H. Matsubara et al., LOGISTIC TIME CONSTANT OF ISOVOLUMIC RELAXATION PRESSURE-TIME CURVE IN THE CANINE LEFT-VENTRICLE - BETTER ALTERNATIVE TO EXPONENTIAL TIME CONSTANT, Circulation, 92(8), 1995, pp. 2318-2326
Background The time constant of left ventricular (LV) relaxation deriv
ed from a monoexponential model has been widely used as an index of LV
relaxation rate or lusitropism, although this model has several well-
recognized problems. In the present study, we proposed a logistic mode
l and derived a ''logistic'' time constant (T-L) as a better alternati
ve to the conventional ''exponential'' time constant (T-E). Methods an
d Results A total of 189 beats (147 isovolumic and 42 ejecting beats)
were investigated in seven canine excised cross-circulated heart prepa
rations. We found that the logistic model fitted much more precisely a
ll the observed LV isovolumic relaxation pressure-time [P(t)] curves t
han the monoexponential model (P<.05). The logistic model also fitted
well both the time curve of the first derivative of the observed P(t)
(dP/dt) and the dP/dt-P(t) phase-plane curve. Like T-E, T-L indicated
that volume loading depressed LV lusitropism and that increasing heart
rate and ejection fraction augmented it. T-L was independent of the c
hoice of cutoff point defining the end of isovolumic relaxation; T-E w
as dependent on that choice. Conclusions We conclude that the logistic
model better fits LV isovolumic relaxation P(t) than the monoexponent
ial model in the present heart preparation. We therefore propose T-L a
s a better alternative to T-E for evaluating LV lusitropism.