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 cuf fs (bracelets) on cardiovascular adaptation and deconditioning in 0 g. The cardiovascular parameters of sir; cosmonauts were measured by echocardiogra phy, Doppler, and plethysmography, during three 6-month MIR space-flights. Measurements were made at rest during preflight (-30 days), inflight (1, 33 , and 5-5.5 months) without cuffs (morning) and after 5 h with cuffs, and d uring postflight ( + 3 and + 7 days). Lower-body negative pressure (LBNP) m easurements were performed 1 day after each resting session. Inflight value s 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 vei n cross-sectional areas (A(jv), and An, respectively) were enlarged (A(jv): by 23-30%, P < 0.001 A(fv): by 33-70% P < 0.01. The renal and femoral vasc ular resistances (R-ra and R-fa, respectively) decreased (R-ra: by -15 to - 16%, P < 0.01: R-fa: by -5 to -11%, P < 0.01). Inflight, the thigh cuffs re duced the A(jv) (by -12 to -20%, P < 0.02), but enlarged the A(fv) (A(fv): by 9-20%, P < 0.02) and increased the vascular resistance (R-ra: by 8-13%, P < 0.05; R-fa: by 10-16%, P < 0.01) compared to corresponding inflight, wi thout-cuffs values. During LBNP (-45 mmHg, where 1 mmHg = 133.3 N/ m(2)), R -fa and the ratio between cerebral and femoral blood flow Q(ca)/Q(fa)) incr eased less inflight and postflight (+ 25% for R-fa and + 30% for Q(ca)/Q(fa )) than during preflight (60% for R-fa and 75% for Q(ca)/Q(fa), P < 0.01). This reduced vasoconstrictive response and less efficient flow redistributi on toward the brain was associated with orthostatic intolerance during post flight stand tests in all of the cosmonauts. The calf circumference increas ed less inflight and postflight (6% P < 0.05) than preflight (9% P < 0.05), The vascular response to LBNP remained similarly altered throughout the fl ight. The thigh cuffs compensated partially for the cardiovascular changes induced by exposure to 0 g, but did not interfere with 0 g deconditioning.