Extracellular volume measurements using bioimpedance spectroscopy-Hanai method and wrist-ankle resistance at 50 kHz.

A method for extrapolating the extracellular water (ECW) resistance from wrist-ankle resistance at 50 kHz (R (50)) is proposed in this paper, in order to enable 50 kHz impedancemeters to use the BIS-Hanai equation for determination of ECW. Values of R (50) and the ECW resistance extrapolated at zero frequency R (e) were measured in a first group of 57 healthy volunteers, using a Xitron 4200 multifrequency impedancemeter and mean values (b) of the ratio R (50)/R (e) in men and women were used to determine individual values of R (e50), the ECW resistance extrapolated from R (50), which were substituted to R (e) in the BIS-Hanai equation. For validation, the method was compared against ECW measured with the Xitron (V (ex)) in a second group of 31 healthy volunteers, using values of b of first group. Values of R (e50) in this second group were found to be not significantly different from corresponding values of R (e) with p-values of Student test of 0.346 for men and 0.300 for women. ECW volumes (V (e50)) calculated from R (e50) were also found not significantly different from those of the Xitron with Student paired test p values of 0.277 in men and 0.393 in women. Our method gave a better agreement with V (ex) than two bioimpedance analysis methods from the literature, especially in women. It was also tested on a 50 kHz single frequency impedancemeter (BodyExplorer, Juwell Medical) on a third group of 21 subjects and gave ECW volumes not significantly from those of the Xitron with p = 0.531 for men and 0.096 for women.