Journal of Applied Physiology, Vol 70, Issue 5 1991-1995, Copyright © 1991 by American Physiological Society
Effects of left atrial pressure on the pulmonary vascular response to hypoxic ventilation
S. A. Gu, J. Ducas, U. Schick and R. M. Prewitt
Department of Medicine, University of Manitoba, Winnipeg, Canada.
We investigated the effects of hypoxic ventilation on the pulmonary
arterial pressure- (P) flow (Q) relationship in an intact canine
preparation. Mean pulmonary P-Q coordinates were obtained during hypoxic
ventilation and during ventilation with 100% O2 at normal and at increased
left atrial pressure. Specifically, we tested the hypothesis that, over a
wide range, changes in left atrial pressure would alter the effects of
hypoxic ventilation on pulmonary P-Q characteristics. Seven dogs were
studied. When left atrial pressure was normal (5 mmHg), the mean value of
the extrapolated intercept (PI) of the linear P-Q relationship was 10.9
mmHg and the slope (incremental vascular resistance, IR) of the P-Q
relationship was 2.2 mmHg.l-1.min. Hypoxic ventilation increased PI to 18
mmHg (P less than 0.01) but did not affect IR. Subsequently, during
ventilation with 100% O2, when left atrial pressure was increased to 14
mmHg by inflation of left atrial balloon, PI increased to 18 mmHg. IR was
1.6 mmHg.l-1.min. Again, hypoxic ventilation caused an isolated change in
PI. Hypoxia increased PI from 18 to 28 mmHg (P less than 0.01). As in the
condition of normal left atrial pressure, hypoxic ventilation did not
affect IR. We conclude that, in an anesthetized intact canine preparation,
hypoxic ventilation causes an isolated increase in the extrapolated
pressure intercept of the pulmonary P-Q relationship. Furthermore the
effects of hypoxic ventilation on pulmonary P-Q characteristics are not
affected by the resting left atrial pressure.
