LEFT-VENTRICULAR HEMODYNAMICS DURING RESPIRATION

We have investigated the mechanisms involved in the inspiratory fall in left ventricular stroke volume (LVSV), utilizing a spontaneously breathing dog on right-heart bypass (RHBP). We have been able to control lung volume, pulmonary artery inflow, and right-heart volume (RHV). During Mueller maneuvers in one series, RHV was allowed to increase as pleural pressure (Ppl) fell; in a second series, changes in RHV were excluded. In both series LVSV fell significantly, associated with a significant rise in the transmural (relative to Ppl) aortic diastolic pressure, reflecting an increase in the effective LV afterload. The transmural left ventricular filling pressure did not fall, a fact inconsistent with decreased pulmonary venous return, causing the fall in LVSV. The LVSV fell significantly more when RHV was allowed to increase as when it was held constant with all other variables showing no statistical change. Thus, increases in both RHV and effective LV afterload are created by the inspiratory fall in Ppl and summate to decrease LVSV.