Effect of pressure suit inflation on pulmonary capillary blood volume

¹ Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana

Compression of the lower part of the body by an aviator's G suit produces acute pulmonary vascular engorgement and increases pulmonary vascular pressure. In previous studies, pulmonary diffusing capacity for carbon monoxide (Dl) was increased by this procedure, presumably due to increase in the pulmonary capillary blood volume (Vc), and apparently indicating that the pulmonary capillary bed can be passively dilated by increased intravascular pressure. In the present study, the effect of G-suit inflation on Dl was again studied in 12 normal subjects, but also with determinations of Dl at different alveolar O₂ tensions so that Vc and the true pulmonary membrane diffusing capacity (Dm) could be calculated. Studies were made in each subject with the suit on, uninflated and then inflated. With suit inflation, Dl was increased in all 12 subjects (27%), Vc was increased in 11 subjects (33%), and Dm was increased in 10 subjects (21%). These studies show that the pulmonary capillary bed can be passively dilated by increased intravascular pressure, but it is not possible to distinguish between the two possible mechanisms, dilatation of open capillaries or opening of previously closed ones.