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Scuba diving is one of the most rapidly growing participant sports. Commercial diving is of economic importance and necessary for public safety—for example, in offshore oil exploration and underwater inspection of bridge supports and ships hulls. Diving involves physiological stresses that are not encountered in other circumstances, so that the fitness requirements for divers differ from other sports and occupations. There are variations in regulations between nations and organisations. In the United Kingdom the medical requirements are laid out in regulations issued by the Health and Safety Executive for professional divers and in guidelines issued by the United Kingdom Sport Diving Medical Committee for amateur divers. As a general rule, any condition that causes a significantly increased risk of incapacity in or under water or that predisposes to diving related disease will disqualify an individual from diving.
Physiological effects of diving
Immersion alone (which occurs in water at a temperature near to body temperature) rapidly redistributes blood from the legs to the thorax. This increases intrathoracic blood volume by up to 700 ml, right atrial pressures by 18 mm Hg, cardiac output by over 30%, and blood pressure slightly.1 ,2 To correct the increased central blood volume natriuresis and diuresis are stimulated. After immersion for many hours the reduction in plasma volume can be so great that when a casualty is removed from the water and hydrostatic support of venous return is removed hypovolaemic shock and sometimes death may result.
The seas are colder than body temperature. Water has thermal capacity and thermal conductivity, respectively, about 3000 and 32 times greater than air. The venoconstrictor effects of cold potentiate the effects of immersion by increasing filling pressures further, but more importantly arteriolar constriction increases blood pressure, left ventricular wall stress, and myocardial oxygen consumption.3 …