Journal of Applied Physiology, Vol 49, Issue 5 846-850, Copyright © 1980 by American Physiological Society
Stability of alveolar hypoxic vasoconstriction with intermittent hypoxia
M. A. Miller and C. A. Hales
Repeated intermittent global hypoxia has been reported to markedly enhance
hypoxic pulmonary vasoconstriction in dogs. We have reexamined this
phenomenon but with intermittent unilateral alveolar hypoxia, avoiding
complications of systemic hypoxemia. Fifteen anesthetized dogs were
intubated with a double-lumen endotracheal tube, allowing separate
ventilation of one lung with 100% N2 as a hypoxic challenge and the other
lung with 100% O2 to maintain adequate systemic oxygenation. Distribution
of lung perfusion was determined with intravenous 133Xe and external chest
detectors. Each dog alternately breathed air or the unilateral alveolar
hypoxia combination for 15 min each for a total of 12 hypoxic challenges or
6 h. Two groups emerged on the basis of the strength of their
vasoconstrictor responses to successive hypoxic challenge. In group I (n =
6), perfusion to the hypoxic lung decreased 29% with the first challenge
and decreased comparably with successive challenges. In group II,
vasoconstriction was initially weak with perfusion decreasing only 5%, but
perfusion decreased further with time alone (n = 5) or successive
challenges (n = 4), falling 35% on the 12th challenge (comparable to group
I). Delayed achievement of hypoxic vasoconstriction in group II may be
secondary to a vasodilating prostanoid that disappears with time.
