Validation of bio-impedance spectroscopy: Effects of degree of obesity and ways of calculating volumes from measured resistance values

Abstract

BACKGROUND: Bioelectrical-impedance spectroscopy (BIS) is a very attractive method for body composition measurements in a clinical setting. However, validation studies often yield different results. This can partly be explained by the different approaches used to transform measured resistance values into body compartments. OBJECTIVE: The aim of this study was to compare the linear regression (LR) method with the Hanai Mixture theory (HM). Secondly, the effect of degree of overweight on the accuracy of BIS was analysed. DESIGN: In 90 people (10 M, 80 F; body mass index (BMI) 23 ± 62 kgam 2 ) total body water (TBW) and extracellular water (ECW) were measured by deuterium and NaBr dilution methods, respectively, and by BIS. Resistance values of ECW (R ECW ) and TBW (R TBW ) were used for volume calculations. Data of half the group were used for LR based on L 2 aR (L length, R resistance) to predict TBW and ECW and to calculate the constants used in the HM (k ECW ), k p ). Prediction equations and constants were cross-validated in Group 2. RESULTS: Bland and Altman analysis showed that the LR method underestimated TBW by 1.1 l (P`0.005) and ECW by 1.1 l (P`0.005). The HM approach underestimated ECW by 0.8 l (P`0.005). The correlations with the dilution methods and the SEEs for TBW and ECW were comparable for the two approaches. The prediction error of BIS for TBW and ECW correlated with BMI. The constant k ECW , and the speci®c resistivities of the ECW and intracellular water (ICW) p ECW and p ICW were also correlated with BMI. CONCLUSIONS: The mixture approach is slightly more accurate than linear regression, but not sensitive enough for clinical use. The constants used in the HM model are not constants in a population with a wide variation in degree of overweight. The physical causes of the correlation between BMI and constants used in the model should be studied further in order to optimize the mixture model.

Body composition in patients with short bowel syndrome: An assessment by bioelectric impedance spectroscopy (BIS) and dual–energy absorptiometry (DXA)

“…The wide limits of agreement associated with DXA and BIS, as shown in the present study and by others (Cox-Reijven & Soeters, 2000;Lehnert et al, 2001;Carlsson et al, 2002), limits its clinical utility.…”

“…The method is quick and noninvasive. The accuracy of the method in different clinical settings has been questioned, for example, reduced accuracy has been described in obese subjects (Cox-Reijven & Soeters, 2000), cirrhotic patients (Lehnert et al, 2001) and children (Ellis et al, 1999). In one of our female patients with liver failure and ascites, no values were obtained from BIS because the software was unable to perform the calculations.…”

Interorgan ammonia and amino acid metabolism in metabolically stable patients with cirrhosis and a TIPSS

“…Furthermore, patients drank a mixture of 20 g of deuterium oxide dilution (99.9 atom%, D-4501, Sigma, St. Louis, MO) and 30 mL of 150 mmol/L sodium bromide (Clinical Pharmacy, Maastricht, The Netherlands) to determine total body water and extracellular water. 7 Portography was performed under analgesia (pethidine, 1 mg/kg body weight) and sedation (midazolam, 0.1 mg/kg body weight). If the shunt was shown to be patent (portal pressure gradient Ͻ12 mm Hg), the following catheters were inserted under direct radiograph screening.…”

“…15 Amino acid and bromide concentrations were determined by a fully automated high-performance liquid chromatography system. 7,16 Deuterium was analyzed with an isotope ratio mass spectroscope. 7 Calculations.…”

“…7,16 Deuterium was analyzed with an isotope ratio mass spectroscope. 7 Calculations. Plasma flow rate (mL/kg body weight/ min) of the portal vein, liver, kidneys, and one leg were calculated by using formulae based on the method of indicator dilution and Fick's principle.…”