BRIEF REVIEWS A Reexamination of the Influence of Muscle Length on Myocardial Performance

THIS EXTRACT from a former Brief Review by Sonnenblick and Skelton provides a very neat summary of the essence of our understanding of how cardiac output is regulated. The interplay envisaged is between muscle length (which is governed by diastolic volume) and contractility (which can be altered by inotropic interventions), and these two factors are generally thought to influence myocardial performance through quite separate mechanisms. Muscle length and contractility or the inotropic state of the muscle have been regarded as amenable to independent manipulation as experimental variables, and the quest for the perfect index of contractility has rested squarely on the belief that some fortunate person would, one day, find a measure of mechanical performance that could be shown to depend on the inotropic state of the muscle and to be independent of muscle length. The conclusion reached in this article is that (in the isolated papillary muscle at least) there can be no such index of contractility because the inotropic state of the muscle is strongly influenced by its length.