Functional aspects of canine bronchial-pulmonary vascular communications

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Abstract
Experiments in anesthetized open-chest dogs indicated that blood from the canine bronchial circulation may drain into the arterial and venous sides of the alveolar vessel bed. Evan''s blue dye injected into the systemic circulation appeared in the effluence from a left lower lobe, pulmonary arterial segment, in which inflow was stopped with a snare and outflow through the alveolar vessel bed was stopped by maintaining zone 1 conditions. To determine the influence of mean systemic arterial pressure on lobar bronchial flow, flows from arterial and venous cannulas were measured at different mean systemic arterial pressures (lung volume history constant). Influence of lung volume and transpulmonary pressure (Ptp) changes were each examined utilizing the hysteresis characteristics of the lung pressure-volume curve. Mean total flows ranged from 2.26-5.26 ml/min with 43-61% draining through the arterial side. Flow decreased with lower systemic arterial pressure, higher Ptp and higher lung volume. Distribution of flow was influenced only by lung volume changes. The communication sites contributing to the arterial drainage apparently are located within the alveolar vessel bed. Since bronchial flow drains to both sides of the alveolar vessel bed, it must be considered when interpreting results from isolated pulmonary circulation preparations.