FEMORAL FLOW RESPONSE TO LOWER-BODY NEGATIVE-PRESSURE - AN ORTHOSTATIC TOLERANCE-TEST

The objective was to check, during a lower body negative pressure (LBN P) lest, new vascular parameters for the detection of orthostatic into lerance induced by head down-tilt (HDT) and spaceflight. METHODS: The lower-limb volume flow and vascular resistance were evaluated by Doppl er ultrasound. The HDT population consisted of two groups: control [6 subjects resting in a HDT (-6 degrees) position for 28 d] and counterm easure (6 subjects also in HDT for 28 d, but with repeated LBNP and ex ercise). The LBNP orthostatic lest (four steps: -20, -30, -40, -50 mm Hg, of 3 min each) was performed before, during, and after the HDT. Fo r the 14-d spaceflight (Antares) the cosmonaut underwent the LBNP test (10 min al -25 mm Hg and 10 min at -45 mm Hg) at preflight (3 times), inflight (day 11), and postflight (twice). RESULTS: HDT-As the LBNP p ressure decreased, the femoral blood flow decreased and the lower-limb vascular resistances increased in both HDT groups. In the control gro up the femoral flow was less reduced, at each of the 4 levels of depre ssure (p < 0.01). The amplitude of the leg vascular resistances was re duced at -40 mm Hg, and at -50 mm Hg, on HDT day 15 in both groups (be fore LBNP, after 1 week's exercise for the countermeasure group), and on post-HDT day 1 (p < 0.01) only in the control group. The femoral va scular resistance response had completely recovered in the countermeas ure group on post-HDT day 1. During the post-HDT tilt table test, all 6 controls had a drop in blood pressure of 20 mm Hg (4 subjects) or 10 mm Hg (2 subjects); 3 had pre-syncopal symptoms. The HDT countermeasu re subjects had neither any clinical signs of orthostatic intolerance nor any blood pressure drop. 14d-Spaceflight-During the flight, the co smonaut did not use any countermeasures (exercise, LBNP). On flight da y +11, and postflight day 3, the femoral vascular resistance response to LBNP were decreased as observed in the control group on HDT day +15 and post HDT. On postflight day 7, the femoral response had completel y recovered. The middle cerebral flow response to the various pre-, in -, and postflight LBNP rests consisted of a slight decrease of the cer ebral flow together with resistances of comparable amplitude (-10 to - 20%) to those measured during the same LBNP test in the HDT control gr oup. CONCLUSION: The femoral hemodynamics are much more disturbed than the cerebral ones in vascular deconditioning. The assessment of the l ower limb vascular reactivity will be of interest in predicting orthos tatic intolerance, and checking the efficiency of counter-measures.