Dynamic effects of positive-pressure ventilation on canine left ventricular pressure-volume relations

Positive-pressure ventilation (PPV) may affect left ventricular (LV) perfor mance by altering both LV diastolic compliance and pericardial pressure (Pp c). We measured the effect of PPV on LV intraluminal pressure, Ppc, LV volu me, and LV cross-sectional area in 17 acute anesthetized dogs. To account f or changes in lung volume independent of changes in Ppc and differences in contractility, measures were made during both open- and closed-chest condit ions, during closed chest with and without chest wall binding, and after pr opranolol-induced acute ventricular failure (AVF). Apneic end-systolic pres sure-volume relations (ESPVR) were generated by inferior vena caval occlusi ons. With the open chest, PPV had no effects. With the chest closed, PPV in spiration decreased LV end-diastolic volume (EDV) along its diastolic compl iance curve and decreased end-systolic volume (ESV) such that the end-systo lic pressure-volume domain was shifted to a point left of the LV ESPVR, eve n when referenced to Ppc. The decrease in EDV was greater in control than i n AVF conditions, whereas the shift of the ESV to the left of the ESPVR was greater with AVF than in control conditions. We conclude that the hemodyna mic effects of PPV inspiration are due primarily to changes in intrathoraci c pressure and that the inspiration-induced decreases of LV EDV reflect dir ect effects of intrathoracic pressure on LV filling. The decreases in LV ES V exceed the amount explained solely by a reduction in LV ejection pressure .