Effect of chamber eccentricity on equatorial fiber stress during systole.

A survey was conducted of methods of assessing stress in the left ventricle. Although simultaneous measurements have been made of average wall force and thickness in the dog left ventricle (from which stress can be computed), the experimental procedures are not applicable to man. However, two mathematical models based on ellipsoidal representations of ventricular geometry have been shown to predict average circumferential stress reasonably well. Although both of these models are sensitive to errors in average equatorial wall thickness, they appear to be the most reliable models currently available for estimating stress. One of these models was applied to an analysis of midwall equatorial fiber stress and force in the normal conscious dog left ventricle. It was found that variations in chamber eccentricity during systole were much less important in evaluating this stress than variations in the ratio of equatorial wall thickness to semi-minor radius. A formula was derived that relates fiber stress to fiber force. It was found that fiber stress and force decrease more rapidly during ejection than intraventricular pressure, consistent with previous results.