Optimization of cardiac fiber orientation for homogeneous fiber strain during ejection

The strain of muscle fibers in the heart is likely to be distributed unifor mly over the cardiac walls during the ejection period of the cardiac cycle. Mathematical models of left ventricular (LV) wall mechanics have shown tha t the distribution of fiber strain during ejection is sensitive to the orie ntation of muscle fibers in the wall. In the present study, we tested the h ypothesis that fiber orientation in the LV wall is such that fiber strain d uring ejection is as homogeneous as possible. A finite-element model of LV wall mechanics was set up to compute the distribution of fiber strain at th e beginning (BE) and end (EE) of the ejection period of the cardiac cycle, with respect to a middiastolic reference state. The distribution of fiber o rientation over the LV wall, quantified by three parameters, was systematic ally varied to minimize regional differences in fiber shortening during eje ction and in the average of fiber strain at BE and EE. A well-defined optim um in the distribution of fiber orientation was found which was not signifi cantly different from anatomical measurements. After optimization, the aver age of fiber strain at BE and EE was 0.025 +/-0.011 (mean+/-standard deviat ion) and the difference in fiber strain during ejection was 0.214+/-0.018. The results indicate that the LV structure is designed for maximum homogene ity of fiber strain during ejection. (C) 1999 Biomedical Engineering Societ y. [S0090-6964(99)01603-3].