Hybrid logistic characterization of isometric twitch force curve of isolated ferret right ventricular papillary muscle

We previously found that the isovolumic pressure curve of the left ventricl e and the isometric twitch force curve of the right ventricular in situ pap illary muscle, both of the blood-perfused canine heart, were precisely fitt ed by our newly proposed hybrid logistic function. This function describes the difference between the two S-shaped logistic functions for the rising a nd falling components: A/[1 +exp{-(4B/A)(t-C)}]-D/[1 + exp{-(4E/D)(t - F)}] + G. This function characterizes comprehensively both ventricular and in si tu papillary muscle contraction and relaxation. In the present study, we hy pothesized that this function could also characterize the force curve of th e most popular, standard-type, isolated and Tyrode-superfused papillary mus cle preparation. To test this hypothesis, we investigated how precisely the hybrid logistic function could fit 112 isometric twitch force curves obser ved in eight isolated and Tyrode-superfused ferret right ventricular papill ary muscles at different muscle lengths and extracellular Ca2+ concentratio ns, We always obtained a precise curve fitting with a correlation coefficie nt above 0.9987. This fitting was much more precise than sinusoidal and pol ynomial exponential function curve fittings, These results supported the pr esent hypothesis, We conclude that our hybrid logistic function reasonably characterizes the force curve of the isolated myocardial preparation. This result broadens the generality of the hybrid logistic characterization of v entricular isovolumic pressure and myocardial isometric twitch force genera tion. The hybrid logistic characterization seems to be an integrative expre ssion of contractile processes in myocardial twitch contraction.