Metabolic consequences of submersion asphyxia in mammals and birds

On submersion, the cardiovascular system of naturally diving animals is virtually transformed into a heart-brain-lung preparation as the result of intense and highly selective neurogenic vasoconstriction. A supply of oxygen from the circulating blood cells to the heart and the brain is thereby secured. Peripheral tissues, e.g. muscles and kidneys, have to depend on local stores of oxygen, i.e. myoglobin, or, when these are exhausted, on anaerobic metabolism. In spite of such physiological adjustments, however, arterial pO2 will inevitably decrease throughout the underwater episode. In prolonged dives values lower than 10mmHg can be observed. Moreover, the ischaemia in the peripheral tissues will, in some animals, e.g. arctic seals and whales, result in a profound decrease in the temperature of tissues such as the skin. The aim of the present report is to review some of the more important biochemical mechanisms that allow diving mammals and birds to cope with the above-mentioned combined asphyxic and temperature stresses for prolonged periods. Some of the osmotic problems arising from the rapid wash-out of acidic metabolic end products from the previously ischaemic tissues on emergence are also discussed.