AJP - Heart and Circulatory Physiology, Vol 247, Issue 1 8-16, Copyright © 1984 by American Physiological Society
Short-term memory in the in situ canine myocardium
O. Nwasokwa, K. Sagawa and H. Suga
We studied the effect of intracycle (short-term) mechanical history on
canine myocardial performance. Intracycle muscle force and/or length
history was varied, and the resultant changes in end-systolic force-length
relationship were analyzed. Antecedent isotonic shortening impaired,
whereas isometric force development enhanced end-systolic myocardial
performance. A history of shortening concurrent with force development
produced an intermediate effect. We conclude that decreasing force or
length impairs whereas increasing length or force enhances performance in
the same cycle. Different combinations of antecedent force and length
changes affect end-systolic performance by algebraic summation
(superposition) of their disparate effects. Time measurements established
that 1) total systolic time varied little with altered history, 2) isotonic
shortening took longer than isometric contraction in reaching a point P in
the force-length plane, and 3) less time was therefore available for
contraction after P with antecedent isotonic shortening than with
antecedent isometric force development. This history-dependent time
differential accounts for the corresponding differential in performance.
