2-PORT ANALYSIS OF SYSTEMIC VENOUS AND ARTERIAL IMPEDANCES

Hemodynamic properties of the systemic vasculature were measured in ei ght anesthetized dogs using two-port impedance analysis. Blood pressur es and flows were measured at the aortic root and the caval-atrial jun ction. Impedances were computed from 0.05 to 20 Hz to characterize the systemic vasculature. Pseudorandom variations in flow were produced w ith an extra-corporeal perfusion system. Impedance measurements were m ade at carotid baroreceptor pressures of 50, 125, and 200 mmHg. A six- parameter lumped-element model best fitted the measured impedance spec tra. At 125 mmHg, the mean parameter values were venous inertance, 13. 5 g . kg. cm-4; venous and arterial compliances, 0.769 and 0.0214 ml . mmHg-1 . kg-1; venous and arterial characteristic impedances, 0.028 a nd 0.084 mmHg . kg . min . ml-1; and arterial-to-venous small-vessel r esistance, 0.706 mmHg . kg . min . ml-1. Regression analysis showed si gnificant dependence of small-vessel resistance on baroreceptor pressu re. The other parameters were not dependent on carotid sinus pressure, which is consistent with baroreflex control of venous unstressed volu me but not compliance. We conclude that two-port impedance analysis is a useful tool for studying venous hemodynamics and the dynamic coupli ng between the veins and the right heart.