Engineering Mechanics for Successive States in Canine Left Ventricular Myocardium

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Abstract
The relations between end-diastolic (D) and end-systolic (S) cavitary volumes (Vc), wall volumes (V10), and cavitary dimensions have been studied in the canine and human left ventricle. However, the models selected for left ventricular myocardium do not represent the real heart adequately for a fiber-by-fiber analysis of fiber orientation and sarcomere length during successive states of the ejection cycle. In this study, the endocardial and epicardial surfaces were postulated to be a nested set of truncated ellipsoidal shells of revolution where wall volumes were preserved from D to S. Shell dimensions on the semiminor and semimajor axes, R and Z, respectively, were related to Vc and Vw by two representations: confocal and nonconfocal. If the focal length C = )1/2 and C is the same for each shell, then the shells are confocal, otherwise they are nonconfocal. From measured Vc, Vw, and epicardial Z in D, shell dimensions were calculated for states D and S, using both confocal and nonconfocal representations, and compared with the measured dimensions. When no empirical corrections were made, the calculated endocardial R in S underestimated the measured R in S by 12%; moreover, the calculated epicardial R in S overestimated the measured R in S by 4%. Endocardial and epicardial C measured 3.73 ± 0.33 (SE) cm and 3.79 ±0.34 cm, respectively, in D and 3.77±0.11 cm and 3.71 ±0.10 cm, respectively, in S.