A REASSESSMENT OF MERCURY IN SILASTIC STRAIN-GAUGE PLETHYSMOGRAPHY FOR MICROVASCULAR PERMEABILITY ASSESSMENT IN MAN

1. We have used non-invasive mercury in a silastic strain gauge system to assess the effect of pressure step size, on the time course of the rapid volume response (RVR) to occlusion pressure. We also obtained v alues for hydraulic conductance (K(f)), isovolumetric venous pressure (P(vi)) and venous pressure (P(v)) in thirty-five studies on the legs of twenty-three supine control subjects.2. The initial rapid volume re sponse to small (9.53 +/- 0.45 mmHg, mean +/- s.E.m.) stepped increase s in venous pressure, the rapid volume response, could be described by a single exponential of time constant 15.54 +/- 1.14 s. 3. Increasing the size of the pressure step, to 49.8 +/- 1.1 mmHg, gave a larger va lue for the RVR time constant (mean 77.3 +/- 11-6 s). 4. We propose th at the pressure-dependent difference in the duration of the rapid volu me response, in these two situations, might be due to a vascular smoot h muscle-based mechanism, e.g. the veni-arteriolar reflex. 5. The mean (+/- S.E.M.) values for K(f), P(vi) and P(v) were 4.27 +/- 0.18 (unit s, ml min-1 (100 g)-1 mmHg-1 x 10(-3)), 21.50 +/- 0.81 (units, mmHg) a nd 9.11 +/- 0.94 (units, mmHg), respectively. 6. During simultaneous a ssessment of these parameters in arms and legs, it was found that they did not differ significantly from one another. 7. We propose that the mercury strain gauge system offers a useful, non-invasive means of st udying the mechanisms governing fluid filtration in human limbs.