[Reproducibility of venous occlusion plethysmography. Value of a computerized system of calculation]

The manual interpretation of identical occlusive venous plethysmography curves by different technicians is subject to a wide variation. The object of this study is to verify this state of affairs and to propose an automatic calculation of the different parameters usually used: the percentage volume increase (delta V), the time taken to half empty (t V/2) and the maximal venous outflow (MVO). We compared the variations, due to the operators, in the measurement of the parameters characterising identical curves obtained by occlusive venous plethysmography. Sixty curves from 30 patients, were photocopied and each was measured independently by four different operators. The results were compared with the measurements obtained automatically from a micro-computer connected to the plethysmograph. The measurements of the percentage volume increase and the time taken to half empty differed among the operators and the computer by less than 2%. However, the maximal venous outflow was subject to very large variations amongst the operators (up to 60%). This uncertainty is due to the operators choice of the point on the curve where the tangent is measured. The micro-computer, by fixing this point at 0.3 second after releasing the cuff allows a standardisation of this parameter.