Stability of alveolar hypoxic vasoconstriction with intermittent hypoxia

Abstract

Repeated intermittent global hypoxia apparently markedly enhances hypoxic pulmonary vasoconstriction in dogs. This phenomenon was reexamined 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 1 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 i.v. 133Xe and external chest detectors. Each dog alternately breathed air or the unilateral alveolar hypoxia combination for 15 min each for 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 1st 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.