MATHEMATICAL-ANALYSIS OF CORONARY AUTOREGULATION AND VASCULAR RESERVEIN CLOSED-LOOP CIRCULATION

The autoregulatory capacity of the coronary circulation has traditiona lly been studied in open-loop animal models where the coronary circula tion was decoupled from the systemic circulation. In the closed-loop c irculation, changes in arterial pressure alter coronary flow. Pressure variations can be caused by changes in cardiac contractility, preload , afterload, and heart rate. These changes also affect myocardial oxyg en consumption. To maintain equilibrium between oxygen supply and cons umption, coronary flow is altered by the autoregulation mechanism. Cor onary resistance must change to produce the required change in coronar y flow. The direction of change in coronary resistance is not directly predictable. Increased arterial pressure may result in either increas ed or decreased coronary resistance. To study the changes in coronary resistance in response to changes in arterial pressure that are produc ed by circulatory parameters, we used mathematical models. Coronary re sistance was calculated to obtain equilibrium between ventricular oxyg en consumption and supply for different values of contractility, prelo ad, afterload, and heart rate. Maximum coronary resistance, indicating largest coronary vascular reserve and highest efficiency of arterial pressure generation, was defined as an optimal condition. The model pr edicted that the optimal value of cardiac contractility is its resting value. Minimizing end-diastolic volume and heart rate and maximizing peripheral resistance were shown to improve ventricular coronary vascu lar reserve. These observations suggest that afterload reduction thera py may not be beneficial for improving myocardial oxygen balance while venous vasodilatation and heart rate reduction result in greater coro nary reserve. (C) 1994 Academic Press, Inc.