Description and validation of a novel liquid metal-free device for venous congestion plethysmography

We present a newly developed electromechanical sensor with automated calibr ation for strain-gauge plethysmography (filtrass) and compare it to a conve ntional mercury-in-Silastic strain-gauge plethysmograph (MSG). Fluid filtra tion capacity (K-f) and isovolumetric venous pressure (Piv) of the limb wer e assessed noninvasively with both devices in 29 healthy volunteers. We fou nd significantly higher K-f and Piv values with MSG [4.6 +/- 2.0 x 10(-3) m l.min(-1).mmHg(-1).100 ml tissue(-1) (K-f units; KfU) and 21.2 +/- 8.1 mmHg for Pvi], than with filtrass, giving values of 3.1 +/- 0.8 KfU and 15.1 +/ - 7.1 mmHg. Because K-f and Piv are profoundly influenced by the calibratio n, we investigated the quality of the calibration signal and its impact on the obtained values. We could show that the reproducibility of repeated cal ibrations was higher with filtrass (58% lower mean I SD). The data were gro uped according to the quality of calibration, and we found no significant d ifference in K-f and Piv between filtrass (3.0 +/- 0.7 KfU and 15.9 +/- 6.9 mmHg, respectively) and MSG with good calibration signal (3.3 +/- 0.8 KfU and 18.6 +/- 7.1 mmHg, respectively; no significant difference). However, w e obtained significantly higher MSG values (5.6 +/- 2.0 KfU and 23.1 +/- 8. 4 mmHg, respectively; P < 0.001) in the group with a bad calibration signal . We suggest that the filtrass sensor, which performs an automatic, standar dized calibration procedure and shows a linear signal response to stretch, gives highly reproducible and reliable results and thus is more suitable fo r routine application.