LEG VENOUS HEMODYNAMICS AND LEG VOLUMES DURING A 42-DAY -6-DEGREES HEAD-DOWN BEDREST

Seven healthy subjects were submitted to a 42-day head down bedrest, w here leg venous compliance (venous distensibity index VDI) and leg vol umes were assessed by mercury strain gauge plethysmography with venous occlusion and optoelectronic plethysmography, respectively. Plethysmo graphic and volometric measurements were made, before, during (at days 1, 4, 7, 14, 21, 26, 34 and 41), and after bedrest (days 1, 4, 7, 11 and 30 of the recovery period). Results showed a continuous decrease i n leg volumes throughout bedrest, when VDI increased until day 26 of b edrest, and then decreased afterwards. The recovery period was charact erized by a rapid return of VDI to prebedrest levels while leg volumes progressively normalised. These results showed that leg venous compli ance changes are not always dependant upon skeletal muscle changes, an d that factors other than size of muscle compartment are able to deter mine increases in leg venous compliance during long-term bedrest.