Regional distribution of ventilation and perfusion as a function of body position.

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Abstract
Regional subdivisions of lung volume and the distribution of pulmonary ventilation and perfusion were the distribution of pulmonary ventilation and perfusion were studied using xenon I33 in 8 normal subjects in supine, prone, and right and left lateral positions. In all postures, the regional residual volume, functional residual capacity, and expiratory reserve volume were relatively greater in upper than in dependent lung regions; the regional inspiratory and vital capacities were, by contrast, greater in dependent zones. Except at lung volumes lower than the functional residual capacity, pulmonary ventilation and perfusion were greater in dependent than in upper zones in all postures, indicating that distribution of both ventilation and perfusion is gravity dependent. Differences in ventilation were constant in relation to the vertical axis whatever the body position, and presumably are to be ascribed to regional differences in pleural pressure, which in turn are related to the weight of the lungs. The distribution of perfusion down the vertical axis varied somewhat between the different body positions, but was related to the relative magnitudes of regional pulmonary vascular and alveolar pressures.

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