Relation of Rhythm to Force of Contraction of Mammalian Cardiac Muscle

Abstract

In the isolated papillary muscle of the cat there is a direct relationship between the force and frequency of contraction. Following an abrupt change in- rate, the force of contraction only gradually assumes that characteristic of the new frequency; the first few contractions are subnormal when the rate is increased and augmented when decreased. A single extra stimulus applied close to one in the regular series results in a marked increase in the succeeding response. The closer the interval the greater the response. In the absence of further stimulation the influence of the closely spaced extra stimulus persists for several minutes, but is gradually dissipated. It is concluded that the factor responsible for the increased force of contraction during the treppe and at higher frequencies of stimulation or following a single extra stimulus is the rhythm or spacing between stimuli, rather than the increased activity per se.