[Variations in venous physiology in the healthy subject. Postural and venous occlusion plethysmography studies].

The principal characteristic of the venous network is its distensibility, the reason for its role as blood reservoir and cardiovascular adaptation system. This distensibility varies continuously as a function of venous tone, of neurocardiovascular adaptation and of the method used for its determination. The importance of variability of venous physiology was investigated by postural and venous occlusion plethysmography. Two series of tests were performed in 3 healthy volunteers, each being treated over one month: one series involved 19 determinations during May 1985, the other 14 determinations in December 1985. Two plethysmographic methods were employed: conventional venous occlusion plethysmography in decubitus with compression of 50 mm Hg and postural plethysmography with venous occlusion only, using gravity force during variations in position of subjects. Venous filling, a function of venous distensibility, varied between 16.7 and 17.8% during venous occlusion and 23.9 and 31.7% during postural plethysmography. Emptying half-life was from 20.7 to 40.7%. Emptying rate was, by the 6th second, 17.3 to 21.6% for venous occlusion and 27.3 to 32.3% for postural plethysmography. A relation was not found between results for the two methods, suggesting that they explore different phenomena. Variability of venous physiology parameters is marked, modulations being due to general or local factors, the former acting on both legs simultaneously: exterior temperature, neurocardiovascular physiology, digestion, stress, relaxation. Factors can have their effects reduced by differential study of the two limbs.(ABSTRACT TRUNCATED AT 250 WORDS)