Positive end-expiratory pressure decreases bronchial blood flow in the dog.

Positive end-expiratory pressure (PEEP) increases pulmonary vascular resistance, but its effect on the bronchial circulation is unknown. We have compared two techniques for measuring bronchial blood flow in anesthetized, open-chest, ventilated dogs at varying levels of PEEP. Bronchial blood flow ( Qbr ) to the left lower lobe (LLL) and trachea was measured with radiolabeled microspheres. Total Qbr was partitioned into tracheal, bronchial, and parenchymal fractions. We also measured the bronchopulmonary anastomotic flow ( Qbra ) by attaching cannulas from the lobar pulmonary artery and vein to reservoirs, interrupting the LLL pulmonary blood flow and collecting the flow going into the reservoirs. We measured Qbr and Qbra in 10 animals ventilated with varying levels of PEEP (3, 10, and 15 cmH2O) applied randomly. Pulmonary venous pressure was kept at 0 cmH2O. There was no difference observed between Qbr and Qbra at PEEP 3 and 10 cmH2O, but at PEEP 15 cmH2O, Qbr was greater than Qbra , suggesting that at low left atrial pressures bronchial blood flow drains mainly to the left atrium, whereas at elevated alveolar pressures a larger fraction empties into the right side of the heart. PEEP decreased LLL Qbr and Qbra (P less than 0.01). That fraction of Qbr going to the trachea did not change with PEEP. However, the bronchial and parenchymal fractions decreased.