Load Independence of the Instantaneous Pressure-Volume Ratio of the Canine Left Ventricle and Effects of Epinephrine and Heart Rate on the Ratio

Abstract

As a means of assessing ventricular performance, we analyzed the time-varying ratio of instantaneous pressure, P(t), to instantaneous volume, V(t), in the canine left ventricle. Intraventricular volume was measured by plethysmography, while the right heart was totally bypassed. The cardiac nerves were sectioned, and an epinephrine infusion was used to alter the contractile state. The instantaneous pressure-volume ratio was defined aswhere V d is an experimentally determined correction factor. We found that (1) all the E(t) curves thus defined were similar in their basic shape and attained their peak near the end of the ejection phase regardless of the mechanical load, the contractile state, or the heart rate, (2) under a constant heart rate and contractile state extensive changes in preload, afterload, or both did not alter the peak value of E ( t ) , Emax, or the time to Emax from the onset of systole, Tmax, and (3) these parameters of E(t) markedly changed with epinephrine infusion or increases in heart rate. At an epinephrine infusion rate of 2 fig/kg min" 1 , Emax increased to 12.2 ± 4.5 (SD) mm Hg/ml (N = 9) from its control value of 6.6 ± 1.2 mm Hg/ml before the infusion. Simultaneously, Tmax shortened from 191 ± 29 msec to 157 ± 26 msec. Increases in the paced heart rate proportionally shortened Tmax (45% per 100-beats/min change in heart rate) without any effect on Emax. We concluded that E ( t ) , represented by Emax and Tmax, explicitly reflects the ventricular contractility.

The step response of left ventricular pressure to ejection flow: A system oriented approach

“…It was demonstrated that the value of e did not change if the contractile conditions within the myocardial muscle did not change. Also, e increased and decreased with positive and negative inotropic interventions (95).…”

“…Its usefulness is based on the fact that under certain restrictions, during ventricular ejection, there is a unique, instantaneous, nearly linear relation between ventricular volume and ventricular pressure (95); according to the equation:…”

Biomechanics of the Right Ventricle in Health and Disease (2013 Grover Conference Series)

“…End-systolic elastance (E es ) is measured at the upper left corner of a squareshaped pressure-volume loop. 12 Because of low pulmonary vascular impedance, the normal RV pressure-volume loop has a triangular shape, and E max occurs before the end of ejection, or end systole. However, a satisfactory definition of E max can be obtained by the generation of a family of pressure-volume loops at decreasing venous return, as illustrated in Figure 2.…”

Mode of frequency distribution of external work efficiency of arrhythmic beats during atrial fibrillation remains normal in canine heart

“…Briefly, we first obtained V 0 ( Fig. 1) as the V-axis intercept of the straight line drawn through the end-systolic P-V points of the shrinking P-V loops while clamping the inferior vena cava during 10-20 regular beats, as described elsewhere [1,3]. We then obtained LV E max as the slope of the line connecting V 0 and the left-upper, end-systolic corner of each P-V loop (Fig.…”

“…c on a per-beat basis in regular beats [1,2]. Here, PVA is the LV pressure-volume (P-V) area as a measure of the LV total mechanical energy [1], E max is the LV end-systolic elastance or P-V ratio as an index of contractility [3], a is a constant O 2 cost of PVA, b is a constant O 2 cost of E max , and c is the basal metabolic VO 2 , all per beat [1]. The above formula proved to hold in steady-state beats under stable LV contractile and loading conditions where VO 2 per beat is simply equal to VO 2 per min divided by the regular heart rate [1].…”