Journal of Applied Physiology, Vol 79, Issue 4 1290-1298, Copyright © 1995 by American Physiological Society

ARTICLES

Pulmonary gas exchange and its determinants during sustained microgravity on Spacelabs SLS-1 and SLS-2

G. K. Prisk, A. R. Elliott, H. J. Guy, J. M. Kosonen and J. B. West
Department of Medicine, University of California, San Diego, La Jolla 92093-0931, USA.

We measured resting pulmonary gas exchange in eight subjects exposed to 9 or 14 days of microgravity (microG) during two Spacelab flights. Compared with preflight standing measurements, microG resulted in a significant reduction in tidal volume (15%) but an increase in respiratory frequency (9%). The increased frequency was caused chiefly by a reduction in expiratory time (10%), with a smaller decrease in inspiratory time (4%). Anatomic dead space (VDa) in microG was between preflight standing and supine values, consistent with the known changes in functional residual capacity. Physiological dead space (VDB) decreased in microG, and alveolar dead space (VDB-VDa) was significantly less in microG than in preflight standing (-30%) or supine (-15%), consistent with a more uniform topographic distribution of blood flow. The net result was that, although total ventilation fell, alveolar ventilation was unchanged in microG compared with standing in normal gravity (1 G). Expired vital capacity was increased (6%) compared with standing but only after the first few days of exposure to microG. There were no significant changes in O2 uptake, CO2 output, or end-tidal PO2 in microG compared with standing in 1 G. End-tidal PCO2 was unchanged on the 9-day flight but increased by 4.5 Torr on the 14-day flight where the PCO2 of the spacecraft atmosphere increased by 1-3 Torr. Cardiogenic oscillations in expired O2 and CO2 demonstrated the presence of residual ventilation-perfusion ratio (VA/Q) inequality. In addition, the change in intrabreath VA/Q during phase III of a long expiration was the same in microG as in preflight standing, indicating persisting VA/Q inequality and suggesting that during this portion of a prolonged exhalation the inequality in 1 G was not predominantly on a gravitationally induced topographic basis. However, the changes in PCO2 and VA/Q at the end of expiration after airway closure were consistent with a more uniform topographic distribution of gas exchange.

This article has been cited by other articles:

				G. K. Prisk, K. Yamada, A. C. Henderson, T. J. Arai, D. L. Levin, R. B. Buxton, and S. R. Hopkins Pulmonary perfusion in the prone and supine postures in the normal human lung J Appl Physiol, September 1, 2007; 103(3): 883 - 894. [Abstract] [Full Text] [PDF]

				G. K. Prisk, J. M. Fine, T. K. Cooper, and J. B. West Vital capacity, respiratory muscle strength, and pulmonary gas exchange during long-duration exposure to microgravity J Appl Physiol, August 1, 2006; 101(2): 439 - 447. [Abstract] [Full Text] [PDF]

				G. K. Prisk, J. M. Fine, T. K. Cooper, and J. B. West Pulmonary gas exchange is not impaired 24 h after extravehicular activity J Appl Physiol, December 1, 2005; 99(6): 2233 - 2238. [Abstract] [Full Text] [PDF]

				W. A. Altemeier, S. McKinney, M. Krueger, and R. W. Glenny Effect of posture on regional gas exchange in pigs J Appl Physiol, December 1, 2004; 97(6): 2104 - 2111. [Abstract] [Full Text] [PDF]

				G. K. Prisk, H. J. B. Guy, J. B. West, and J. W. Reed Validation of measurements of ventilation-to-perfusion ratio inequality in the lung from expired gas J Appl Physiol, March 1, 2003; 94(3): 1186 - 1192. [Abstract] [Full Text] [PDF]

				D. Bettinelli, C. Kays, O. Bailliart, A. Capderou, P. Techoueyres, J. L. Lachaud, P. Vaida, and G. Miserocchi Effect of gravity and posture on lung mechanics J Appl Physiol, December 1, 2002; 93(6): 2044 - 2052. [Abstract] [Full Text] [PDF]

				P. M. Gustafsson, O. Eiken, and M. Gronkvist Effects of hypergravity and anti-G suit pressure on intraregional ventilation distribution during VC breaths J Appl Physiol, August 1, 2001; 91(2): 637 - 644. [Abstract] [Full Text] [PDF]

				ANN. R. ELLIOTT, S. A. SHEA, D.-J. DIJK, J. K. WYATT, E. RIEL, D. F. NERI, C. A. CZEISLER, J. B. WEST, and G. K. PRISK Microgravity Reduces Sleep-disordered Breathing in Humans Am. J. Respir. Crit. Care Med., August 1, 2001; 164(3): 478 - 485. [Abstract] [Full Text] [PDF]

				T. T. Schlegel, T. E. Brown, S. J. Wood, E. W. Benavides, R. L. Bondar, F. Stein, P. Moradshahi, D. L. Harm, J. M. Fritsch-Yelle, and P. A. Low Orthostatic intolerance and motion sickness after parabolic flight J Appl Physiol, January 1, 2001; 90(1): 67 - 82. [Abstract] [Full Text] [PDF]

				R. W. Glenny, H. T. Robertson, and M. P. Hlastala Vasomotor tone does not affect perfusion heterogeneity and gas exchange in normal primate lungs during normoxia J Appl Physiol, December 1, 2000; 89(6): 2263 - 2267. [Abstract] [Full Text] [PDF]

				Y. Verbandt, M. Wantier, G. K. Prisk, and M. Paiva Ventilation-perfusion matching in long-term microgravity J Appl Physiol, December 1, 2000; 89(6): 2407 - 2412. [Abstract] [Full Text] [PDF]

				R. W. Glenny, W. J. E. Lamm, S. L. Bernard, D. An, M. Chornuk, S. L. Pool, W. W. Wagner Jr, M. P. Hlastala, and H. T. Robertson Physiology of a Microgravity Environment: Selected Contribution: Redistribution of pulmonary perfusion during weightlessness and increased gravity J Appl Physiol, September 1, 2000; 89(3): 1239 - 1248. [Abstract] [Full Text] [PDF]

				G. K. Prisk Physiology of a Microgravity Environment: Invited Review: Microgravity and the lung J Appl Physiol, July 1, 2000; 89(1): 385 - 396. [Abstract] [Full Text] [PDF]

				G. K. Prisk, A. R. Elliott, and J. B. West Sustained microgravity reduces the human ventilatory response to hypoxia but not to hypercapnia J Appl Physiol, April 1, 2000; 88(4): 1421 - 1430. [Abstract] [Full Text] [PDF]

				R. W. Glenny, S. Bernard, H. T. Robertson, and M. P. Hlastala Gravity is an important but secondary determinant of regional pulmonary blood flow in upright primates J Appl Physiol, February 1, 1999; 86(2): 623 - 632. [Abstract] [Full Text] [PDF]

				A.-M. Lauzon, A. R. Elliott, M. Paiva, J. B. West, and G. K. Prisk Cardiogenic oscillation phase relationships during single-breath tests performed in microgravity J Appl Physiol, February 1, 1998; 84(2): 661 - 668. [Abstract] [Full Text] [PDF]