The volume of the extra and intrapulmonary segments of the pulmonary artery in intact dogs

The relative contributions of the extra and intrapulmonary segments of the pulmonary artery to the total pulmonary arterial blood volume (VPA) at functional residual capacity (FRC) and during lung inflation were investigated in anesthetized intact dogs. VPA was determined by an ether pneumotachographic method and the volume of the extrapulmonary segment (VPAep) by an angiographic technique. The volume of the intrapulmonary segment (VPAiP) was calculated by subtraction of VPAep from VPA. Using transvenous phrenic nerve stimulation, changes in transmural pulmonary arterial pressure and transpulmonary pressure (PTP) were measured during open airway lung inflation. Some of the dogs were then subjected to hypoxia by breathing mixtures of 7-10% oxygen in nitrogen and repeat measurements taken. The results indicate that VPA is evenly distributed between the extra and intrapulmonary segments of the pulmonary artery and that this relationship is not affected by either lung inflation or hypoxia.