Mechanical properties of the ventricle during systole.

The systolic mechanical properties of the ventricular chamber, such as its volume elasticity and apparent viscosity or resistance, provide a useful framework for studying ventricular contraction. During systole, elasticity describes the dependence of pressure generated by the ventricle on chamber volume, while resistance describes changes in pressure related to the rate of ejection. Elastic stiffness increases throughout contraction and is sensitive to changes in inotropic state. Resistance also increases during contraction in parallel with ventricular pressure, but changes in inotropic state do not alter the relation between resistance and pressure. These two mechanical properties offer an insight into the performance of the ventricle as a pump; hence, they may be useful in assessing changes in pump function. This review examines several different approaches to the measurement of elasticity and resistance during systole: one approach lumped all the mechanical properties into a mean value expressed as an average impedance; another focused on elasticity, particularly the maximum elasticity achieved at end-systole; a third approach examined elasticity and resistance at high frequencies of volume oscillation; and the final method utilized a flow-pulse technique to study the variations in both elasticity and resistance throughout systole.