Efficiency of Ventricular-Arterial Coupling and Baroreflex Regulation of Blood Pressure

Abstract

The heart contracts incessantly over the lifetime. The average number of contractions for human beings exceeds 2.5 billion. Since each ejection requires a large amount of energy, the energy expenditure by the heart becomes enormous. Thus conceivable that, in response to changes in demands of the heart, the regulatory system adjusts ventricular contraction to maximize energy efficiency. Indeed, stroke power output of the normal excised feline left or right ventricle was maximum when the ventricle was loaded with normal arterial impedance (1–3). This was true in the open-chest cat (4–6). In the canine left ventricle, external work was expected to be nearly maximum under normal loading conditions (7,8), as was indeed the case (9–12). Although all these studies indicated that external work or mechanical efficiency was well optimized in conscious animals as well as in anesthetized animals, it was not known whether the optimization principle holds in animals under exercise stress, where the metabolic demand of the heart is greatly increased. Thus in chronically instrumented dogs, we investigated the effect of exercise on mechanical energy transmission from the left ventricle to the arterial system (13).