Bio-impedance analysis for estimation of total body potassium,total body water,and fat-free mass in white,black, and Asian adults

Bio-impedance analysis (BIA) measurements have been used to predict components of body composition. Their validation is required for populations varying in race, sex, and age. In 371 Whites, 182 Blacks and 225 Asians, single-frequency BIA at 50 kHz (RJL-100) resistance and reactance measurements were correlated with same-day measurements of total body water (TBW) by THO dilution, total body potassium (TBK) by whole body ⁴⁰K counting, and fat-free mass (FFM) by dual-photon absorptiometry. BIA correlation coefficients with TBW, TBK, FFM, and fat varied by sex and race for all measured body composition components. The highest correlation was for FFM, and the lowest was for fat mass. Prediction equations were further improved by including age, stature, and weight for each of the study cohorts. The SEE for predictions were in the ranges of 5–6, 6–8, and 7–10% of measured FFM, TBW, and TBK, respectively. BIA was effective in predicting body composition when subjects are specified by age, sex, stature, weight, and race for subjects from 18 to 94 years of age. © 1995 Wiley-Liss, Inc.     

Proximal electrode placement improves the estimation of body composition in obese and lean elderly during segmental bioelectrical impedance analysis

Bioelectrical impedance analysis (BIA) is an affordable, non-invasive, easy-to-operate, and fast alternative method to assess body composition. However, BIA tends to overestimate the percent body fat (%BF) in lean elderly and underestimate %BF in obese elderly people. This study examined whether proximal electrode placement eliminates this problem. Forty-two elderly men and women (64–96 years) who had a wide range of BMI [22.4 ± 3.3 kg/m² (mean ± SD), range 16.8–33.9 kg/m²] and %BF (11.3–44.8%) participated in this study. Using ²H and ¹⁸O dilutions as the criterion for measuring total body water (TBW), we compared various BIA electrode placements; wrist-to-ankle, arm-to-arm, leg-to-leg, elbow-to-knee, five- and nine-segment models, and the combination of distal (wrists or ankles) and proximal (elbows or knees) electrodes. TBW was most strongly correlated with the square height divided by the impedance between the knees and elbows (H ²/Z _proximal; r = 0.965, P < 0.001). In the wrist-to-ankle, arm-to-arm, leg-to-leg, and five-segment models, we observed systematic errors associated with %BF (P < 0.05). After including the impedance ratio of the proximal to distal segments (P/D) as an independent variable, none of the BIA methods examined showed any systematic bias against %BF. In addition, all methods were able to estimate TBW more accurately (e.g., in the wrist-to-ankle model, from R ² = 0.90, SEE = 1.69 kg to R ² = 0.94, SEE = 1.30 kg). The results suggest that BIA using distal electrodes alone tends to overestimate TBW in obese and underestimate TBW in lean subjects, while proximal electrodes improve the accuracy of body composition measurements.     

Best method for estimating urea volume of distribution: comparison of single pool variable volume kinetic modeling measurements with bioimpedance and anthropometric methods

The urea volume of distribution (Vurea) is a key component of the Kt/V parameter calculated during urea kinetic modeling. The Vurea parameter has been approximated empirically using total body water (TBW) estimates derived from anthropometric formulas or measured by bioelectric impedance analysis (BIA). The author compared TBW values derived using various anthropometric formulas (Watson, Hume, Randall, Tzamaloukas, Chertow) and BIA to the Vurea parameter calculated using three point variable volume single pool urea kinetic modeling. A total of 127 chronic hemodialysis patients were studied (mean age 66 +/- 13 years; 42% female; 37% black; 47% diabetic). Agreement between anthropometric formulas, BIA, and Vurea values was assessed by linear regression and Bland Altman analyses. The closest correlations were obtained with the BIA (r = 0.972), Chertow (r = 0.917), and Tzamaloukas (r = 0.905) methods. When compared with Vurea, 95% confidence intervals by Bland Altman analysis were lowest with BIA (4L) and highest with the Watson method (8L). These results indicate that BIA best approximates Vurea in dialysis patients.     

Body composition in urban South Asian women; development of a bioelectrical impedance analysis prediction equation

Abstract

Background: Assessment of body composition plays a significant role in combating chronic disease among South Asians. Accurate assessment of body composition by bioelectrical impedance analysis (BIA) requires population-specific equations which are currently unavailable for urban South Asian women.

Aim: To assess validity of direct BIA assessment and selected equations for prediction of total body water (TBW), against Deuterium (²H₂O) dilution and develop and validate a population-specific TBW equation for urban South Asian women.

Subjects and method: Data of 80 urban Sri Lankan women (30–45 years) were used for this analysis. Body composition was assessed by ²H₂O dilution (reference) and BIA. Available BIA equations were assessed for validity. A new TBW equation was generated and validated.

Results: Direct BIA measurements and other equations did not meet validation criteria in predicting TBW. TBW by the new equation (TBW?=?3.443?+?0.342?×?(height²/impedance)?+?0.176?×?weight) correlated (p?<?0.001) with TBW by reference method. TBW using the new equation was not significantly different (25.30?±?2.4?kg) from the reference (25.32?±?2.7?kg).

Conclusion: Direct use of TBW by instrument and existing equations are less suitable for this population. The new TBW equation is suitable for body composition assessment in urban South Asian women.     

Estimation of total body water by bioelectrical impedance analysis in blacks

Several differences exist between the body composition of blacks and whites. This study was designed to investigate the applicability of bioelectrical impedance analysis (BIA) in blacks, using prediction equations developed in whites. A multiple regression equation developed on 79 white adults, using deuterium oxide dilution space total body water (D₂O-TBW) as the reference method, was prospectively applied to 88 blacks aged 19–50 years. Although the regression line of D₂O-TBW on BIA-TBW was not significantly different from the line of identity (r = 0.98, SEE = 1.71 liters), mean TBW was significantly underestimated by 0.84 liter. Other BIA equations from the literature also underestimated D₂O-TBW in blacks, except for an equation developed on a mixed black and white population. Multiple regression analysis on the data of the black and white subjects combined showed that race, offered as a separate independent variable, improved the correlation with D₂O-TBW slightly but significantly (P < 0.01). It was concluded that BIA may be valuable in the assessment of body composition in blacks as well as in whites. In this study a small underestimation of TBW occurred in blacks, using (BIA) equations from whites. This may be due to racial differences in body composition or to factors unrelated to ethnicity.     

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 impedancemeter 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.     

Determination of total body water by multifrequency bio-electric impedance: development of several models

Multifrequency bio-electronic impedance analysis (MF BIA) measurements are taken from a heterogeneous group of patients, varying in size between obese and slim. The measuring system uses four electrodes: two current and two potential electrodes. Three new models are developed to calculate total body water (TBW) from the BIA data, and the resulting TBW values are compared with TBW determined by D₂O dilution. The results demonstrate that the most simple model provides the best TBW values. For individual patients, TBW can be determined by means of bioimpedance measurement with an accuracy of 3 litres. In the most simple model (model 1), the body is electrically represented by a cylinder, and corrections are made for the amount of fat. This is an extension of the model used by Xitron. In the more advanced models (2 and 3), the body is represented by a cylinder for the trunk, and truncated cones represent the arms and legs. In model 2, ΔTBW amounts to 3 litres. It is shown that the resistance of the trunk is proportional to the square root of the length. In model 3, it is assumed that subcutaneous fat is a poor conductor if electric current. An equation is developed that describes the partition of subcutaneous fat, and the fat layer is then removed from the cones representing arms and legs and from the cylinder that models the trunk.     

Use of bioelectrical impedance in hydration status assessment: reliability of a new tool in psychophysiology research.

Adequate hydration is crucial in maintaining optimal physical and mental functioning and the need for a fast and reliable hydration status assessment in behavioral medicine research has become increasingly important. The goal of this study was to determine the reliability of bioelectrical impedance assessment (BIA) in assessing total body water (TBW), extracellular water (ECW) and intracellular water (ICW) and to assess whether individuals can be reliably classified as being hypohydrated or hyperhydrated using lower and upper quartiles, respectively. TBW, ECW and ICW were assessed via BIA (Bodystat, Isle of Man, UK) in 52 male and 48 female college students on 2 separate days within 1 week. Results revealed strong test-retest reliability for TBW (r=0.983), ECW (r=0.972) and ICW (r=0.988) (all P's<0.001). Following the initial and follow-up assessments, participants were then classified as being either hypohydrated or hyperhydrated based on the percentage of body weight accounted for by TBW. Test-retest reliability of hydration status within classifications was then assessed by gender. Test-retest reliability was found for TBW, ECW and ICW among hypohydrated (r=0.985, r=0.972 and r=0.99, respectively) and hyperhydrated (r=0.994, r=0.989 and r=0.994, respectively) males (all P's<0.001). Significant test-retest correlations were also found for females classified as being hypohydrated (r=0.97, r=0.956 and r=0.976, respectively) and hyperhydrated (r=0.973, r=0.976 and r=0.976, respectively) (all P's<0.001). These findings suggest that hydration status, as indexed by bioelectrical impedance technique, is reliable across time and is also reliable within individuals who are chronically hyperhydrated or hypohydrated.     

Bias and limits of agreement between hydrodensitometry, bioelectrical impedance and skinfold calipers measures of percentage body fat

Previous research has often used correlations as a statistical method to show agreement; however, this is not a valid use of the statistic. The purpose of this study was to investigate the bias and limits of agreement for three methods of estimating percentage body fat for 117 male and 114 female university athletes: hydrodensitometry (HYD), bioelectrical impedance (BIA) and skinfold calipers (SKF). The mean (SD) percentage body fat for males as assessed by HYD, BIA and SKF methods, respectively, were 13.2 (3.3)%, 14.1 (3.3)% and 13.0 (3.2)%. Female body fat measurements were 22.5 (3.9)%, 23.7 (4.3)% and 23.8 (4.2)%, respectively. Pearson product moment correlations for male and female body fat percentages between the three methods were high, ranging from 0.81 to 0.86 (P < 0.05). However, compared to the criterion measure of body fat percentage (HYD), the magnitude of agreement BIA and SKF revealed a different pattern. The mean absolute difference between HYD and BIA measurements of body fat for males was −0.8 (2.0)% fat, and between HYD and SKF was it was 0.2 (1.7)% fat. The mean absolute difference for females between HYD and BIA was −1.2 (2.5)%; for HYD and SKF it was −1.4 (2.2)%. Compared to the HYD measures for males and females, the BIA and SKF measures were as much as a 3.8% underestimation and a 6.2% overestimation of body fat. This study provides evidence that the strength of a correlation does not indicate agreement between two methods. In future, reliability and validity studies should examine the absolute differences between two variables and calculate limits of agreement around which a practitioner can appreciate the precision of the methodologies. Accepted: 26 August 1997     

Is bioelectrical impedance spectroscopy accurate in estimating total body water and its compartments in elite athletes?

Background: Bioelectrical impedance spectroscopy (BIS) provides an affordable assessment of the body's various water compartments: total body water (TBW), extracellular water (ECW) and intracellular water (ICW). However, little is known of its validity in athletes.

Aim: To validate TBW, ECW and ICW by BIS in elite male and female Portuguese athletes using dilution techniques (i.e. deuterium and bromide dilution) as criterion methods.

Subjects and methods: Sixty-two athletes (18.5 ± 4.1 years) had TBW, ECW and ICW assessed by BIS during their respective pre-season.

Results: BIS significantly under-estimated TBW by 1.0 ± 1.7 kg and ICW by 0.9 ± 1.9 kg in relation to the criterion methods, with no differences observed for ECW. The values for the concordance correlation coefficient were 0.98 for TBW and ECW and 0.95 for ICW. Bland-Altman analyses revealed no bias for the various water compartments, with the 95% confidence intervals ranging from ? 4.8 to 2.6 kg for TBW, ? 1.5 to 1.6 kg for ECW and ? 4.5 to 2.7 kg for ICW.

Conclusions: Overall, these findings demonstrate the validity of BIS as a valid tool in the assessment of TBW and its compartments in both male and female athletes.     

Prediction of total body water and fatness from anthropometry: Importance of skinfold measurements

Prediction equations for total body water (TBW) generally use weight and height as predictors, but their ability may be limited because they implicitly assume a constancy of TBW among individuals of similar body size. The objective of this study was to evaluate the relative importance of anthropometric dimensions in predicting TBW and body composition. TBW determined by doubly labeled water (DLW) dilution techniques was used as the frame of reference in 23 healthy Aymara subjects, 4–65 years, in a rural community of the Bolivian Andes. Predictive performances of anthropometric variables for TBW were examined with multiple regression analyses. The generated equations were tested for cross-validity, using published data for U.S. adults. The resulting errors were compared with those of the published prediction equations of Mellits and Cheek (M&C) and Durnin and Womersley (D&W). The simplified prediction equation using weight and the triceps skinfold (Eq-A1:R² = 0.989, SEE = 1.041 L) and that using weight and the triceps and subscapular skinfolds (Eq-A2: R² = 0.990, SEE = 1.020 L) had better R² and smaller SEE than those using any combination of variables, weight, height, age, and sex. In the cross-validation sample, Eq-A1 and Eq-A2 demonstrated higher precision than the D&W and M&C equations. Evaluated by the method of Bland and Altman (mean difference ± 2SD), prediction errors for fat mass and fat percent were 0.2 ± 2.8 kg and 0.4 ± 5.2% in Eq-A2, 1.1 ± 3.5 kg, and 1.8 ± 6.1% in Eq-A1, −2.4 ± 3.6 kg and −3.4 ± 5.1% in D&W, and −2.3 ± 7.6 kg and −2.6 ± 10.3% in M&C. Significant underestimation of fat mass and sex differences in the biases were observed with D&W and M&C (P < 0.05), but not with Eq-A2. By including skinfold measurements, a single prediction equation for TBW was valid for males and females across different population samples. © 1996 Wiley-Liss, Inc.     

Total body water and the exchangeable hydrogen. II. A review of comparative data from animals based on isotope dilution and desiccation, with a report of new data from the rat.

Total body water (TBW) determination by tritium space could be factitiously elevated by exchangeable H+ contained within water-soluble chemical configurations. Should this nonaqueous (molecular) exchangeable H+ turn out to be a large fraction of total exchangeable H+, TBW measurement by tritiated water (THO) dilution would display a systematic upward and non-random error. TBW was measured by THO dilution and subsequently by total body desiccation in 21 rats (weight 227+/-83 g, mean+/-SD). TBW was 71.38+/-2.4% by THO dilution and 70.20+/-1.5% by body desiccation. Analysis of variance of TBW vs. body weight showed a highly significant correlation both with desiccation (P less than 0.0005, r=-0.78) and dilution (P less than 0.03, r= -0.50). Convariance analysis of both methods showed no difference in slope (P greater than 0.9). There was a difference in variance (P less than 0.001) and means (P less than 0.03). Tritium space is 1.2% of body weight larger than TBW measured by desiccation. TBW measured by THO dilution gives a 1.71% overestimation of TBW as measured by desiccation. TBW measurement by THO dilution is accurate within less than 2% error. These findings have particular significance in the light of our theoretical model of the total nonaqueous exchangeable H+ in fat, protein, and carbodhydrate in the living vertebrate.     

Error analysis of the quantification of hepatic perfusion using a dual-input single-compartment model

We performed an error analysis of the quantification of liver perfusion from dynamic contrast-enhanced computed tomography (DCE-CT) data using a dual-input single-compartment model for various disease severities, based on computer simulations. In the simulations, the time-density curves (TDCs) in the liver were generated from an actually measured arterial input function using a theoretical equation describing the kinetic behavior of the contrast agent (CA) in the liver. The rate constants for the transfer of CA from the hepatic artery to the liver (K(1a)), from the portal vein to the liver (K(1p)), and from the liver to the plasma (k(2)) were estimated from simulated TDCs with various plasma volumes (V(0)s). To investigate the effect of the shapes of input functions, the original arterial and portal-venous input functions were stretched in the time direction by factors of 2, 3 and 4 (stretching factors). The above parameters were estimated with the linear least-squares (LLSQ) and nonlinear least-squares (NLSQ) methods, and the root mean square errors (RMSEs) between the true and estimated values were calculated. Sensitivity and identifiability analyses were also performed. The RMSE of V(0) was the smallest, followed by those of K(1a), k(2) and K(1p) in an increasing order. The RMSEs of K(1a), K(1p) and k(2) increased with increasing V(0), while that of V(0) tended to decrease. The stretching factor also affected parameter estimation in both methods. The LLSQ method estimated the above parameters faster and with smaller variations than the NLSQ method. Sensitivity analysis showed that the magnitude of the sensitivity function of V(0) was the greatest, followed by those of K(1a), K(1p) and k(2) in a decreasing order, while the variance of V(0) obtained from the covariance matrices was the smallest, followed by those of K(1a), K(1p) and k(2) in an increasing order. The magnitude of the sensitivity function and the variance increased and decreased, respectively, with increasing disease severity and decreased and increased, respectively, with increasing stretching factor except for V(0). Identifiability analysis showed that the identifiability between K(1)(p) and k(2) was lower than that between K(1)(a) and k(2) or between K(1a) and K(1p). In conclusion, this study will be useful for understanding the accuracy and reliability of the quantitative measurement of liver perfusion using a dual-input single-compartment model and DCE-CT data.     

Bioelectrical impedance analysis in dialysis patients

Identification of malnutrition is imperative in chronic dialysis patients. Bioelectrical impedance (BIA) is a noninvasive method to measure body composition and estimate total body water (TBW), lean body mass (LBM) and body cell mass (BCM). Studies suggest BIA has good reliability as compared to other accepted methods of body composition analysis. Preliminary data also suggest that BIA-derived parameters (reactance and phase angle) predict clinical outcome in chronic hemodialysis patients. Overall, BIA is a promising nutritional assessment tool to monitor health status, long-term follow-up, tailor nutrition support, and detect early subtle losses of LBM in chronic dialysis patients.     

Validation of different bioimpedance analyzers for predicting cell mass against whole-body counting of potassium (40K) as a reference method.

This study compared two different tetrapolar bioimpedance (BIA) devices for estimating body cell mass (BCM), validated them against whole-body counting of (40)K (TBK method), and developed improved prediction equations for estimating BCM from BIA. In 50 healthy volunteers (age 23-65 years, BMI 18.6-27.7 kg/m(2)), BCM was estimated with the BIA devices Nutriguard-M (Data Input, Germany) and Soft-Tissue-Analyzer-STA (Akern, Italy) and by the TBK method. Methods were compared by the Bland-Altman procedure. New prediction equations for BCM were developed by multiple stepwise regression analysis based on a single BIA parallel model. The Akern device gives similar mean estimates of BCM compared to the Data Input device in males (33.5 vs. 33.3 kg, P = 0.789), but higher values in females (24.6 vs. 22.8 kg; P < 0.001). Both BIA devices overestimate mean BCM relative to the TBK method; in males by 5.0 kg (Data Input, P < 0.001) and 5.1 kg (Akern, P < 0.001); in females by 2.3 kg (Data Input, P < 0.001) and 4.1 kg (Akern, P < 0.001). Limits of agreement between BIA and TBK methods are for males +/-4.99 kg (Data Input) and +/-7.16 kg (Akern); for females, +/-4.69 kg (Data Input) and +/-4.12 kg (Akern). New equations were developed for estimating BCM for both BIA analyzers (Data Input, R(2) = 0.91, SEE = 1.46 kg; Akern, R(2) = 0.90, SEE = 1.48 kg). Since estimates of BCM by the present BIA devices do not differ in males, they might be interchangeable. This does not hold true for females. Because both BIA devices overestimate BCM, the newly developed device-specific equations which reduce bias and limits of agreement should be applied.     

Comparison of D2O and ethanol dilutions in total body water measurements in humans

Total body water was measured by ethanol dilution and D₂O stable isotope dilution in a group of 20 healthy volunteers (5 females and 15 males), predominantly 23- to 31-year-old students. Both indicator substances were given orally with an ethanol burden of 0.8 g/kg body weight and a D₂O burden of 0.1 g/kg body weight after 12-h food and fluid restriction. This first direct comparison of total body water (TBW) from ethanol and D₂O dilutions revealed the ethanol compartments to be smaller than those of D₂O. The quotient of TBW (ethanol)/TBW (D₂O) was 97.7% , which is the order of the quotient TBW (H₂ ¹⁸O)/TBW (D₂O) (=97%), well known from the literature and taken to represent relatively exactly the value of TBW overestimation (based on H/D exchange for acid protons) following D₂O dilution [36]. Thus the value of TBW (ethanol) is almost identical to that of H₂ ¹⁸O, which provides direct evidence that ethanol is distributed only in the body water.Abbreviations TBW total body water - BIW water content in whole blood - GC gas chromatography     

Growth of the pig: changes in body weight and body fluid compartments.

Body weight and the rate of change in TBW, ECW, and ICW were measured in 252 anesthetized pigs during the first 12 weeks after birth. After TBW was measured with 3H2O, 55 of the pigs were killed and TBW measured by desiccation. 3H2O overestimated TBW by 6.5% of body weight and 4.9% of fat-free wet weight, compared to desiccation (P less than 0.001); mean figures for 3H2O were 78.6 +/- 1.02% of body weight, and for desiccation, 72.1 +/- 0.45%; on a FFWW basis, 88.6 +/- 0.94% for 3H2O, and 83.7 +/- 0.13% for desiccation. TBW decreased significantly from 85.0% of body weight at birth (1.5 dg) to 75% at 5 kg (day 28) at a rate of ---3.2% body wt/kg body wt (P less than 0.001 from a zero rate). After that the rate of decrease was not different from zero: --0.117% body wt/kg body wt. ECW decreased significantly from 48% at birth to 35% at day 28 at a rate of --3.802% body wt/kg body wt (P less than 0.001 from a zero rate), and after day 28 the rate of decrease was not different from zero (--0.149% body wt/kg body wt) through week 12. ICW decreased, but not significantly, at a rate of --0.099% body wt/kg body wt. The changes in the rate of decrease in TBW and ECW coincided with weaning, and it was speculated that there was a direct relationship between the two events.     

Lower-limb and whole-body tissue composition assessment in healthy active older women

AIM: The study evaluated, in active elderly women, the accuracy and bias of anthropometry and bioelectrical impedance analysis (BIA) for lower-limb and whole-body tissue composition measures using dual-energy X-ray absorptiometry (DXA) as the criterion method. METHODS: Nineteen individuals (66.1 +/- 4.2 years) participated in the study. Whole-body fat mass (FM) and fat-free mass (FFM) were measured by anthropometry, BIA and DXA. Lower-limb volume (LLV) and lower-limb FFM (LLFFM) were assessed by anthropometry and DXA. RESULTS: LLV and LLFFM were significantly overestimated by anthropometry vs. DXA (p < 0.05 and p < 0.001, respectively) but significant relationships were observed [coefficient of determination (R(2)) > 0.25, p < 0.05]. No significant difference was observed between FM(A) (where (A) stands for anthropometry) vs. FM(DXA) and FFM(A) vs. FFM(DXA) and significant relationships were observed [R(2) = 0.93, p < 0.001, coefficient of variation (CV) = 7.3%; and R(2) = 0.85, p < 0.001, CV = 4.4%, respectively]. No significant difference was observed between FM(BIA) and FM(DXA) and a significant relationship was observed (R(2) = 0.80, p < 0.001, CV = 11.6%). FFM was significantly underestimated by BIA vs. DXA (p < 0.01). CONCLUSIONS: In active elderly women, (i) compared with DXA, anthropometry overestimates LLV and LLFFM; (ii) anthropometry can be an accurate method for assessing whole-body composition; and (iii) despite a non-significant bias for the FM measurement, the BIA tends to overestimate FM and underestimate FFM.     

Hemodialysis (HD) versus peritoneal dialysis (PD): latent overhydration in PD patients?

Data on the difference in fluid status between hemodialysis (HD) and peritoneal dialysis (PD) patients are scarce. Bio-electrical impedance analysis (BIA) is able to detect total body water (TBW) and its distribution in intracellular (ICW) and extracellular water (ECW). Echographic determination of the diameter of the inferior caval vein (VCD) provides information about the intravascular space (IVS). Nineteen PD-patients and 20 HD-patients in stable clinical condition were studied. In HD-patients a significant decrease in VCD, mean arterial pressure (MAP), TBW and ECW was noted due to ultrafiltration. Both ratios of VCD to ICW/ECW and of VCD to ECW/TBW decreased. No significant differences were found in these variables between PD-patients and HD-patients before HD. In both patient groups the measured variables pointed towards overhydration and the increased ratios both of VCD to ICW/ECW and VCD to ECW/TBW towards the storage of surplus of fluid in the intravascular space. It can be concluded that both PD-patients and HD-patients before HD have a surplus of fluid in the extracellular compartment, predominantly stored in the intravascular space.     

Total body water,extracellular water,plasma volume,and total body potassium in cirrhosis of the liver

Summary Extracellular water (EWC; 82-bromide), total body water (TBW; 3-THO), intracellular water (ICW=TBW-ECW), plasma volume (PV; 51-Cr), and total body potassium (TBK; 40-K) were studied in patients with cirrhosis of the liver (n=12) and in controls (n=12). ECW (39%), TBW (28%), ICW (19%), and PV (24%) increased, TBK (28%) however, decreased in cirrhosis. The results indicate that it is less the lean body mass, but rather the intracellular potassium concentration that is lowered (cirrhosis: 84±21 mmol/l ICW; controls: 115±23 mmol/l ICW). Decreased potassium per cell (mmol) and increased intracellular water are discussed as possible reasons for this. The correlation between TBK (%) and serum potassium (mmol/l) was found to ber=0.56 (p<0.002). Correlations between the biochemical parameters gamma-globulins, cholin esterase, serum sodium and serum albumin (g/l PV) and characteristic fluid disturbances in cirrhosis are highly significant whereas albumin (g/kg bodyweight) was the same in both groups. We can support the overflow theory of ascites formation [19].This paper is part of a medical doctorate of O. Schober