Journal of Applied Physiology, Vol 61, Issue 6 2136-2143, Copyright © 1986 by American Physiological Society
Regional pulmonary blood flow during 96 hours of hypoxia in conscious sheep
D. C. Curran-Everett, K. McAndrews and J. A. Krasney
The effects of acute hypoxia on regional pulmonary perfusion have been
studied previously in anesthetized, artificially ventilated sheep (J. Appl.
Physiol. 56: 338-342, 1984). That study indicated that a rise in pulmonary
arterial pressure was associated with a shift of pulmonary blood flow
toward dorsal (nondependent) areas of the lung. This study examined the
relationship between the pulmonary arterial pressor response and regional
pulmonary blood flow in five conscious, standing ewes during 96 h of
normobaric hypoxia. The sheep were made hypoxic by N2 dilution in an
environmental chamber [arterial O2 tension (PaO2) = 37-42 Torr, arterial
CO2 tension (PaCO2) = 25-30 Torr]. Regional pulmonary blood flow was
calculated by injecting 15-micron radiolabeled microspheres into the
superior vena cava during normoxia and at 24-h intervals of hypoxia.
Pulmonary arterial pressure increased from 12 Torr during normoxia to 19-22
Torr throughout hypoxia (alpha less than 0.049). Pulmonary blood flow,
expressed as %QCO or ml X min-1 X g-1, did not shift among dorsal and
ventral regions during hypoxia (alpha greater than 0.25); nor were there
interlobar shifts of blood flow (alpha greater than 0.10). These data
suggest that conscious, standing sheep do not demonstrate a shift in
pulmonary blood flow during 96 h of normobaric hypoxia even though
pulmonary arterial pressure rises 7-10 Torr. We question whether global
hypoxic pulmonary vasoconstriction is, by itself, beneficial to the sheep.
