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INNOVATIVE METHODOLOGY

Effects of hypergravity on the distributions of lung ventilation and perfusion in sitting humans assessed with a simple two-step maneuver

Section of Environmental Physiology, Department of Physiology and Pharmacology, Karolinska Institutet, SE-171 77 Stockholm, Sweden

Submitted 17 June 2003 ; accepted in final form 10 December 2003

Increased gravity impairs pulmonary distributions of ventilation and perfusion. We sought to develop a method for rapid, simultaneous, and noninvasive assessments of ventilation and perfusion distributions during a short-duration hypergravity exposure. Nine sitting subjects were exposed to one, two, and three times normal gravity (1, 2, and 3 G) in the head-to-feet direction and performed a rebreathing and a single-breath washout maneuver with a gas mixture containing C₂H₂, O₂, and Ar. Expirograms were analyzed for cardiogenic oscillations (COS) and for phase IV amplitude to analyze inhomogeneities in ventilation (Ar) and perfusion [CO₂-to-Ar ratio (CO₂/Ar)] distribution, respectively. COS were normalized for changes in stroke volume. COS for Ar increased from 1-G control to 128 ± 6% (mean ± SE) at 2 G (P = 0.02 for 1 vs. 2 G) and 165 ± 13% at 3 G (P = 0.002 for 2 vs. 3 G). Corresponding values for CO₂/Ar were 135 ± 12% (P = 0.04) and 146 ± 13%. Phase IV amplitude for Ar increased to 193 ± 39% (P = 0.008) at 2 G and 229 ± 51% at 3 G compared with 1 G. Corresponding values for CO₂/Ar were 188 ± 29% (P = 0.02) and 219 ± 18%. We conclude that not only large-scale ventilation and perfusion inhomogeneities, as reflected by phase IV amplitude, but also smaller-scale inhomogeneities, as reflected by the ratio of COS to stroke volume, increase with hypergravity. Except for small-scale ventilation distribution, most of the impairments observed at 3 G had been attained at 2 G. For some of the parameters and gravity levels, previous comparable data support the present simplified method.

cardiogenic oscillations; closing volume; single-breath washout; stroke volume

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