Influences of thigh cuffs on the cardiovascular system during 7-day head-down bed rest

Thigh cuffs, presently named 'bracelets," consist of two straps fixed to th e upper part of each thigh, applying a pressure of 30 mmHg. The objective w as to evaluate the cardiac, arterial, and venous changes in a group of subj ects in head-down tilt (HDT) for 7 days by using thigh cuffs during the day time, and in a control group not using cuffs. The cardiovascular parameters were measured by echography and Doppler. Seven days in HDT reduced stroke volume in both groups (-10%; P < 0.05). Lower limb vascular resistance decr eased more in the cuff group than in the control group (-29 vs. -4%; P < 0. 05). Cerebral resistance increased in the control group only (+6%; P < 0.05 ). The jugular vein increased (+45%; P < 0.05) and femoral and popliteal ve ins decreased in cross-sectional area in both groups (-45 and -8%, respecti vely; P < 0.05),Carotid diameter tended to decrease (-5%; not significant) in both groups. Heart rate, blood pressure, cardiac output, and total resis tance did not change significantly. After 8 h with thigh cuffs, the cardiac and arterial parameters had recovered their pre-HDT level except for blood pressure (+6%; P < 0.05). Jugular vein size decreased from the pre-HDT lev el (-21%; P < 0.05), and femoral and popliteal vein size increased (+110 an d +136%, respectively; P < 0.05). The thigh cuffs had no effect on the deve lopment of orthostatic intolerance during the 7 days in HDT.