Use of multi-frequency bioelectrical impedance analysis for the estimation of extracellular fluid.

Thomasset (Lyon Medicine (1962): 207, 107-118; (1963): 209, 1325-1350; (1965): 214, 131-143) and others suggested that low-frequency impedance measurements could be used to estimate extracellular fluid and that high-frequency measurements could be used for the assessment of total body water. It was the purpose of this study to examine the relationship between body fluid compartments and multi-frequency bioelectrical impedance analysis (MF-BIA). Total body water (TBW) and extracellular fluid (ECF) were measured using deuterium and sodium bromide dilution procedures. Intracellular fluid volume (ICF) was calculated as the difference between TBW and ECF. A tetrapolar arrangement of surface electrodes was used to measure whole-body resistance (R), reactance (Xc), impedance (Z), and phase angle (P) at 25 frequencies ranging from 1 kHz to 1.35 MHz. Subjects (n = 60; 40 male and 20 female) were between the ages of 19 and 65 years. Mean ratios (+/- SEM) of ECF/ICF and ECF/TBW were 0.83 +/- 0.021 and 0.45 +/- 0.011, respectively. Individuals with the largest fat-free mass (FFM) had the highest ECF value. Whole-body resistive index values most correlated to ECF were at 224, 300, 400, 548 and 1 kHz with correlations ranging from 0.93 to 0.84. All possible subset regression analysis was used to develop a prediction equation for ECF: R2 = 0.924 and SEE = 1.061: ECF = 5.17753 + (0.09989*RI224) + (0.09322*WT) - (1.3962*SEX), where RI = resistive index (HT2/R) at the specific frequency of 224kHz; WT = weight in kilograms; sex was dummy-coded, males = 0, females = 1.