Hypoxic Pulmonary Vasoconstriction and Regional and Whole-lung PEEP in the Dog

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Abstract
In open-chested (Group I) and closed-chested (Group II) dogs, the effects of the application of regional and whole-lung PEEP [positive end-expiratory pressure] (10 torr) on the partitioning of electromagnetically measured blood flow between a normoxic and a hypoxic compartment of the lung were studied. In Group I and Group II when the left lower lobe (LLL) was made the hypoxic compartment by ventilation with N2, 95% and CO2, 5%, or by causing complete absorption atelectasis, LLL blood flow-to-total pulmonary blood flow ratio (.ovrhdot.QLLL/.ovrhdot.Qt) decreased 32-56% PEEP to the normoxic compartment (rest of the lung) during LLL hypoxia increased .ovrhdot.QLLL/.ovrhdot.Qt significantly in Group I (from 12 .+-. 2 to 35 .+-. 7%) and Group II (from 8 .+-. 1 to 11 .+-. 1%), but the increase was much greater in Group I, and transmural pulmonary arterial pressure increased significantly (6 .+-. 1 torr) in Group I only. PEEP to both the hypoxic LLL and the normoxic rest of the lung increased .ovrhdot.QLLL/.ovrhdot.Qt significantly in Group I only (from 12 .+-. 2 to 19 .+-. 4%) and transmural pulmonary arterial pressure increased significantly (7 .+-. 1 torr) in Group I only. PEEP to just the hypoxic LLL decreased .ovrhdot.QLLL/.ovrhdot.Qt significantly in Group I (from 12 .+-. 2 to 7 .+-. 1%) and Group II (from 8 .+-. 1 to 5 .+-. 0.4%). In addition to the usual increase in regional functional residual capacity, the effect of PEEP on diseased lung is a summation of its beneficial and deleterious regional effects on the partitioning of blood flow between hypoxic and normoxic compartments of the lung.