Varying elastance concept may explain coronary systolic flow impediment

We measured phasic arterial coronary inflow in the blood-perfused isolated cat heart (n = 5) with a balloon in the left ventricle under well-defined conditions, i.e., constant perfusion pressure, constant vasomotor tone (maximal vasodilation), and heart rate. The normalized amplitude (A) between systolic flow (Fs) and diastolic flow (Fd) A = (Fd - Fs)/Fd was related to systolic left ventricular pressure (Ps, range 1.6-17 kPa, 1 kPa = 7.5 mmHg) for different isovolumic beats obtained by changes in balloon volume and for low load isobarically ejecting beats (pressure 0.2 kPa). The data were fitted to A = a + bPs with a = 0.70 +/- 0.15 (SD) and b = 0.005 +/- 0.005 kPa-1. This relation indicates a very weak effect of left ventricular systolic pressure on normalized flow amplitude. Thus the hypothesis that left ventricular pressure is the sole determinant impeding coronary flow could not be confirmed. However, our data could be explained on basis of the time-varying elastance concept (H. Suga, K. Sagawa, and A. A. Shoukas. Circ. Res. 32: 314-322, 1973). The intravascular and luminal (cavity) compartments both are assumed to be subject to a time-varying elastance. The time-varying luminal elastance is similar for isovolumic and isobaric beats. We assume that the elastance of the vascular compartment also behaves the same for these beats, and therefore coronary flow is affected similarly.(ABSTRACT TRUNCATED AT 250 WORDS)