Effect of gravity on the distribution of pulmonary ventilation.

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Abstract
Regional variations in lung volume and in the distribution of ventilation have been measured with Xe133 during normal gravity and during increased positive (+Gz) acceleration on a human centrifuge. All subjects were studied at +I Gz [distribution of regional lung volume and of ventilation at normal gravity.], 3 at +2 G , and one at +3 Gz. At +I Gz the top of the lung was relatively more expanded than the bottom but the increment in volume (i.e., ventilation) is greater at the bottom than the top when inspiring above functional residual capacity. During increased acceleration these regional differences were magnified. In addition, the static pressure-volume curves were measured on each subject using different balloon depths during normal and increased acceleration. The shape of the static pressure-volume curve did not change significantly during increased acceleration. The probable cause of the regional differences in volume and ventilation which have been demonstrated is a gradient of static transpulmonary pressure down the lung. This gradient appears to be related to the weight of the lung, since it has been shown to be proportional to the magnitude of the acceleration. Extrapolation of the data to the o G condition indicates that in weightlessness the regional lung volumes and ventilation distribution should be uniform.