Restoring forces assessed with left atrial pressure clamps.
Bell, Stephen P., Judit Fabian, Akihiro Higashiyama, Zengyi Chen, Marc
D. Tischler, Matthew W. Watkins, and Martin M. Lewinter.
Cardiology Unit, University of Vermont College of Medicine,
Burlington, Vermont 05405
APStracts 2:0379H, 1995.
A negative pressure (P) in the fully relaxed left ventricle (LV)
indicates the presence of restoring forces (RFs) generated during
contraction. In order to assess RFs in the intact LV under
physiologic filling conditions, a servomotor system was used in
anesthetized open chest dogs (n = 8) to produce non-filling diastoles
by left atrial (LA) P clamping during systole such that LAP was
< LVP during the subsequent diastole. Steady state LV end
-diastolic pressure (EDP) was varied by volume infusion from 4.0 1.5 (
SD) mm Hg to 12.8 2.1 mm Hg. The corresponding fully relaxed LVPs
increased from -2.1 1.9 mm Hg to 1.1 3.2, p < 0.001. LAP
clamping increased the rate of LVP fall by 34 28 % (p < 0.001)
during 10 msec after the LVP dropped below the level of the LVP-LAP
crossover of the preceding normal beat. During clamped beats, 2D echo
revealed substantial downward displacement of the mitral valve (MV)
leaflets despite the reversed LA-LV gradient and absence of filling.
Thus, 1) RFs are present at low physiologic EDP but absent at high
physiologic EDP; 2) filling retards the rate of fall of LVP; 3) even
in the absence of filling, the process of LV relaxation facilitates
MV opening.
Received 6 March 1995; accepted in final form 21 August 1995.
APS Manuscript Number H208-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 15 September 1995.