Influence of pressure suit inflation on pulmonary diffusing capacity in man

¹ Department of Physiology, Graduate School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania; and Department of Medicine, Indiana University, School of Medicine, Indianapolis, Indiana

Previous investigations of the effect of inflation of a pressure suit on pulmonary diffusing capacity (D_L) have been reported from our two laboratories, one (Indianapolis) finding an increase and the other (Philadelphia) finding no change. The present investigation was carried out in Philadelphia, using some of the same subjects and pressure suits in order to reconcile the contradictory results. The earlier contradictory results were confirmed. The pressure suit used in the investigations at Philadelphia (suit P) covered the entire body below the nipples, whereas the suit used in the investigations at Indianapolis (suit I) extended cephalad only as far as the costal margin. When suit P was inflated in the present study, D_L again did not increase significantly in two subjects. However, when the upper part of the suit was folded down so that the thoracic cage was not covered, inflation of the suit did produce a significant increase in D_L. Inflation of suit P when it covered the chest made it difficult for a subject not to perform a Valsalva maneuver during breath holding and caused more decrease in alveolar volume (Va) than when it was inflated in the folded-down position. In two subjects studied, we found no difference in air trapping with inflation of suit P in the two positions. The discrepancy between the results of the two earlier studies appears to have resulted from the different construction of the two pressure suits used. We conclude that pressure suit inflation in man will produce an increase in D_L, presumably by means of pulmonary congestion.