Half-logistic time constant: a more reliable lusitropic index than monoexponential time constant regardless of temperature in canine left ventricle.
Temperature changes influence cardiac diastolic function. The monoexponential time constant (tauE), which is a conventional lusitropic index of the rate of left ventricular (LV) pressure fall, increases with cooling and decreases with warming. We have proposed that a half-logistic time constant (tauL) is a better lusitropic index than tauE at normothermia. In the present study, we investigated whether tauL can remain a superior measure as temperature varies. The isovolumic relaxation LV pressure curves from the minimum of the first time derivative of LV pressure (dP/dtmin) to the LV end-diastolic pressure were analyzed at 30, 33, 36, 38, and 40 degrees C in excised, cross-circulated canine hearts. tauL and tauE were evaluated by curve-fitting using the least squares method and applying the half-logistic equation, P(t) = PA/[1 + exp(t/tauL)] + PB, and the monoexponential equation, P(t) = P0exp(-t/tauE) + Pinfinity. Both tauL and tauE increased significantly with decreasing temperature and decreased with increasing temperature. The half-logistic correlation coefficient (r) values were significantly higher than the monoexponential r values at the 5 above-mentioned temperatures. This implies that the superiority of the goodness of the half-logistic fit is not temperature dependent. The half-logistic model characterizes the amplitude and time course of LV pressure fall more reliably than the monoexponential model. Hence, we concluded that tauL is a more useful lusitropic index regardless of temperature.
Mizuno
Ju
J
Department of Cardiovascular Physiology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama 700-8558, Japan. mizuno_ju4@yahoo.co.jp
Matsubara
Hiromi
H
Mohri
Satoshi
S
Shimizu
Juichiro
J
Suzuki
Shunsuke
S
Mikane
Takeshi
T
Araki
Junichi
J
Hanaoka
Kazuo
K
Akins
Robert
R
Morita
Shigeho
S
D000465:Algorithms; D000704:Analysis of Variance; D000818:Animals; D001831:Body Temperature / Q000502:physiology*; D003971:Diastole / Q000502:physiology*; D004285:Dogs; D006439:Hemodynamics / Q000502:physiology; D066298:In Vitro Techniques; D016015:Logistic Models; D013318:Stroke Volume; D013997:Time Factors; D016277:Ventricular Function, Left / Q000502:physiology; D017725:Ventricular Pressure / Q000502:physiology