Adaptations to a 7-day head-down bed rest with thigh cuffs

Purpose: Thigh cuffs were two elastic strips fixed at the upper part of eac h thigh, which limits the shift of fluid from the legs into the cardio-thor acic region. The purpose of this study was to examine the effects of thigh cuffs on hormonal and plasma volume responses and orthostatic tolerance dur ing a 7-day head-down bed rest (HDBR). Methods: Orthostatic tolerance, plas ma volume, total body water, blood volume-regulating hormones, and hydro-el ectrolyte responses were measured in eight healthy men (age range, 25-40 yr ), using thigh cuffs 10 h daily during 7 d of -6 degrees HDBR. Results: Thi gh cuffs worn during HDBR attenuated the decrease in plasma volume observed after HDBR (thigh cuffs: -5.85 +/- 0.95% vs control: -9.09 +/- 0.82%, P le ss than or equal to 0.05). During this experiment, there was no significant change in total body water. Thus, the hypovolemia did not result from a lo ss of water but from a fluid shift from the brood compartment into the inte rstitial and/or intracellular compartment. Hormonal responses during HDBR a nd stand test were not modified by the thigh cuffs. Thigh cuffs had no sign ificant effect on the clinical symptoms of orthostatic intolerance after HD BR. Conclusions: Thigh cuffs worn during HDBR blunted the decrease in plasm a volume but did not reduce orthostatic intolerance: thus, they are not a c ompletely effective countermeasure. Furthermore, hypovolemia seems to be ne cessary but not sufficient to induce orthostatic intolerance after HDBR.