BODY VOLUME CHANGES DURING SIMULATED MICROGRAVITY .2. COMPARISON OF HORIZONTAL AND HEAD-DOWN BED REST

Changes in segmental fluid volume were measured in 10 male subjects du ring 7 d of either horizontal (0-degrees) or antiorthostatic (-6-degre es) head-down bed rest as part of the Joint U.S./U.S.S.R. Hypokinesia Program. Impedance plethysmography (IPG) was used to measure leg, pelv ic, thoracic, and arm volume changes prior to, during, and following b ed rest. Results of this study demonstrate that antiorthostatic bed re st produces a larger and more persistent thoracic fluid shift than hor izontal bed rest. Segmental volume responses found during this investi gation are compared to those obtained during other simulated or actual space-flight experiments. Antiorthostatic thoracic volume changes fro m this study were found to closely approximate those estimated to take place in space while leg volume changes produced by either 0-degrees or -6-degrees bed rest were much less than those observed by others in the microgravity environment.