Bioelectrical impedance analysis measurements of total body water and extracellular water in healthy elderly subjects.

Abstract

To address whether: (1) bioelectrical impedance analysis (BIA) can provide precise and accurate estimates of total body water (TBW) and extracellular water (ECW) in healthy elderly subjects, that display age-induced changes in body composition, (2) BIA models are improved by introducing variables related to geometrical body-shape and osmolarity. Cross-validation of available BIA models and models developed in the study. 58 healthy elderly subjects (31 women, 27 men, 66.8+/-4.7 y, mean +/- s.d.) BIA at 5, 50 and 100 kHz, 18O labelled water measurements of TBW, Br measurements of ECW, anthropometric variables, plasma osmolarity. 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) involving height2/resistance, weight, gender, circumferences and plasma osmolarity were established with data from 30 subjects chosen at random. Cross-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). We conclude that BIA models with increased accuracy and precision for predicting ECW and TBW can be derived in healthy elderly subjects. Repeated measures had a mean difference of 0.2+/-1.2 L.