With & figures Printed in Great Britain DYNAMICS OF BLOOD FLOW THROUGH THE HEARTS AND ARTERIAL SYSTEMS OF ANTJRAN AMPHIBIA

1. Blood pressures in the ventricle, conus arteriosus, systemic arch and pulmocutaneous arch along with blood flows in the systemic and pulmo-cutaneous arches have been recorded in Rana catesbeiana, R. pipiens, R. tempo-raria and Xenopus laevis. Central pressure and flow waveforms exhibited the same qualitative features in all species. 2. Blood pressure in both the systemic and pulmocutaneous arches passively followed ventricular pressure throughout ventricular ejection. Since diastolic pressure run-off was faster in the pulmocutaneous arch, pressure rose and ejection started in this arch first. The subsequent delay before the onset of ejection and pressure rise in the systemic arch was directly attributable to the time taken for ventricular pressure to rise from pulmocutaneous to systemic levels. 3. Details of arch pressure profiles previously attributed to contraction of the conus, and a consequent occlusion of pulmocutaneous outflow, persisted when conus contraction was eliminated by ligature of the coronary blood supply to the conus for one week. Thus descriptions of a central (cardiac) mechanism for shunting blood to or from the lungs, based on such an active occlusion of pulmocutaneous outflow, are disproven. It is concluded that distribution of blood by the heart to the systemic and pulmocutaneous systems is controlled only by vasomotion in the vascular beds. 4. The cardiac pulse travelled through major arteries with a velocity of 3-1 m/s and thus traversed the complete arterial tree in a very small fraction of a cardiac cycle. Consequently wave transmission phenomena are not important in the arterial systems of Anura. Pressure pulses recorded in peripheral arteries were virtually identical to the central pulse. In addition a simple windkessel model, depicting the arterial tree in terms of a central elastic reservoir supplying peripheral resistance vessels, gave reasonable predictions of arterial pressure-flow relationships