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

Jacques R. Rouleau,John G. Kingma,Bernard Cantin

doi:10.4236/wjcd.2017.77020

Abstract

Changes in intramyocardial tissue pressure modulate the relationship between coronary pressure and flow during the cardiac cycle. The present study compared the relation between measured and calculated diastolic subendocardial tissue pressure and coronary pressure at zero flow in anesthetized dogs after modulation of either coronary sinus (i.e. Fogarty catheter) or left ventricular intracavity (i.e. volume loading) pressure. Experiments were conducted in anesthetized, instrumented dogs; coronary pressure flow relations were constructed during pharmacologic vasodilatation and intramyocardial tissue pressure was measured using micromanometer pressure sensors. Elevated coronary sinus pressures did not affect subendocardial pressure-flow relations signifying that diastolic tissue pressure within this layer is the effective coronary back pressure. Higher left ventricular intracavity pressure did not affect either diastolic subendocardial tissue pressure or pressure flow relations within this layer. Results show a direct linear relation (y = 1.106x - 0.652; r2 = 0.59. P = 0.001) between measured and calculated diastolic subendocardial tissue pressure and coronary pressure at zero-flow over a wide range of pressures after either LV systemic or coronary sinus pressure modulation. Knowledge of back pressure in the subendocardium is useful for the evaluation of efficacy of cardiac interventions on myocardial perfusion particularly at the level of the microcirculation.

Highlights

Changes in intramyocardial tissue pressure during the cardiac cycle can strongly affect the complex relationship between coronary pressure and flow
Experiments were conducted in anesthetized, instrumented dogs; coronary pressure flow relations were constructed during pharmacologic vasodilatation and intramyocardial tissue pressure was measured using micromanometer pressure sensors
The existence of tissue pressure gradients across the left ventricular wall during the cardiac cycle is well documented [4] [5] [6] [7]; intramyocardial pressure increases from subepicardium to subendocardium [6] [8] and during diastole is higher than intracavitary pressure [9]

Summary

Introduction

Changes in intramyocardial tissue pressure during the cardiac cycle can strongly affect the complex relationship between coronary pressure and flow. 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] Both hypotheses postulate that myocardial tissue pressure is partly responsible for genesis of Pzf. The existence of tissue pressure gradients across the left ventricular wall during the cardiac cycle is well documented [4] [5] [6] [7]; intramyocardial pressure increases from subepicardium to subendocardium [6] [8] and during diastole is higher than intracavitary pressure [9]. We already established in normal, in situ canine beating hearts that elevated coronary sinus pressure had no effect on subendocardial PFR; at the same time the slope of the subepicardial PFR decreased [5] These findings suggested that diastolic intramyocardial tissue pressure could be the effective back pressure in the subendocardium. As such, during diastole, subendocardial tissue pressure (measured with needle-tip transducers) and Pzf should be comparable; we examined this hypothesis in the present study after modulations of either left ventricular chamber, or coronary sinus, pressures in anesthetized dogs

Methods

Results

Conclusion