AJP - Heart and Circulatory Physiology, Vol 258, Issue 5 1348-H1356, Copyright © 1990 by American Physiological Society
Time dependence of regional systolic left ventricular relationships in intact hearts
W. P. Miller, S. H. Nellis and A. J. Liedtke
Department of Medicine, University of Wisconsin School of Medicine, Madison 53792.
In intact hearts the beat-to-beat left ventricular systolic pressure-length
relationship is not uniquely defined, but rather is history dependent and
appears hysteretic. The purpose of these studies was to assess the time
course of this phenomenon. In an open chest swine heart preparation, left
ventricular pressure, regional lengths, and wall thickness were measured.
Loading conditions were altered by the infusion of volume into the left
ventricle to increase peak systolic pressure approximately 30 mmHg. The
resultant interbeat systolic pressure-dimension relationships were
hysteretic. The first part of the study (n = 13) was to test whether the
myocardium exhibited a long-term memory of prior mechanical events.
Measurements obtained 30 and 120 s after volume loading revealed no
residual differences in pressure or dimension compared with preinjection
values. Thus the phenomenon was transient and complete (reversible) by 30
s. To better characterize this event, the temporal effects of myocardial
loading were studied (n = 8). A randomized comparison of two different
rates of volume infusions (27 +/- 2 vs. 56 +/- 2 ml/s, P less than 0.001)
was performed. Varying the volume loading resulted in similar increases in
peak left ventricular pressure (35 +/- 3 vs. 31 +/- 3 mmHg) but at
different increments of development, i.e., greater than 5-7 cardiac cycles
at the slower rate of volume infusion vs. greater than 2-3 cardiac cycles
(P less than 0.001) at the faster rate. The isochronal systolic
pressure-dimension relationships were quantitated by measuring the area of
the hysteretic relationship and its slope.(ABSTRACT TRUNCATED AT 250 WORDS)
