Artificial gravity with ergometric exercise can prevent enhancement of popliteal vein compliance due to 4-day head-down bed rest

Changes of venous compliance may contribute in part to postflight orthostatic intolerance. The purpose of the present study was to determine whether intermittent artificial gravity exposure with ergometric exercise could prevent venous compliance changes in the lower limbs due to simulated weightlessness. Twelve healthy male volunteers were exposed to simulated microgravity for 4 days of head-down bed rest (HDBR). Six subjects were randomly loaded 1.0–2.0 Gz intermittent artificial gravity (at foot level) with 40 W of ergometric workload every day (countermeasure group, CM). The six others served as the control (CON group). Venous compliance was estimated by measuring the corresponding change of cross-sectional area (CSA) of popliteal vein at each minute of various venous occlusion pressure stages. Basal CSA was significantly lower after bed rest in the control group, and preserved in the countermeasure group. The percent increase in the CSA of CON group was significantly greater almost at each minute of various venous cuff pressures after bed rest than before. Compliance of popliteal vein of CON group was significant greater when 40, 60 and 80 mmHg cuff pressure applied after bed rest than before of CON group. In conclusions, a 4-day simulated weightlessness leads to increase of popliteal venous compliance; centrifuge-induced artificial gravity with ergometric exercise can prevent enhancement of popliteal venous compliance due to 4-day head-down tilt bed rest, the effect of the countermeasure on compliance might involve changes in venous filling and changes in venous structure.