EFFECTS OF VOLUME LOADING ON PULMONARY VENOUS FLOW PATTERN IN DOGS WITH NORMAL LEFT-VENTRICULAR FUNCTION

The effects of altered loading conditions on the pattern of pulmonary venous flow are poorly understood. The authors investigated such effects, therefore, by using volume loading in 6 open-chest dogs. The pulmonary venous flow volume rate curve was obtained with a transit-time ultrasonic flowmeter at a fixed heart rate. Measurements were performed in the control and several states during the intravenous infusion of dextran. The influences of volume loading on hemodynamic and pulmonary venous flow variables were compared between the control state and three interventional states in which mean left atrial pressure was approximately 1, 2, and 3 mm Hg above the control value. The systolic flow volume (SI), which corresponds to left atrial reservoir volume, significantly increased, but the early diastolic flow volume (DI), which corresponds to left atrial conduit volume, did not show significant change with volume loading. The flow volume during left atrial contraction significantly increased with volume loading. The flow volume during one cardiac cycle (PVF) significantly increased with volume loading. Approximately 73% of increased PVF was distributed to the systolic flow. The rest was distributed to the early diastolic flow (14%) and to the flow during left atrial contraction (12%). The change in the ratio of SI/DI significantly and positively correlated with the change in mean left atrial pressure (r=0.87, P < 0.001). These findings indicate that increased pulmonary venous flow induced by volume loading in dogs with normal left ventricular function is mainly distributed to the left atrial reservoir volume.