Curvilinearity of the diastolic pressure-flow relationship in autoregulating and maximally vasodilated coronary beds; effects on estimates of zero-flow pressure and differences between zero-flow and intracavitary diastolic pressures. Role of capacitive effects in the determination of zero-flow pressure from long diastoles

Abstract

Bellamy's recent studies (1) suggest that coronary driving pressure is overestimated importantly when downstream pressure is taken as right atrial or left ventricular diastolic pressure. In these provocative observations the relationship between instantaneous left circumflex (LC) inflow and pressure showed a high correlation coefficient and was taken as linear over the range of pressure studied; extrapolation was frequently required in the determination of the pressure at which inflow ceased, i.e., the pressure-axis intercept or "zero flow" pressure (P~ = 0 ).The present studies were intended to define diastolic coronary pressure-flow relationships in settings in which LC diastolic inflow could be followed to zero during a single cardiac cycle, both with autoregulation intact and during sustained maximum vasodilation (carbocromen). Mean and phasic LC inflow and pressure were measured continuously with an electromagnetic flowmeter and downstream LC catheter in open-chest, heart-blocked dogs paced at 100 beats per minute. 66 prolonged postpacing diastoles in which LC inflow fell to zero were obtained in seven animals with stable systolic pressures of 100-125 mm Hg. Although instantaneous LC pressure and flow did show consistently high correlation coefficients during single diastoles (0.97 _ 0.01 [SD]), concavity to the flow axis developed at lower LC pressures and second-order equations gave statistically better fits than linear equations (p < 0.01) in 97 % of cases. Curvilinearity of the pressure-flow relationship was apparent in maximally vasodilated (n = 26) as well as autoregulating (n = 40) beds, indicating a role in the curvilinearity of factors not directly related to vascular smooth muscle. The pressure-axis intercept obtained from each second-990

Peer Review #1 of "Influence of isoflurane on the diastolic pressure-flow relationship and critical occlusion pressure during arterial CABG surgery: a randomized controlled trial (v0.2)"

“…Earlier experimental and clinical studies investigating the effects of massive coronary vasodilatation on diastolic P-F demonstrated that the linearity of the relationship between pressure and flow velocity was not influenced. The slope increased and COP decreased after vasodilatation in these studies (Dole et al 1984;Klocke et al 1981;Nanto et al 2001).…”

Cross-Talk Between Cardiac Muscle and Coronary Vasculature

“…Figure 6 shows the steady state, or autoregulation curve, together with instantaneous pressure-flow relationships as determined from a range of steady-state pressures (36). The instantaneous relationships in general appear to be straight (36) or curvilinear (237,238) with a so-called zero-flow pressure intercept, P fϭ0 , i.e., with negligible flow, pressure is still present. The inverse of the slope of the instantaneous pressureflow relationship is the instantaneous resistance (R i ).…”

“…The instantaneous resistance and the intercept pressure both depend on the vasoactive state of the coronary bed. For increased perfusion pressure, the vasculature constricts as a result of autoregulation, and the resistance and intercept of the instantaneous pressure-flow relation increase, thereby keeping mean flow in the steady-state constant (107,238). In humans, the zero-flow pressure intercept of the instantaneous pressure-flow relation is ϳ40 mmHg in control and ϳ15 mmHg in vasodilation (307).…”

“…The instantaneous pressure-flow relationship should be considered with caution. It has been shown that the relationship may not be linear (238). The relationships may include a contribution of arterial compliance, because the flow that fills the arterial compliance depends on the rate of change of perfusion.…”

Influence of isoflurane on the diastolic pressure-flow relationship and critical occlusion pressure during arterial CABG surgery: a randomized controlled trial

“…Earlier experimental and clinical studies investigating the effects of massive coronary vasodilatation on diastolic P-F demonstrated that the linearity of the relationship between pressure and flow velocity was not influenced. The slope increased and COP decreased after vasodilatation in these studies ( Dole et al, 1984 ; Klocke et al, 1981 ; Nanto et al, 2001 ). Intracoronary injections of angiographic contrast medium or adenosine triphosphate depressed vasomotor activity and induced an atrioventricular blockade followed by a non-physiological increase in diastole.…”