Assessing total body and extracellular water from bioelectrical response spectroscopy.

We developed and validated assessments for total body water (TBW) and extracellular water (ECW) by using two resistance values of a new electric circuit model (CM) (two resistors; a capacitor and an inductor) with or without body mass. Fluid shifts occurring after 40 min of supine rest did not increase the validity of either estimate. CM estimates were valid; r = 0.941 to 0.969, low SE of estimates of 1.15-2.28 kg, nonsignificant mean differences (CM - dilution; %delta = -0.4 to 1.3%) that were close to the expected measurement errors for TBW (+/- 1%) and ECW (+/- 5%), and Bland-Altman pairwise comparisons that showed equivalence between methods. The CM estimates of TBW and ECW had marginally better validity than the previously published bioimpedance models. The advantage of the CM model is its assessments of multiple fluid spaces and that it does not require gender-specific equations. We conclude that CM estimate of TBW is acceptable, whereas further validation is needed before the ECW estimate should be used in a clinical or research setting.

Determining blood and plasma volumes using bioelectrical response spectroscopy.

We hypothesized that an electric field (inductance) produced by charged blood components passing through the many branches of arteries and veins could assess total blood volume (TBV) or plasma volume (PV). Individual (N = 29) electrical circuits (inductors, two resistors, and a capacitor) were determined from bioelectrical response spectroscopy (BERS) using a Hewlett Packard 4284A Precision LCR Meter. Inductance, capacitance, and resistance from the circuits of 19 subjects modeled TBV (sum of PV and computed red cell volume) and PV (based on 125I-albumin). Each model (N = 10, cross validation group) had good validity based on 1) mean differences (-2.3 to 1.5%) between the methods that were not significant and less than the propagated errors (+/- 5.2% for TBV and PV), 2) high correlations (r > 0.92) with low SEE (< 7.7%) between dilution and BERS assessments, and 3) Bland-Altman pairwise comparisons that indicated "clinical equivalency" between the methods. Given the limitation of this study (10 validity subjects), we concluded that BERS models accurately assessed TBV and PV. Further evaluations of the models' validities are needed before they are used in clinical or research settings.