COMPARATIVE-STUDY OF THE RELATIONSHIP BETWEEN MULTIFREQUENCY IMPEDANCE AND BODY-WATER COMPARTMENTS IN 2 EUROPEAN POPULATIONS

To investigate possible differences in the relationship between multi- frequency impedance and body-water compartments (total body water (TBW ) and extracellular water (ECW)) measured by dilution techniques in tw o European populations, we studied forty Italian (twenty male and twen ty female) and forty-three Dutch (twenty-three male and twenty female) healthy subjects aged 19-41 years. The main differences in body build between the two groups were height, trunk length and the two ratios T BW/height and ECW/height. Population-specific prediction formulas for ECW (at 1 kHz) and TBW (at 100 kHz) were developed. The prediction err ors for ECW and TBW were about 0.6 and 1.5 kg respectively, (CV 4%) in both groups. Cross-validation analysis showed no significant error in the prediction of TBW but a slight error (range -4.9 to + 2.8 %) in t he ECW prediction. The biases in both TBW and ECW were correlated with ECW/TBW (r -0.44, P < 0.0005 and r + 0.52, P < 0.0005 respectively) i n the two groups; the biases in ECW were also related to ECW/height (r 0.51, P < 0.001), TBW/height (r 0.25, P < 0.05), trunk length (r 0.36 , P < 0.001) and Z(1)/Z(100) (r 0.32, P < 0.01). In conclusion, the wa ter distribution between the extra- and intracellular compartments eme rged in the present study as the major cause of error in the predictio n of body water, and in particular of ECW from impedance measurements with a population-specific equation. Moreover, body build, expressed a s TBW/height and ECW/height, had an impact on the bias.