Femoral to cerebral arterial blood flow redistribution and femoral vein distension during orthostatic tests after 4 days in the head-down tilt position or confinement |
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Authors: | P Arbeille D Sigaudo A Pavy Le Traon S Herault M Porcher and C Gharib |
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Institution: | (1) Unité de Médecine et Physiologie Spatiales, Faculté de Médecine, Centre Hospitalier Universitaire CHU Trousseau, F-37044 Tours, France, FR;(2) Département Physiologie de l'environnement, Faculté Grange Blanche, F-69373, Lyon, France, FR;(3) Institut de Médecine Spatiale (MEDES), Bld Edouard Belin, F-31055, Toulouse, France, FR |
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Abstract: | The first objective of this study was to confirm that 4 days of head-down tilt (HDT) were sufficient to induce orthostatic
intolerance, and to check if 4 days of physical confinement may also induce orthostatic intolerance. Evidence of orthostatic
intolerance during tilt-up tests was obtained from blood pressure and clinical criteria. The second objective was to quantify
the arterial and venous changes associated with orthostatic intolerance and to check whether abnormal responses to the tilt
test and lower body negative pressure (LBNP) may occur in the absence of blood pressure or clinical signs of orthostatic intolerance.
The cerebral and lower limb arterial blood flow and vascular resistance, the flow redistribution between these two areas,
and the femoral vein distension were assessed during tilt-up and LBNP by ultrasound. Eight subjects were given 4 days of HDT
and, 1 month later, 4 days of physical confinement. Tilt and LBNP test were performed pre- and post-HDT and confinement. Orthostatic
intolerance was significantly more frequent after HDT (63%) than after confinement (25%, P<0.001). Cerebral haemodynamic responses to tilt-up and LBNP tests were similar pre- and post-HDT or confinement. Conversely,
during both tilt and LBNP tests the femoral vascular resistances increased less (P<0.002), and the femoral blood flow reduced less (P<0.001) after HDT than before HDT or after confinement. The cerebral to femoral blood flow ratio increased less after HDT
than before (P<0.002) but remained unchanged before and after confinement. This ratio was significantly more disturbed in the subjects who
did not complete the tilt test. The femoral superficial vein was more distended during post-HDT LBNP than pre-HDT or after
confinement (P<0.01). In conclusion, 4 days of HDT were enough to alter the lower limb arterial vasoconstriction and venous distensibility
during tilt-up and LBNP, which reduced the flow redistribution in favour of the brain in all HDT subjects. Confinement did
not alter significantly the haemodynamic responses to orthostatic tests. The cerebral to femoral blood flow ratio measured
during LBNP was the best predictor of orthostatic intolerance.
Accepted: 12 December 1997 |
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Keywords: | Femoral artery and vein Cerebral artery Confinement Orthostatic intolerance |
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