Dynamics of myocardial adaptation to low-flow ischemia and
hypoxemia.
Merati, Giampiero, Sonia Allibardi, Lucilla D. Monti, Jan Willem De
Jong, and Michele Samaja.
Department of Biomedical Science & Technology, University of
Milan, Scientific Institute H. San Raffaele, Milan, Italy, and
Thoraxcenter, Erasmus University Rotterdam, The Netherlands
APStracts 3:0308H, 1996.
We investigated whether a single or more than one factor controls
performance in O2-limited hearts. For this purpose, we measured the
dynamics of myocardial adaptation to reduced O2 supply with a
specially designed set up, analyzing early changes after reduction in
either flow of the perfusion medium or its pO2. For 10 min, 38
isolated rat hearts underwent low-flow ischemia or hypoxemia, matched
for O2 supply. Early during ischemia, developed pressure declined at
a rate of 311 +/- 25 mmHg/s; lactate release increased, and then
leveled off to 3.4 +/- 0.7 [mu]mol/min within 2 min. During hypoxemia
pressure dropped initially, as observed during ischemia. Then,
however, it increased before it slowly decreased. Lactate release
during hypoxemia peaked at 13.0 +/- 2.3 [mu]mol/min after 2 min,
leveling off to 3.5 +/- 1.3 [mu]mol/min. Glycogen decreased by 52 and
81% in ischemic and hypoxemic hearts, respectively (P < 0.05).
Re-exposure to ischemia or hypoxemia induced comparable changes in
both groups. We conclude that at the beginning of ischemia a single
factor does limit myocardial performance. This variable, which
remains undisturbed for 10 min, is presumably O2 availability. In
contrast, about 20 s after induction of hypoxemia, glycolytic ATP
production can partially override low O2 availability by providing
most of the energy needed. During repeated restriction of O2 supply,
O2 availability alone limits performance during both ischemia and
hypoxemia.
Received 17 October 1995; accepted in final form 30 May 1996.
APS Manuscript Number H967-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 25 July 1996