This study investigates the distribution of blood flow in an isolated dog lung and its relationship to vascular and alveolar pressures. The left lung was removed, ventilated with negative pressure, and perfused with venous blood. Pulmonary arterial, venous, and alveolar pressures were varied, and blood flow distribution was measured using xenon-138. The results showed that blood flow was absent above the level where alveolar pressure equaled arterial pressure. Below this level, blood flow increased linearly with distance down the lung when venous pressure was low. Raising venous pressure made the flow distribution more uniform, though flow still increased in this zone. The flow distribution was explained by mechanical effects of pressure inside and outside blood vessels, which behaved like Starling resistances. The study simulated human flow distributions in various physiological and pathological states. The lung is unique in separating liquid and gas through a thin membrane, leading to different transmural pressures at various levels. In humans, pulmonary blood flow increases ninefold from the apex to the base of an upright lung. Various conditions alter this distribution, such as posture, exercise, and intracardiac shunts. Pulmonary venous pressure also affects flow distribution, as seen in patients with mitral stenosis. Changes in alveolar pressure are thought to affect flow distribution in both humans and dogs, though direct measurements of pressures and flow distributions are lacking. The study used radioactive gases to measure regional blood flow in an isolated perfused dog lung. The lung was suspended in a Lucite box, ventilated with negative pressure, and perfused with venous blood. Blood flow was measured using saline manometers and radioactive xenon. The results showed a linear increase in blood flow from the base to the top of the lung when venous pressure was low. Raising venous pressure made the flow distribution more uniform. The study also used other techniques, such as radiographic contrast and Evans blue solution, to examine flow distribution. The results showed that blood flow distribution was influenced by pulmonary arterial, venous, and alveolar pressures. When arterial pressure was low, blood flow was concentrated at the base of the lung. When arterial pressure was high, blood flow was more evenly distributed. Alveolar pressure also affected flow distribution, with higher alveolar pressure reducing flow at the top of the lung. Venous pressure had a similar effect, with higher venous pressure making flow distribution more even. The study concluded that the distribution of blood flow in the lung is determined by mechanical effects of pressure inside and outside blood vessels, which behave like Starling resistances. The findings have implications for understanding pulmonary circulation in both normal and pathological conditions.This study investigates the distribution of blood flow in an isolated dog lung and its relationship to vascular and alveolar pressures. The left lung was removed, ventilated with negative pressure, and perfused with venous blood. Pulmonary arterial, venous, and alveolar pressures were varied, and blood flow distribution was measured using xenon-138. The results showed that blood flow was absent above the level where alveolar pressure equaled arterial pressure. Below this level, blood flow increased linearly with distance down the lung when venous pressure was low. Raising venous pressure made the flow distribution more uniform, though flow still increased in this zone. The flow distribution was explained by mechanical effects of pressure inside and outside blood vessels, which behaved like Starling resistances. The study simulated human flow distributions in various physiological and pathological states. The lung is unique in separating liquid and gas through a thin membrane, leading to different transmural pressures at various levels. In humans, pulmonary blood flow increases ninefold from the apex to the base of an upright lung. Various conditions alter this distribution, such as posture, exercise, and intracardiac shunts. Pulmonary venous pressure also affects flow distribution, as seen in patients with mitral stenosis. Changes in alveolar pressure are thought to affect flow distribution in both humans and dogs, though direct measurements of pressures and flow distributions are lacking. The study used radioactive gases to measure regional blood flow in an isolated perfused dog lung. The lung was suspended in a Lucite box, ventilated with negative pressure, and perfused with venous blood. Blood flow was measured using saline manometers and radioactive xenon. The results showed a linear increase in blood flow from the base to the top of the lung when venous pressure was low. Raising venous pressure made the flow distribution more uniform. The study also used other techniques, such as radiographic contrast and Evans blue solution, to examine flow distribution. The results showed that blood flow distribution was influenced by pulmonary arterial, venous, and alveolar pressures. When arterial pressure was low, blood flow was concentrated at the base of the lung. When arterial pressure was high, blood flow was more evenly distributed. Alveolar pressure also affected flow distribution, with higher alveolar pressure reducing flow at the top of the lung. Venous pressure had a similar effect, with higher venous pressure making flow distribution more even. The study concluded that the distribution of blood flow in the lung is determined by mechanical effects of pressure inside and outside blood vessels, which behave like Starling resistances. The findings have implications for understanding pulmonary circulation in both normal and pathological conditions.