UNALTERED PULMONARY CAPILLARY SURFACE-AREA IN THE PRESENCE OF CHANGING ARTERIAL RESISTANCE

We hypothesized that capillary recruitment may not be solely dependent on extracapillary factors. To test this hypothesis, rabbits were anes thetized and placed on total cardiac bypass at a constant, physiologic al pulmonary blood flow. Vascular occlusion techniques were combined w ith measurement of the transpulmonary metabolism of an angiotensin-con verting enzyme substrate, allowing the concomitant assessment of chang es in segmental resistances and dynamically perfused capillary surface area. Intra-arterial serotonin infusion increased upstream pulmonary vascular resistances without affecting dynamically perfused capillary surface area. Intra-arterial isoproterenol infusion diminished seroton in-induced increased upstream resistances, also without affecting capi llary surface area. These findings support the hypothesis that pulmona ry capillary recruitment may not be solely dependent on extracapillary factors.