[Evaluation of posturally-induced vasomotor reflexes of the leg in the healthy subject].

The authors' aim was to assess, using a routinely usable methodology, the distal vasomotor reflexes induced by postural changes of the lower limbs in 36 healthy volunteers (18 women and 18 men, mean age: 22.3 years, range 19-26). These distal vasomotor changes were recorded on the great toe using mercury-strain-gauge plethysmography. In the first step, the authors have measured the veno-arterial reflex obtained by elective lowering of the leg, the subject lying strictly horizontally under standardized conditions. Secondly was assessed the distal vasomotor reflex due to orthostatism (seated position, legs hanging). Correlations between these postural reflexes and height, weight, sex, length of the lower limbs, femoral venous diameters assessed by echography were studied. The veno-arterial reflex obtained by elective verticalization of the leg (0.68 +/- 0.21) corresponds to a 32% mean decrease in the amplitude of the plethysmographic recording as compared to the initial amplitude in horizontal position. It is all the more marked as the subject is male and the leg is long, thus inducing a equivalent change of hydrostatic venous pressure during verticalization of this part of the limb. On the other hand, this adaptative reflex appears all the more intense as the basal vascular tone in horizontal position is low. Passing to orthostatism induces a distal vasoconstriction corresponding to a 51% mean decrease in the amplitude of the plethysmographic signal as compared to the initial basal amplitude. This general reflex, playing a part in the keeping of hemodynamic conditions when passing to orthostatism, appeared significantly correlated to the diameter of the common femoral vein when the subject is lying horizontally.