Effect of cardiac output on pulmonary hemodynamics.

The purpose of this study was to test the hypothesis that there is a direct relation between pulmonary arterial input resistance and compliance in seven anesthetized cats. Cardiac output was altered by varying the direction and flow through an arteriovenous fistula with a roller pump. Pulmonary arterial input impedance was calculated from the Fourier analysis of the pressure and flow waveforms. Input resistance, pulmonary arterial compliance and characteristic impedance were estimated from the impedance spectra with a lumped parameter model. We found that pulmonary arterial compliance increased with cardiac output (P less than 0.002) but characteristic impedance was independent of flow. The observed response has the effect of reducing the hydraulic power lost by the pulmonary vasculature due to wave reflection. In three additional cats we measured the diameter of the main pulmonary artery by sonomicrometry. We found a linear relation between mean pulmonary arterial pressure and pulmonary arterial diameter during alterations of cardiac output. This result suggests that the increase of pulmonary arterial compliance with cardiac output is due to geometric factors rather than changes in vascular elastic properties.