FACTORS AFFECTING BRONCHIAL BLOOD-FLOW THROUGH BRONCHOPULMONARY ANASTOMOSES IN DOGS

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Abstract
Most of the bronchial arterial blood flow (.ovrhdot.Qbr) drains through bronchopulmonary anastomoses into the pulmonary circulation, and the remainder goes into the systemic venous system via the bronchial veins. We studied the relationship between blood flow through bronchopulmonary anastomoses, and alveolar pressure and pulmonary vascular pressures as well as hydrostatic pressure in the bronchial veins in 10 adult dogs. The pulmonary artery and vein of the experimental left lower lobes (LLL) of open-chested, anesthetized dogs were isolated and connected to reservoirs. The part of the .ovrhdot.Qbr that flowed through bronchopulmonary anastomoses into the reservoirs was continuously measured at constant pulmonary vascular pressures of 0 cm H2O relative to the lung base. Any bronchial blood volume that retained within the LLL was estimated from changes in lobe weight. The lobe was distended with 5% CO2 and air, at alveolar pressures of 5, 10, or 20 cm H2O in a random sequence. Because bronchial veins drain into the azygos vein, the bronchial venous pressure was elevated by snaring the azygos vein. The mean anastomotic .ovrhdot.Qbr was 4.4 .+-. 1.1 (mean .+-. SEM) ml/min and it decreased by 23 and 39% when alveolar pressure was raised from 5 cm H2O to 10 and 20 cm H2O, respectively (p < 0.05). Approximately 75% of the total anastomotic .ovrhdot.Qbr was collected from the pulmonary venous reservoir at all alveolar pressures. When both pulmonary artery and venous pressures were increased higher than the alveolar pressure (zone III), azygos snaring increased the anastomotic .ovrhdot.Qbr by 13 and 31% at alveolar pressures of 10 and 20 cm H2O, respectively (p < 0.05). However, when pulmonary vascular pressures were kept at 0 cm H2O (zone 1), azygos vein snaring caused no change in anastomotic .ovrhdot.Qbr. These data suggest that bronchopulmonary anastomoses are more numerous on the pulmonary venous side of the capillary and that the anastomotic .ovrhdot.Qbr is affected by the alveolar pressure, pulmonary vascular pressures, and azygos vein pressure.