Plethysmographic findings in normal subjects using a capacitance mode.

A new strain-gauge plethysmographic system, Phlebotest, was evaluated in 19 normal subjects, yielding 38 lower limbs for study. A capacitance mode was used which allowed both the left and right calves to reach their maximal volume expansion before releasing the cuff pressure (60 mmHg in this study). Parameters such as the maximum volume change (V sec), the outflow rate during the first second after deflation (F 1.0), the expelled volume in four seconds (EV 4.0) and the surface area over the curve during the first four seconds after deflation (IND) were automatically calculated and their side differences between the left and right legs were determined respectively. There was a good linear correlation between EV 4.0 and V sec (r = 0.9274, p less than 0.0005) and the EV 4.0/V sec ratio was calculated. In contrast to the previous reports, between three consecutive determinations there were no significant differences in the measurements of these parameters, and V sec consistently kept an identical mean value. These results suggest that using this new system only one determination of calf expansion is required. The reason might be that, in addition to some technical improvements, the computer-controlled capacitance function can secure the optimal venous filling in every determination.