Pulmonary venoconstriction caused by elevated cerebrospinal fluid pressure in the dog.

Previously we found that raising cerebrospinal fluid pressure (PCSF) caused pulmonary vasoconstriction mediated by adrenal catecholamines. To localize the site of this vasoconstriction we used the outflow occlusion technique to divide changes in the pulmonary arteriovenous pressure gradient (Pa-v) into upstream and downstream pressure drops. Experiments were conducted in 10 dogs in which the animal's left lower lung lobe was denervated and perfused at constant flow and outflow pressure with blood pumped from the dog's pulmonary artery. Raising PCSF to 218 Torr caused Pa-v to rise from 9.0 to 12.5 Torr. Most (83%) of this increase resulted from an increase in the downstream pressure drop. Previous studies have indicated that changes in the upstream and downstream pressure drops, as measured by this technique, are highly correlated with changes in the resistance of the arterial and venous sides of the vascular bed. Thus, it appears that elevated PCSF caused primarily pulmonary venoconstriction. Similar results were obtained with norepinephrine and epinephrine infusion. This is consistent with previous studies, indicating that adrenal catecholamines are responsible for the increase in Pa-v in response to PCSF in this preparation.