Zero-Flow Pressures and Pressure-Flow Relationships during Single Long Diastoles in the Canine Coronary Bed before and during Maximum Vasodilation

Abstract

A B S T R A C T The proposal that diastolic coronary flow is regulated by an intramyocardial "back-pressure" that substantially exceeds coronary venous and ventricular diastolic pressures has been examined in an open-chest canine preparation in which instantaneous left circumflex pressure and flow could be followed to cessation of inflow during prolonged diastoles. Despite correlation coefficients consistently >0.90, pressureflow data during individual diastoles were concave to the flow axis before and during pharmacologically induced maximum coronary vasodilation. Data were better fitted (P < 0.01) by second-order equations than by linear equations in >90% of cases. Second-order pressure-axis intercepts (Pf=o)l averaged 29±+7 (SD)

Determination of Coronary Zero Flow Pressure by Analysis of the Baseline Pressure-Flow Relationship in Humans.

“…During reactive hyperemia or adenosine-induced vasodilation, the instantaneous P-F relationship showed a greater slope (interpreted as an increase in coronary conductance) and a decrease in Pzf to approximately 20 mmHg. [2][3][4] In the present study, Pzf during the long diastole was in good agreement with the experimental data of Pzf obtained when infused with vasodilators such as adenosine. [3][4][5] We also found that Pzf under vasodilatation was lower than that under normal conditions, although Pzf in the present study was calculated from the P-F relationship obtained during a normal cardiac cycle.…”

“…1 During reactive hyperemia or adenosine-induced vasodilatation, the instantaneous P-F relationship exhibited an increase in the slope (interpreted as an increase in coronary conductance) and a decrease in Pzf to approximately 20 mmHg. [2][3][4][5] Although Pzf is likely to provide meaningful information about the characteristics of coronary circulation, there are few available data on Pzf in humans. 6 In addition, Pzf is usually overestimated when calculated using P-F data during a normal cardiac cycle because a steady-state P-F curve, which is necessary for determining Pzf, has not been achievable in humans.…”

Effects of pressure gradients between branches of the left coronary artery on the pressure axis intercept and the shape of steady state circumflex pressure-flow relations in dogs.

“…Some previous studies in which circumflex preparations were used (Verrier et al, 1980;Klocke et al, 1981;Vlahakes et al, 1982) reported little or no significant effect of collateral flow on circumflex pressure-flow relations. These investigators lowered the pressure in the circumflex artery and then, after a steady state was reached, occluded the left anterior descending artery transiently to exclude collateral flow; they failed to find any resulting change in circumflex pressure or flow.…”

“…To avoid errors from assessing pressure axis intercepts by extrapolation (Klocke et al, 1981) we included in each pressure-flow relation points at very low pressures and flows, down to zero flow.…”

“…The pressure axis intercept of these relations has been interpreted as the downstream pressure opposing forward flow in the coronary circulation; however, this pressure has greatly exceeded the coronary sinus pressure, which traditionally has been assumed to be the downstream pressure. The shape of these relations, found to be linear by some (Dole and Bishop, 1982;Eng et al, 1982) but curvilinear by others (L'Abbate et al, 1980;Klocke et al, 1981), is thought to convey information about the conductance of the coronary circulation. Because of this variability of the pressure axis intercept and the shape of coronary arterial pressure-flow relations, the physiological significance of both remains uncertain.…”