Theoretical Relationship among Myocardial Tissue and Cavity Pressures, Contractility, and Vascular Volume Change

Abstract

The intramyocardial pump model introduced by Spaan et al. [1] to explain the reduction of coronary inflow during cardiac contraction has been recently questioned by Krams et al. [2–4]. The latter authors demonstrated that the systolic coronary inflow impediment is only weakly dependent on left ventricular cavity pressure, but is affected more by cardiac contractility and perfusion pressure. Since the pump model, in its simplest form, assumes a direct proportionality between intramyocardial tissue pressure (IMP) and left ventricular cavity pressure (with one zero if the other is zero) it would appear that the pump model fails to explain the results of Krams et al. A recent letter by Kresh [5] discusses the controversy further. In view of the interest and importance of this subject, it seemed helpful to develop a relatively simple model from which various factors affecting IMP can studied. In particular, the relationship between IMP and left ventricular pressure is clarified, and simple formulas are given that can be used in conjunction with a pump model.