This article was downloaded by: [New York University] On: 13 May 2015, At: 15:59 Publisher: Routledge Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Journal of the American College of Nutrition Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/uacn20
Predicting total body water and extracellular fluid volumes from bioelectrical measurements of the human body. a
a
a
H L Johnson , S P Virk , P Mayclin & T Barbieri
a
a
US Department of Agriculture, Western Human Nutrition Research Center, Presidio of San Francisco, CA 94129. Published online: 02 Sep 2013.
To cite this article: H L Johnson, S P Virk, P Mayclin & T Barbieri (1992) Predicting total body water and extracellular fluid volumes from bioelectrical measurements of the human body., Journal of the American College of Nutrition, 11:5, 539-547, DOI: 10.1080/07315724.1992.10718259 To link to this article: http://dx.doi.org/10.1080/07315724.1992.10718259
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
Predicting Total Body Water and Extracellular Fluid Volumes From Bioelectrical Measurements of the Human Body Herman L. Johnson, PhD, FACN, Satinder P.S. Virk, DVM, Patrick Mayclin, AS, and Teresa Barbieri, MA US Department ofAgriculture, Western Human Nutrition Research Center, Presidio ofSan Francisco, CA
Downloaded by [New York University] at 15:59 13 May 2015
Key words: intracellular fluid volume, body composition methods, biological impedance, biological electrical conductivity, deuterium dilutional volume, bromide space, body hydration status Two biological impedance analyzers, a 50 kHz (RJL) and 20-100 kHz (BMA) instrument, and a total body electrical conductivity (TOBEC) instrument were used to estimate total body water (TBW), extracellular (ECF) and intracellular (ICF)fluidvolumes by repeated measurements of 16 normal men (19-38 years old) to assess which, if any, would provide the best estimates. At 3-week intervals, TBW was determined by deuterium dilution, ECF by bromide dilution, ICF by difference (TBW-ECF) and lean body mass by density. Prediction equations were obtained by regression; predicted values for the body fluid volumes were calculated and the results were statistically evaluated. Both the TOBEC and the BMA provided rapid and reliable estimates for body fluid volumes with standard errors of the estimates of about 0.5-1.1 L for ECF, 1.0-1.8 L for TBW, and 1.0-1.3 L for ICF. Part of the error was attributable to standard tracer-dilution methods. Abbreviations: ANOVA = analysis of variance, BMA = Berkeley Medical Instru ments' biological impedance analyzer, BMI = body mass index, Br = bromine, CI = confidence interval, Cl, Cm, Cu = conductivities of the lower, middle and upper body, respectively, D2O = deuterim oxide, ECF = extracellular fluid, FC0, FC1, FC2 = zero, first and second order Fourier coefficients of the TOBEC's phase average values, respectively, Ht = height, ICF = intracellular fluid, LBM = lean body mass, R = electrical resistance, 1/R = electrical conductivity, r = correlation coefficient, R2 = R squared or regression coefficient, RJL = RJL System's biological impedance analyzer, SEE = standard error of the estimate, TOBEC = total body electrical conductivity analyzer, TBW = total body water, Wt = weight, Xc = electrical reactance, Z = electrical impedance
INTRODUCTION
impedance was reduced. Evaluating the ECF-ICF components, as well as TBW, is important in monitoring many clinical and nutritional syndromes; however, the tracer-dilution reference methods are tedious, time consuming and variable. Bioelectrical analyzers, on the other hand, provide rapid and repeatable data related to the body's fluid space. This study was designed to examine how accurately the total body electri cal conductivity analyzer (TOBEC, model HA-2, DICKEY-John Co, Auburn, IL), RJL biological imped ance analyzer (RJL, model BIA-101, RJL Systems, Detroit, MI) and BMA biological impedance analyzer (BMA, model BMR-2000, Berkeley Medical Instruments, San
Newer methods for the assessment of human body composition are based on measurements of electrical impedance and conductivity [1-6]. These properties are related to the body's content of water and electrolytes, and have been used to estimate total body water (TBW) [1,3-6]. Thomasset [7,8] was the first to estimate fluid volumes with a bipolar whole-body impedance technique. Tedner [9] and Hoffer et al [10] reported that most of the current at frequencies < 10 kHz flowed through only extracellular fluid (ECF); but, at 50-100 kHz, both intra cellular fluid (ICF) and ECF conducted the current and
Address reprint requests to Herman L. Johnson, PhD, USDA/ARS/WHNRC, PO Box 29997, Presidio of San Francisco, CA 94129.
Journal of the American College of Nutrition, Vol. 11, No. 5, 539-547 (1992) Published by the American College of Nutrition 539
Body Fluids From Bioelectrical Values Leandro, CA) could measure these volumes compared to the aforementioned reference methods.
SUBJECTS AND METHODS
Downloaded by [New York University] at 15:59 13 May 2015
Subjects Sixteen normal male volunteers, 19-38 years old, com pleted three trials at 3-week intervals to permit the excre tion of tracers. Pertinent characteristics of the men are shown in Table 1. Weights (76.7 ± 13.6 kg, mean ± standard deviation) ranged from 52 to 107 kg while body mass indexes (BMI, weight in kg/height2 in m, 23.8 ± 2.7) and body fat contents (20.6 ± 6.5%) were typical of young adult males. The two men with >27% body fat (subjects 11 and 14) had relatively low BMI values while subject 9, with a BMI of 30.3, had 24.3% fat. Study design, proce dures and volunteer agreements were reviewed and ap proved by the Letterman Army Medical Center's (Presidio of San Francisco, CA) Human Use Committee and USDA Agriculture Research Services's (Beltsville, MD) Human Studies Review Committee. Protocol Subjects arrived at the laboratory after fasting overnight for at least 10 hours. Initial blood and urine samples for measuring baseline concentrations of the tracers were ob tained between 7:30 and 8 a.m. Blood was drawn without
stasis from a forearm vein. The men ingested 1.5 g of tracer solution (0.06 g NaBr and 0.15 g D 2 0) per kg of body weight between 8 and 8:30 a.m. This was followed by ingestion of distilled water rinses (total of 100-150 ml) of the container. The men fasted for the next 7 hours until measurements and samplings were completed. Urine pro duced during the first 3.5 hours was collected to correct for tracer loss during total body equilibration. Tracerdilutions were calculated from blood and urine samples collected at 4.5, 5.5 and 6.5 hours after tracer ingestion. Body Fluids Blood samples were centrifuged and the serums were used for bromide analysis by fluorescent excitation [1113]. ECF was calculated, by the method of Price et al [12], as 0.873 times the bromide dilutional space. Samples (1.5 ml) of the urine and oral tracer solutions were vacuum distilled and their deuterium concentrations were deter mined by infrared spectroscopy [14] for calculating TBW volumes. The correlations of variation for the bromide and deuterium analyses were between 1.3 and 1.6% de pending on the analyte concentrations. ICF was calculated as the difference between TBW and ECF. Bioelectrical properties of the body were measured with three commer cial analyzers and were used to estimate these volumes. TOBEC was measured at 2.5 mHz with a prototype instru ment and TBW was estimated using a published equation [4]. The body's electrical resistance (R) was measured with
Table 1. Characteristics of Male Subjects #
Age (yrs)
Ethnic group*
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Mean SD
28 29 33 21 21 38 18 32 19 36 26 33 28 33 33 36 29.1 6.3
C C C H B C C C C C A F B C F C
Subj
BMIt 21.08 22.47 20.79 20.23 23.81 25.81 23.92 26.16 30.31 24.08 20.93 23.32 24.87 22.80 23.37 27.37 23.832 2.66
Ht (cm) 182.3 180.2 179.1 161.2 187.3 182.0 178.1 195.1 187.7 169.5 173.8 171.4 184.3 181.3 172.1 176.1 178.84 8.19
% fat§
Wt (kg)
Meani
SD*
Mean
70.07 72.95 66.68 52.58 83.53 85.50 75.87 99.57 106.77 69.19 63.22 68.52 84.48 74.95 69.23 84.87
0.85 0.48 0.73 0.86 0.41 0.53 0.35 1.03 1.70 0.25 1.19 0.92 0.84 0.38 0.19 0.45
15.86 8.56 17.73 8.71 11.77 26.52 20.88 26.81 24.29 22.41 27.43 23.22 19.07 29.77 22.11 24.27
76.749
20.588
13.622
6.538
SD 1.82 1.07 0.13 0.13 2.59 1.16 0.91 0.94 2.10 0.72 1.00 0.36 0.48 0.76 1.17 0.65
* Caucasian, Hispanic, Black, Asian and Filipino. t Body mass index = kg/m2. φ Mean and standard deviation of values obtained at weeks 1, 4 and 7. § From underwater weighing.
540
VOL. 11, NO. 5
Body Fluids From Bioelectrical Values two instruments: the RJL introduced 800 μΑ of 50 kHz current to measure R and reactance (Xc) values (electrodes placed on right hand, wrist, ankle and foot) and the man ufacturer provided a provisional equation (TBW(L) = 0.616 Ht2/R) to estimate TBW; and the BMA (electrodes on both ankles and both wrists) provided conductivity (1/ R) values, scanning through 250 frequencies from 20 to 100 kHz, from the upper, middle and lower (Cu, Cm and Cl, respectively) body and estimates of ECF and ICF, derived from TBW". Only these three conductivities and estimates for body components were printed; the program and other data were considered proprietary by the manu facturer. For the RJL, impedance (Z) was calculated as Z = (R2 + Xc2)05.
Downloaded by [New York University] at 15:59 13 May 2015
Body Weights and Densities Body weights were obtained from an electronic balance with a sensitivity of 50 g and heights were recorded to the nearest mm from a wall-mounted steel ruler. Body density was obtained by underwater weighing [15] with the simul taneous measurement of residual lung volume [16]. At least three replicates of each measurement were made throughout the morning, between the fluid samplings. Body density was used to calculate lean body mass (LBM) using the Siri equation [17] and TBW was assumed to equal 0.732 times LBM [17]. Statistical Analyses Data were statistically analyzed by computer using SAS programs (SAS Institute, Cary, NC) and STATOOLS (Ger ard E. Dallai, Maiden, MA). Routines used included re peated measures analyses of variance (ANOVA), correla tions, stepwise regressions, and errors-in-variables regres sion. Initial equations to predict TBW, ECF and ICF were obtained using all the measured and calculated variables from the three analyzers so the statistical routine could select which of these analyzers would yield the best vari ables for the predictions. Then prediction equations were obtained for each instrument for comparisons among the instruments. Comparisons were made using predicted val ues from each of the equations and the errors-in-variables regression, a statistical routine that permits apportioning the variability to both the dependent and independent variables by setting a ratio for their magnitudes. This ratio was set at one for these analyses on the assumption that the magnitude of errors were similar. Structural analysis from errors-in-variables regression compares the changes in the dependent variable to the changes in the independ ent variable and minimizes the perpendicular distance of each point to the regression line. Evaluations are based upon the proximity of the slope to 1.00 indicating equiv* Personal communication with the manufacturer's representative.
aient changes in the two variables, the width of the 95% confidence interval (CI) reflecting the quantitative devia tions of the points from the line and the intercept that shows the amount of bias between the two measurements and/or predictions. Significance testing was done at the 5% level. Root mean squared error was used as the stand ard error of the estimate (SEE) in comparing regression equations.
RESULTS Data obtained from the reference methods for both fluids and LBM and the three bioelectrical analyzers are summarized in Table 2. Repeated measures ANOVA in dicated that none of the values changed significantly during the study; therefore, these values are averages over time. Only the bioelectrical variables which were directly meas ured or available from the bioelectric analyzers are pre sented. Correlation coefficients (r) between TBW, ECF and ICF values obtained from reference methods and manufac turer/literature algorithms are shown in Table 3. The r with deuterium derived TBW were similar for the three analyzers and density TBW values (0.92 to 0.96). The highest r among the TBW values was for TOBEC vs density, 0.97. Of the three bioelectric analyzers, only the BMA yielded values for ECF and ICF and the r of these values with the reference values were 0.87 and 0.86 for ECF and ICF, respectively. The r among the variables measured independently by the reference methods were 0.71 (ECF vs ICF), 0.89 (TBW vs ECF) and 0.95 (TBW vs ICF).
Table 2. Subjects' Directly Measured Variables Variable
Mean*
SD
Body weight (kg) D 2 0 TBW (L) B r ECF (L) ICF (by diff.) (L) LBM (kg) TOBEC measurements PhasAvg (mho) FCOf FC1 FC2 RJL measurements R (ohm) Xc (ohm) BMA conductivity measurements Cu (mho) Cm (mho) Cl (mho)
76.75 47.25 20.22 26.94 60.66
13.62 7.36 3.18 4.49 9.84
594.32 477.47 216.10 76.12
124.75 101.12 52.54 10.44
489.30 72.021
48.77 6.671
26.77 34.75 31.77
1.17 1.63 1.43
* Mean and standard deviation for 16 men. t Fourier coefficients of phase average data [4].
JOURNAL OF THE AMERICAN COLLEGE OF NUTRITION
541
Body Fluids From Bioelectncal Values Table 3. Correlations Among Weekly Values (16 Men, 3 Trials) Derived from Reference and Previously Established Methods Total body water TOBEC
Downloaded by [New York University] at 15:59 13 May 2015
D 2 0 TBW TOBEC TBW RJLTBW BMA TBW Density TBW BrECF BMA ECF Analyzed ICF (difference)
0.959
Extracell. fid.
Intracell. fid.
RJL
BMA
Density
BrDil
BMA
TBW-ECF
BMA
0.943 0.947
0.925 0.963 0.936
0.945 0.975 0.916 0.945
0.889 0.906 0.875 0.871 0.864
0.922 0.967 0.932 0.999 0.944 0.872
0.946 0.878 0.869 0.853 0.878 0.710 0.848
0.925 0.968 0.937 1.000 0.945 0.870 0.998 0.855
Since none of the measured variables changed signifi cantly during the study, mean values for each were used in regression analyses to develop the prediction equations shown in Table 4. The adjusted R 2 with bioelectric values for TBW, ECF and ICF ranged from 0.89 to 0.99. The SEE for the equations from bioelectncal analyzers variables ranged from 0.6 to 1.8 L for TBW, 0.5 to 1.1 L for ECF and 0.9 to 1.3 L for ICF. When variables from all the instruments were included in the regression, only TOBEC and BMA variables were used and the adjusted R 2 and SEE were improved compared to individual analyzer equa tions. Equations based on RJL variables had largest SEE and lowest adjusted R2. These prediction equations were used to calculate body fluid values for each trial, and the data were analyzed by
correlation and errors-in-variables analyses. The r with deuterium oxide (D 2 0) TBW were 0.89-0.96 for ECF and 0.94-0.96 for ICF whether determined or predicted (Table 5). Correlations with bromine (Br) ECF were 0.86-0.89 for TBW, 0.71 for analyzed ICF and 0.83-0.88 for pre dicted ICF. The r with the analyzed (by difference) ICF were TOBEC TBW 0.91, D 2 0 TBW 0.95, RJL TBW 0.90, BMA TBW 0.90, Br ECF 0.71 and all other ECF 0.850.88. Correlations among the predicted values for TBW, ECF and ICF within each of the analyzers were 0.96-0.99 (TOBEC), 0.90-0.99 (RJL) and 0.96-0.99 (BMA). Errors-in-variables analyses of the weekly data for these men (Table 6) depicts the slopes, their 95% CI and the intercepts for the structural relations. None of the 95% CI among the original estimations for TBW encompasses
Table 4. Prediction of Body Fluid Volumes (L) Using Values From Three Bioelectrical Analyzers and Regression Equations Fluid
SEE
Adj. R2
TBW
0.647
0.9923
ECF ICF
0.476 0.871
0.9776 0.9603
TBW ECF ICF
1.104 0.534 1.187
0.9775 0.9719 0.9263
Using TOBEC variables 24.327 + .02134HtFCl05 - 3.81013FC205 16.164 - 1.64948FC205 + .03090PhasAvg 1.784 + .00904HtPhaseAvg05 - 0.18648FC2
TBW ECF ICF
1.017 0.662 1.002
0.9809 0.9568 0.9475
Using BMA variables -95.815 + 0.48385Ht + .01154(Cu + Cm)2 + 5314.7WtHr2 -20.607 + 0.18314Wt + .00988Cm2 + 2.62243C105 -61.513 + 0.33580Ht + .00749(Cu + Cm)2
TBW ECF ICF
1.819 1.065 1.265
0.9389 0.8880 0.9162
Using RJL variables -31.766 + 0.81372ZHt2 + 0.21839Xc + 8.374ZWtHr2 0.291 +0.11787Wt + 0.1631Ht2R-' -34.752 + 45.1081 lHtZ 05 + .30879Ht - 1.47523RXC"1
Prediction equation* Using variables from all instruments -12.613 + .01149HtPhasAvg05 + .00907(Cu + Cm)2 - 0.16112FC2 - .01023Cm2 25.180 + .03331FC0 - 2.6046FC205 + .0000036Wt3 -71.208 + .00888HtPhasAvg05 - .0000097Wt3 + 12.42297Cu05
' See Table 2 for variable indentification.
542
VOL. 11, NO. 5
Body Fluids From Bioelectrical Values Table 5. Correlations Among Predicted Values (16 Men, 3 Trials; n = 48) D20 TBW
Downloaded by [New York University] at 15:59 13 May 2015
Dns. TBW D 2 0 TBW TOBEC TBW RJLTBW BMA TBW Bromide ECF TOBEC ECF RJLECF BMA ECF Ani ICF* TOBEC ICF RJLICF
0.945*
Predicted TBW
Predicted ECF
BRECF
TOBEC
RJL
BMA
0.952 0.968
0.929 0.961 0.9611
0.927 0.953 0.953 0.924
0.864 0.889 0.890 0.878 0.862
TOBEC
RJL
BMA
0.970 0.963 0.980 0.953 0.949 0.919
0.933 0.934 0.937 0.956 0.915 0.901 0.970
0.926 0.941 0.944 0.937 0.980 0.875 0.952 0.949
Ani ICFf 0.878 0.947 0.907 0.895 0.896 0.710 0.876 0.847 0.871
Predicted ICF TOBEC
RJL
BMA
0.936 0.965 0.995 0.954 0.948 0.878 0.963 0.914 0.933 0.910
0.903 0.948 0.951 0.987 0.899 0.843 0.919 0.904 0.895 0.896 0.953
0.907 0.945 0.947 0.915 0.990 0.828 0.919 0.870 0.955 0.906 0.952 0.911
* Underlined numbers are correlations between values obtained from the reference methods. f Ani ICF is calculated as the difference of D 2 0 TBW minus Br ECF. t Bold numbers are correlations among body component values derived from different bioelectrical analyzers.
1.00. Data from the currently developed prediction equa tions yielded slopes close to 1.00, small intercepts and relatively small 95% CI, with RJL predicted values having the larger intervals. Despite large CI, the slope of BMA predicted ECF with the Br values did not approach 1.00. Slopes for the currently developed prediction values with Br ECF as the independent variable ranged from 0.90 to 0.94 with large 95% CI. All slopes for structural relation ships between values from currently developed predictions were close to 1.00, but their 95% CI were large. Although all 95% CI using analyzed ICF as the independent variable were large enough to include 1.00, the slopes ranged from 0.86 to 0.94 and the intercepts were large. Slopes for the predicted values from the three bioelectric analyzers ap proached 1.00 with small intercepts, but large 95% CI.
DISCUSSION This study was conducted to examine the relationships of bioelectrical variables with ECF and TBW, and to evaluate the use of these biological impedance and the conductivity analyzers for monitoring body hydration. Of the three instruments examined, only the BMA provided estimates for ECF and ICF and this was done by appor tioning TBW to the two fluid volumes. Since neither the TOBEC nor the BIA had been used previously to measure ECF, prediction equations had to be developed before the analyzers could be evaluated as potential analyzers for ECF. These equations would be specific for this population of average-weight, normal adult men. Therefore, an equiv alent evaluation of the BMA required the development of its population-specific equation. The three analyzers pro vided values for TBW. However, most laboratories develop their own population specific prediction equations [1-3].
Furthermore, no one has reported a comparative evalua tion of several of these analyzers for TBW or other fluid spaces in one homogenous population. Our evaluation was done by obtaining TBW values from either the manufac turer's algorithms or a previously published equation (TO BEC) and from the population-specific equations devel oped in this study. I would emphasize that all of our prediction equations were developed using the mean values (from the three measurements of each man) to reduce the variability and obtain the best equations, and all of the comparisons of one instrument to another, or to the ref erence methods, were conducted on the individual values from each measurement period since this would be the normal analytical procedure. Therefore, although the val ues used to develop the equations were not fully independ ent of the ones used in the comparisons, they were not the same values and the predictions from each instrument were made independently from those of the other instru ments. Correlations (Table 3) of values derived from manufac turer's or published equations with those derived from tracer dilution techniques were high for TOBEC TBW with D 2 0 TBW (0.959); but, somewhat less with Br ECF (0.906) and analyzed ICF (0.878). The high r of TOBEC TBW with D 2 0 TBW was expected since this equation had been developed previously in this laboratory for pre dicting TBW [4]. Compared with those for TOBEC TBW, the r for the RJL manufacturer's equation for TBW were only slightly lower, 0.943,0.875 and 0.869 with D 2 0 TBW, Br ECF and analyzed ICF, respectively. Although the BMA provided values for both the ECF and ICF, correlations of these values with the reference method values for TBW (0.925), ECF (0.871) and ICF (0.853) were not better than those of the TOBEC and RJL. The equivalent r for the BMA's TBW, ECF and ICF with each tracer-derived vol-
JOURNAL OF THE AMERICAN COLLEGE OF NUTRITION
543
Body Fluids From Bioelectrical Values Table 6. Errors-in-Variables Analyses Using Each Man's Values at Each Trial (n = 48; 16 Men x 3 Trials) X
D 2 0 TBW
Old TOBEC Old BMA
Downloaded by [New York University] at 15:59 13 May 2015
Old RJL TBW Pred. by All Pred. by TOBEC Pred. by BMA Br. Dil
Pred. by All Pred. by TOBEC Pred. by BMA Ani. ICF
Pred. by All Pred. by TOBEC Pred. by BMA
Slope
Y
95% Conf. Int
Intere.
Old* TOBEC Old BMA Old RJL Density Pred. by All Pred. by TOBEC Pred. by BMA Pred. by RJL Old BMA Old RJL Density Old BIA Density Density Pred. by TOBEC Pred. by BMA Pred. by RJL Pred. by BMA Pred. by RJL Pred. by RJL
Total body water 1.092 0.8568 0.7323 0.9718 0.9869 0.9784 0.9838 0.9690 0.7906 0.6708 0.8918 0.8507 1.130 1.338 0.9917 0.9971 0.9821 1.006 0.9907 0.9847
1.000 0.7568 0.6583 0.8760 0.9226 0.9061 0.9033 0.8817 0.7315 0.6049 0.8329 0.7596 1.020 1.177 0.9421 0.9546 0.8881 0.9235 0.9010 0.8699
1.193 0.9677 0.8119 1.078 1.056 1.056 1.071 1.065 0.8533 0.7409 0.9543 0.9507 1.254 1.529 1.044 1.042 1.086 1.095 1.089 1.114
-6.418 4.368 11.18 -1.414 0.640 1.030 0.786 1.523 9.125 15.47 4.202 7.630 -6.020 16.76 0.392 0.135 0.886 -0.266 0.479 0.765
Old BMA Pred. by All Pred. by TOBEC Pred. by BMA Pred. by RJL Pred. by TOBEC Pred. by BMA Pred. by RJL Pred. by BMA Pred. by RJL Pred. by RJL
Extracellular fluid 0.6796 0.9438 0.9396 0.9307 0.8970 0.9958 0.9881 0.9571 0.9923 0.9609 0.9684
0.5715 0.8288 0.8261 0.8051 0.7589 0.9621 0.9226 0.8769 0.9215 0.8731 0.8771
0.7997 1.074 1.068 1.074 1.057 1.031 1.058 1.044 1.068 1.057 1.069
2.664 1.101 1.182 1.359 2.049 0.081 0.233 0.868 0.152 0.793 0.646
Old BMA Pred. by All Pred. by TOBEC Pred. by BMA Pred. by RJL Pred. by TOBEC Pred. by BMA Pred. by RJL Pred. by BMA Pred. by RJL Pred. by RJL
Intracellular fluid 0.8597 0.9418 0.9019 0.9121 0.9071 0.9574 0.9700 0.9622 1.012 1.006 0.9935
0.7151 0.8013 0.7868 0.7855 0.7881 0.8629 0.9028 0.8480 0.9206 0.9146 0.8681
1.028 1.105 1.032 1.057 1.042 1.062 1.042 1.091 1.113 1.106 1.137
5.294 1.694 2.773 2.501 2.638 1.159 0.819 1.033 -0.328 -0.157 0.177
* "Old" values are derived from the manufacturer supplied algonths or previously published equations.
urne reflects that the former values are directly propor tional to each other. Therefore, both the TOBEC and the RJL provided better estimates for TBW in this population than the BMA using the original equations. A major difficulty in developing the prediction equa tions is the uncertainty in measuring the independent variable. Although we used the best available established methods of tracer dilutions and underwater weighing, the
544
assumptions and errors associated with each of these have been reported in numerous publications and were recently reviewed by Lukaski [6]. These errors among the reference methods are shown by correlations in Table 3. The corre lation between D 2 0 TBW and Br derived ECF was only 0.889, although these are the standards. Some of the vari ability that reduced this correlation was probably due to biological differences in the ratio of TBW to ECF, even in
VOL. 11, NO. 5
Downloaded by [New York University] at 15:59 13 May 2015
Body Fluids From Bioelectrical Values this relatively homogenous population. Since the reference method's results were so variable, values from the three trials for each man were averaged for use in the regression equations to reduce the variability and improve the prediction equations. To allow the regres sion procedure to discriminate among the analyzers, vari ables from all of the analyzers were used with the stepwise procedure for the initial prediction equation. Under these circumstances, two TOBEC and two BMA (selected alter nately between analyzers) variables were used to predict TBW, two different TOBEC variables were used for ECF, and one TOBEC and one BMA variable were selected to predict ICF. Since these three volumes are so interrelated with TBW = ECF + ICF, it would be expected that the prediction equations for each of them would use the same or similar variables; however, most of the variables differed for these predictions suggesting that each prediction was independent and did not reflect this close relationship for the volumes. The preponderance of TOBEC variables in these three equations indicates that this instrument pro vides the best estimates (increased R2 and reduced SEE and intercept) for these volumes. Few laboratories would use three analyzers, therefore, the maximum R procedure was used to develop the best prediction equation for each fluid volume for each instru ment. These equations were used to compared the three analyzers. The best prediction equations for TBW and ICF were those of the BMA, and for ECF, it was using TOBEC variables. The RJL's prediction equations for the respective fluids had consistently lower adjusted R2 and higher SEE than those for BMA and TOBEC. Lukaski and Bolunchuk [19] used the RJL for predicting TBW and ECF. They measured R and electrical reactance (Xc) from the arm to the leg, both ipsilaterally and contralaterally, and selected the lowest value to estimate the fluid volumes similar to Lukaski et al's [1] earlier method for estimating LBM. With this method they were able to obtain an R2 = 0.975 and SEE = 1.50 L for TBW and an R2 = 0.884 and SEE = 1.01 L for ECF for their stepwise multiple regression prediction equations. Both equations selected height (Ht2)/ R and weight (Wt) and included age and gender for TBW and Ht2/Xc for ECF. Corresponding equations from our all male population using the maximum R procedure for ECF also selected Ht2/R as the first RJL variable; but, only Wt/Ht2 significantly increased R2 (0.868 with SEE = 1.245 L); and, for TBW, ZHt2 replaced Ht2/R, and Xc and ZWtHr 2 increased R2 to 0.951 (SEE =1.819 L). The standard methods for measuring TBW and ECF are time consuming and require ingestion or injection of a tracer solution, and collection of two or three hourly urine, blood or saliva samples after equilibration. Tracer concentrations in these samples are determined and used to calculate the volumes. We used these tracer-derived volumes and the predicted values from our regression
equations in correlation and errors-in-variables regression (structural relationships) analyses to evaluate these instru ments. Correlations among the reference method values ranged from 0.88 for ICF with TBW to 0.71 for ECF with ICF. The low value for the latter comparison was antici pated since the ICF value is calculated by the difference between TBW and ECF. Correlations of the predicted TBW from each of the analyzers with D20-determined TBW, and with each other, were high (0.95-0.97) indicat ing that each of these equations was providing good esti mates of TBW. However, the errors-in-variables analyses (Table 6) showed that none of the instruments, using the original (old) equations, provided valid estimates for D 2 0derived TBW based on slopes unequal to 1.00 and 95% CI that did not encompass 1.00. The density-based esti mation had a slope = 0.972 with a large CI that included 1.00 compared to D 2 0 TBW. On the other hand, all of the predictions of TBW based on currently derived equations were comparable to each other based on slopes, CI and small intercepts; therefore, they appeared to be measuring the same volume. Similarly, the original BMA values for ECF were not comparable to the ECF derived from Br dilution. Although all the currently developed analyzerbased values yielded similar slopes with the Br ECF, these slopes were low (0.90-0.94) and had large 95% CI. Com parisons among ECF values from the currently developed equations showed that the BMA-predicted ECF were com parable to those of the TOBEC and were quite similar to RJL's predictions based on the slopes. Structural compar isons of the ICF showed that the original BMA values also had a weak relationship (slope = 0.86) to the reference ICF volumes (D 2 0 TBW minus Br ECF). Although the cur rently developed prediction equations were obtained from the mean values for each of these men, the individualpredicted values had lower than anticipated relationships (slopes = 0.90-0.94) with the weekly values for ICF. In contrast, each of the predictions had strong structural relationships with each other (slopes = 0.98-1.01), but the 95% CI were large. This is consistent with the hypothesis that each of the analyzers provided better estimates for these fluid volumes and were more consistent with each other than with either the values obtained from the original manufacturer's equations or those obtained from the older reference methods. Comparisons of our currently developed prediction equations with the previous algorithms for estimating these tracer-derived values (Tables 3 and 6) showed that the largest improvement was for the BMA's prediction, pri marily due to the poor correlations for its original algo rithm values with the reference values. Using our equa tions, the BMA provided the best predictions for TBW and ICF volumes. SEE for the volumes were comparable for BMA and TOBEC predictions, and were lower than the SEE from RJL predictions. It would be of considerable
JOURNAL OF THE AMERICAN COLLEGE OF NUTRITION
545
Downloaded by [New York University] at 15:59 13 May 2015
Body Fluids From Bioelectrical Values clinical significance and interest to ascertain whether these instruments could reliably measure the different water compartments in hypohydrated and/or edematous states observed in malnutrition, environmental stress or disease states. These SEE and the adjusted R2 are comparable to those reported by Segal et al [2] and by Lukaski et al [1] for RJL predictions for LBM and TBW. Part of this SEE is probably due to inaccuracies in the reference methods. The better structural relationships (Table 6, slopes and confidence intervals) among the analyzer-predicted values, compared to those between the reference methods values and pre dicted values especially for ECFs and ICFs, suggest that these newer analyzers are providing better estimates than the reference methods. Furthermore, each of these instruments provides instan taneous values for conductivity or impedance which can be. processed through a computer providing body fluid data in
Journal of the American College of Nutrition Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/uacn20
Predicting total body water and extracellular fluid volumes from bioelectrical measurements of the human body. a
a
a
H L Johnson , S P Virk , P Mayclin & T Barbieri
a
a
US Department of Agriculture, Western Human Nutrition Research Center, Presidio of San Francisco, CA 94129. Published online: 02 Sep 2013.
To cite this article: H L Johnson, S P Virk, P Mayclin & T Barbieri (1992) Predicting total body water and extracellular fluid volumes from bioelectrical measurements of the human body., Journal of the American College of Nutrition, 11:5, 539-547, DOI: 10.1080/07315724.1992.10718259 To link to this article: http://dx.doi.org/10.1080/07315724.1992.10718259
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
Predicting Total Body Water and Extracellular Fluid Volumes From Bioelectrical Measurements of the Human Body Herman L. Johnson, PhD, FACN, Satinder P.S. Virk, DVM, Patrick Mayclin, AS, and Teresa Barbieri, MA US Department ofAgriculture, Western Human Nutrition Research Center, Presidio ofSan Francisco, CA
Downloaded by [New York University] at 15:59 13 May 2015
Key words: intracellular fluid volume, body composition methods, biological impedance, biological electrical conductivity, deuterium dilutional volume, bromide space, body hydration status Two biological impedance analyzers, a 50 kHz (RJL) and 20-100 kHz (BMA) instrument, and a total body electrical conductivity (TOBEC) instrument were used to estimate total body water (TBW), extracellular (ECF) and intracellular (ICF)fluidvolumes by repeated measurements of 16 normal men (19-38 years old) to assess which, if any, would provide the best estimates. At 3-week intervals, TBW was determined by deuterium dilution, ECF by bromide dilution, ICF by difference (TBW-ECF) and lean body mass by density. Prediction equations were obtained by regression; predicted values for the body fluid volumes were calculated and the results were statistically evaluated. Both the TOBEC and the BMA provided rapid and reliable estimates for body fluid volumes with standard errors of the estimates of about 0.5-1.1 L for ECF, 1.0-1.8 L for TBW, and 1.0-1.3 L for ICF. Part of the error was attributable to standard tracer-dilution methods. Abbreviations: ANOVA = analysis of variance, BMA = Berkeley Medical Instru ments' biological impedance analyzer, BMI = body mass index, Br = bromine, CI = confidence interval, Cl, Cm, Cu = conductivities of the lower, middle and upper body, respectively, D2O = deuterim oxide, ECF = extracellular fluid, FC0, FC1, FC2 = zero, first and second order Fourier coefficients of the TOBEC's phase average values, respectively, Ht = height, ICF = intracellular fluid, LBM = lean body mass, R = electrical resistance, 1/R = electrical conductivity, r = correlation coefficient, R2 = R squared or regression coefficient, RJL = RJL System's biological impedance analyzer, SEE = standard error of the estimate, TOBEC = total body electrical conductivity analyzer, TBW = total body water, Wt = weight, Xc = electrical reactance, Z = electrical impedance
INTRODUCTION
impedance was reduced. Evaluating the ECF-ICF components, as well as TBW, is important in monitoring many clinical and nutritional syndromes; however, the tracer-dilution reference methods are tedious, time consuming and variable. Bioelectrical analyzers, on the other hand, provide rapid and repeatable data related to the body's fluid space. This study was designed to examine how accurately the total body electri cal conductivity analyzer (TOBEC, model HA-2, DICKEY-John Co, Auburn, IL), RJL biological imped ance analyzer (RJL, model BIA-101, RJL Systems, Detroit, MI) and BMA biological impedance analyzer (BMA, model BMR-2000, Berkeley Medical Instruments, San
Newer methods for the assessment of human body composition are based on measurements of electrical impedance and conductivity [1-6]. These properties are related to the body's content of water and electrolytes, and have been used to estimate total body water (TBW) [1,3-6]. Thomasset [7,8] was the first to estimate fluid volumes with a bipolar whole-body impedance technique. Tedner [9] and Hoffer et al [10] reported that most of the current at frequencies < 10 kHz flowed through only extracellular fluid (ECF); but, at 50-100 kHz, both intra cellular fluid (ICF) and ECF conducted the current and
Address reprint requests to Herman L. Johnson, PhD, USDA/ARS/WHNRC, PO Box 29997, Presidio of San Francisco, CA 94129.
Journal of the American College of Nutrition, Vol. 11, No. 5, 539-547 (1992) Published by the American College of Nutrition 539
Body Fluids From Bioelectrical Values Leandro, CA) could measure these volumes compared to the aforementioned reference methods.
SUBJECTS AND METHODS
Downloaded by [New York University] at 15:59 13 May 2015
Subjects Sixteen normal male volunteers, 19-38 years old, com pleted three trials at 3-week intervals to permit the excre tion of tracers. Pertinent characteristics of the men are shown in Table 1. Weights (76.7 ± 13.6 kg, mean ± standard deviation) ranged from 52 to 107 kg while body mass indexes (BMI, weight in kg/height2 in m, 23.8 ± 2.7) and body fat contents (20.6 ± 6.5%) were typical of young adult males. The two men with >27% body fat (subjects 11 and 14) had relatively low BMI values while subject 9, with a BMI of 30.3, had 24.3% fat. Study design, proce dures and volunteer agreements were reviewed and ap proved by the Letterman Army Medical Center's (Presidio of San Francisco, CA) Human Use Committee and USDA Agriculture Research Services's (Beltsville, MD) Human Studies Review Committee. Protocol Subjects arrived at the laboratory after fasting overnight for at least 10 hours. Initial blood and urine samples for measuring baseline concentrations of the tracers were ob tained between 7:30 and 8 a.m. Blood was drawn without
stasis from a forearm vein. The men ingested 1.5 g of tracer solution (0.06 g NaBr and 0.15 g D 2 0) per kg of body weight between 8 and 8:30 a.m. This was followed by ingestion of distilled water rinses (total of 100-150 ml) of the container. The men fasted for the next 7 hours until measurements and samplings were completed. Urine pro duced during the first 3.5 hours was collected to correct for tracer loss during total body equilibration. Tracerdilutions were calculated from blood and urine samples collected at 4.5, 5.5 and 6.5 hours after tracer ingestion. Body Fluids Blood samples were centrifuged and the serums were used for bromide analysis by fluorescent excitation [1113]. ECF was calculated, by the method of Price et al [12], as 0.873 times the bromide dilutional space. Samples (1.5 ml) of the urine and oral tracer solutions were vacuum distilled and their deuterium concentrations were deter mined by infrared spectroscopy [14] for calculating TBW volumes. The correlations of variation for the bromide and deuterium analyses were between 1.3 and 1.6% de pending on the analyte concentrations. ICF was calculated as the difference between TBW and ECF. Bioelectrical properties of the body were measured with three commer cial analyzers and were used to estimate these volumes. TOBEC was measured at 2.5 mHz with a prototype instru ment and TBW was estimated using a published equation [4]. The body's electrical resistance (R) was measured with
Table 1. Characteristics of Male Subjects #
Age (yrs)
Ethnic group*
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Mean SD
28 29 33 21 21 38 18 32 19 36 26 33 28 33 33 36 29.1 6.3
C C C H B C C C C C A F B C F C
Subj
BMIt 21.08 22.47 20.79 20.23 23.81 25.81 23.92 26.16 30.31 24.08 20.93 23.32 24.87 22.80 23.37 27.37 23.832 2.66
Ht (cm) 182.3 180.2 179.1 161.2 187.3 182.0 178.1 195.1 187.7 169.5 173.8 171.4 184.3 181.3 172.1 176.1 178.84 8.19
% fat§
Wt (kg)
Meani
SD*
Mean
70.07 72.95 66.68 52.58 83.53 85.50 75.87 99.57 106.77 69.19 63.22 68.52 84.48 74.95 69.23 84.87
0.85 0.48 0.73 0.86 0.41 0.53 0.35 1.03 1.70 0.25 1.19 0.92 0.84 0.38 0.19 0.45
15.86 8.56 17.73 8.71 11.77 26.52 20.88 26.81 24.29 22.41 27.43 23.22 19.07 29.77 22.11 24.27
76.749
20.588
13.622
6.538
SD 1.82 1.07 0.13 0.13 2.59 1.16 0.91 0.94 2.10 0.72 1.00 0.36 0.48 0.76 1.17 0.65
* Caucasian, Hispanic, Black, Asian and Filipino. t Body mass index = kg/m2. φ Mean and standard deviation of values obtained at weeks 1, 4 and 7. § From underwater weighing.
540
VOL. 11, NO. 5
Body Fluids From Bioelectrical Values two instruments: the RJL introduced 800 μΑ of 50 kHz current to measure R and reactance (Xc) values (electrodes placed on right hand, wrist, ankle and foot) and the man ufacturer provided a provisional equation (TBW(L) = 0.616 Ht2/R) to estimate TBW; and the BMA (electrodes on both ankles and both wrists) provided conductivity (1/ R) values, scanning through 250 frequencies from 20 to 100 kHz, from the upper, middle and lower (Cu, Cm and Cl, respectively) body and estimates of ECF and ICF, derived from TBW". Only these three conductivities and estimates for body components were printed; the program and other data were considered proprietary by the manu facturer. For the RJL, impedance (Z) was calculated as Z = (R2 + Xc2)05.
Downloaded by [New York University] at 15:59 13 May 2015
Body Weights and Densities Body weights were obtained from an electronic balance with a sensitivity of 50 g and heights were recorded to the nearest mm from a wall-mounted steel ruler. Body density was obtained by underwater weighing [15] with the simul taneous measurement of residual lung volume [16]. At least three replicates of each measurement were made throughout the morning, between the fluid samplings. Body density was used to calculate lean body mass (LBM) using the Siri equation [17] and TBW was assumed to equal 0.732 times LBM [17]. Statistical Analyses Data were statistically analyzed by computer using SAS programs (SAS Institute, Cary, NC) and STATOOLS (Ger ard E. Dallai, Maiden, MA). Routines used included re peated measures analyses of variance (ANOVA), correla tions, stepwise regressions, and errors-in-variables regres sion. Initial equations to predict TBW, ECF and ICF were obtained using all the measured and calculated variables from the three analyzers so the statistical routine could select which of these analyzers would yield the best vari ables for the predictions. Then prediction equations were obtained for each instrument for comparisons among the instruments. Comparisons were made using predicted val ues from each of the equations and the errors-in-variables regression, a statistical routine that permits apportioning the variability to both the dependent and independent variables by setting a ratio for their magnitudes. This ratio was set at one for these analyses on the assumption that the magnitude of errors were similar. Structural analysis from errors-in-variables regression compares the changes in the dependent variable to the changes in the independ ent variable and minimizes the perpendicular distance of each point to the regression line. Evaluations are based upon the proximity of the slope to 1.00 indicating equiv* Personal communication with the manufacturer's representative.
aient changes in the two variables, the width of the 95% confidence interval (CI) reflecting the quantitative devia tions of the points from the line and the intercept that shows the amount of bias between the two measurements and/or predictions. Significance testing was done at the 5% level. Root mean squared error was used as the stand ard error of the estimate (SEE) in comparing regression equations.
RESULTS Data obtained from the reference methods for both fluids and LBM and the three bioelectrical analyzers are summarized in Table 2. Repeated measures ANOVA in dicated that none of the values changed significantly during the study; therefore, these values are averages over time. Only the bioelectrical variables which were directly meas ured or available from the bioelectric analyzers are pre sented. Correlation coefficients (r) between TBW, ECF and ICF values obtained from reference methods and manufac turer/literature algorithms are shown in Table 3. The r with deuterium derived TBW were similar for the three analyzers and density TBW values (0.92 to 0.96). The highest r among the TBW values was for TOBEC vs density, 0.97. Of the three bioelectric analyzers, only the BMA yielded values for ECF and ICF and the r of these values with the reference values were 0.87 and 0.86 for ECF and ICF, respectively. The r among the variables measured independently by the reference methods were 0.71 (ECF vs ICF), 0.89 (TBW vs ECF) and 0.95 (TBW vs ICF).
Table 2. Subjects' Directly Measured Variables Variable
Mean*
SD
Body weight (kg) D 2 0 TBW (L) B r ECF (L) ICF (by diff.) (L) LBM (kg) TOBEC measurements PhasAvg (mho) FCOf FC1 FC2 RJL measurements R (ohm) Xc (ohm) BMA conductivity measurements Cu (mho) Cm (mho) Cl (mho)
76.75 47.25 20.22 26.94 60.66
13.62 7.36 3.18 4.49 9.84
594.32 477.47 216.10 76.12
124.75 101.12 52.54 10.44
489.30 72.021
48.77 6.671
26.77 34.75 31.77
1.17 1.63 1.43
* Mean and standard deviation for 16 men. t Fourier coefficients of phase average data [4].
JOURNAL OF THE AMERICAN COLLEGE OF NUTRITION
541
Body Fluids From Bioelectncal Values Table 3. Correlations Among Weekly Values (16 Men, 3 Trials) Derived from Reference and Previously Established Methods Total body water TOBEC
Downloaded by [New York University] at 15:59 13 May 2015
D 2 0 TBW TOBEC TBW RJLTBW BMA TBW Density TBW BrECF BMA ECF Analyzed ICF (difference)
0.959
Extracell. fid.
Intracell. fid.
RJL
BMA
Density
BrDil
BMA
TBW-ECF
BMA
0.943 0.947
0.925 0.963 0.936
0.945 0.975 0.916 0.945
0.889 0.906 0.875 0.871 0.864
0.922 0.967 0.932 0.999 0.944 0.872
0.946 0.878 0.869 0.853 0.878 0.710 0.848
0.925 0.968 0.937 1.000 0.945 0.870 0.998 0.855
Since none of the measured variables changed signifi cantly during the study, mean values for each were used in regression analyses to develop the prediction equations shown in Table 4. The adjusted R 2 with bioelectric values for TBW, ECF and ICF ranged from 0.89 to 0.99. The SEE for the equations from bioelectncal analyzers variables ranged from 0.6 to 1.8 L for TBW, 0.5 to 1.1 L for ECF and 0.9 to 1.3 L for ICF. When variables from all the instruments were included in the regression, only TOBEC and BMA variables were used and the adjusted R 2 and SEE were improved compared to individual analyzer equa tions. Equations based on RJL variables had largest SEE and lowest adjusted R2. These prediction equations were used to calculate body fluid values for each trial, and the data were analyzed by
correlation and errors-in-variables analyses. The r with deuterium oxide (D 2 0) TBW were 0.89-0.96 for ECF and 0.94-0.96 for ICF whether determined or predicted (Table 5). Correlations with bromine (Br) ECF were 0.86-0.89 for TBW, 0.71 for analyzed ICF and 0.83-0.88 for pre dicted ICF. The r with the analyzed (by difference) ICF were TOBEC TBW 0.91, D 2 0 TBW 0.95, RJL TBW 0.90, BMA TBW 0.90, Br ECF 0.71 and all other ECF 0.850.88. Correlations among the predicted values for TBW, ECF and ICF within each of the analyzers were 0.96-0.99 (TOBEC), 0.90-0.99 (RJL) and 0.96-0.99 (BMA). Errors-in-variables analyses of the weekly data for these men (Table 6) depicts the slopes, their 95% CI and the intercepts for the structural relations. None of the 95% CI among the original estimations for TBW encompasses
Table 4. Prediction of Body Fluid Volumes (L) Using Values From Three Bioelectrical Analyzers and Regression Equations Fluid
SEE
Adj. R2
TBW
0.647
0.9923
ECF ICF
0.476 0.871
0.9776 0.9603
TBW ECF ICF
1.104 0.534 1.187
0.9775 0.9719 0.9263
Using TOBEC variables 24.327 + .02134HtFCl05 - 3.81013FC205 16.164 - 1.64948FC205 + .03090PhasAvg 1.784 + .00904HtPhaseAvg05 - 0.18648FC2
TBW ECF ICF
1.017 0.662 1.002
0.9809 0.9568 0.9475
Using BMA variables -95.815 + 0.48385Ht + .01154(Cu + Cm)2 + 5314.7WtHr2 -20.607 + 0.18314Wt + .00988Cm2 + 2.62243C105 -61.513 + 0.33580Ht + .00749(Cu + Cm)2
TBW ECF ICF
1.819 1.065 1.265
0.9389 0.8880 0.9162
Using RJL variables -31.766 + 0.81372ZHt2 + 0.21839Xc + 8.374ZWtHr2 0.291 +0.11787Wt + 0.1631Ht2R-' -34.752 + 45.1081 lHtZ 05 + .30879Ht - 1.47523RXC"1
Prediction equation* Using variables from all instruments -12.613 + .01149HtPhasAvg05 + .00907(Cu + Cm)2 - 0.16112FC2 - .01023Cm2 25.180 + .03331FC0 - 2.6046FC205 + .0000036Wt3 -71.208 + .00888HtPhasAvg05 - .0000097Wt3 + 12.42297Cu05
' See Table 2 for variable indentification.
542
VOL. 11, NO. 5
Body Fluids From Bioelectrical Values Table 5. Correlations Among Predicted Values (16 Men, 3 Trials; n = 48) D20 TBW
Downloaded by [New York University] at 15:59 13 May 2015
Dns. TBW D 2 0 TBW TOBEC TBW RJLTBW BMA TBW Bromide ECF TOBEC ECF RJLECF BMA ECF Ani ICF* TOBEC ICF RJLICF
0.945*
Predicted TBW
Predicted ECF
BRECF
TOBEC
RJL
BMA
0.952 0.968
0.929 0.961 0.9611
0.927 0.953 0.953 0.924
0.864 0.889 0.890 0.878 0.862
TOBEC
RJL
BMA
0.970 0.963 0.980 0.953 0.949 0.919
0.933 0.934 0.937 0.956 0.915 0.901 0.970
0.926 0.941 0.944 0.937 0.980 0.875 0.952 0.949
Ani ICFf 0.878 0.947 0.907 0.895 0.896 0.710 0.876 0.847 0.871
Predicted ICF TOBEC
RJL
BMA
0.936 0.965 0.995 0.954 0.948 0.878 0.963 0.914 0.933 0.910
0.903 0.948 0.951 0.987 0.899 0.843 0.919 0.904 0.895 0.896 0.953
0.907 0.945 0.947 0.915 0.990 0.828 0.919 0.870 0.955 0.906 0.952 0.911
* Underlined numbers are correlations between values obtained from the reference methods. f Ani ICF is calculated as the difference of D 2 0 TBW minus Br ECF. t Bold numbers are correlations among body component values derived from different bioelectrical analyzers.
1.00. Data from the currently developed prediction equa tions yielded slopes close to 1.00, small intercepts and relatively small 95% CI, with RJL predicted values having the larger intervals. Despite large CI, the slope of BMA predicted ECF with the Br values did not approach 1.00. Slopes for the currently developed prediction values with Br ECF as the independent variable ranged from 0.90 to 0.94 with large 95% CI. All slopes for structural relation ships between values from currently developed predictions were close to 1.00, but their 95% CI were large. Although all 95% CI using analyzed ICF as the independent variable were large enough to include 1.00, the slopes ranged from 0.86 to 0.94 and the intercepts were large. Slopes for the predicted values from the three bioelectric analyzers ap proached 1.00 with small intercepts, but large 95% CI.
DISCUSSION This study was conducted to examine the relationships of bioelectrical variables with ECF and TBW, and to evaluate the use of these biological impedance and the conductivity analyzers for monitoring body hydration. Of the three instruments examined, only the BMA provided estimates for ECF and ICF and this was done by appor tioning TBW to the two fluid volumes. Since neither the TOBEC nor the BIA had been used previously to measure ECF, prediction equations had to be developed before the analyzers could be evaluated as potential analyzers for ECF. These equations would be specific for this population of average-weight, normal adult men. Therefore, an equiv alent evaluation of the BMA required the development of its population-specific equation. The three analyzers pro vided values for TBW. However, most laboratories develop their own population specific prediction equations [1-3].
Furthermore, no one has reported a comparative evalua tion of several of these analyzers for TBW or other fluid spaces in one homogenous population. Our evaluation was done by obtaining TBW values from either the manufac turer's algorithms or a previously published equation (TO BEC) and from the population-specific equations devel oped in this study. I would emphasize that all of our prediction equations were developed using the mean values (from the three measurements of each man) to reduce the variability and obtain the best equations, and all of the comparisons of one instrument to another, or to the ref erence methods, were conducted on the individual values from each measurement period since this would be the normal analytical procedure. Therefore, although the val ues used to develop the equations were not fully independ ent of the ones used in the comparisons, they were not the same values and the predictions from each instrument were made independently from those of the other instru ments. Correlations (Table 3) of values derived from manufac turer's or published equations with those derived from tracer dilution techniques were high for TOBEC TBW with D 2 0 TBW (0.959); but, somewhat less with Br ECF (0.906) and analyzed ICF (0.878). The high r of TOBEC TBW with D 2 0 TBW was expected since this equation had been developed previously in this laboratory for pre dicting TBW [4]. Compared with those for TOBEC TBW, the r for the RJL manufacturer's equation for TBW were only slightly lower, 0.943,0.875 and 0.869 with D 2 0 TBW, Br ECF and analyzed ICF, respectively. Although the BMA provided values for both the ECF and ICF, correlations of these values with the reference method values for TBW (0.925), ECF (0.871) and ICF (0.853) were not better than those of the TOBEC and RJL. The equivalent r for the BMA's TBW, ECF and ICF with each tracer-derived vol-
JOURNAL OF THE AMERICAN COLLEGE OF NUTRITION
543
Body Fluids From Bioelectrical Values Table 6. Errors-in-Variables Analyses Using Each Man's Values at Each Trial (n = 48; 16 Men x 3 Trials) X
D 2 0 TBW
Old TOBEC Old BMA
Downloaded by [New York University] at 15:59 13 May 2015
Old RJL TBW Pred. by All Pred. by TOBEC Pred. by BMA Br. Dil
Pred. by All Pred. by TOBEC Pred. by BMA Ani. ICF
Pred. by All Pred. by TOBEC Pred. by BMA
Slope
Y
95% Conf. Int
Intere.
Old* TOBEC Old BMA Old RJL Density Pred. by All Pred. by TOBEC Pred. by BMA Pred. by RJL Old BMA Old RJL Density Old BIA Density Density Pred. by TOBEC Pred. by BMA Pred. by RJL Pred. by BMA Pred. by RJL Pred. by RJL
Total body water 1.092 0.8568 0.7323 0.9718 0.9869 0.9784 0.9838 0.9690 0.7906 0.6708 0.8918 0.8507 1.130 1.338 0.9917 0.9971 0.9821 1.006 0.9907 0.9847
1.000 0.7568 0.6583 0.8760 0.9226 0.9061 0.9033 0.8817 0.7315 0.6049 0.8329 0.7596 1.020 1.177 0.9421 0.9546 0.8881 0.9235 0.9010 0.8699
1.193 0.9677 0.8119 1.078 1.056 1.056 1.071 1.065 0.8533 0.7409 0.9543 0.9507 1.254 1.529 1.044 1.042 1.086 1.095 1.089 1.114
-6.418 4.368 11.18 -1.414 0.640 1.030 0.786 1.523 9.125 15.47 4.202 7.630 -6.020 16.76 0.392 0.135 0.886 -0.266 0.479 0.765
Old BMA Pred. by All Pred. by TOBEC Pred. by BMA Pred. by RJL Pred. by TOBEC Pred. by BMA Pred. by RJL Pred. by BMA Pred. by RJL Pred. by RJL
Extracellular fluid 0.6796 0.9438 0.9396 0.9307 0.8970 0.9958 0.9881 0.9571 0.9923 0.9609 0.9684
0.5715 0.8288 0.8261 0.8051 0.7589 0.9621 0.9226 0.8769 0.9215 0.8731 0.8771
0.7997 1.074 1.068 1.074 1.057 1.031 1.058 1.044 1.068 1.057 1.069
2.664 1.101 1.182 1.359 2.049 0.081 0.233 0.868 0.152 0.793 0.646
Old BMA Pred. by All Pred. by TOBEC Pred. by BMA Pred. by RJL Pred. by TOBEC Pred. by BMA Pred. by RJL Pred. by BMA Pred. by RJL Pred. by RJL
Intracellular fluid 0.8597 0.9418 0.9019 0.9121 0.9071 0.9574 0.9700 0.9622 1.012 1.006 0.9935
0.7151 0.8013 0.7868 0.7855 0.7881 0.8629 0.9028 0.8480 0.9206 0.9146 0.8681
1.028 1.105 1.032 1.057 1.042 1.062 1.042 1.091 1.113 1.106 1.137
5.294 1.694 2.773 2.501 2.638 1.159 0.819 1.033 -0.328 -0.157 0.177
* "Old" values are derived from the manufacturer supplied algonths or previously published equations.
urne reflects that the former values are directly propor tional to each other. Therefore, both the TOBEC and the RJL provided better estimates for TBW in this population than the BMA using the original equations. A major difficulty in developing the prediction equa tions is the uncertainty in measuring the independent variable. Although we used the best available established methods of tracer dilutions and underwater weighing, the
544
assumptions and errors associated with each of these have been reported in numerous publications and were recently reviewed by Lukaski [6]. These errors among the reference methods are shown by correlations in Table 3. The corre lation between D 2 0 TBW and Br derived ECF was only 0.889, although these are the standards. Some of the vari ability that reduced this correlation was probably due to biological differences in the ratio of TBW to ECF, even in
VOL. 11, NO. 5
Downloaded by [New York University] at 15:59 13 May 2015
Body Fluids From Bioelectrical Values this relatively homogenous population. Since the reference method's results were so variable, values from the three trials for each man were averaged for use in the regression equations to reduce the variability and improve the prediction equations. To allow the regres sion procedure to discriminate among the analyzers, vari ables from all of the analyzers were used with the stepwise procedure for the initial prediction equation. Under these circumstances, two TOBEC and two BMA (selected alter nately between analyzers) variables were used to predict TBW, two different TOBEC variables were used for ECF, and one TOBEC and one BMA variable were selected to predict ICF. Since these three volumes are so interrelated with TBW = ECF + ICF, it would be expected that the prediction equations for each of them would use the same or similar variables; however, most of the variables differed for these predictions suggesting that each prediction was independent and did not reflect this close relationship for the volumes. The preponderance of TOBEC variables in these three equations indicates that this instrument pro vides the best estimates (increased R2 and reduced SEE and intercept) for these volumes. Few laboratories would use three analyzers, therefore, the maximum R procedure was used to develop the best prediction equation for each fluid volume for each instru ment. These equations were used to compared the three analyzers. The best prediction equations for TBW and ICF were those of the BMA, and for ECF, it was using TOBEC variables. The RJL's prediction equations for the respective fluids had consistently lower adjusted R2 and higher SEE than those for BMA and TOBEC. Lukaski and Bolunchuk [19] used the RJL for predicting TBW and ECF. They measured R and electrical reactance (Xc) from the arm to the leg, both ipsilaterally and contralaterally, and selected the lowest value to estimate the fluid volumes similar to Lukaski et al's [1] earlier method for estimating LBM. With this method they were able to obtain an R2 = 0.975 and SEE = 1.50 L for TBW and an R2 = 0.884 and SEE = 1.01 L for ECF for their stepwise multiple regression prediction equations. Both equations selected height (Ht2)/ R and weight (Wt) and included age and gender for TBW and Ht2/Xc for ECF. Corresponding equations from our all male population using the maximum R procedure for ECF also selected Ht2/R as the first RJL variable; but, only Wt/Ht2 significantly increased R2 (0.868 with SEE = 1.245 L); and, for TBW, ZHt2 replaced Ht2/R, and Xc and ZWtHr 2 increased R2 to 0.951 (SEE =1.819 L). The standard methods for measuring TBW and ECF are time consuming and require ingestion or injection of a tracer solution, and collection of two or three hourly urine, blood or saliva samples after equilibration. Tracer concentrations in these samples are determined and used to calculate the volumes. We used these tracer-derived volumes and the predicted values from our regression
equations in correlation and errors-in-variables regression (structural relationships) analyses to evaluate these instru ments. Correlations among the reference method values ranged from 0.88 for ICF with TBW to 0.71 for ECF with ICF. The low value for the latter comparison was antici pated since the ICF value is calculated by the difference between TBW and ECF. Correlations of the predicted TBW from each of the analyzers with D20-determined TBW, and with each other, were high (0.95-0.97) indicat ing that each of these equations was providing good esti mates of TBW. However, the errors-in-variables analyses (Table 6) showed that none of the instruments, using the original (old) equations, provided valid estimates for D 2 0derived TBW based on slopes unequal to 1.00 and 95% CI that did not encompass 1.00. The density-based esti mation had a slope = 0.972 with a large CI that included 1.00 compared to D 2 0 TBW. On the other hand, all of the predictions of TBW based on currently derived equations were comparable to each other based on slopes, CI and small intercepts; therefore, they appeared to be measuring the same volume. Similarly, the original BMA values for ECF were not comparable to the ECF derived from Br dilution. Although all the currently developed analyzerbased values yielded similar slopes with the Br ECF, these slopes were low (0.90-0.94) and had large 95% CI. Com parisons among ECF values from the currently developed equations showed that the BMA-predicted ECF were com parable to those of the TOBEC and were quite similar to RJL's predictions based on the slopes. Structural compar isons of the ICF showed that the original BMA values also had a weak relationship (slope = 0.86) to the reference ICF volumes (D 2 0 TBW minus Br ECF). Although the cur rently developed prediction equations were obtained from the mean values for each of these men, the individualpredicted values had lower than anticipated relationships (slopes = 0.90-0.94) with the weekly values for ICF. In contrast, each of the predictions had strong structural relationships with each other (slopes = 0.98-1.01), but the 95% CI were large. This is consistent with the hypothesis that each of the analyzers provided better estimates for these fluid volumes and were more consistent with each other than with either the values obtained from the original manufacturer's equations or those obtained from the older reference methods. Comparisons of our currently developed prediction equations with the previous algorithms for estimating these tracer-derived values (Tables 3 and 6) showed that the largest improvement was for the BMA's prediction, pri marily due to the poor correlations for its original algo rithm values with the reference values. Using our equa tions, the BMA provided the best predictions for TBW and ICF volumes. SEE for the volumes were comparable for BMA and TOBEC predictions, and were lower than the SEE from RJL predictions. It would be of considerable
JOURNAL OF THE AMERICAN COLLEGE OF NUTRITION
545
Downloaded by [New York University] at 15:59 13 May 2015
Body Fluids From Bioelectrical Values clinical significance and interest to ascertain whether these instruments could reliably measure the different water compartments in hypohydrated and/or edematous states observed in malnutrition, environmental stress or disease states. These SEE and the adjusted R2 are comparable to those reported by Segal et al [2] and by Lukaski et al [1] for RJL predictions for LBM and TBW. Part of this SEE is probably due to inaccuracies in the reference methods. The better structural relationships (Table 6, slopes and confidence intervals) among the analyzer-predicted values, compared to those between the reference methods values and pre dicted values especially for ECFs and ICFs, suggest that these newer analyzers are providing better estimates than the reference methods. Furthermore, each of these instruments provides instan taneous values for conductivity or impedance which can be. processed through a computer providing body fluid data in
