BIOELECTRICAL-IMPEDANCE ANALYSIS MEASUREMENTS OF TOTAL-BODY WATER ANDEXTRACELLULAR WATER IN HEALTHY ELDERLY SUBJECTS

OBJECTIVE: To address whether: (1) bioelectrical impedance analysis (B IA) can provide precise and accurate estimates of total body water (TB W) and extracellular water (ECW) in healthy elderly subjects, that dis play age-induced changes in body composition, (2) BIA models are impro ved by introducing variables related to geometrical body-shape and osm olarity, DESIGN: Cross-validation of available BIA models and models d eveloped in the study. SUBJECTS: 58 healthy elderly subjects (31 women , 27 men, 66.8 +/- 4.7 y, mean +/- s.d.) MEASUREMENTS: BIA at 5, 50 an d 100 kHz, O-18 labelled water measurements of TBW, Br measurements of ECW, anthropometric variables, plasma osmolarity, RESULTS: Published BIA models for estimating TBW, entail various degrees of bias. Precise models (SEE of the models 0.8 L at 100 kHz, 1.0 L at 50 kHz) involvin g height(2)/resistance, weight, gender, circumferences and plasma osmo larity were established with data from 30 subjects chosen at random. C ross-validation of an independent group (n = 28) showed no bias (-1.5 +/- 3.2 L at 100 kHz, -1.4 +/- 3.2 L at 50 kHz, P = NS). CONCLUSION: W e conclude that BIA models with increased accuracy and precision for p redicting ECW and TBW can be derived in healthy elderly subjects. Repe ated measures had a mean difference of 0.2 +/- 1.2 L.