Comparative study of the relationship between multi-frequency impedance and body water compartments in two European populations (original) (raw)

1996, British Journal of Nutrition

To investigate possible differences in the relationship between multi-frequency impedance and bodywater compartments (total body water (TBW) and extracellular water (ECW)) measured by dilution techniques in two European populations, we studied forty Italian (twenty male and twenty female) and forty-three Dutch (twenty-three male and twenty female) healthy subjects aged 1 9 4 1 years. The main differences in body build between the two groups were height, trunk length and the two ratios TBW/height and ECW/height. Population+pecific prediction formulas for ECW (at 1 kHz) and TBW (at 100 kHz) were developed. The prediction errors 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 the ECW prediction. The biases in both TBW and ECW were correlated with ECW/TBW (Y -0.44, P < 0.0005 and Y +0.52, P < 0.0005 respectively) in 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 c 0.03, trunk length (r 0.36, P < 0-001) and Z1/Z,, (r 032, P < 0.01). In conclusion, the water distribution between the extra-and intracellular compartments emerged in the present study as the major cauw of error in the prediction of body water, and in particular of ECW from impedance measurements with a population-specific equation. Moreover, body build, expressed as TBW/height and ECW/height, had an impact on the bias. Body composition: Total body water : Multi-frequency bioimpedance In the average adult individual 5 0 4 0 % of body weight is water; the intracellular component of body water accounts for about 40% of body weight and the extracellular component for about 20 YO. Approximately 25 YO of the extracellular component is in the vascular system (plasma) and 75 % outside the blood vessels (interstitial fluid). In general, the extracellular water: total body water ratio (ECW/TBW) is higher in females and children. In healthy adults ECW/TBW increases with age from an average of 0.42 at age 30 years to 048 at 80 years (Forbes, 1987).