chambers of the heart. A fairly common developmental abnormality, VSD often merits surgical correction if the defect is large. Because of the large difference in pressures between the left and right ventricles, blood flow through the defect is nearly always from left to right. The individual with ventricular septal defects may experience long-term consequences.

Fitness and Diving Issue: While the normal pressures in the chambers of the heart favor blood flowing from left to right through an ASD and VSD, periods in which this flow is reversed can occur, particularly for ASD. Although individual variations exist, Doppler studies have shown that most divers will have venous bubbles after a dive of significant depth and bottom time. These usually pose no significant threat, and the diver remains symptom-free.

Having a defect that allows bubbles to cross from the right side of the heart to the left is a whole different matter, however: once in the left side of the heart, bubbles may then be transported through the arteries to areas of the body where they can do some harm (e.g., to the brain, kidneys, and spinal cord). Several studies have demonstrated that a rate of ASD (and other defects in the wall separating the right and left sides of the heart) in divers treated for decompression illness was higher than expected, compared to the general population.

Someone with an ASD or VSD who wants to take up scuba diving should be discouraged from doing so. The diver with a known ASD or VSD should know of the potential increased risk of decompression illness and make an educated decision whether to continue diving. Individuals with a VSD, where the shunt is small and runs uniformly from left to right as determined by an echocardiogram, may be able to dive if it is determined to be safe by a physician knowledgeable in diving medicine.

Raynaud's Syndrome/Phenomenon

Description of Condition: Raynaud's Syndrome is a condition where a person experiences episodes of decreased effective blood flow to the extremities, most significantly fingers and toes; this results in cold, pale fingers and toes, followed by pain and redness in these areas as blood flow returns. The underlying problem is constriction of the blood vessels in response to cold, stress or some other phenomenon supplying these areas. Symptoms are often mild. Raynaud's phenomenon may occur as an isolated problem, but it is more often associated with autoimmune and connective tissue disorders such as scleroderma, rheumatoid arthritis and lupus.

Fitness and Diving Issue: Raynaud's Syndrome poses a threat to a diver who is so severely affected that he or she may lose function or dexterity in the hands and fingers during the dive. If coldness is a trigger that causes symptoms in the individual, immersion in cold water will likely do the same. These individuals should avoid diving in water cold enough to elicit symptoms in an ungloved hand. The pain may be significant enough that, for all practical purposes, the diver will not be able to use his or her hands. Less severely affected individuals may be able to function adequately in the water.

Medication Used in Treatment: Calcium channel blockers may be prescribed for individuals with severe symptoms; lightheadedness when going from a sitting or supine position to standing may be a significant side effect.

Patent Foramen Ovale

Description of Condition: The foramen ovale is an opening that exists between the right and left atria, the two upper chambers of the heart. During the fetal period, this communication is necessary for blood to bypass the circulation of the lungs (since there is no air in the lungs at this time) and go directly to the rest of the body. Within the first few days of life, this opening seals over, ending the link between these heart chambers. In approximately 25-30 percent of individuals, this communication persists as a small opening, called a patent foramen ovale (PFO).

A PFO may be very small, physiologically insignificant, or it may be larger and occasionally a route for the bypass or shunting of blood. Usually, because the pressure in the left atrium exceeds that in the right atrium, no blood crosses the PFO (when patent, or open, there is still a flap of tissue in the left atrium that overlies the opening of the PFO).

Fitness and Diving Issue: As in the case of atrial and ventricular septal defects, under certain circumstances, a PFO can result in shunting of blood from the right side of the heart to the left side. This is much more likely to occur in the atria than the ventricles because of the pressure differences between the chambers. Innocuous bubbles that may develop in the venous side of the circulation after a dive (see "Atrial and Ventricular Septal Defects," above) may be shunted to the left side of the heart and then distributed through the arteries. The result is that a paradoxical gas embolism or severe decompression sickness can result from a seemingly innocent dive profile.

Studies of divers with severe decompression sickness have shown a rate of patent foramen ovale higher than that observed in the general population. Special Doppler bubble contrast studies can identify a PFO. The diver with a known PFO should know the potential increased risk of decompression illness. A diver with a PFO who has suffered an embolism or serious decompression sickness after a low-risk dive profile should likely refrain from future diving.

At present, most diving physicians agree that the risk of a problem associated with a PFO is not significant enough to warrant widespread screening of all divers. An episode of severe decompression illness that is not explained by the dive profile should initiate an evaluation for the existence of a PFO.

Heart Valve Replacement

Description of Condition: Doctors in the United States perform more than 70,000 heart valve replacements each year. From birth, an individual may have an abnormal heart valve that requires replacement due to accelerated wear and tear (e.g., this happens with bicuspid aortic valves), or valve damage may occur following an infection or as an extension of damage to the adjacent heart muscle.

Most commonly, valve replacement develops from the consequences of bacterial throat infections, such as Strep throat. In the body's attempt to fight off the bacterial infection, the heart valves, as innocent bystanders, sustain damage (called rheumatic heart disease). With the use of antibiotics, rheumatic heart disease occurs less commonly today, but individuals who had this problem during childhood may now, as adults, experience the consequences of the damage to the valves.

Fitness and Diving Issue: Anyone who has had heart surgery should be scrutinized a little more carefully regarding medical fitness to dive. With a properly functioning heart valve and no symptoms of cardiovascular disease, the real concern for a diver with an artificial heart valve is the anticoagulation (blood thinning) medication required to keep the valve functioning.

A mechanical valve (made of metal, polymer etc.) requires medication to keep blood clots from forming on the valve. This, of course, increases the risk of bleeding, and the diver needs to be aware of this risk, especially as it relates to trauma. Heart valves from pigs are also used to replace damaged native valves. These do not require anticoagulation medication, but they wear out sooner and require replacement earlier than mechanical valves.

LCDR James Caruso (M.D.) is Attending Pathologist and Diving Medical Officer for the U.S. Navy at the Naval Hospital, Pensacola, Fla., and a consulting physician for DAN. These opinions are his own and do not reflect the official policy of the Department of the Navy, Department of Defense, or the U.S. government.

From the July/August 1999 issue of Alert Diver

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The First Diver

2009-02-26T06:47:00.001-08:00

The first known diver in history

Perhaps one of the first famous divers in history is the greek Skyllias from Skione.

In ancient times, diving was an activity strictly for the lower classes and the main objective was to use marine creatures as food rather than the greed to find gold and other valuable objects.

During the Medic Wars, Skyllias and his daughter Hydna served persian king Xerxes (486-465 BC), rescueing for him several underwater treasures.

But when Xerxes threathened to attack Greece with his fleet, Skyllias and Hydna took advantage of a storm to cut off the ships anchor lines, leaving the fleet defenseless and at the mercy of the storm. Finally, the storm dragged the ships against the rocks destroying them and leaving the persian army helpless and defeated.

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Effects of pressure on a diver lungs

2009-02-22T10:43:00.001-08:00

Never hold your breath while scuba diving!

The lung capacity on an average adult is 6 Lts of air. This air volume will be affected by the increasing underwater pressure as the diver descends (See "Pressure, Volume and Density")

As the diver descends, the lungs volume will decrease as a result of the increase of pressure. This change of volume will be proportional to the number of atmospheres at a given depth.

At 10 Mts / 33 Feet, where the pressure is 2 bar /ata, lung volume will be one half smaller than at the surface. At 30 Mts / 100 Feet (The recommended depth for recreational divers) the lungs volume will be as small as one quarter smaller than at the surface.

But even when the lung volume keeps becoming smaller as the diver descends, the air capacity remains the same. So when we breath compressed air at depth, we are actually adding an extra amount of air to our lungs in order to equalize them to the surrounding pressure. If a diver holds his / her breath while scuba diving, serious lung damage may occur.

That is why rule number one of scuba diving states: "Never Hold your Breath"

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Diving and Asthma

2009-02-22T08:37:00.000-08:00

Diving & Asthma

In general, asthma is a lung disorder in which there is a tendency for the muscle surrounding the bronchi (breathing tubes) to contract excessively, causing narrowing, or broncho-constriction. As a result, this causes increased breathing resistance, which can manifest as wheezing, chest "tightness", cough, or breathlessness. In asthmatics, broncho-constriction can be precipitated by exposure to allergens, noxious fumes, cold air, exercise or respiratory infections such as a "cold". People with asthma may experience broncho-constriction due to more than one of these factors, but many asthmatics will experience a measurable increase in breathing resistance after exposure to any one or several of them. The increase in breathing resistance caused by bronchial narrowing may be compounded by the accumulation of mucus within the airways.

Serious potential risks may make scuba diving, which is often performed in isolated locations and far from competent medical care, an unwise elective sport for an individual with asthma. There are primarily two issues.

During scuba diving the diver experiences a reduction in breathing capacity due to the effects of immersion and an increase in breathing resistance caused by the higher gas density at depth. At 33-feet underwater, the maximum breathing capacity of a normal scuba diver is only 70-percent of the surface value. At 100-feet underwater, this reduction is approximately 50-percent. If, for example, a diver’s breathing capacity is already reduced because of asthma, there may not be sufficient reserve to accommodate the required increase demanded by exertion.

Both narrowing of the bronchi and excessive mucus production can inhibit exhalation of air during ascent, and could predispose the diver to pulmonary barotrauma leading to pneumothorax, pneumo-mediastinum and/or arterial gas embolism.

For these reasons, physicians trained in diving medicine have traditionally recommended that people with asthma should never dive. However, a consensus of experts at a 1995 workshop held under the auspices of the Undersea and Hyperbaric Medical Society (UHMS) proposed more liberal guidelines. Essentially, the UHMS workshop panel felt that the risk of diving is probably acceptable if, the diving candidate with some asthmatic ‘history’ demonstrates normal pulmonary function at rest (FVC, mid-expiratory flow, FEV1, FEF 25-75) and then again after strenuous exercise. It was also concluded that the degree of competency in making a medical assessment of diving fitness is enhanced if the examining doctor has relevant knowledge or experience of the diving environment and its associated hazards.

It is important to note that asthma severity can wax and wane. Symptoms may worsen for 4-6 weeks after a "cold" or during certain seasons (for example in response to high levels of pollen in the air.) Therefore, even if a person with asthma fulfills the criteria listed above, diving is not recommended unless the diver is free of respiratory symptoms before each dive.

Reference:

Elliott, D.H. (1996) Are Asthmatics Fit To Dive?, Undersea and Hyperbaric Medical Society (UHMS) – Annual Scientific Meeting, 21-June-1995
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Dive Equipment

2009-01-20T08:09:00.000-08:00

BCD (Buoyancy Control Device)

Regulator

Alternate Air Source

Dive Mask

Snorkel

Fins

Exposure Protection (wet or dry suit)

Scuba Tank

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Heat loss underwater

2009-01-19T08:12:00.000-08:00

Even when diving in tropical waters (27 C/78 F) divers may experience a significant loss of body heat.

Water is able to conduct heat more efficiently because is more dense than air. Therefore, energy is conducted easier underwater.

Undwewater we lose body heat twenty times faster than in air. So it is highly recommended to dive with some kind of exposure protection at all times.

Failing to do so may lead to hypotermia, a condition in which your body cools so much it that it can´t function normally.

There are two types of exposure protection: Wet suits and dry suits. The first ones are usually made of neoprene rubber and the reason why they are called wet suits is because the diver gets wet when using them.

Wet suit reduce heat loss by putting a layer of insulating foam neoprene over your skin. Water enters at the wrists, ankles and neck and gets trapped between the diver´s skin and the suit.

The diver´s body heats the water quickly, and as long as it remains trapped the diver remains warm. That is why is important that wet suits fit well.

A dry suit will keep the diver dry and it is a recommended option when diving in waters about18 C/ 65 F). They provide the most thermal protection of all suits used by recreational divers.

Because air conducts heat relatively poorly, dry suits insulate divers with a layer of air, as well as with insulating materials such as undergarment within the suit.

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Pressure, Volume and Density

2009-01-13T12:39:00.000-08:00

As you descent underwater you will be affected by the changes of pressure.

Underwater, pressure increases one bar every 10 Mts/33 Feet, but as divers we can not ignore the atmosperic pressure having to add it as one bar/atm. That means that at 10 Mts/33 Feet the surrounding pressure is 2 bar/atm.

As we descent and pressure increases, any volume of air is affected by this pressure changes. The ari volume will decrease as the surounding pressure increases.

At the same time, Density will be affected also by the pressure changes. Density will increase as pressure increases.

As divers, is important to understand these changes, since they will affect us directly while underwater.

As we descend, the increase of pressure will affect both our ears and lungs since they are air spaces in our body. The increase of pressure will also affect our air consumption, needing more air as we descend deeper since the volume of our lungs will keep decreasing proportionally to the number of bar or atmospheres at a given depth.

As we descend underwater, the pressure of our body`s ear spaces (ears and lungs) decrease so it is necessary to equalize them to the surrounding pressure underwater.

To equalize our ears, we can pinch our nostrils and blow gently. we need to do this every 1 Meter /3 Feet as we descend, before feeling any discomfort. Should we feel any pain as we descend, we will need to ascend a few feet until discomfort disappears and then try equalizing our ears again.

To equalize our lungs, we simply keep breathing. In fact, breathing is the rule number one on scuba diving. Holding your breath while scuba diving may result in serious lung damage.

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