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Chapter 35 — 3
CONTRIBUTING CAUSES
There are a number of ways death or incapacity from cardiac diseases can come about and
they are usually precipitated by one or more
trigger factors
encountered while diving.
Some of these are:
Exercise
Severe exercise can cause sudden death by a number of mechanisms. Probably the most
well known example was the death of the first marathon runner who dropped dead after
running from Marathon to Athens to deliver the news of the Greek victory over the
Persians. In reality, his death was probably due to heat stroke or heat exhaustion. Usually
exercise will cause cardiac deaths only in those with some cardiac disease or malfunction.
A diver is at a disadvantage in some ways during exercise. During exertion on land, the
cardiac output increases to meet the metabolic demands of the exercising muscles. In doing
this, the work of the heart is made easier by blood vessel dilatation in the peripheral
circulation, reducing the resistance to blood flow. In an exercising diver however, the skin
blood vessels do not dilate because they are trying to conserve heat in response to the
surrounding cold water. The diver's heart has to pump against an increased resistance and so
work harder for a given amount of exercise, compared to a land athlete.
One of the limitations to exercise on land is the inability to disperse the metabolic heat of
exercise. With the diver, much of this heat is conducted away by the water. As a result, it is
possible to exercise in the water to a greater degree without the "hot and sweaty"
discomfort.
It is therefore possible to exercise to a great degree in the water, with less discomfort but at
a greater strain on the heart. In a trained athlete with a healthy heart this probably is only of
academic interest. In a middle aged (i.e. over 40 years) diver with some degree of coronary
artery disease ("narrowing of the arteries") the diver can overload the heart without realising
it. This can result in sudden death.
Exercise, even in fit healthy divers, has been shown to cause significant arrhythmias with
diving. It is much more likely to cause incapacitating or fatal arrhythmias in divers with
cardiac disease.
Psychological and Personality Factors
Some personalities are more susceptible to cardiac disease than others. The so called
Type
A
or
Type D personality
is believed to be most prone to cardiac disease. These individuals
are intensely competitive, aggressive and as a result, by society standards, usually
successful. They drive themselves hard and do not give up. They are twice as likely to
develop coronary artery disease than others, and when they develop it they are likely to
push their diseased heart beyond its limitations.
Traditionally this has been a
male personality trait
, but in a more competitive and equal
society it is probable that a similar disease pattern will emerge in women competing in
previously male dominated areas. Sudden death is not uncommon in Type A personalities.