Half-Logistic Time Constants as Inotropic and Lusitropic Indices for Four Sequential Phases of Isometric Tension Curves in Isolated Rabbit and Mouse Papillary Muscles

Abstract

SummaryThe waveforms of myocardial tension and left ventricular (LV) pressure curves are useful for evaluating myocardial and LV performance, and especially for inotropism and lusitropism. Recently, we found that half-logistic (h-L) functions provide better fits for the two partial rising and two partial falling phases of the isovolumic LV pressure curve compared to mono-exponential (m-E) functions, and that the h-L time constants for the four sequential phases are superior inotropic and lusitropic indices compared to the m-E time constants. In the present study, we tested the hypothesis that the four sequential phases of the isometric tension curves in mammalian cardiac muscles could be curvefitted accurately using h-L functions. The h-L and m-E curve-fits were compared for the four phases of the isometric twitch tension curves in 7 isolated rabbit right ventricular and 15 isolated mouse LV papillary muscles. The isometric tension curves were evaluated in the four temporal phases: from the beginning of twitch stimulation to the maximum of the first order time derivative of tension (dF/dt max ) (Phase I), from dF/dt max to the peak tension (Phase II), from the peak tension to the minimum of the first order time derivative of tension (dF/dt min ) (Phase III), and from dF/dt min to the resting tension (Phase IV). The mean h-L correlation coefficients (r) of 0. 9958, 0.9996, 0.9995, and 0.9999 in rabbit and 0.9950, 0.9996, 0.9994, and 0.9997 in mouse for Phases I, II, III, and IV, respectively, were higher than the respective m-E r-values (P < 0.001). The h-L function quantifies the amplitudes and time courses of the two partial rising and two partial falling phases of the isometric tension curve, and the h-L time constants for the four partial phases serve as accurate and useful indices for estimation of inotropic and lusitropic effects. (Int Heart J 2009; 50: 389-404)

Calcium-induced calcium release from the sarcoplasmic reticulum can be evaluated with a half-logistic function model in aequorin-injected cardiac muscles

“…The experimental procedures have been previously described in detail [4,6,7]. In short, seven albino rabbits (Japan White; body weight 2.0-2.5 kg) and 15 mice (C57BL/6; body weight 25-30 g) were anesthetized with intravenous (1.5-2.0 mg/kg) and intraperitoneal (15-20 mg/kg) pentobarbital sodium, respectively.…”

“…To maximize the amount of useful information extracted from the CaT, myocardial tension, and LV pressure waveforms, many investigators have attempted to curve-fit the waveforms by using various mathematical models. We previously found that the half-logistic (h-L) function, which is a half-curve of a non-linear sigmoid logistic function with a boundary at the inflection point, curve-fits the first half of the ascending phases of (1) the isometric myocardial tension curve from twitch stimulation to the maximum of the first-order time derivative of tension (dF/dt max ) [4] and (2) the isovolumic LV pressure curve from the point corresponding to QR on the electrocardiogram (ECG) to the maximum of the first-order time derivative of LV pressure (dP/dt max ) [5] better than the mono-exponential (m-E) function. The first half of the ascending phase of the CaT curve (faCaT) is expected to change in parallel with the amplitudes and time courses of the myocardial tension and LV pressure curves.…”