AJP - Heart and Circulatory Physiology, Vol 266, Issue 5 1935-H1943, Copyright © 1994 by American Physiological Society
Accelerated myocardial relaxation in conscious dogs during acute cardiac tamponade
Y. Nishikawa, J. P. Roberts, M. R. Talcott, R. C. Dysko, P. Tan and H. S. Klopfenstein
Cardiology Section, Bowman Gray School of Medicine, Winston-Salem, North Carolina 27157.
Eight chronically instrumented conscious dogs were used to test the
hypothesis that left ventricular (LV) relaxation is accelerated during
cardiac tamponade. The time constant of LV transmural pressure fall was
measured before and during intrapericardial (IP) saline infusion (baseline)
with and without beta-adrenergic blockade (propranolol 1 mg/kg iv). Heart
rate was controlled by atrial pacing. Increasing IP pressure caused a
progressive linear decrease in stroke volume before and during
beta-blockade in each animal. The time constant of LV transmural pressure
fall also decreased continuously with an increase in IP pressure from 26
+/- 7 ms during baseline to 18 +/- 5 ms during severe cardiac tamponade (P
< 0.01) before beta-blockade. However, after beta-blockade, the time
constant of LV transmural pressure fall was constant over a wide range of
IP pressures despite a continuous decrease in LV end-diastolic volume. The
time constant of LV transmural pressure fall was not altered by vena caval
occlusions that caused the same decrease in LV preload observed during
cardiac tamponade. We concluded that despite decreased pump function, LV
relaxation was accelerated progressively during graded cardiac tamponade,
and this change was dependent not on changes in loading conditions but on
an intact beta-adrenergic influence.
