The validity of bioelectrical impedance models in clinical populations

Formulation of a dry weight bioimpedance index in hemodialysis patients

Hydration status has a major impact on hemodialysis (HD) patients. Overhydration is related to hypertension, pulmonary and peripheral edema, and other cardiovascular events; while dehydration is related to hypotension, and other severe ischemic symptoms. All result in increased morbidity and mortality. Bioimpedance has been newly developed to measure the amount of water in the body. Several predictive equations were used, taken from demographic and anthropometric data. The purpose of this study was to evaluate the body composition of HD patients and to propose a hydration index. We performed bioimpedance measures with the Tanita TBF-300 scale, which calculates Total Body Water (TBW). The tool was reliable, with good reproducibility. However, we found significant differences between weight variations (dW) and TBW variations (dTBW) during HD sessions. This paper proposes a hydration index (I=dW-dTBW), with the hypothesis that dry weight is reached when I=0, while I>0 or I<0 indicate overhydrated or dehydrated, respectively. In this study, the changes in the index corresponded to the variations in weight and hydration state. We conclude that impedancemetry is a currently available technique that can be used to estimate TBW in HD patients. Although the index has to be improved by complementary studies, it may be a good guide to assess the dry weight achieved.

Comparing measures of fat-free mass in overweight older adults using three different bioelectrical impedance devices and three prediction equations

OBJECTIVES

To compare measures of fat-free mass (FFM) by three different bioelectrical impedance analysis (BIA) devices and to assess the agreement between three different equations validated in older adult and/or overweight populations.

DESIGN

Cross-sectional study.

SETTING

Orthopaedics ward of Brisbane public hospital, Australia.

PARTICIPANTS

Twenty-two overweight, older Australians (72 yr ± 6.4, BMI 34 kg/m² ± 5.5) with knee osteoarthritis.

MEASUREMENTS

Body composition was measured using three BIA devices: Tanita 300-GS (foot-to-foot), Impedimed DF50 (hand-to-foot) and Impedimed SFB7 (bioelectrical impedance spectroscopy (BIS)). Three equations for predicting FFM were selected based on their ability to be applied to an older adult and/ or overweight population. Impedance values were extracted from the hand-to-foot BIA device and included in the equations to estimate FFM.

RESULTS

The mean FFM measured by BIS (57.6 kg ± 9.1) differed significantly from those measured by foot-to-foot (54.6 kg ± 8.7) and hand-to-foot BIA (53.2 kg ± 10.5) (P < 0.001). The mean ± SD FFM predicted by three equations using raw data from hand-to-foot BIA were 54.7 kg ± 8.9, 54.7 kg ± 7.9 and 52.9 kg ± 11.05 respectively. These results did not differ from the FFM predicted by the hand-to-foot device (F = 2.66, P = 0.118).

CONCLUSIONS

Our results suggest that foot-to-foot and hand-to-foot BIA may be used interchangeably in overweight older adults at the group level but due to the large limits of agreement may lead to unacceptable error in individuals. There was no difference between the three prediction equations however these results should be confirmed within a larger sample and against a reference standard.

Comparison of body fat-free masses calculated from hand-to-foot and foot-to-foot resistances with DXA measurements

This article compares the determination of body fat-free-mass (FFM) by impedance, using either hand-to-foot resistance (R₁₃) or foot-to-foot one (R₃₄) from comparison with dual X-ray absorptiometry (DXA) measurements in a normal population. The first goal was to see if the foot-to-foot resistance used in body fat analysers provides less accurate information for body FFM than the hand-to-foot one used by medical impedance-meters. Another goal was to compare the prediction accuracy of six different regression equations of FFM for each sex and for each resistance relatively to DXA. The impedancemeter used in this study was a Tefal prototype with 4 plantar electrodes and 4 additional electrodes for the hands and providing hand-to-foot and foot-to-foot resistances. Coefficients of these correlations were determined by comparison with FFM measured by DXA in a 1st cohort of 170 healthy adults. For an independent validation, these equations were tested in a 2nd cohort of 86 adults who underwent the same impedance and DXA protocols, using Student's paired t-tests. The accuracy of FFM prediction increased generally with the number of physiologic parameters included in the regression, but none of our equations gave FFM predictions significantly different from DXA. FFM calculated from the foot-to-foot resistance were closer to DXA values than those calculated from hand-to-foot resistance, as their average P-value of comparison with DXA was higher at 0.695 against 0.387 for R₁₃.

Body fat and fat-free mass measured by bioelectric impedance spectroscopy and dual-energy X-ray absorptiometry in obese and non-obese adults

The aim of the present study was to compare body fat mass (FM) and fat-free mass (FFM) estimates by bioelectric impedance spectroscopy (BIS), with respective estimates by dual-energy X-ray absorptiometry (DXA), in obese and non-obese subjects. Body composition was measured in ninety-three obese and non-obese men and women by BIS device, BodyScout (Fresenius Kabi, Bad Homburg, Germany) and DXA device, Lunar iDXA (GE Healthcare, Madison, WI, USA). Mean difference between the methods was analysed by t tests, and Bland-Altman plots were generated to further examine the differences between the methods. Mean difference between the estimates by DXA and BIS (ΔDXA - BIS and Bland-Altman 95 % limits of agreement) were as follows: FM 4·1 ( - 2·9, 11·2) kg and 4·5 ( - 2·9, 11·8) %, FFM - 4·1 ( - 11·2, 2·9) kg and - 4·5 ( - 11·9, 2·9) %, indicating large inter-individual variation and statistically significant underestimation of FM and overestimation of FFM by BIS, as compared to DXA. The underestimation of FMkg (FM measured in kg) and overestimation of FFMkg (FFM measured in kg) were more pronounced in men than in women, and the underestimation of FM% (FM measured in percent) and overestimation of FFM% (FFM measured in percent) were more pronounced in normal weight (BMI = 20·0-24·9 kg/m2) than in overweight and obese (BMI ≥ 25·0 kg/m2) subjects. BIS may be suitable for classification of a population into groups according to FM and FFM. However, the large inter-individual variation suggests that this BIS device with the proprietary software is insufficient for estimation of single individual body FM and FFM.

A practical guide to bioelectrical impedance analysis using the example of chronic obstructive pulmonary disease

Bioelectrical impedance analysis (BIA) is a simple, inexpensive, quick and non-invasive technique for measuring body composition. The clinical benefit of BIA can be further enhanced by combining it with bioelectrical impedance vector analysis (BIVA). However, there is a substantial lack of information on the practical aspects of BIA/BIVA for those primarily interested in learning how to use and interpret this method in practice. The purpose of this article is to provide some guidance on the use of BIA/BIVA with special attention to practical considerations.This report reflects the authors' practical experience with the use of single-frequency BIA in combination with BIVA, particularly in COPD patients. First, the method and principles of BIA/BIVA are briefly described. Then, a practice-oriented approach to the interpretation and analysis of characteristic examples of altered nutritional and fluid status as seen with BIA/BIVA in COPD patients (e.g. malnutrition in obese and underweight patients with COPD, water retention) is presented.As our examples show BIA/BIVA is an attractive and easy-to-learn tool for quick nutritional assessment and is therefore of great clinical benefit in daily practice.

A comparison between two methods for measuring limb resistances with wrist and ankle electrodes

Segmental measurements of limb resistances permit to evaluate the regional distribution of fat-free-mass (FFM). As shown by Organ et al. (J Appl Physiol 1994;77:98-112) "virtual" limb resistances can be measured with only peripheral electrodes at ankle and wrist, which is faster and does not require undressing. This paper presents a different method for obtaining "virtual" limb resistances from peripheral electrodes and compares it with that of Organ et al. and with segmental measurements using same protocol. It is found that virtual arm resistances of both methods were overestimated as compared to segmental values, by 6.8% in men and 5.8% in women for our method and by 7.4% and 8% for Organ et al. one. Virtual leg resistances were found, for both methods, to be slightly lower than segmental leg resistances measured with proximal waist electrodes, which were a little overestimated. But after correcting this overestimation using Organ et al. data, we evaluated the overestimation of virtual leg resistances to be 2.3% in men and 2.8% in women by our method versus 4.4% and 5.9%, respectively, for Organ et al. one. An important finding was the strong correlation between virtual resistances of both methods and segmental ones, as their ratio had a small standard deviation between 0.019 and 0.024 for arms and legs. Thus, the overestimation of limb resistance is automatically corrected when FFM is determined by an equation calibrated with DXA segmental measurements.

The relationship between resting blood pressure, body mass index and lean body mass index in British children

BACKGROUND

Elevated blood pressure (BP) in childhood is associated with overweight and obesity. However, lean body mass index (LBMI, cm(2)/kg) has been suggested as a better means than body mass index (BMI, kg/m(2)) by which to consider the relations between weight status and health indices in children.

OBJECTIVE

To assess the relationship between resting BP and weight status in youth whilst considering BMI and LBMI when examining this issue.

METHODS AND PROCEDURES

Height, body mass and resting blood pressure were assessed in 384 boys and 277 girls, aged 11-14 years from Central England.

RESULTS

SBP was significantly lower in 'normal weight' children compared to overweight and obese children and in overweight compared to obese children (both p = 0.0001). DBP was significantly lower in 'normal weight' children compared to those classified as overweight (p = 0.006). BMI and LBMI were both significant predictors of SBP and DBP (p = 0.0001). However, LBMI was normally distributed, unlike BMI, and was a better predictor of BP than BMI.

CONCLUSIONS

Overweight and obesity is associated with higher resting BP in British children. However, when examining the effect of weight status on BP, the researcher should consider use of LBMI over BMI.

Rapid in vivo whole body composition of rats using cone beam μCT

Precise, noninvasive analysis and quantification of in vivo body composition is essential for research involving longitudinal, small-animal disease models. We investigated the feasibility and precision of a rapid, flat-panel μCT scanner to report whole body adipose tissue volume (ATV), lean tissue volume (LTV), skeletal tissue volume (STV), and bone mineral content (BMC) in 25 postmortem female and 52 live male Sprague-Dawley rats. μCT images, acquired in three 90-mm segments and reconstructed with 308 μm of isotropic voxel spacing, formed contiguous image volumes of each entire rat specimen. Three signal-intensity thresholds (determined to be -186, 5, and 155 HU) were used to classify each voxel as adipose, lean, or skeletal tissue, respectively. Tissue masses from the volume fractions of ATV, LTV, and STV were calculated from assumed tissue densities of 0.95, 1.05, and 1.92 g/cm(-3), respectively. A CT-derived total mass was calculated for each rat and compared with the gravimetrically measured mass, which differed on average for the postmortem female and the live male group by 2.5 and 1.1%, respectively. To evaluate the accuracy of the CT-derived body composition technique, following the live male study excised muscle tissue in the lower right leg of all rats in group B were compared with the image-derived LT measurement of the same regional compartment and found to differ on average by 2.2%. Through repeated CT measurements of postmortem specimens, the whole body ATV, LTV, STV, and BMC measurement analysis gave a precision value of ±0.6, 1.9, 1.7, and 0.5% of the average value, respectively.

Assessing Body Fat Changes during Moderate Weight Loss with Anthropometry and Bioelectrical Impedance

BACKGROUND/OBJECTIVES: Monitoring changes in total fat mass and abdominal adiposity are important in understanding the impact of different types of weight loss interventions on health risks. Our objective was to assess the usefulness of anthropometry and bioelectrical impedance analysis (BIA) in predicting fat mass changes during moderate weight loss. SUBJECTS/METHODS: Fat mass changes were assessed in 34 overweight adults (24 females, 10 males) after a 12-week supervised weight loss induced by caloric restriction (-30% of requirement) using BIA and DXA. Agreement between BIA and DXA measurements were assessed by Bland-Altman plots. Linear regression modeling was used to predict body and truncal fat mass from anthropometric measures. RESULTS: Diet intervention resulted in a significant decrease in body weight (- 7.86 ± 2.87 kg), body mass index (BMI - 2.69 ± 0.98 kg/m(2)), total body fat (- 5.22 ± 2.32 kg), truncal fat (- 2.80 ± 1.94 kg) and waist circumference (- 5.52 ± 3.57 cm). BMI and body weight were highly correlated with body fat (0.83 and 0.92 in females and 0.94 and 0.92 in males respectively) and truncal fat (0.75 and 0.87 in females; 0.90 and 0.84 in males respectively) during weight loss. Waist circumference was more correlated with truncal fat in males than females (0.94 vs. 0.85 in females). Compared to DXA, BIA underestimated total body fat changes in males (- 8.8 kg, p<0.001) and overestimated total body fat changes in females (+ 2.1 kg, p< 0.001). CONCLUSIONS: Body mass index, body weight, and waist circumference provide simple and more accurate than BIA estimates of relative changes in total and truncal fat during moderate weight loss in adults.

Rapid measurement of total body water to facilitate clinical decision making in hospitalized elderly patients

BACKGROUND

Bioelectrical impedance analysis (BIA) is a noninvasive rapid and simple bedside technique that can be used to predict total body water (TBW), extracellular water (ECW), and intracellular water (ICW) and identify altered fluid distribution following critical illness.

METHODS

An equivalence study of BIA in 32 hospitalized elderly patients was compared with reference standard dilutional measurements of deuterated water (TBW) and sodium bromide (ECW). The results were compared with anthropometric equations commonly used to predict TBW.

RESULTS

There was variability in TBW content among the participating hospitalized elderly patients. This variability was within (+/-5 L) and the percent difference between the standard and BIA was as follows: mean (range) -4.1% (-18.5 to 11.2). BIA reliably predicted TBW and ECW in individual participants, whereas standard prediction equations uniformly over- or underestimated TBW in individuals and whole group population.

CONCLUSION

TBW in hospitalized elderly patients can be estimated noninvasively by bedside BIA. Standardized anthropometric equations have to be used with caution in this population.

Precision and reliability of strength (Jamar vs. Biodex handgrip) and body composition (dual-energy X-ray absorptiometry vs. bioimpedance analysis) measurements in advanced cancer patients

Important deteriorations in body composition and strength occur and need to be accurately measured in advanced cancer patients (ACPs). The aim of this study was to establish the relationship between a single-frequency bioimpedance analyzer (BIA) and the dual-energy X-ray absorptiometer (DXA), as well as the Jamar handgrip dynometer and the Biodex handgrip attachment, and to determine the precision of each of these instruments in ACPs. Eighty-one ACPs with non-small-cell lung cancer and gastrointestinal cancer were recruited from the McGill University Health Centre (Montreal, Que.). Consecutive paired measurements, with repositioning between measurements, were obtained for total-body DXA, BIA, Biodex handgrip, and BIA plus Jamar handgrip. The total-body percent coefficient of variation (%CV) for the BIA and DXA were 1.34 and 1.56 for fat mass (FM), respectively, and 0.42 and 0.72 for fat free mass (FFM), respectively. The %CV for the Jamar and Biodex handgrips were 6.3 and 16.7, respectively. Bland–Altman plots were used to characterize the limits of agreement between DXA and BIA for FM (4.60 ± 7.80 (–3.19 to 12.39) kg) and FFM (–1.87 ± 7.16 (–9.03 to 5.29) kg). Both DXA and BIA demonstrate good short-term precision in ACPs. However, given its poor accuracy, it remains to be determined if BIA can be used to monitor ACPs for changes in total-body tissue composition as a function of time, whether for observation or response to treatment. Furthermore, because of wide limits of agreement, the DXA and BIA cannot be used interchangeably in research or clinical settings. The Jamar handgrip dynamometer shows more consistency than the Biodex handgrip attachment in ACPs, and should therefore be the preferred measure of changes in strength over time.

Extracellular volume measurements using bioimpedance spectroscopy-Hanai method and wrist-ankle resistance at 50 kHz

A method for extrapolating the extracellular water (ECW) resistance from wrist-ankle resistance at 50 kHz (R (50)) is proposed in this paper, in order to enable 50 kHz impedancemeters to use the BIS-Hanai equation for determination of ECW. Values of R (50) and the ECW resistance extrapolated at zero frequency R (e) were measured in a first group of 57 healthy volunteers, using a Xitron 4200 multifrequency impedancemeter and mean values (b) of the ratio R (50)/R (e) in men and women were used to determine individual values of R (e50), the ECW resistance extrapolated from R (50), which were substituted to R (e) in the BIS-Hanai equation. For validation, the method was compared against ECW measured with the Xitron (V (ex)) in a second group of 31 healthy volunteers, using values of b of first group. Values of R (e50) in this second group were found to be not significantly different from corresponding values of R (e) with p-values of Student test of 0.346 for men and 0.300 for women. ECW volumes (V (e50)) calculated from R (e50) were also found not significantly different from those of the Xitron with Student paired test p values of 0.277 in men and 0.393 in women. Our method gave a better agreement with V (ex) than two bioimpedance analysis methods from the literature, especially in women. It was also tested on a 50 kHz single frequency impedancemeter (BodyExplorer, Juwell Medical) on a third group of 21 subjects and gave ECW volumes not significantly from those of the Xitron with p = 0.531 for men and 0.096 for women.

Is bioelectrical impedance accurate for use in large epidemiological studies?

Percentage of body fat is strongly associated with the risk of several chronic diseases but its accurate measurement is difficult. Bioelectrical impedance analysis (BIA) is a relatively simple, quick and non-invasive technique, to measure body composition. It measures body fat accurately in controlled clinical conditions but its performance in the field is inconsistent. In large epidemiologic studies simpler surrogate techniques such as body mass index (BMI), waist circumference, and waist-hip ratio are frequently used instead of BIA to measure body fatness. We reviewed the rationale, theory, and technique of recently developed systems such as foot (or hand)-to-foot BIA measurement, and the elements that could influence its results in large epidemiologic studies. BIA results are influenced by factors such as the environment, ethnicity, phase of menstrual cycle, and underlying medical conditions. We concluded that BIA measurements validated for specific ethnic groups, populations and conditions can accurately measure body fat in those populations, but not others and suggest that for large epdiemiological studies with diverse populations BIA may not be the appropriate choice for body composition measurement unless specific calibration equations are developed for different groups participating in the study.

Multifrequency bioelectrical impedance analysis and bioimpedance spectroscopy for monitoring fluid and body cell mass changes after gastric bypass surgery

BACKGROUND & AIMS

There is a growing need for clinically applicable body composition assessment tools for extremely obese individuals. The objective of this research was to evaluate several bioimpedance techniques for monitoring changes in fluid, particularly intracellular water (reflecting body cell mass) after bariatric surgery.

DESIGN

Fifteen extremely obese women (body mass index: 48.9+/-7.0 kg/m(2); age: 48+/-9 years) were assessed before (baseline; T1), and approximately 6 weeks after gastric bypass surgery (T2) by several multifrequency bioelectrical impedance analysis approaches (MFBIA; QuadScan 4000), a bioimpedance spectroscopy device (BIS; Hydra 4200), and multiple dilution.

RESULTS

BIS provided intracellular water estimates that were comparable to criterion, based on mean comparisons, at both time points (T1: criterion: 24.2+/-3.1L, BIS: 24.0+/-3.7 L; T2: criterion: 20.6+/-3.7 L, BIS: 19.7+/-3.2L). MFBIA (with Deurenberg equations) provided comparable measures to criterion only at T2 (criterion: 20.3+/-3.7L, MFBIA: 20.6+/-2.7 L). Both MFBIA (with QuadScan proprietary equations) and BIS produced estimates of intracellular water change that were comparable to dilution. There was substantial variability in individual volume measures.

CONCLUSIONS

Although MFBIA and BIS hold promise as convenient techniques for assessing fluid changes, individual variability in measurements makes them impractical for assessment of extremely obese patients in the clinical setting.

Body fluid volumes measurements by impedance: A review of bioimpedance spectroscopy (BIS) and bioimpedance analysis (BIA) methods

This paper reviews various bioimpedance methods permitting to measure non-invasively, extracellular, intracellular and total body water (TBW) and compares BIA methods based on empirical equations of the wrist-ankle resistance or impedance at 50 kHz, height and weight with BIS methods which rely on an electrical model of tissues and resistances measured at zero and infinite frequencies. In order to compare these methods, impedance measurements were made with a multifrequency Xitron 4200 impedance meter on 57 healthy subjects which had undergone simultaneously a Dual X-ray absorptiometry examination (DXA), in order to estimate their TBW from their fat-free-mass. Extracellular (ECW) and TBW volumes were calculated for these subjects using the original BIS method and modifications of Matthie[Matthie JR. Second generation mixture theory equation for estimating intracellular water using bioimpedance spectroscopy. J Appl Physiol 2005;99:780-1], Jaffrin et al. [Jaffrin MY, Fenech M, Moreno MV, Kieffer R. Total body water measurement by a modification of the bioimpédance spectroscopy method. Med Bio Eng Comput 2006;44:873-82], Moissl et al. [Moissl UM, Wabel P, Chamney PW, Bosaeus I, Levin NW, et al. Body fluid volume determination via body composition spectroscopy in health and disease. Physiol Meas 2006;27:921-33] and their TBW resistivities were compared and discussed. ECW volumes were calculated by BIA methods of Sergi et al. [Sergi G, Bussolotto M, Perini P, Calliari I, et al. Accuracy of bioelectrical bioimpedance analysis for the assessment of extracellular space in healthy subjects and in fluid retention states. Ann Nutr Metab 1994;38(3):158-65] and Hannan et al. [Hannan WJ, Cowen SJ, Fearon KC, Plester CE, Falconer JS, Richardson RA. Evaluation of multi-frequency bio-impedance analysis for the assessment of extracellular and total body water in surgical patients. Clin Sci 1994;86:479-85] and TBW volumes by BIA methods of Kushner and Schoeller [Kushner RF, Schoeller DA. Estimation of total body water by bioelectrical impedance analysis. Am J Clin Nutr 1986;44(3):417-24], Lukaski et al. [Lukaski HC, Bolonchuk WW. Estimation of body fluid volumes using tetrapolar bioelectrical impedance measurements. Aviat Space Environ Med 1988;59:1163-9], Hannan et al. [Hannan WJ, Cowen SJ, Fearon KC, Plester CE, Falconer JS, Richardson RA. Evaluation of multi-frequency bio-impedance analysis for the assessment of extracellular and total body water in surgical patients. Clinical Science 1994;86:479-85], Deurenberg et al. [Deurenberg P, van der Koy K, Leenen R, Westrate JA, Seidell JC. Sex and age specific prediction formulas for estimating body composition from bioelectric impedance: a cross validation study. Int J Obesity 1991;15:17-25] These volumes were compared against those given by BIS method and, in the case of TBW, with those by DXA. For ECW, a good agreement was found between various BIS methods and that of Sergi while Hannan's values were higher. Both Matthie's and Moissl's methods gave mean TBW resistivities and volumes lower than those of Jaffrin's and DXA methods. Kushner et al. method gave values of TBW not significantly different from those of Jaffrin et al. and DXA, as Hannan's method in men, but Lukaski and Deurenberg methods led to an underestimation.

A bridge from bioimpedance spectroscopy to 50 kHz bioimpedance analysis: application to total body water measurements

This paper presents a method for extrapolating the total body water (TBW) resistance R(t50) from the resistance measured at 50 kHz (R(50)). A DXA examination and impedance measurements were carried out in a 1st group of 57 healthy volunteers with a Xitron 4200 multifrequency impedancemeter, in order to determine their values of R(t50) by comparison with resistances extrapolated at an infinite frequency by the Xitron (R(infinity)). TBW volumes were calculated using our modified BIS method (Jaffrin et al 2006 Med. Biol. Eng. Comput. 44 873-82) from R(infinity), R(t50) and from the fat-free mass measured by DXA, assuming a hydration rate of 73.2%. The same protocol and calculations were also carried out on a 2nd group of 21 subjects for independent validation. Data of the 1st group showed that values of R(t50), not significantly different from those of R(infinity), could be obtained by dividing R(50) by 1.231 in men and by 1.224 in women. Applying this method to the 2nd group yielded also values of R(t50) not significantly different from R(infinity). TBW volumes V(t50) obtained from R(t50) were not significantly different from those of our modified BIS method V(tn), or from TBW volumes obtained from DXA in both groups. A comparison with three BIA methods of TBW determination showed that our new method gave results in better agreement with TBW from DXA and from our modified BIS method.

Total body water estimations in healthy men and women using bioimpedance spectroscopy: a deuterium oxide comparison

Background

Total body water (TBW) estimations have been used to estimate body composition, particularly fat-free mass, to aid in nutritional interventions, and to monitor hydration status. In the past, bioimpedance spectroscopy (BIS) devices have been used to estimate TBW. Previous investigations have examined the validity of the XiTRON 4000B (XiTRON Technologies) BIS device for estimating TBW. Recently, a new BIS device (Imp™ SFB7) has become available, claiming greater precision when estimating TBW. The Imp™ SFB7 (SFB7) is based on similar BIS principles, while offering increased portability and a greater range of frequencies when compared to older devices, such as the XiTRON 4000B (4000B). The purpose of this study was to examine the validity of the SFB7 for estimating total body water in healthy college-age men and women compared to the 4000B and deuterium oxide (D₂O).

Methods

Twenty-eight Caucasian men and women (14 men, 14 women; 24 ± 4 yrs; 174.6 ± 8.7 cm; 72.80 ± 17.58 kg) had their TBW estimated by the SFB7, the 4000B, and D₂O.

Results

Both BIS devices produced similar standard error of estimate (SEE) and r values (SFB7, SEE = 2.12L, r = 0.98; 4000B, SEE = 2.99L, r = 0.96) when compared to D₂O, though a significant constant error (CE) was detected for the 4000B (2.26L, p ≤ 0.025). The 4000B produced a larger total error (TE) and CE (TE = 3.81L, CE = 2.26L) when compared to the SFB7 (TE = 2.21L, CE = -0.09L). Additionally, the limits of agreement were larger for the 4000B (-3.88 to 8.39L) than the SFB7 (-4.50 to 4.31L). These results were consistent when sex was analyzed separately, though women produced lower SEE and TE values for both devices.

Conclusion

The 4000B and SFB7 are valid BIS devices when compared to D₂O to estimate TBW in college-age Caucasian men and women. Furthermore, the new SFB7 device displayed greater precision in comparison to the 4000B, which may decrease the error when estimating TBW on an individual basis.

Accuracy of bioelectrical impedance consumer devices for measurement of body composition in comparison to whole body magnetic resonance imaging and dual X-ray absorptiometry

OBJECTIVE

To compare body composition determined by bioelectrical impedance (BIA) consumer devices against criterion estimates determined by whole body magnetic resonance imaging (MRI) and dual energy X-ray absorptiometry (DXA) in healthy normal weight, overweight and obese adults.

METHODS

In 106 adults (54 females, 52 males, age 54.2 +/- 16.1 years, BMI 25.8 +/- 4.4 kg/m(2)) fat mass (FM), skeletal muscle mass (SM), total body bone-free lean mass (TBBLM), and level of visceral fat mass (VF) were estimated by 3 single-frequency bipedal (foot-to-foot) and one tretrapolar BIA device, and compared to body composition measured by MRI and DXA. Bland-Altman and simple linear regression analyses were used to determine agreement between methods.

RESULTS

%FMDXA, SMMRI or TBBLMDXA showed good relative and absolute agreement with two bipolar and one tetrapolar instrument (r(2) = 0.92-0.96; all p < 0.001; mean bias <1.5 %FM and <1 kg SM or TBBLM) and less relative and absolute agreement for another bipolar device (r(2) = 0.82 and 0.84, mean bias approximately 3 %FM and approximately 3 kg SM). The 95% limits of agreement (bias +/- 2 SD) were narrowest for the tetrapolar device (-6.59 to 4.61 %FM and -4.62 to 4.74 kg SM) and widest for bipolar instruments (up to -14.54 to 8.58 %FM and -9.52 to 3.92 kg SM). Systematic biases for %FM were found for all bipedal devices, but not for the tetrapolar instrument.

CONCLUSION

Because of the lower agreement between foot-to-foot BIA and DXA or MRI for the assessment of body composition in individuals, tetrapolar electrode arrangement should be preferred for individual or public use. Bipolar devices provide accurate results for field studies with group estimation.

Hydration of exercised standardbred racehorses assessed noninvasively using multi-frequency bioelectrical impedance analysis

REASONS FOR PERFORMING STUDY

In human and animal clinical practice, multi-frequency bioelectrical impedance analysis (MF-BIA) is increasingly used as a diagnostic tool to assess hydration of intra-and extracellular fluid compartments. Accurate determination of changes in hydration status within individuals over time has remained problematic due to the requirement for complete impedance-frequency relationships at the time points of interest.

OBJECTIVES

To use MF-BIA in 13 Standardbred racehorses and 7 'endurance' research horses to determine if MF-BIA could be used to track changes in total body water (TBW), intracellular fluid volume (ICFV) and extracellular fluid volume (ECFV) resulting from exercise.

METHODS

Jugular venous blood was sampled at rest and for 2-13 h following exercise. TBW, ECFV and plasma volume (PV) were measured at rest using indicator dilution techniques (D2O, thiocyanate and Evans Blue, respectively). TBW, ECFV, ICFV and PV were correlated to impedance measures and predictive equations used to determine hydration status from MF-BIA measures.

RESULTS

TBW loss continued throughout the recovery period, and was primarily borne by the ECF compartment at 90 min of recovery.

CONCLUSIONS

MF-BIA predictions of compartmental hydration status were significantly correlated to measured/calculated decreases in these compartments.

POTENTIAL RELEVANCE

Practical applications for MF-BIA in horses include monitoring of hydration status during transport and competition, assessment of body compostion, clinical health assessment and critical care management.

Use of bioelectrical impedance analysis in the evaluation, treatment, and prevention of overweight and obesity

PURPOSE

To present an overview of bioelectrical impedance analysis (BIA) and to familiarize nurse practitioners (NPs) with the potential benefits of using BIA in prevention, monitoring, and long-term follow-up of healthy individuals and those with chronic conditions (e.g., obesity).

DATA SOURCES

Original research articles and comprehensive review articles identified through Medline, CINAHL, OVID, and electrical engineering databases.

CONCLUSIONS

Obtaining serial measurements of percent body fat using BIA can identify patients at greatest health risk and gives NPs an additional tool to assess treatment response in patients seeking to lose or maintain body weight and/or increase muscle mass.

IMPLICATIONS FOR PRACTICE

Traditionally, height/weight tables and body mass index have been used to assess body composition and diagnose overweight and obesity. More recently, BIA has emerged as a portable and simple-to-operate instrument to evaluate body composition in the clinical setting.

Bioelectrical impedance vs. four-compartment model to assess body fat change in overweight adults

OBJECTIVE

The Tanita TBF-305 body fat analyzer is marketed for home and clinical use and is based on the principles of leg-to-leg bioelectrical impedance analysis (BIA). Few studies have investigated the ability of leg-to-leg BIA to detect change in percentage fat mass (%FM) over time. Our objective was to determine the ability of leg-to-leg BIA vs. the four-compartment (4C) model to detect small changes in %FM in overweight adults.

RESEARCH METHODS AND PROCEDURES

Thirty-eight overweight adults (BMI, 25.0 to 29.9 kg/m2; age, 18 to 44 years; 31 women) participated in a 6-month, randomized, double-blind, placebo-controlled study of a nutritional supplement. Body composition was measured at 0 and 6 months using the Tanita TBF-305 body fat analyzer [using equations derived by the manufacturer (%FM(T-Man)) and by Jebb et al. (%FM(T-Jebb))] and the 4C model (%FM(4C)).

RESULTS

Subjects in the experimental group lost 0.9%FM(4C) (p = 0.03), a loss that did not reach significance using leg-to-leg BIA (0.6%FM(T-Man), p = 0.151; 0.6%FM(T-Jebb), p = 0.144). We observed large standard deviations (SDs) in the mean difference in %FM between the 4C model and the Tanita(Manufacturer) (2.5%) and Tanita(Jebb) (2.2%). Ten subjects fell outside +/-1 SD of the mean differences at 0 and 6 months; those individuals were younger and shorter than those within +/-1 SD.

DISCUSSION

Leg-to-leg BIA performed reasonably well in predicting decreases in %FM in this group of overweight adults but resulted in wide SDs vs. %FM(4C) in individuals. Cross-sectional determinations of %FM of overweight individuals using leg-to-leg BIA should be interpreted with caution.

Total body water measurement by a modification of the bioimpedance spectroscopy method

We propose a method for calculating directly total body water (TBW) volumes (V (t)) from whole body resistance extrapolated at infinite frequency (R (infinity)) using a XITRON 4200 impedance meter. Mean TBW resistivities for men and women were determined from measurements of R (infinity) and fat-free mass (FFM(d)) measured by DXA in 58 healthy subjects assuming an average hydration coefficient of 73.2%. Mean differences between V (t) measured by our new method and those deduced from DXA data were +0.11 +/- 1.61 L for women and +0.13 +/- 2.16 L for men. For validation, this method was tested with the same resistivities against a 2nd group of 16 volunteers and the mean difference between V (t) from impedance and DXA was -0.80 +/- 1.43 L. Since the resistance at 50 kHz (R (50)) was found to be equal, in average, to 1.230 R (infinity) for men and 1.223 R (infinity) for women, this method can also be applied at 50 kHz with a similar accuracy by estimating R (infinity) from R (50). When our new method was applied to the monitoring of water loss during 28 dialysis runs performed on 13 patients, it predicted a mean water loss equal to 94% of ultrafiltered volume.

Determination of Cole parameters in multiple frequency bioelectrical impedance analysis using only the measurement of impedances

Conventional bioimpedance spectrometers measure resistance and reactance over a range of frequencies and, by application of a mathematical model for an equivalent circuit (the Cole model), estimate resistance at zero and infinite frequencies. Fitting of the experimental data to the model is accomplished by iterative, nonlinear curve fitting. An alternative fitting method is described that uses only the magnitude of the measured impedances at four selected frequencies. The two methods showed excellent agreement when compared using data obtained both from measurements of equivalent circuits and of humans. These results suggest that operational equivalence to a technically complex, frequency-scanning, phase-sensitive BIS analyser could be achieved from a simple four-frequency, impedance-only analyser.

Development of methods for body composition studies

This review is focused on experimental methods for determination of the composition of the human body, its organs and tissues. It summarizes the development and current status of fat determinations from body density, total body water determinations through the dilution technique, whole and partial body potassium measurements for body cell mass estimates, in vivo neutron activation analysis for body protein measurements, dual-energy absorptiometry (DEXA), computed tomography (CT) and magnetic resonance imaging (MRI, fMRI) and spectroscopy (MRS) for body composition studies on tissue and organ levels, as well as single- and multiple-frequency bioimpedance (BIA) and anthropometry as simple easily available methods. Methods for trace element analysis in vivo are also described. Using this wide range of measurement methods, together with gradually improved body composition models, it is now possible to quantify a number of body components and follow their changes in health and disease.

Body composition measurement in severe obesity

PURPOSE OF REVIEW

Severe obesity is accompanied by large increases in fat mass and alterations in the composition of fat free mass, in particular total body water and its extracellular compartment. The physical size limitations imposed by severe obesity, and variations in body composition from that of normal weight, pose tremendous challenges to the measurement of body composition. This review focuses on some of the methodological and practical issues associated with the use of common body composition methods, and identifies available published information on feasible methods for use in the severely obese.

RECENT FINDINGS

There is little published research regarding what body composition methods can be used with confidence in the severely obese populations. A simple three-compartment model combining measurements of body density by air displacement plethysmography and total body water by bio-electrical impedance can provide measurements of percentage body fat in the severely obese that are comparable with a traditional, highly technical three-compartment model requiring facilities such as isotope ratio mass spectrometry along with a substantial technical expertise.

SUMMARY

This review highlights some of the basic challenges faced by researchers and clinicians when conducting body composition assessments in severely obese patients. A simple three-compartment model that is accurate and easy to perform appears to be promising for use in this population. Further research is needed, however, on this and other feasible methods of body composition assessment in a diverse group of severely obese people.

Bioelectrical impedance analysis in clinical practice: a new perspective on its use beyond body composition equations

PURPOSE OF REVIEW

The bioelectrical impedance analysis is not a direct method for estimating body composition. Its accuracy depends on regression equations, and recent papers have suggested that this approach should not be used in several clinical situations. Another option is to obtain information about the electrical properties of tissues by using raw bioelectrical impedance measurements, resistance and reactance. They can be expressed as a ratio (phase angle) or as a plot (bioelectrical impedance vector analysis). This review describes their use in clinical practice.

RECENT FINDINGS

The phase angle changes with sex and age. It is described as a prognostic tool in many clinical situations. There are some controversies about considering it as a nutritional marker. Studies in burn victims and sickle-cell disease corroborate its ability to evaluate cell membrane function. Bioelectrical impedance vector analysis allows a semi-quantitative estimation of body composition from information from tissue hydration and soft-tissue mass in a plot. It can be used in healthy individuals or patients, for a population or individual evaluation of fluid imbalance or an assessment of soft-tissue mass. It has also been used as a prognostic tool in dialysis and cancer patients.

SUMMARY

The phase angle can be considered a global marker of health, and future studies are needed to prove its utility in intervention studies. Bioelectrical impedance vector analysis has increased its utility in clinical practice, even when the equations may be inaccurate for body composition analysis.

Limitations and validation of bioelectrical impedance analysis in morbidly obese patients

PURPOSE OF REVIEW

Several factors limit the use of bioelectrical impedance analysis as a valid predictor of the amount of body fat in morbidly obese individuals. The purpose of this review is to examine the theory and assumptions that may limit the use of bioelectrical impedance analysis in such individuals.

RECENT FINDINGS

There is currently insufficient validation of bioelectrical impedance analysis equations in obese individuals with body mass indices greater than 34 kg/m. Several factors limit the application of bioelectrical impedance analysis in morbidly obese individuals. Obese individuals have a relatively high amount of extracellular water and total body water, which may overestimate fat-free mass and underestimate fat mass. Central body fat will generally overestimate the percentage of fat-free mass and underestimate the percentage of fat mass in overweight and obese adults with the use of prediction formulas developed in normal weight individuals.

SUMMARY

A relatively increased amount of total body water and a relative increase in extracellular water will result in an underestimation of the percentage of body fat and an overestimation of fat-free mass in the morbid obesity state. A different body build disposition (mainly in those with severe abdominal obesity) will result in an overestimation of the percentage of body fat. New equations are needed to validate bioelectrical impedance analysis in morbidly obese patients.