An alternative method for calculating changes in arterial calf blood flow at rest. An initial study.

In 20 patients we studied the changes in calf arterial blood flow (AF) following spinal and epidural blocks, using venous occlusion strain gauge plethysmography (SGP). AF was calculated both in the conventional way by drawing a tangent to the initial upslope of the curve, and by a new method which measures the time to the point when 50% of venous capacity is reached (tVC50). The statistical differences within and between the spinal and epidural groups for AF and tVC50 were determined. In measuring the post-block changes in AF as compared with the control values, a statistically significant correlation (rs = -0.85, p less than 0.01) was observed between the two methods. We conclude that the new variable, tVC50, seems to be potentially useful in calculating changes in arterial blood flow at rest, and could be used, for example, in connection with surgical and pharmacological interventions, especially when the initial upslope of the SGP curve is equivocal.