Effect of alveolar hypoxia on pulmonary vascular resistance

The responses to graded hypoxia in 58 excised dog lung lobe preparations have been measured during constant perfusion and ventilation. When perfused with blood, alveolar hypoxia always evoked a pressor response, whereas a dilator response always appeared when a synthetic perfusate was used. Hexame-thonium, atropine, and brom-lysergic acid diethylamide did not alter the pressor response; Dibenzyline appeared to dimin-ish the response but this may have been due to the reversal of effect of any epinephrine present. A pressor response could also be produced with KCN. The response to alveolar hypoxia was shown to be unrelated to pulmonary arterial blood Paz, but: the resistance increase was demonstrated to be in the precapil-lary vessels. The hypoxic pressor response was transient: and easily depressed by a period of severe hypoxia even though pres-sor drug responses remained unchanged. The possibility o