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Cardiovascular Fitness and Diving

Scuba diving exposes you to many effects, including immersion, cold, hyperbaric gases, elevated breathing pressure, exercise and stress, as well as a post-dive risk of gas bubbles circulating in your blood. Your heart’s capacity to support an elevated blood output decreases with age and with disease. Having a healthy heart is of the utmost importance to your safety while scuba diving as well as to your ability to exercise generally and your life span.

Below are some common cardiovascular issues that could affect a diver, including their implications in diving and possible medical treatments.

HYPERTENSION

Hypertension, or high blood pressure, is one of the most common medical conditions seen in the diving population — no surprise 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.

Implications in Diving:
 
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

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 industrialised countries, coronary artery disease is the leading cause of death.

Implications in Diving:
 
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 (HEART ATTACK)

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.

Implications in Diving:
 
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-minute 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

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.

Implications in Diving:
 
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 stabilisation 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

Mitral valve prolapse (MVP) 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.

Implications in Diving:

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

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.

Implications in Diving:
 
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

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.

Implications in Diving:

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 & VENTRICULAR SEPTAL DEFECTS

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.

Implications in Diving:
 
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

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.

Implications in Diving:
 
Raynaud’s Syndrome poses a threat to a diver who is so severely affected that they 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

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).

Implications in Diving:
 
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

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.

Implications in Diving:
 
Anyone who has had heart surgery should be scrutinised 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.

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Recompression chamber Recompression treatment Recompression Recycle Reef Chcek Reef Conservation Reef Environmental Education Foundation Reef safe Reef surveyors Refractive correction Regal Sea Goddesses Regulator failure Regulators Regulator Remote areas Remote islands Renewable Report incidents Rescue Divers Rescue Procedure Rescue breathing Rescue breaths Rescue diver Rescue skills Rescue skill Rescue training Rescue Research Resume diving Return To Diving Return to diving Reuseable items Risk Assessments Risk assesments Risk assessment Risk elements Risk management Risks of Seizures Roatan Marine Park Roatan SABS 019 SMB SafariLive Safe diving practices Safety Concerns Safety Gear Safety Stop Safety in Air Safety SaherSafe Barrier Salish Seas Salty Wanderer Sanitising Sara Andreotti Sardine Run Sargassum sea Saturation Diving Save our seas Schrimps Science Scoliosis Scombroid Poisoning Scorpion Fish Scuba Air Quality Scuba Guru Scuba Injury Scuba Instructor Scuba children Scuba divers Scuba dive Scuba education Scuba health Scubalearners Scubalife Sea Horses Sea Turtles Sea slugs Seagrass Sealcolonies Sealife Seals Seasickness Seaweeds Seaweed Sea Self Rescue Shallow dives Shark Protection Shark Research Shark conservation Shark diving Sharks Shipwrecks Shore entries Shoulder strength Sideplank Signs and Symptoms Silty bottoms Sit-ups Sixgill Sharks Skills in action Skin Bends Skin outbreak Skin rash Smart phone photography Snells Window Snorkeling Snorkels Social Distancing Sodwana Bay Solomon Islands Sonnier bank South Africa SpareAir Sperm Whales Spinal Bend Spinal bends Spinal cord DCS Spinal dura Spinal pain Spinner dolphins Splits Sports medicine Squeezes Squid Run Stability exercise Standars Statin Mediction Stay Fit Steel Stents Step ups Stephen Frink Stepping up Stockton Rush Stonetown Stretch band exercise Stretch bands Strobe Lighting Strobes Stroke Submerge tech Submerged Sudafed Sulawesi Sun protection Sunscreen Supplemental oxygen Surface Marker Buoys Surface supplied Air Surfaced Surgeries Surgery Suspension training Swim Fitness Swimmers health SwimmingIn wateractivities Swimming Symbiosis Symbiosys TRavel safety Tabata protocol Talya Davidoff Tanzania Tattoes Tec Clark Technical Diving Technical divng The Bends The Titanic Wreck The Wild Coast The greatest Shoal The truth Thermal Notions Thermoregulation Thomas Peschak Thunder Bay National Marine Sanctuary Tides Tips and trick Tonga Tooth squeeze Transplants Travel destinations Travel smarter Travel tips Travel Tropical Coastal Management Tunnelling Turks and Caicos Turtles Tweezers Ultrsound Umkomaas Unconscious diver Unconsciousness Underground work Underseaa world Underwaater Photos Underwater Photography Underwater Photograper Underwater Photograpgraphy Underwater Photographer Manirelife Underwater Research Underwater critters Underwater floral Gardens Underwater hockey Underwater imaging Underwater photographer Underwater photography Underwater pho Underwater sound Underwatercommunications Underwater University of Stellenbosch Unresponsive Urinary retention. VGE Vacations Vaccines Vagus nerve Valsalva manoeuvers Valve stem seals Vape Vaping Vasopressors Vasvagal Syncope Venous gas emboli Ventilate Venting Verna van Schak Videography Virus infections Volatile fuels WWII wrecks War stories Washout treatments Wastewater Watchman device Water Resistance Water Weakness Weigang Xu Weights West Papua Western Cape Diving Wet Lenses Wet diving bell Wetsuit fitting Wetsuites Wetsuits White balance Whitetpped Sharks Wide Angle Photos Wide angles Wildlife park Wildlife Winter Wits Underwater Club Wolf Eels Woman and diving Woman in diving Womans health Woman Women In Diving SA Women and Diving Women in diving Womens Month Womens health Work of Breathing Workout World Deeepst Dive Record World Records Wound dressings Wreck History Wreck divers Wreck dive Wreck diving Wreck exploration Wreckdiving Wrecks Yoga Youth diver Zandile Ndholvu Zanzibar Zoology Zooplankton \ Blennies abrasion absolute pressure acoustic neuroma excision adverse seas air-cushioned alert diver altitude alveolar walls anemia antibiotics anticoagulants antiseptics bandages barodontalgia bent-over barbell rows bioassays biodiversity bloodcells body art breathing air calories burn canal blockage carbon dioxide toxicity cardiovascular career developments cerebrospinal fluid cervical spine checklist chemo port children child chronic obstructive pulmonary disease clearances closed circuit scuba coral growth corrective lenses currents cuts cylinder filling dead lift decompression algorithms decongestants decongestion dehydration dive injuries dive medicing dive ready child dive reflex dive tribe divecomputers diver in distress diver rescue diver training dive diving attraction doctors domestic travel dri-suits drowning dry mucous membranes dry suits dry e-cigarettes ear spaces elearning electrolyte imbalance electroytes emergency action plans emergency assessment emergency training environmentally friendly equalising equalizing exposure injuries eyes fEMAL DIVERS fire rescue fish watching fitness Balance fitnes flexible tubing frediving freedivers gas bubble gas poisoning gastric acid gene expression health heartburn histidine hospital humidity hypobaric hypoxia immersion and bubble formation immersion pulmonary edema (IPE informal education isopropyl alcohol jaundice join DAN knee laparoscopic surgery life jackets longevity lower stress lox oxygen level malaise marielife marine pathogens medical issues medical procedures medical risk assesment medications mental challenge mental preparedness micro-organisims micro minor illness mucous membranes multilineage dysplasia myelodysplasia nasal steroids nasal near drowning nematocysts neurological newdivers nitrogen bubbles off-gassed operating theatre operations orthopeadic otitis media out planting outgas pain perforation phillippines phrenic nerve physical challenges pinched nerves plasters pneumoperitoneum polyester-TPU polyether-TPU post dive posture prescription mask preserve prevention proper equalization psychoactive pulmonary barotrauma. pulmonary injury. pulmunary barotrauma radiation rebreather mask rebreathers retinal detachment risk areas safety stops saturation scissors scuba equipment scuba sea goddesses single use sinus infections situationalawarenes smoking snorkeling. spearfishing sterilising stings strength sub-aquatic sunscreen lotion swimmers ears tattoo care tecnical diver thermal protection tissue damage toxicity training trimix unified standards upwelling vision impaired vomiting warmers water quality zinc oxide