Cardiovascular events associated with spontaneous apnea in the Australian short‐finned eel, Anguilla australis

Heart output, arterial pressures, and buccal pressure were measured in conscious, unrestrained eels (Anguilla australis). The branchial ventilatory pattern comprised alternating periods of eupnea and apnea. The transition from eupnea to apnea was always associated with significant decreases in ventral aortic blood pressure (−20%), dorsal aortic blood pressure (−16%), ventral aortic blood flow (−39%) and heart rate (−27%), and a significant increase in systemic vascular resistance (+39%). Although there were, significant decreases in cardiac stroke volume in some animals, heart output was primarily determined by heart rate. The rapidity of the transition to apnea and the occasional occurrence of Mayer waves in the circulation of A. australis is considered as evidence in favour of the neural regulation of systemic vascular resistance.