Effects of spontaneous respiration on canine left ventricular function.

The purpose of this study was to determine the mechanism of the decrease in left ventricular stroke volume during spontaneous inspiration. We determined the transmural pressures of the left heart by measuring left atrial and diastolic left ventricular pressures relative to esophageal pressure. We estimated the directional changes in end-systolic and end-diastolic volumes of the left ventricle by determining the transit time of sound transmission between two ultrasonic crystals facing each other across the minor axis of the left ventricle. Left ventricular stroke volume decreased with spontaneous inspiratory effort as pleural pressure fell, regardless of whether lung volume increased or remained constant. The stroke volume was decreased during the fall in pleural pressure because of an increase in end-systolic volume with an essentially unchanged diastolic volume. Thus, the decrease in stroke volume was due to a decrease in ejection, rather than a decrease in filling of the left ventricle. We believe that ...