Matters of the Heart Aging, Wellness and Fitness to Dive
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Matters of the Heart Aging, wellness and fitness to dive Stephen Frink Photo he aging of the dive to physical fitness requirements for SUDDEN CARDIAC DEATH population and an increased scuba diving, however, there is no Sudden cardiac death (SCD) Trate of cardiac-related consensus; divers are generally describes the unexpected natural deaths with age in scuba divers are advised to evaluate the diving death from a cardiac cause within a becoming important concerns to environment before each dive and short time period (generally within one the dive community. In a favorable avoid strenuous conditions that hour of symptom onset) in a person environment, scuba diving is a may exceed their physical without any prior condition that would leisurely physical activity that capabilities. This approach seems appear fatal. Such a rapid death is many people choose for their to work for most divers except often attributed to a cardiac lifetime or late-life recreation. Age those who become victims of dive arrhythmia, but because 40 percent of sudden deaths may be is not considered a disease or a fatalities. Older divers are at greater unwitnessed it is impossible to tell condition that necessarily risk of fatal accidents, and the most with certainty. disqualifies people from diving or common cause of deaths in older any other physical activities, but it divers is an acute cardiac event, SCD may be preceded by is associated with a decrease in which can be considered a sudden nonspecific symptoms such as chest functional capacity and an death. In this article we will briefly pain (indicating ischaemia, i.e. lack increased prevalence of chronic review the epidemiology of sudden of blood supply and therefore diseases. Criteria for medical cardiac death, age-related changes oxygen), palpitations (arrhythmias) or fitness to dive have been defined to the cardiovascular system, difficulty breathing (indicating and used with confidence for more specific stressors in diving, the ways congestive heart failure). In cases of ischaemia or congestive heart failure, than half a century. When it comes these may be related to dive the heart muscle fails, and in cases fatalities and what divers can do to of arrhythmia the synchronisation and mitigate their personal risks. BY DR PETAR DENOBLE timing of heart contractions fail. Both result in an inability to maintain circulation, loss of consciousness and, several minutes after circulation stops, death. SCD occurs annually in 1 out of 1,000 adults in the U.S., accounting for more than 300,000 deaths each year. The risk of SCD in adults increases up to sixfold with age and parallels the risk of ischaemic heart disease. Risk is greater in people with structural heart diseases, but in 50 percent of SCD cases individuals were not previously aware of heart disease, and in 20 percent no structural cardiovascular changes could be found during autopsy. Divers with symptoms of cardiovascular disease should be evaluated by a cardiologist and a physician trained in dive medicine regarding their further participation. In people without symptoms, the risk of SCD may be evaluated using known cardiovascular risk factors like smoking, high blood pressure, high cholesterol, diabetes, lack of Stephen Frink Photo exercise and being overweight. For example, people who smoke have a risk of SCD two and a half times that of nonsmokers. rest and susceptibility to abnormal adjustment between the sympathetic rhythms like atrial fibrillation. and parasympathetic systems result EFFECTS OF ‘HEALTHY’ AGING in a heart-rate variability evident on a With age, all structures of the heart beat-to-beat basis, which is a sign of ON THE CARDIOVASCULAR become more rigid. The muscle of the a healthy control system. With age, SYSTEM left ventricle gets thicker, and the the contribution of the para- We all know a team of young adults heart may increase slightly in size sympathetic side wanes, the will usually outrun and outplay another overall while the volume of the left sympathetic activity increases (even team made up of middle-aged ventricle may decrease. The heart at rest), heart-rate variability adults. Those in their 30s and older may fill more slowly, empty more disappears and heart rhythm have already experienced a decline slowly and, thus, eject less blood into becomes more prone to derailments. in their personal ability to sustain a circulation. The increase in heart rate Low heart-rate variability and high level of exercise for a prolonged and cardiac output in response to increased resting heart rate (due to period. Decrease of exercise capacity physical activity get slower, and the loss of parasympathetic tone) with ‘healthy’ aging can be slowed maximums get smaller (see table). independently increase the risk of down with regular exercise, but it The decreases in maximal heart rate SCD more than two and a half times. cannot be avoided completely. The appear to be an age effect, which is decrease in exercise capacity is more pronounced in sedentary people EFFECTS OF DIVING ON THE caused by weakened functions of all and those with overt cardiovascular CARDIOVASCULAR SYSTEM the body’s systems, but we will keep diseases. our focus on the heart. Diving exposes divers’ bodies to various stressors that independ- The autonomic nervous system changes ently affect cardiovascular function. The heart has a natural pacemaker with age, too. Normally, the The major stressors are exercise system that controls the heartbeat and parasympathetic side sets the basic immersion, exposure to cold, the system of pathways that conduct resting heart rate, while the sympathetic increased partial pressure of oxygen signals to the muscle cells throughout side affects the heart in anticipation of and increased work of breathing. the heart. Over time, the pacemaker and in response to physical activity, loses some of its cells, and pathways stimulating timely and proportional The combined effect of these factors may get damaged. These changes can increases in blood circulation necessary is that the volume of blood in the result in a slightly slower heart rate at to support ongoing activity. Continuous vessels of the chest and heart increases significantly, stretching the rate variability and increase the risk of those whose buoyancy is a bit off, walls of heart and large vessels. arrhythmia. would probably reach their maximal Pressure in the right atrium and blood heart rate while swimming even more pressure slightly increase — more so Although diving is often perceived as a slowly. Some may reach their limit just in cold water. The heart has to work leisurely activity, the level of exertion trying to stay afloat. harder to maintain circulation. These may sometimes exceed the physical conditions contribute to various capacity of divers with functional WHAT ARE THE RISKS? arrhythmias, from bradycardia (slow limitations as well as healthy but older Fatality statistics indicate at least heart rate) caused by cold to divers. In weightless conditions of one-third of all dive fatalities are tachyarrhythmia (racing heart rate) immersion, muscular work is less related to an acute cardiac event. The caused by cardiac and neuroendocrine punishing and divers easily exert risk of cardiac-related death in divers (i.e. various gland releasing hormones themselves beyond their cardio- is continuous, steadily increasing in response to stimulation by the respiratory limits. Most divers regard with age; divers older than 50 have a nervous system) responses to stress. swimming against a 0.5-knot current as risk 10 times that of divers under 50. Older people, especially those with a challenge. Heart rates measured in While some suspected cardiac structural cardiovascular changes and trained military divers during shallow events may be provoked by specific weaker function, are at greater risk of underwater swimming increased to an dive effects, some may be not related adverse reactions to these stresses. average of 101 beats per minute (bpm) to diving at all, as sudden cardiac in a 0.6-knot current and to an average deaths occur in swimming, land- The autonomic nervous system is of 141 bpm in a 1.2-knot current. For based sports, at rest and during affected by diving, too. In healthy many divers this would exceed a sleep. individuals, diving increases sustainable level (which is usually parasympathetic effects on heart rate, considered to be less than 80 percent An acute myocardial infarction (heart and heart-rate variability is preserved. of the maximal heart rate). Even more attack) due to exertion while swimming Diving that is perceived as stressful important, divers who do not regularly against current, waves or excessive pushes the balance of the autonomic practice swimming and do not master negative buoyancy is probably quite nervous system in the other direction: the technique of underwater swimming common among dive-provoked Sympathetic effects prevail and with fins as well as those who do not fatalities. It is caused by insufficient increase the heart rate, diminish heart- streamline their gear and especially blood supply to working heart muscle. MAXIMUM HEART RATE BY AGE Age (years) 20 30 40 50 60 70 80 90 Traditional estimate (220-age), beats per minute 200 190 180 170 160 150 140 130 Healthy non-smokers (208-0.7 x age), beats per minute 194 187 180 173 166 159 152 145 Modified from Tanaka H. Agre-predicted maximal heart rate. J Am Coll Cardiol. 2001;37:153-6. Stephen Frink Photo Alert Diver Asia Pacific 16 This occurs most commonly in middle- FITNESS AND WELLNESS includes fin-swimming skills. Divers aged male divers unaware of their without these skills may not be able to coronary artery disease. PROGRAMS create sufficient propulsion to overcome Physical fitness is the ability to move strong current despite their high aerobic It is also reasonable to expect diving in a physical world and change it by capacity for muscular work.