Cardiac physiology of the spiny dogfish (Squalus acanthias)

The elasmobranch heart is comprised of four sequentially arranged chambers, the sinus venosus, the atrium, the ventricle and the conus arteriosus. The heart lies within a semi-rigid, capacious pericardial cavity which is provided with a communicating duct to the abdomen, the pericardio-peritoneal canal. The first part of this investigation focused on clarifying the role of the conus arteriosus on output pressure and flow. Satchell & Jones (1967) proposed that the contraction of the conus serves to prolong cardiac contraction so that the upper tier of valves of the conus do not face the extreme negative intrapericardial pressure, created due to ventricular ejection. They further concluded that the conus does not contribute to either pressure or flow in the ventral aorta. The present work does not confirm these conclusions. Pressure and flow records from the ventral aorta of anaesthetised and unanaesthetised spiny dogfish (Squalus acanthias) show conclusively that conal contraction contributes to output pressure and flow, prolongs the ejection phase of the heart and may serve a depulsator function. Past research has emphasised that a semi-rigid pericardium allows development of negative intrapericardial pressure during ventricular ejection (Sudak 1965a, Johansen 1965, Satchell 1971, Shabetai et al 1985) which in turn aids in filling of the heart through suction (vis-d-fronte filling). However, recent studies on leopard sharks (Lai et al 1990) suggested that filling of the heart through suction is not important. Instead the heart is filled by positive venous pressure (vis-a-tergo [Page iii of abstract missing in original document]Science, Faculty ofZoology, Department ofGraduat