Coronary diastolic pressure-flow relation and zero flow pressure explained on the basis of intramyocardial compliance.

Abstract

In the controversy about the mechanisms determining the high zero flow pressures and the further interpretation of coronary diastolic pressure flow relations, this paper takes a stand in favor of intramyocardial compliance as the primary cause of the high zero flow pressures. An attempt has been made to estimate the compliance distribution within the coronary circulation and to show the specific effect of intramyocardial compliance on arterial and venous pressure-flow relations. Since no data are available on the distensibility of coronary arterioles and capillaries, these data were taken from studies on mesenteric vessels. Based on these data, it is shown that, depending on the transmural pressure, smooth muscle tone may either increase or decrease arteriolar compliance. A compliance distribution has been proposed based on assumed pressure, volume, and distensibility distributions. For all but the venous division of the circulation, experimental data on volume could be found in the literature. Based on this compartmental analysis, it is predicted that overall intramyocardial compliance may exceed epicardial arterial compliance by a factor 45. The literature presenting functional evidence for intramyocardial compliance effects has been reviewed. Experimental results on venous outflow during long diastoles have been analyzed. Pf = 0 coronary pressure at zero flow, is higher when measured later in diastole. It is shown that this may be explained by charging of intramyocardial compliance in the period before flow ceases. The discrepancy between results on pressure-flow relations in the fully dilated bed and autoregulated bed are related to the differences in pressure, resistance, and compliance distributions.

Physiological Basis of Clinically Used Coronary Hemodynamic Indices

“…29 An elevated Pzf can be found because of capacitive flow from epicardial and particularly intramyocardial microcirculation. 26,30 This interpretation is strongly supported by the observation that coronary venous outflow continues even when pressure has decayed to Pzf. 31 This venous outflow at cessation of inflow has to come from a pool of blood within the microcirculation, which also constitutes the intramyocardial compliance.…”

“…25 This corresponds with earlier studies in which intramural blood volume was measured in different ways. 26 Moreover, pressure dependence of coronary resistance was clearly demonstrated by experiments in which coronary flow increased when the arterial-venous pressure difference was kept constant by increasing both pressures by the same amount, which is only possible when resistance decreases with pressure. 27 These findings are important because they imply that a stenosis not only adds resistance to flow in the epicardial arteries but additionally impedes myocardial perfusion by increasing microvascular resistance via the passive elastic behavior of the microvascular walls at vasodilation.…”

Scalability and in vivo validation of a multiscale numerical model of the left coronary circulation

“…The compliances C 1 and C2 were 0.013 and 0.254 ml·mmHg Ϫ1 ·100 g Ϫ1 , respectively, while V0,1 and V0,2 were 2.5 and 8.0 ml/100 g (62,65), with a subendocardial-to-subepicardial ratio of 1.14 for both parameters (11,74). In preliminary simulations, we found that accounting for the volume-dependence of compliance using the method described by Bruinsma et al (11) had a negligible effect on coronary flow waveforms (as in Ref .…”

“…Given the general principle that compliance is higher in vascular beds with lower resistance, one might therefore expect weight-corrected intramyocardial compliance to be higher in newborn lambs. However, if we assume that the similar capillary density and luminal area in the LV of newborn and adult sheep (60) implies similar overall vascularity, it follows that weight-corrected vascular volume should be similar in both groups (62). Assuming similar volume distensibility, then in the absence of more firm data it is also reasonable to assume similar vascular compliance in both groups.…”

Comparison between Diastolic Subendocardial Tissue Pressures Measured Directly or Calculated from Pressure-Flow Relations

“…Those studies, performed in conscious dogs, documented a positive coronary zero flow pressure (Pzf) intercept that exceeded venous pressure in the absence of coronary vascular smooth muscle tone; however, in the presence of intact tone Pzf is noticeably lower. The higher Pzf values during vasodilatation could be explained by either a Starling resistor effect within resistance vessels [1] [2] or a compliance effect of intramyocardial vessels [3]. Indeed, both hypotheses postulate that myocardial tissue pressure is partly responsible for genesis of Pzf.…”