A bridge from bioimpedance spectroscopy to 50 kHz bioimpedance analysis: application to total body water measurements
Résumé
This paper presents a method for extrapolating the total body water (TBW)
resistance Rt50 from the resistance measured at 50 kHz (R50). A DXA
examination and impedance measurements were carried out in a 1st group of 57
healthy volunteers with a Xitron 4200 multifrequency impedancemeter, in order
to determine their values of Rt50 by comparison with resistances extrapolated
at an infinite frequency by the Xitron (R∞). TBW volumes were calculated
using our modified BIS method (Jaffrin et al 2006 Med. Biol. Eng. Comput.
44 873–82) from R∞, Rt50 and from the fat-free mass measured by DXA,
assuming a hydration rate of 73.2%. The same protocol and calculations were
also carried out on a 2nd group of 21 subjects for independent validation. Data
of the 1st group showed that values of Rt50, not significantly different from
those of R∞, could be obtained by dividing R50 by 1.231 in men and by 1.224 in
women. Applying this method to the 2nd group yielded also values of Rt50 not
significantly different from R∞. TBW volumes Vt50 obtained from Rt50 were
not significantly different from those of our modified BIS method Vtn, or from
TBW volumes obtained from DXA in both groups. A comparison with three
BIA methods of TBW determination showed that our new method gave results
in better agreement with TBW from DXA and from our modified BIS method.