Cardiac dynamics.

Abstract

The studies reported here were selected because of renewed interest in these areas, particularly as they relate to the evaluation and management of patients with coronary artery disease and heart failure. The first section emphasized a new conceptual approach to changes in the diastolic pressure-volume relation of the left ventricle. Although previous studies have concentrated on mathematical models which describe wall stress and stiffness as derived from the pressure-volume relationship, this review emphasizes that hemodynamic factors are very important in acutely altering the pressure-volume relationship of the left ventricle. This is partly due to alterations in right ventricular pressure, which subsequently influence the left ventricular pressure-volume relationship. In addition, recent studies have pointed out that compliance indices measured at low end-diastolic pressures differ from the indices measured at high end-diastolic pressures, so that limited information from one portion of the curve may not be generalized to describe the entire curve. The section on afterload emphasized the importance of this factor in influencing cardiac function, particularly in the presence of heart failure. In patients with both acute and chronic heart failure, vasodilator drugs which reduce ventricular afterload have produced substantial hemodynamic benefit by reducing the filling pressures of the right and left ventricles and increasing forward cardiac output. This hemodynamic improvement in response to afterload reduction is predictable from the different quantitative descriptions of ventricular afterload. Nevertheless, it is still unclear which method best describes afterload. Although wall stress, impedance, vascular resistance, and aortic pressure have all been utilized as a measure of afterload, each has some shortcomings which may limit its applicability. The final section reviewed approaches to the measurement of regionally ischemic myocardium. Since current studies have emphasized the importance of identifying and preserving ischemic, but viable, myocardium, this section has reviewed techniques for measuring local mechanical performance. Previous studies with the Walton-Brodie strain gauge and epicardial length gauge did not appear to be as satisfactory as more recent measurements with ultrasonic crystals, which can simultaneously measure wall thickness and segment length. These methods form the basis for ongoing experiments designed to evaluate approaches for preserving ischemic myocardium in the setting of experimental myocardial infarction.