Double exponential curve fitting of isometric force decline in
physiologically sequenced and fully isometric relaxation in blood
perfused canine papillary muscle..
Tamiya, Kouichi, Toshiyuki Beppu, Kazuaki Ishihara.
Departments of Surgical Science and Pediatric Cardiovascular
Surgery, The Heart Institute of Japan, Tokyo Women's Medical College,
Tokyo 162, JAPAN
APStracts 2:0025H, 1995.
New indices for evaluation of isometric myocardial relaxation were
proposed. In fully isometric and physiologically sequenced twitches,
the time course of isometric force decline well fitted in with Gom
pertz's double exponential curve (r>/=0.9995). We conformed the original
equation to suit myocardial mechanics, i.e., F(t)=[GAMMA]0-[GAMMA] x exp[-
[alpha] x exp( -[beta]t)] (t=1,2, x x x ,n), where F(t) denotes force as a
function of time t. [GAMMA]0 and [GAMMA] relate upper asymptote and force
amplitude, respectively. Phase-plane analysis of F(t) revealed that [alpha]
[3.56+/-0.67 (mean+/-SD)] related to the phasic delay of relaxation onset, but
did not affect F(t) vs. dF(t)/dt relation. [beta] (0.127+/-0.021) and [GAMMA]
linearly related to negative dF(t)/dtmax, however, terminal slope of
the phase-plane diagram was governed by [beta] alone. [tau][beta] (0.081+/-
0.017 sec), a reciprocal of [beta] multiplied by sampling time, was
practically independent of preload, total load and muscle shortening. In
isometric twitches, global ischemia, isoproterenol, and CaCl2
substantially decreased [tau][beta], but reperfusion increased it. [alpha] was
independent of inotropic interventions, but significantly fell during
ischemia and increased by reperfusion.
Received 2 June 1994; accepted in final form 27 January 1995.
APS Manuscript Number H483-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 24 February 1995.