Adaptations to diving in the harbor seal: cardiac output during diving

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Abstract
Measurements of cardiac output, heart rate, stroke volume, aortic, pulmonary artery, and ventricular blood pressures, and flipper blood flow were performed in the harbor seal before, during, and after prolonged diving. The mean predive cardiac output averaged 5.18 [plus or minus] 2.33 liters/min. During diving the output fell to 0.62 [plus or minus] 0.35 liters/min. In the early postdive period it rose to 8.27 [plus or minus] 4.20 liters/min. The bradycardia during diving, previously described by oth others, was confirmed. The development of profound arterial constriction during diving with loss of flipper blood flow was documented by using a dye-indicator technique. Aortic, pulmonary artery, and left and right ventricular pressures remained essentially unchanged during prolonged diving. These studies suggest that the primary diving adaptation consists of arterial constriction. With loss of blood flow to peripheral tissues, there is preservation of available O2 and substrate for brain O2-dependent metabolism.

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