Flow dynamics of the crocodilian heart.

We report for the first time the flow events corresponding to the pressure patterns in the left and right aorta (LAo and RAo) during the cardiac cycle in the caiman (Caiman crocodylus ssp). These experiments show a complex LAo flow pattern; an initial small anterograde flow in the early systole is reversed to a backflow at midsystole. At the end of systole there is again a small anterograde flow. This second flow pulse corresponds to a pressure peak ("foramen spike") in the LAo pressure trace. The observed pattern is compatible with the view that the foramen Panizzae is obstructed by the medial cusp of the RAo valve during part of the systole. LAo pressure remains normally above right ventricular pressure throughout the cardiac cycle and there is thus no contribution to LAo flow from the right ventricle. The net flow in the LAo normally equals the flow through the foramen Panizzae and is very small compared with the systemic flow in the RAo.