Load independence of the rate of isovolumic relaxation in man

Abstract

This investigation was designed to determine whether the rate of isovolumic left ventricular pressure decline is affected by load in man. Fourteen patients were instrumented with micromanometer left ventricular and right atrial pacing catheters to maintain a constant heart rate during control conditions and infusion of methoxamine or nitroprusside. The isovolumic relaxation period was defined as the time from peak (-)dP/dt to 5 mm Hg above left ventricular end-diastolic pressure of the followig beat. The rate of isovolumic relaxation was calculated as time constants (Tau) from the linear regression of natural log pressure vs time (T(ln)) and instantaneous (-)dP/dt vs pressure (T(D)), which includes a variable asymptote (P(B)). The mean heart rates and average (+)dP/dt values normalized at 40 mm Hg development pressure (DP40) did not differ significantly, despite 33% and 43% increases in left ventricular peak and end-diastolic pressures during the infusion of methoxamine (p < .001 and p < .01, respectively) and 24% and 29% decreases during the infusion of nitroprusside (p < .001 and p