Journal of Ultrasound in Medicine, Vol 20, Issue 11 1207-1217, Copyright © 2001 by American Institute of Ultrasound in Medicine
Doppler measurement of cerebral and lower limb flow during a lower body negative pressure test for predicting orthostatic intolerance
N. Tobal, J. Roumy, S. Herault, G. Fomina and P. Arbeille
Unite de Medecine et Physiologie Spatiales, Faculte de Medecine, Centre Hospitalier Universitaire Trousseau, Tours, France.
OBJECTIVE: To quantify the cardiovascular response to an orthostatic test
for predicting orthostatic intolerance. METHODS: Cerebral and lower limb
arterial flow and resistance were assessed by Doppler ultrasonography
during lower body negative pressure (7 minutes each at -25 and -45 mm Hg).
Cardiovascular deconditioning was induced by 42 days in head-down tilt at
-6 degress (7 subjects) and 6-month spaceflights (10 cosmonauts). RESULTS:
Orthostatic intolerance during a stand test was observed in 57% of the
head-down-tilt subjects and 83% of the cosmonauts. At the lower body
negative pressure after head-down tilt and during or after flight, the
average cerebral flow velocity and vascular resistance did not change
significantly from before head-down tilt and before flight. Conversely,
there was a lack of lower limb arterial vasoconstriction (-24% from before
head-down tilt and -43% from before flight; P < .01), and the
cerebral-femoral flow ratio increased less (-27% from before head-down tilt
and -52% from before flight; P < .01). The lack of vasoconstriction was
more pronounced in intolerant subjects (-25% from before head-down tilt and
-48% from before flight) compared with tolerant subjects (-22% from before
head-down tilt and -14% from before flight; P > .01). Also, the lack of
a cerebral-femoral flow ratio increase was more pronounced in intolerant
subjects (-49% from before head-down tilt and -55% from before flight; P
< .01) than in tolerant subjects (-1% from before head-down tilt and
-33% from before flight; P < .01). The cerebral flow deficit at the
lower body negative pressure before head-down tilt was greater than 8% in 3
of the 4 intolerant head-down-tilt subjects and less than 8% in the 3
tolerant subjects. The 3 cosmonauts who were intolerant after flight had a
preflight cerebral flow deficit greater than 8%, whereas the tolerant
cosmonaut had a cerebral flow deficit less than 8%. CONCLUSION: Lack of
lower limb vasoconstriction and a lower cerebral-femoral flow ratio during
lower body negative pressure in disadapted subjects were associated with
orthostatic intolerance. A cerebral flow deficit during lower body negative
pressure before disadaptation allowed measurement of the predisposition of
the subjects to become intolerant.
