AJP - Heart and Circulatory Physiology, Vol 263, Issue 4 1011-H1016, Copyright © 1992 by American Physiological Society
Limited left ventricular inotropic response to exercise in early phase of pressure overload in dogs
J. B. Su, L. Hittinger, P. Le Franc and B. Crozatier
Institut National de la Sante et de la Recherche Medicale, Faculte de Medecine, Creteil, France.
To study the mechanisms of myocardial adaptation to increased stress in the
early phase of left ventricular (LV) pressure overload, 12 dogs were
instrumented with LV micromanometer, LV dimensional ultrasonic crystals,
aortic catheter, and aortic occluder cuff. After recovery, animals
performed graded exercise with acute aortic stenosis (AS) or sustained (24
h) aortic stenosis (SS). At baseline, LV functional parameters with SS were
not different from those obtained with AS. LV peak pressure increased
similarly during exercise with AS or SS, but LV peak dP/dt was lower with
SS than with AS (peak values, 6,292 +/- 525 vs. 7,570 +/- 432 mmHg/s; P
< 0.05). LV end-diastolic pressure increased from 9.7 +/- 1.7 to 21.4
+/- 3.3 mmHg (P < 0.05) during exercise with SS, but was unchanged with
AS. The decrease of the time constant of isovolumic pressure fall during
exercise was significantly smaller after SS than during AS (P < 0.05).
In addition, the percentage of subendocardial wall thickening did not
increase during exercise with SS (30.3 +/- 3.6%), while it increased
significantly with AS (from 29.3 +/- 3.3 to 39.4 +/- 4.5%; P < 0.01).
Plasma catecholamine levels were similar at baseline and increased to
similar levels during exercise with AS and SS. In the early phase of
pressure overload, we conclude that exercise capacity is maintained but
that the LV inotropic response to exercise is modified with an altered
relaxation process and a lesser utilization of subendocardial inotropic
reserve.
