Active Stiffness of the Intact Canine Left Ventricle

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Abstract
Three methods were employed to measure the overall active stiffness of the intact left ventricle in anesthetized dogs. In two of these, isovolumic contractions of the ventricle were examined, and in the third the response to a minor increase in afterload was analyzed. The average modulus of active stiffness of the normal left ventricle by all three methods was found to be lower than that reported for the cat papillary muscle (57-76%). Myocardial infarction studied 1 hour and 2 to 3 weeks following ligation of the anterior descending coronary artery did not alter active stiffness of the left ventricle. When sufficient time had elapsed, however, for complete scarring and thinning of the infarction to occur, active stiffness was significantly reduced. It is suggested that a functional defect of the overall active stiffness (series elasticity) of the ventricle may be operative in the pathogenesis of congestive failure due to ventricular aneurysm.