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Residual heterogeneity of intra- and interregional pulmonary perfusion in short-term microgravity

Section of Environmental Physiology, Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden

Submitted 10 November 2004 ; accepted in final form 15 February 2005

We hypothesized that the perfusion heterogeneity in the human, upright lung is determined by nongravitational more than gravitational factors. Twelve and six subjects were studied during two series of parabolic flights. We used cardiogenic oscillations of O₂/SF₆ as an indirect estimate of intraregional perfusion heterogeneity (series 1) and phase IV amplitude (P₄) as a indirect estimate of interregional perfusion heterogeneity (series 2). A rebreathing-breath holding-expiration maneuver was performed. In flight, breath holding and expiration were performed either in microgravity (0 G) or in hypergravity. Controls were performed at normal gravity (1 G). In series 1, expiration was performed at 0 G. Cardiogenic oscillations of O₂/SF₆ were 19% lower when breath holding was performed at 0 G than when breath holding was performed at 1 G [means (SD): 1.7 (0.3) and 2.3 (0.6)% units] (P = 0.044). When breath holding was performed at 1.8 G, values did not differ from 1-G control [2.6 (0.8)% units, P = 0.15], but they were 17% larger at 1.8 G than at 1 G. In series 2, expiration was performed at 1.7 G. P₄ changed with gravity (P < 0.001). When breath holding was performed at 0 G, P₄ values were 45 (46)% of control. When breath holding was performed at 1.7 G, P₄ values were 183 (101)% of control. We conclude that more than one-half of indexes of perfusion heterogeneity at 1 G are caused by nongravitational mechanisms.

human physiology; cardiogenic oscillations; phase 4

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