Site of pulmonary hypoxic vasoconstriction studied with arterial and venous occlusion

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Abstract
The arterial and venous occlusion technique was applied in an in situ, isolated left lower lobe preparation of a dog lung to compare the effects of hypoxia with the effects of airway pressure elevation and the infusion of serotonin, norepinephrine and histamine. The total arteriovenous pressure drop across the lobe was partitioned longitudinally into pressure drops across the relatively indistensible arteries (.DELTA.Pa) and veins (.DELTA.PV) and across the middle distensible vessels (.DELTA.Pm). Hypoxia increased primarily .DELTA.Pm, as did elevation of airway pressure, whereas the vasoactive drugs increased either .DELTA.Pa or .DELTA.PV. The increases in pulmonary arterial pressure (Pa) caused by hypoxia and by elevation of airway pressure were independent of blood flow rate, but increases in Pa induced by the vasoactive drugs were dependent on flow rate. In the dog, hypoxia acts primarily on small distensible vessels, whereas pulmonary vasoactive drugs constrict the relatively indistensible arteries and veins. The increase in pulmonary vascular resistance during hypoxia probably did not involve smooth muscle contraction.