Cardiovascular Defense against Asphyxia

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Abstract
Experimental studies on a series of land and marine animals [Northern elephant seal, Mirounga angustirostis; harbor seal, Phoca vitulina: California sea lion, Zalophus californianus; Pacific bottle-nosed dolphin, Tursiops gilli; pilot whale, Globicephala scammoni: Cuvier''s beaked whale, Ziphius cavirostrisi dog, as well as man, were performed to observe the effects of diving on ob-served cardiac and circulatory adjustments associated with asphyxia. Measurements of arterial blood pressure with modern strain-guage equipment, and of blood flow with the Franklin pulsed ultrasonic flow meter were taken under experimental conditions. For blood-flow studies of humans the Whitney mercury-in-rubber plethysmograph was used. Observations on both bradycardia and tachycardia lead to the conclusion that a widespread and selective vasoconstriction occurred during diving and that this provided for continued oxygenation of vital organs of greater anaerobic capacity such as muscle and intestine. Experiments dealing with newborn or very young animals show that they are much more resistant to asphyxia than adult animals.