Effect of pulmonary venous pressure elevation on vascular resistance and compliance

The effect of pulmonary venous pressure elevation on the longitudinal distribution of resistance and compliance in the canine pulmonary circulation was determined at control vascular tone and after vascular tone was increased with histamine. The arterial, venous, and double-occlusion techniques were used in isolated dog lungs blood perfused at constant flow. The large and small blood vessel resistances and compliances were studied under both vascular tone conditions when pulmonary venous pressure was elevated above isogravimetric venous pressure conditions in successive 5 cmH₂O increments up to 30 cmH₂O. The results of this study indicate that pulmonary venous pressure elevations to 20 cmH₂O above isogravimetric venous pressure significantly decrease total vascular resistance by reducing both the small and large vein resistances, an effect which is more pronounced in the histamine-treated lungs. Also, under control vascular tone, both the middle compartment compliance and total compliance were greatly decreased over this pressure range. Histamine treatment significantly reduced both the large vessel and middle compartment compliance before and during low venous pressure elevation. When venous pressure was then raised to at least 25 cmH₂O above control outflow pressure with histamine present, the middle compartment compliance was again significantly decreased.