Abstract
The purpose of this study was to test the validity of a multiple frequency bioimpedance spectroscopy (BIS) analyzer that estimates extracellular fluid volume (ECV), intracellular fluid volume (ICV) and total body water (TBW). Thirteen healthy males (mean±SD: age, 23 ± 3 yr; body mass, 80.6± 14.7 kg) had their TBW and ECV measured by ingesting dilution tracers(7.27 g D2O, 1.70 g NaBr; blood samples at 0 and 4h). ICV was calculated as TBW minus ECV. Prior to blood samples, impedance values were measured at rest on a nonconducting surface, with a BIS analyzer (Xitron, model 4000B; 50-500 kHz). Electrode placement, posture, hydration state, food intake were controlled. Dilution measures (TBW, 51.00 ± 9.30; ECV, 19.88 ± 3.14; ICV, 31.12 ± 6.80L) and BIS volumes (TBW, 50.03± 7.67; ECV, 20.95 ± 3.33; ICV, 29.04 ± 4.51L) were significantly different for ECV (P<.01) and ICV (P<.05) only. The correlation coefficients of dilution versus BIS volumes (r =.93 to.96) were significant at P<.001. Standard errors of the estimates were: TBW, 2.23L; ECV, 1.26L; and ICV, 1.71L. Although BIS theoretically predicts TBW, ECV and ICV, we concluded that BIS errors of this magnitude may be acceptable in clinical settings, but would be unacceptable in some scientific experiments.
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