HYPOXIA AND PULMONARY VASCULAR RESISTANCE. RELATIVE EFFECTS OF PULMONARY ARTERIAL AND ALVEOLAR P02

The relative effects of pulmonary arterial and alveolar P02 on pulmonary vascular resistance (PVR) have been studied in isolated and ventilated rat lung preparations. The experimental arrangement included two such preparations perfused in series with homologuous blood. Pulmonary arterial hypoxemia (Po2 28–44 mm Hg) without alveolar hypoxia did not elicit vasoconstrictor response. High pulmonary arterial P02 (120–320 mm Hg) reduced the pressor response to alveolar hypoxia. This effect of arterial Po2 could be counteracted by a rise in ventilation frequency. Pulmonary arterial hypoxemia during periods with arrest of ventilation caused brisk vasoconstrictor responses. It was apparent that the combined effect of alveolar and arterial Po2 on PVR depends on the relative intensities of ventilation and perfusion, the alveolar Po, being the main denominator for the vasoconstriction effect. The results have been discussed in relation to the possible shape of the Po2 gradient from alveolar gas to lumen of small resistance vessels. © 1969 Scandinavian Physiological Society