Effect of alveolar hypoxia on pulmonary vascular resistance

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Abstract
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. Hexamethonium, atropine, and brom-lysergic acid diethylamide did not alter the pressor response; Dibenzyline appeared to diminish 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 Po2, but the resistance increase was demonstrated to be in the precapillary vessels. The hypoxic pressor response was transient and easily depressed by a period of severe hypoxia even though pressor drug responses remained unchanged. The possibility of mediation of the arterial narrowing by a reflexlike mechanism is considered. Note: (With the Technical Assistance of Emily McCartney) direct vascular effects of hypoxia; reflex vasoconstriction tissue hypoxia Submitted on March 27, 1964

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