Arterial and venous response to Tilt with LBNP test after a 60 day HDT bedrest (WISE study)

    Abstract

    The objective was to quantify the Cerebral, and Femoral arterial hemodynamics as well as the calf vein section changes induced by a Tilt up test continuing with a Tilt plus LBNP after a 60 day HDT (WISE).
    24 healthy volunteers (25-40 y) underwent a 60 day HDT (-6 degree) bedrest: 8 as Control (Co), 8 with Exercise (Ex: treadmill under LBNP and flywheel), 8 with Nutrition (Nut: daily protein supplement). At R+0 all of them underwent a 10 min 80 degree Tilt up test, to which several LBNP period of 3 min were added (from -10 to -50 mmHg by steps of 10 mmHg) until presyncopal stage. Cerebral and Femoral flow changes were assessed by Doppler. Posterior Tibial, and Gastrocnemian vein were investigated by echography.
    At Post HDT 10 min Tilt: cerebral flow decreased similarly in the 3 groups, but more in the non finishers than in the finishers, while the femoral decreased similarly in all groups. Leg vascular resistance and cerebral/femoral flow ratio increased less in the Co and Nut gr than in the Ex gr, and also in the non finishers than in the finishers. Percent increase in Gastrocnemian and Tibial section was higher in Co and Nut gr than in Ex gr, and in non finishers than in finishers.
    Non exercise and non finisher subjects showed a lack of leg vasoconstriction, and a higher calf vein distensibility at post HDT Tilt test.