PULMONARY-FUNCTION IN-SPACE

The lung is exquisitely sensitive to gravity, and so it is of interest to know how its function is altered in the weightlessness of space. S tudies on National Aeronautics and Space Administration (NASA) Spacela bs during the last 4 years have provided the first comprehensive data on the extensive changes in pulmonary function that occur in sustained microgravity. Measurements of pulmonary function were made on astrona uts during space shuttle flights lasting 9 and 14 days and were compar ed with extensive ground-based measurements before and after the fligh ts. Compared with preflight measurements, cardiac output increased by 18% during space flight, and stroke volume increased by 46%. Paradoxic ally, the increase in stroke volume occurred in the face of reductions in central venous pressure and circulating blood volume. Diffusing ca pacity increased by 28%, and the increase in the diffusing capacity of the alveolar membrane was unexpectedly large based on findings in nor mal gravity. The change in the alveolar membrane may reflect the effec ts of uniform filling of the pulmonary capillary bed. Distributions of blood flow and ventilation throughout the lung were more uniform in s pace, but some unevenness remained, indicating the importance of nongr avitational factors. A surprising finding was that airway closing volu me was approximately the same in microgravity and in normal gravity, e mphasizing the importance of mechanical properties of the airways in d etermining whether they close. Residual volume was unexpectedly reduce d by 18% in microgravity, possibly because of uniform alveolar expansi on. The findings indicate that pulmonary function is greatly altered i n microgravity, but none of the changes observed so far will apparentl y limit long-term space flight. In addition, the data help to clarify how gravity affects pulmonary function in the normal gravity environme nt on Earth.