RADIOGRAPHIC COMPARISON OF HUMAN-LUNG SHAPE DURING NORMAL GRAVITY AND WEIGHTLESSNESS

Human lung shape was measured during zero gravity to decide whether the normal vertical regional differences in ventilation are due directly to distortion of the elastic lung by its own weight, or instead, due indirectly to the effect of gravity on the shape of the rib cage and diaphragm. Weightlessness was reported to virtually abolish the normal topographical inequality of ventilation. Chest radiographs were made after 10 s of a weightless flight trajectory aboard a NASA-Ames Research Center [USA] Learjet in both posterior-anterior and left lateral projections on 5 seated volunteers at residual volume, functional residual capacity and total lung capacity. Lung shape was assessed by measuring lung heights and widths in upper, middle and lower lung regions. No significant differences were found between any of the normal gravity (1 G) and 0 g measurements, although there was a slight tendency for the lung to become shorter and wider at 0 g (mean changes generally less than 3% or about 0.5 cm). By contrast, Grassino et al. found no change in the vertical distribution of ventilation after voluntarily changing lung dimensions by more than 1 cm by moving the abdomen in or out. Gravity produces the topographical distribution of ventilation in the upright human lung by distorting the elastic lung tissue within the chest rather than by altering the shape of the rib cage and diaphragm.