Hypoxia and hyperoxia both transiently affect distribution of pulmonary perfusion but not ventilation in awake sheep

Despite a remarkable gravity independent heterogeneity in both local pulmon ary ventilation and perfusion, the two are closely correlated at rest and d uring exercise in the normal lung. These observations strongly indicate tha t there is a mechanism for coupling of the two so that local (V) over dot/( Q) over dot-ratio is kept fairly uniform throughout the lung. This is also necessary to achieve adequate gas exchange in the lung. it was recently sug gested that oxygen-induced vasoconstriction has a slow and intense componen t that might contribute to the matching of ventilation and perfusion also u nder normal conditions (Vejlstrup & Dorrington 1993). We therefore simultan eously determined distribution of local (approximate to 1 1/2 cm(3) lung pi eces) ventilation and perfusion in eight sheep a? normoxia (FiO(2) 21%) and after 10 min and 2 1/2 h exposure to hypoxia (FiO(2) 12%; four sheep) or h yperoxia (FiO(2) 40%: four sheep). We used a approximate to 1 mu m wet fluo rescent aerosol and 15 mu m radioactive microspheres i.v. to measure local ventilation and perfusion, respectively. Neither hypoxia nor hyperoxia caus ed changes in the distribution of ventilation. After 10 min exposure to hyp oxia or hyperoxia, distribution of perfusion was altered so that the correl ation between values for local ventilation and perfusion decreased. After 2 1/2 h exposure to either hypoxia or hyperoxia, distributions of perfusion and (V) over dot/(Q) over dot-ratio had returned to baseline. These results show that distribution of perfusion is influenced by acute changes in oxyg en tension, so that local matching of ventilation and perfusion is affected . Apparently, some mechanism restores the matching during extended exposure to the altered oxygen tension.