title: Distributions of lung ventilation and perfusion in prone and supine humans exposed to hypergravity.
abstract: When normal subjects are exposed to hypergravity [5 times normal gravity (5 G)] there is an impaired arterial oxygenation that is less severe in the prone compared with supine posture. We hypothesized that under these conditions the heterogeneities of ventilation and/or perfusion distributions would be less prominent when subjects were prone compared with supine. Expirograms from a combined rebreathing-single breath washout maneuver (Rohdin M, Sundblad P, and Linnarsson D. J Appl Physiol 96: 1470-1477, 2004) were analyzed for vital capacity (VC), phase III slope, and phase IV amplitude, to analyze heterogeneities in ventilation (Ar) and perfusion [CO(2)-to-Ar ratio (CO(2)/Ar)] distribution, respectively. During hypergravity, VC decreased more in the supine than in the prone position (ANOVA, P = 0.02). Phase III slope was more positive for Ar (P = 0.003) and more negative for CO(2)/Ar (P = 0.007) in the supine compared with prone posture at 5 G, in agreement with the notion of a more severe hypergravity-induced ventilation-perfusion mismatch in supine posture. Phase IV amplitude became lower in the supine than in the prone posture for both Ar (P = 0.02) and CO(2)/Ar (P = 0.004) during hypergravity as a result of the more reduced VC in the supine posture. We speculate that results of VC and phase IV amplitude are due to the differences in heart-lung interaction and diaphragm position between postures: a stable position of the heart and diaphragm in prone hypergravity, in contrast to supine in which the weight of the heart and a cephalad shift of the diaphragm compress lung tissue.
authors.affiliation: Section of Environmental Physiology, Department of Physiology and Pharmacology, Karolinska Institutet, SE-171 77 Stockholm, Sweden. malin.rohdin@fyfa.ki.se
authors.forename: M
authors.initials: M
authors.lastname: Rohdin
authors.forename: J
authors.initials: J
authors.lastname: Petersson
authors.forename: M
authors.initials: M
authors.lastname: Mure
authors.forename: R W
authors.initials: RW
authors.lastname: Glenny
authors.forename: S G E
authors.initials: SG
authors.lastname: Lindahl
authors.forename: D
authors.initials: D
authors.lastname: Linnarsson
mesh_terms: D000328:Adult; D003964:Diaphragm / Q000502:physiology; D005260:Female; D006321:Heart / Q000502:physiology; D006801:Humans; D018471:Hypergravity / Q000009:adverse effects*; D008168:Lung / Q000502:physiology*; D008297:Male; D011187:Posture / Q000502:physiology*; D016684:Prone Position; D011659:Pulmonary Gas Exchange / Q000502:physiology; D016683:Supine Position