PULMONARY DIFFUSING-CAPACITY AND PULMONARY CAPILLARY BLOOD-VOLUME DURING PARABOLIC FLIGHTS

Data from the Spacelab Life Sciences-1 (SLS-1) mission have shown sust ained but moderate increase in pulmonary diffusing capacity (DL). Beca use of the occupational constraints of the mission, data were only obt ained after 24 h of exposure to microgravity. Parabolic flights are of ten used to study some effects of microgravity, and we measured change s in DL occurring at the very onset of weightlessness. Measurements of DL, membrane diffusing capacity, and pulmonary capillary blood volume were made in 10 male subjects during the 20-s 0-G phases of parabolic flights performed by the ''zero-G'' Caravelle aircraft. Using the sta ndardized single-breath technique, we measured DL for CO and nitric ox ide simultaneously. We found significant increases in DL for CO (62%), in membrane diffusing capacity for CO (47%), in DL for nitric oxide ( 47%), and in pulmonary capillary blood volume (71%). We conclude that major changes in the alveolar membrane gas transfers and in the pulmon ary capillary bed occur at the very onset of microgravity. Because the se changes are much greater than those reported during sustained micro gravity, the effects of rapid transition from hypergravity to microgra vity during parabolic flights remain questionable.