Evaluation of Several Geometric Models for Estimation of Left Ventricular Circumferential Wall Stress

Abstract

Phasic left ventricular wall force and wall thickness were monitored with appropriate transducers to provide a direct measurement of circumferential wall stress in open-chest dogs. Left ventricular pressure and measurements of chamber geometry were used to estimate the wall stress using several geometric models. During the initial control period, peak and end-ejection measured wall stresses were 207 ± 19 and 104 ± 13 g/cm², respectively. The best estimates of these values were 198 ± 18 and 117 ± 11 g/cm² obtained from a modified thin-wall ellipse formula in which the midwall rather than the endocardial radius was used. Wide variations in hemodynamic conditions were produced with intravenous infusions of nitroglycerin, phenylephrine, and isoproterenol. Comparison of directly measured and estimated values during all control periods and during the response to these interventions showed that both the modified thin-wall ellipse and a thick-wall ellipse were generally accurate predictors of the measured wall stress. All other models tended to underestimate measured stress. The sensitivity of the estimated wall stress computed by the models to geometric measurement errors was also evaluated. A thick-wall sphere was the most sensitive to both circumferential length and wall thickness measurement errors, and a thick-wall ellipse was the least sensitive. All models examined were relatively insensitive to base-to-apex length measurement errors.