Effects of increased afterload on left ventricular function in closed-chest dogs.

Mechanical response of the left ventricle (LV) in an intact circulatory system to steady-state increases in afterload may differ from that of an isolated LV, because secondary hemodynamic changes cannot be independently manipulated when the circulation is intact. To evaluate the integrated response of the LV in closed-chest dogs to sustained increases in afterload, six animals chronically instrumented with three orthogonal diameter gauges and LV manometers were studied after autonomic blockade and fentanyl-droperidol anesthesia. End-systolic pressure-volume (PES-VES) and stroke work end-diastolic volume (SW-EDV) relations and the relations between pressure-volume area (PVA, area bounded by PV loop and PES-VES relation) and EDV were quantified. Balloon inflation (BI) in the proximal descending aorta increased LV PES from 100.7 +/- 13.4 to 140.2 +/- 19.3 mmHg (P less than 0.002) and LVEDV from 39.1 +/- 11.3 to 43.3 +/- 12.2 ml (P less than 0.01). The slope of the PES-VES relation was not significantly changed, whereas V100, a volume intercept in the common range of pressures, was reduced from 27.5 +/- 7.3 to 23.7 +/- 6.1 ml (P less than 0.005). PVA-EDV relation was highly linear; its slope was increased after BI. Comparison of beats with matched LVEDV before and after BI showed significant increases in maximum rate of pressure development and PVA; the change in SW after BI was modest and not significant. The efficiency of energy transfer from PVA to SW (TransPVA, SW/PVA X 100) decreased from 52.5 +/- 8.6 to 42.6 +/- 6.3% (P less than 0.002).(ABSTRACT TRUNCATED AT 250 WORDS)