The aging of the divepopulation and an increasedrate of cardiac-related

deaths with age in scuba divers arebecoming important concerns tothe dive community. In a favorableenvironment, scuba diving is aleisurely physical activity thatmany people choose for theirlifetime or late-life recreation. Ageis not considered a disease or acondition that necessarilydisqualifies people from diving orany other physical activities, but itis associated with a decrease infunctional capacity and anincreased prevalence of chronicdiseases. Criteria for medicalfitness to dive have been definedand used with confidence for morethan half a century. When it comes

Matters of the HeartAging, wellness and fitness to dive

BY DR PETAR DENOBLE

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to physical fitness requirements forscuba diving, however, there is noconsensus; divers are generallyadvised to evaluate the divingenvironment before each dive andavoid strenuous conditions thatmay exceed their physicalcapabilities. This approach seemsto work for most divers exceptthose who become victims of divefatalities. Older divers are at greaterrisk of fatal accidents, and the mostcommon cause of deaths in olderdivers is an acute cardiac event,which can be considered a suddendeath. In this article we will brieflyreview the epidemiology of suddencardiac death, age-related changesto the cardiovascular system,specific stressors in diving, the waysthese may be related to divefatalities and what divers can do tomitigate their personal risks.

SUDDEN CARDIAC DEATHSudden cardiac death (SCD)describes the unexpected naturaldeath from a cardiac cause within ashort time period (generally within onehour of symptom onset) in a personwithout any prior condition that wouldappear fatal. Such a rapid death isoften attributed to a cardiacarrhythmia, but because 40 percentof sudden deaths may beunwitnessed it is impossible to tellwith certainty.

SCD may be preceded bynonspecific symptoms such as chestpain (indicating ischaemia, i.e. lackof blood supply and thereforeoxygen), palpitations (arrhythmias) ordifficulty breathing (indicatingcongestive heart failure). In cases ofischaemia or congestive heart failure,the heart muscle fails, and in casesof arrhythmia the synchronisation andtiming of heart contractions fail. Both

result in an inability to maintaincirculation, loss of consciousnessand, several minutes after circulationstops, death.

SCD occurs annually in 1 out of 1,000adults in the U.S., accounting for morethan 300,000 deaths each year. Therisk of SCD in adults increases up tosixfold with age and parallels the riskof ischaemic heart disease. Risk isgreater in people with structural heartdiseases, but in 50 percent of SCDcases individuals were not previouslyaware of heart disease, and in 20percent no structural cardiovascularchanges could be found duringautopsy. Divers with symptoms ofcardiovascular disease should beevaluated by a cardiologist and aphysician trained in dive medicineregarding their further participation. Inpeople without symptoms, the risk ofSCD may be evaluated using knowncardiovascular risk factors likesmoking, high blood pressure, highcholesterol, diabetes, lack ofexercise and being overweight. Forexample, people who smoke have arisk of SCD two and a half times thatof nonsmokers.

EFFECTS OF ‘HEALTHY’ AGINGON THE CARDIOVASCULARSYSTEMWe all know a team of young adultswill usually outrun and outplay anotherteam made up of middle-agedadults. Those in their 30s and olderhave already experienced a declinein their personal ability to sustain ahigh level of exercise for a prolongedperiod. Decrease of exercise capacitywith ‘healthy’ aging can be sloweddown with regular exercise, but itcannot be avoided completely. Thedecrease in exercise capacity iscaused by weakened functions of allthe body’s systems, but we will keepour focus on the heart.

The heart has a natural pacemakersystem that controls the heartbeat andthe system of pathways that conductsignals to the muscle cells throughoutthe heart. Over time, the pacemakerloses some of its cells, and pathwaysmay get damaged. These changes canresult in a slightly slower heart rate at

rest and susceptibility to abnormalrhythms like atrial fibrillation.

With age, all structures of the heartbecome more rigid. The muscle of theleft ventricle gets thicker, and theheart may increase slightly in sizeoverall while the volume of the leftventricle may decrease. The heartmay fil l more slowly, empty moreslowly and, thus, eject less blood intocirculation. The increase in heart rateand cardiac output in response tophysical activity get slower, and themaximums get smaller (see table).The decreases in maximal heart rateappear to be an age effect, which ismore pronounced in sedentary peopleand those with overt cardiovasculardiseases.

The autonomic nervous system changeswith age, too. Normally, theparasympathetic side sets the basicresting heart rate, while the sympatheticside affects the heart in anticipation ofand in response to physical activity,stimulating timely and proportionalincreases in blood circulation necessaryto support ongoing activity. Continuous

adjustment between the sympatheticand parasympathetic systems resultin a heart-rate variability evident on abeat-to-beat basis, which is a sign ofa healthy control system. With age,the contribution of the para-sympathetic side wanes, thesympathetic activity increases (evenat rest), heart-rate variabilitydisappears and heart rhythmbecomes more prone to derailments.Low heart-rate variability andincreased resting heart rate (due toloss of parasympathetic tone)independently increase the risk ofSCD more than two and a half times.

EFFECTS OF DIVING ON THECARDIOVASCULAR SYSTEMDiving exposes divers’ bodies tovarious stressors that independ-ently affect cardiovascular function.The major stressors are exerciseimmersion, exposure to cold,increased partial pressure of oxygenand increased work of breathing.

The combined effect of these factorsis that the volume of blood in thevessels of the chest and heart

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16Alert Diver Asia Pacific

increases significantly, stretching thewalls of heart and large vessels.Pressure in the right atrium and bloodpressure slightly increase — more soin cold water. The heart has to workharder to maintain circulation. Theseconditions contribute to variousarrhythmias, from bradycardia (slowheart rate) caused by cold totachyarrhythmia (racing heart rate)caused by cardiac and neuroendocrine(i.e. various gland releasing hormonesin response to stimulation by thenervous system) responses to stress.Older people, especially those withstructural cardiovascular changes andweaker function, are at greater risk ofadverse reactions to these stresses.

The autonomic nervous system isaffected by diving, too. In healthyindividuals, diving increasesparasympathetic effects on heart rate,and heart-rate variability is preserved.Diving that is perceived as stressfulpushes the balance of the autonomicnervous system in the other direction:Sympathetic effects prevail andincrease the heart rate, diminish heart-

rate variability and increase the risk ofarrhythmia.

Although diving is often perceived as aleisurely activity, the level of exertionmay sometimes exceed the physicalcapacity of divers with functionallimitations as well as healthy but olderdivers. In weightless conditions ofimmersion, muscular work is lesspunishing and divers easily exertthemselves beyond their cardio-respiratory limits. Most divers regardswimming against a 0.5-knot current asa challenge. Heart rates measured intrained military divers during shallowunderwater swimming increased to anaverage of 101 beats per minute (bpm)in a 0.6-knot current and to an averageof 141 bpm in a 1.2-knot current. Formany divers this would exceed asustainable level (which is usuallyconsidered to be less than 80 percentof the maximal heart rate). Even moreimportant, divers who do not regularlypractice swimming and do not masterthe technique of underwater swimmingwith fins as well as those who do notstreamline their gear and especially

those whose buoyancy is a bit off,would probably reach their maximalheart rate while swimming even moreslowly. Some may reach their limit justtrying to stay afloat.

WHAT ARE THE RISKS?Fatality statistics indicate at leastone-third of all dive fatalities arerelated to an acute cardiac event. Therisk of cardiac-related death in diversis continuous, steadily increasingwith age; divers older than 50 have arisk 10 times that of divers under 50.While some suspected cardiacevents may be provoked by specificdive effects, some may be not relatedto diving at all, as sudden cardiacdeaths occur in swimming, land-based sports, at rest and duringsleep.

An acute myocardial infarction (heartattack) due to exertion while swimmingagainst current, waves or excessivenegative buoyancy is probably quitecommon among dive-provokedfatalities. It is caused by insufficientblood 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.

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This occurs most commonly in middle-aged male divers unaware of theircoronary artery disease.

It is also reasonable to expect divingcould provoke an acute arrhythmia,which might result in sudden death. Thearrhythmia is a more likely cause ofdeath for older divers. As Dr. CarlEdmonds describes and DAN dataconfirm, “The victim often appearedcalm just before his final collapse.Some were unusually tired or resting,having previously exerted themselves,or were being towed at the time —suggesting some degree of exhaustion.Some acted as if they did not feel wellbefore their final collapse. Somecomplained of difficulty in breathingonly a few seconds before the collapse,whereas others underwater signalledthat they needed to buddy breathe, butrejected the offered regulator.Explanations for the dyspnea(shortness of breath) includepsychogenic hyperventilation,autonomic-induced ventilatorystimulation and pulmonary oedema —the latter being demonstrated atautopsy. In all cases there was anadequate air supply available,suggesting that their dyspnea was notrelated to equipment problems. Somevictims lost consciousness withoutgiving any signal to their buddy,whereas others requested help in acalm manner.”

SCD occurs at comparable rates anda nearly identical age-related patternin diving and in the general population,but a causative relationship betweendiving and SCD should not bedismissed. SCD cases without anobvious external provocative factor aremore common in older divers. Medicalexaminations in such cases revealsigns of heart disease rather thanidentifying a specific event that causedSCD. Outcomes of these divingfatalities might not be different than SCDcases in the general population exceptthe divers usually do not have a chanceof being resuscitated. The best way toavoid SCD is to prevent heart diseaseand maintain wellness and physicalfitness despite aging.

FITNESS AND WELLNESSPROGRAMSPhysical fitness is the ability to movein a physical world and change it bymuscular effort. There are manycomponents to it; the main one is acapacity to conduct aerobic work.Good health and fitness in older ageis a matter of absence of disease,lifelong healthy habits and fitnessmaintenance. Adopting a healthylifestyle at any age will improvequality of life, but a return to thenormal curve of fitness and longevityis probably proportional to previouslyacquired insults. According torecommendations of the AmericanCollege of Sports Medicine (ACSM)and the American Heart Association(AHA), regular physical activity,including aerobic activity andmuscle-strengthening activity, isessential for healthy aging. The U.S.Department of Health and HumanServices published physical activityguidelines that can be found atwww.health.gov. Benefits of exerciseare many, and they are dosedependent: The more one exercises,the greater the benefits are. Theseinclude reduced risk ofcardiovascular disease (and thus,SCD), trombo-embolic stroke,hypertension, type-2 diabetes,osteoporosis, obesity, colon cancer,breast cancer, anxiety anddepression. The ACSM and AHAmaintain that with sufficient skill,experience, fitness and training, olderadults can achieve high levels ofphysical activity. At the same time,for some older adults, age-relatedfitness loss, chronic diseases andfunctional limitations act as barriersto attaining high levels of activity.

While the health benefits of physicalactivity may be achieved with lowto moderate levels of exercise, thismay not increase aerobic capacityor improve fitness for swimmingagainst a strong current. A highlevel of aerobic fitness may beacquired and maintained only byregular vigorous exercise, asapproved by physician. Fitness forswimming against a current

includes fin-swimming skills. Diverswithout these skills may not be able tocreate sufficient propulsion to overcomestrong current despite their high aerobiccapacity for muscular work. Thus, partof divers’ exercise must be dedicatedto fin swimming.

WELLNESSW ellness may be defined in various ways,but it is in essence a subjective state ofsatisfaction with one’s present condition,which depends greatly on underlyinghealth and, at the same time, helpsimprove health. One example of apractice that may help individualsachieve wellness is yoga. Yoga seemsto affect flexibility, posture, balance andmuscular strength. Relaxation andbreathing techniques seem to reduceoverall sympathetic tone in older adults,increase parasympathetic effects onheart rate and potentiate heart-ratevariability. Regular yoga practice reducesanxiety and improves overall wellness.

Feelings of wellness do not necessarilycoincide with physical fitness. Peoplewho do not do regular, vigorous exercisemay discover their limitations in the faceof a challenge — only when it is toolate. For enthusiastic divers, diving maybe very important for achievingwellness. To promote continued fitnessfor diving, divers should maintain ahealthy lifestyle, exercise regularly,practice specific skills for diving, useall means to achieve wellness and makewise choices in diving.

Editor’s Note:In Australia, from 2003 to2008, inclusive, there were atotal of 46 reported scuba-diving related deaths. Ofthese, 17 deaths (37%) arebelieved to have been cardiac-related. This is a worldwidetrend, as indicated by DrDenoble.