Some effects of apneic underwater diving on blood gases, lactate, and pressure in man

Abstract
Five men of outstanding diving ability performed apneic underwater dives in a specially fitted tank. The divers hyperventilated to extreme degrees of hypocapnia before submerging, and their arterial blood carbon dioxide tensions rarely rose above normal levels during a dive. Arterial blood oxygen content was 15.5 vol % or above at the end of two 3-min resting dives and of three 1.5-min exercise dives. Blood lactate concentrations increased during the latter half of exercise dives and reached peak values after surfacing. A rise in arterial blood pressure began by 10 sec in each dive and persisted, coincident with a falling heart rate, to the end of the dive. The rate of blood pressure rise was greater during a dive in water of 26 C than with breath holding by the same subject out of water. Some differences between the adaptations of diving men and of other diving mammals are briefly discussed. Submitted on April 2, 196

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