Topographical distribution of ventilation in isolated lung.

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Abstract
Isolated perfused dog lungs were used to study the effects of changing the vascular and transpulmonary pressures on the distribution of ventilation. This was measured by scanning the lung from bottom to top after single breaths of radioactive xenon, and also from the rates of washin and washout of the gas in upper and lower lung zones. It was found that the distribution of ventilation was substantially uniform in spite of large changes in the distribution of blood flow. In further experiments, the lung was immersed in egg albumin foam of specific gravity approximately 0.25 to simulate the gradient in pleural pressure down the intact lung. As the lung was inflated in small steps, most of the xenon initially went to the upper zone, out at larger lung volumes, the lower zone was preferentially filled. These studies provide evidence that the uneven distribution of ventilation in the human lung is not caused by the uneven distribution of blood flow but by the vertical gradient of intra-pleural pressure.