How seals avoid myocardial infarction when they should have got it.

ABSTRACT

The arterial oxygen tension of diving seals decreases to values as low as 1.33 kPa at the end of prolonged dives. In spite of this, cardiac function is unimpaired due to a profound reduction of myocardial oxygen demands Heart rate is immediately reduced some 90%, left ventricular dP/dt(max) is reduced some 25%, and ventricular wall tension is slightly reduced. This reduction of myocardial workload even allows coronary blood flow to be reduced some 90% and a significant proportion of myocardial energy expenditure to be covered by anaerobic metabolism based on endogenous stores of glycogen. It is suggested that the myocardial ischaemic defence, as worked out by nature herself, in the diving seal has important implications for the treatment of acute myocardial ischaemia in man.