Cardiac and Respiratory Responses to Hypoxia in the Sea Raven, Hemitripterus americanus, and an Investigation of Possible Control Mechanisms

Abstract

Responses of the sea raven (Hemitripterus americanus) to hypoxia consisted of an increase in rate and amplitude of breathing and an increase in dorsal and ventral aortic pressure. Changes in heart rate seldom occurred. Bilateral transection of cranial nerves IX and X resulted in a fall in dorsal aortic PO2 to a sustained low level but did not alter the dorsal and ventral aortic blood pressure or breathing responses induced by hypoxia.Pressure changes in the opercular cavity during breathing seldom exceeded.5 cm H2O and rarely exceeded 1 cm H2O under extreme hypoxia. There were no obvious differences in opercular pressure wave forms before and after bilateral section of nerves IX and X.An artificial "heart-gill" machine was devised with which blood PO2 could be altered outside the fish and the blood perfused into either the dorsal or ventral aorta. Breathing amplitude was increased by perfusing blood of low PO2 into the dorsal aorta. While maintaining dorsal aortic PO2 high and constant, increases in breathing amplitude were induced by low ambient PO2 levels.Vasomotor changes in blood pathways other than the gills probably contribute to the changes in blood pressure observed during hypoxia. Preliminary evidence for both central and peripheral sites of oxygen receptor activity is provided.