End-systolic left ventricular pressure-dimension shift during acute relief of volume overload in the conscious dog.

To test whether left ventricular (LV) end-systolic dimensions are determined only by end-systolic pressure for a given inotropic state, 7 conscious dogs were studied during abrupt closure of a fistula created between the left subclavian artery and the left atrial appendage. The dogs were instrumented with an LV pressure micromanometer and ultrasonic crystals measuring LV major- and minor-axis diameters and ventricular wall thickness. During beta-blockade treatment and for the same end-systolic pressure, closure of the fistula produced a 40% decrease in cardiac output; end-diastolic diameter decreased by 1.5 mm and end-systolic diameter decreased by 0.9 mm. Calculated end-systolic volume was similarly decreased by 1.3 ml for a decrease of 2.9 ml of end-diastolic volume. Thus, large end-diastolic dimensional variations associated with peripheral resistance decrease significantly modify the end-systolic pressure-diameter (and volume) relations in the conscious animal. It is suggested that indexes obtained from these relations should not be used in patients when systolic pressure variations are associated with large stroke volume variations.