Pathophysiological effects of hemodilution in chronic mountain
sickness in rats.
Du, H. K., Y. J. Lee, G. L. Colice, J. C. Leiter, and L. C. Ou.
Department of Physiology and Medicine, Dartmouth Medical School,
Lebanon, NH 03756 and the Department of Medicine, White River
Junction VA Hospital, White River Junction, VT 05001
APStracts 2:0487A, 1995.
We examined the effect of isovolemic hemodilution in a rat model of
Chronic Mountain Sickness (CMS). After 30 days at simulated high
altitude (5,500 m), Hilltop rats had developed evidence of CMS:
severe hypoxemia, polycythemia and pulmonary arterial hypertension.
Isovolemic hemodilution to a mean hematocrit of 46+/-5% was well
tolerated by both the hypoxia sensitive Hilltop rats and the
companion Madison rat strain, which does not develop CMS. Following
hemodilution, we found no evidence of sustained improvements in
ventilation or gas exchange in either strain. Despite the fall in
blood viscosity, cardiac output increased only marginally, and
pulmonary artery hypertension persisted in the Hilltop rats. Vascular
hindrance increased after hemodilution; preventing a significant
decline in pulmonary and systemic vascular resistance in the Hilltop
rats. Blood oxygen content and the coefficient of oxygen delivery
fell after hemodilution, but oxygen consumption was sustained at a
normal level after hemodilution by increasing the extraction fraction
in the Hilltop strain. There was systemic hypotension through the
first day of hemodilution, but this was the only apparent adverse
effect of hemodilution. We conclude that isovolemic hemodilution was
well tolerated despite the reduction in tissue oxygen delivery.
However, hemodilution failed to improve any of the respiratory and
cardiovascular manifestations of CMS in Hilltop rats.
Received 23 June 1995; accepted in final form 19 September 1995.
APS Manuscript Number A673-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 November 95