Cardiac, arterial and venous adaptation to weightlessness during 6-month MIR spaceflights with and without thigh cuffs (bracelets)

The objectives of this investigation were to study the effects of thigh cuffs (bracelets) on cardiovascular adaptation and deconditioning in 0 g. The cardiovascular parameters of six cosmonauts were measured by echocardiography, Doppler, and plethysmography, during three 6-month MIR spaceflights. Measurements were made at rest during preflight (-30 days), inflight (1, 3-4, and 5-5.5 months) without cuffs (morning) and after 5 h with cuffs, and during postflight (+3 and +7 days). Lower-body negative pressure (LBNP) measurements were performed 1 day after each resting session. Inflight values of left ventricle end-diastolic volume and stroke volume measured without the thigh cuffs (-8 to -24% and -10 to -16%, respectively, both P < 0.05) were lower than corresponding preflight values. The jugular and femoral vein cross-sectional areas (Ajv and Afv, respectively) were enlarged (Ajv: by 23-30%, P < 0.001; Afv: by 33-70% P < 0.01). The renal and femoral vascular resistances (Rra and Rfa, respectively) decreased (Rra: by -15 to -16%, P < 0.01; Rfa: by -5 to -11%, P < 0.01). Inflight, the thigh cuffs reduced the Ajv (by -12 to -20%, P < 0.02), but enlarged the Afv (Afv: by 9-20%, P < 0.02) and increased the vascular resistance (Rra: by 8-13%, P < 0.05; Rfa: by 10-16%, P < 0.01) compared to corresponding inflight, without-cuffs values. During LBNP (-45 mmHg, where 1 mmHg = 133.3 N/ m2), Rfa and the ratio between cerebral and femoral blood flow (Qca/Qfa) increased less inflight and postflight (+25% for Rfa and +30% for Qca/Qfa) than during preflight (60% for Rfa and 75% for Qca/Qfa, P < 0.01). This reduced vasoconstrictive response and less efficient flow redistribution toward the brain was associated with orthostatic intolerance during postflight stand tests in all of the cosmonauts. The calf circumference increased less inflight and postflight (6% P < 0.05) than preflight (9% P < 0.05). The vascular response to LBNP remained similarly altered throughout the flight. The thigh cuffs compensated partially for the cardiovascular changes induced by exposure to 0 g, but did not interfere with 0 g deconditioning.