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

Abstract

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 C(2)H(2), O(2), and Ar. Expirograms were analyzed for cardiogenic oscillations (COS) and for phase IV amplitude to analyze inhomogeneities in ventilation (Ar) and perfusion [CO(2)-to-Ar ratio (CO(2)/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 CO(2)/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 CO(2)/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.