Changes of XXXX cerebral bottom arterial hemodynamics during 21 d head-down tilt (-6 degrees) bed-rest.

@entity1 @entity135 @entity9623
OBJECTIVE: To investigate the change of @entity1 cerebral bottom arterial hemodynamics during 21 d simulated weightlessness. METHOD: 21 d -6 degrees @entity135 ( @entity135 ) were used to simulate weightlessness. 6 healthy male, aged 24.8 +/- 6.1 served as subjects. Systolic blood velocity (Vs), diastolic blood velocity (Vd), mean blood velocity (Vm), pulsatility index (PI), resistance index (RI) and other indices of middle cerebral arteries ( @entity9623 ), anterior cerebral artery (ACA) and posterior cerebral artery (PCA) were measured by transcranial ultrasound Doppler before @entity135 and on day 0 (D0), 1, 3, 7, 10, 21 of @entity135 . HUT +75 degrees 20 min orthostatic tolerance tests were done on day -1, 10, and 21 of @entity135 . RESULT: During HUT +75 degrees 20 min orthostatic tolerance test on day 10 and 21 of @entity135 , the average standing time were shorter than that of the pre- @entity135 values (P<0.05). On day 3 and 21 of @entity135 , Vs of right @entity9623 reduced significantly than pre- @entity135 (P<0.05 or P<0.01). On day 1, 3, 7, 10 and 21 of @entity135 , Vs of right @entity9623 were obviously lower than that on D0 (P<0.05 or P<0.01). Left @entity9623 Vs on D0 increased significantly than that of pre- @entity135 (P<0.05), and both were significantly higher than those of the 3rd day of @entity135 (P<0.01). Right @entity9623 Vm on the 3rd and 21st day of @entity135 were significantly lower than those pre- @entity135 and D0 (P<0.05 or P<0.01). On day 10 of @entity135 , Vm of right @entity9623 were significantly reduced than that on D0 (P<0.05). Both @entity9623 bilateral velocity difference (right Vm-left Vm) on the 3rd, 10th, 21st day of @entity135 , and @entity9623 inter-hemispheric asymmetry index on the 10th, 21st day of @entity135 were significantly lower than that of pre- @entity135 (P<0.05 or P<0.01). CONCLUSION: 21 d @entity135 bed-rest decreased orthostatic tolerance, Vs of both side @entity9623 , and Vm of right @entity9623 . Lower Vs of both side @entity9623 and the inter-hemispheric asymmetry of @entity9623 during @entity135 maybe responsible, in part, for the increased risk of orthostatic intolerance.
