ASSESSMENT OF POSTURALLY INDUCED VASOMOTO R REFLEXES OF THE LOWER-LIMBS 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 t he great toe using mercury-strain-gauge plethysmography. In the first step, the authors have measured the veno-arterial reflex obtained by e lective lowering of the leg, the subject lying strictly horizontally u nder standardized conditions. Secondly was assessed the distal vasomot or reflex due to orthostatism (seated position, legs hanging). Correla tions between these postural reflexes and height, weight, sex, length of the lower limbs, femoral venous diameters assessed by echography we re studied. The veno-arterial reflex obtained by elective verticalizat ion of the leg (0,68 +/- 0,21) corresponds to a 32 % mean decrease in the amplitude of the plethysmographic recording as compared to the ini tial amplitude in horizontal position. It is all the more marked as th e subject is male and the leg is long, thus inducing a equivalent chan ge 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 correspond ing to a 51 % mean decrease in the amplitude of the plethysmographic s ignal 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