PULMONARY HYPERTENSIVE EFFECTS OF LUNG-INFLATION IN CHRONIC HYPOXIA -A STUDY IN RATS

Lung inflation was compared in isolated perfused lungs of control (C) and chronically hypoxic (CH) rats; in the latter, there is musculariza tion and loss of compliance in the pulmonary arterial system, During v entilation hypoxia, high alveolar pressure (Palv) elevated the pulmona ry artery pressure (Ppa) less in C than in CH rats; Ppa fell during su stained inflation, rose on deflation, and after inflation hypoxic vaso constriction was attenuated. Opposite changes took place in CH rats; P pa often rose during inflation, fell on deflation, and after inflation hypoxic vasoconstriction was enhanced. Inflation also increased Ppa m ore in CH than C rats during air ventilation. Ppa/Palv relations measu red during incremental inflation revealed normoxic tone in ''extra-alv eolar'' vessels in both rat groups, which usually increased during hyp oxia,In CH, but not C rats, there was also evidence for constriction i n ''alveolar'' vessels during hypoxia, The effects of inflation were n ot changed by NO synthase blockade in either rat group. Pulmonary hype rtensive effects of inflation in chronically hypoxic rats can be attri buted to vascular remodelling.