Vertical gradient of perfusion in the erect human lung

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Abstract
A quantitation examination is made of a number of mechanisms which might contribute to the gross nonuniformity of blood flow observed in the erect lung. Passive distension of the small vessels by the increased transmural pressures in the base of the lung is shown to be an insufficient explanation of their heightened blood flow. A vertical assemblage of vascular units operating under “waterfall” conditions shows a rapid change of flow per unit with height. These conditions may be caused to apply over a range of heights near the center of the lung by the assumption of critical closing pressures in the capillary bed. If these pressures are allowed to have a range of values in accordance with the anatomical range of capillary diameters the height-flow relationship is brought close to that observed. The expected behavior of a model of this type is discussed. pulmonary circulation; distensibility of small pulmonary vessels; vertical distribution of pulmonary blood flow; waterfall effect; critical closing pressures in pulmonary circulation Submitted on August 17, 1964