Single- and multifrequency models for bioelectrical impedance analysis of body water compartments.

The 1994 National Institutes of Health Technology Conference on bioelectrical impedance analysis (BIA) did not support the use of BIA under conditions that alter the normal relationship between the extracellular (ECW) and intracellular water (ICW) compartments. To extend applications of BIA to these populations, we investigated the accuracy and precision of seven previously published BIA models for the measurement of change in body water compartmentalization among individuals infused with lactated Ringer solution or administered a diuretic agent. Results were compared with dilution by using deuterium oxide and bromide combined with short-term changes of body weight. BIA, with use of proximal, tetrapolar electrodes, was measured from 5 to 500 kHz, including 50 kHz. Single-frequency, 50-kHz models did not accurately predict change in total body water, but the 50-kHz parallel model did accurately measure changes in ICW. The only model that accurately predicted change in ECW, ICW, and total body water was the 0/infinity-kHz parallel (Cole-Cole) multifrequency model. Use of the Hanai correction for mixing was less accurate. We conclude that the multifrequency Cole-Cole model is superior under conditions in which body water compartmentalization is altered from the normal state.     

Predicting body cell mass with bioimpedance by using theoretical methods: a technological review

De Lorenzo, A., A. Andreoli, J. Matthie, and P. Withers.Predicting body cell mass with bioimpedance by using theoretical methods: a technological review. J. Appl.Physiol. 82(5): 1542-1558, 1997.The body cellmass (BCM), defined as intracellular water (ICW), was estimated in 73 healthy men and women by total body potassium (TBK) and by bioimpedancespectroscopy (BIS). In 14 other subjects, extracellular water (ECW) andtotal body water (TBW) were measured by bromide dilution and deuteriumoxide dilution, respectively. For all subjects, impedance spectral datawere fit to the Cole model, and ECW and ICW volumes were predicted byusing model electrical resistance terms R_E andR_I in an equation derived from Hanai mixture theory,respectively. The BIS ECW prediction bromide dilution wasr = 0.91, standard error of theestimate (SEE) 0.90 liter. The BIS TBW prediction of deuterium spacewas r = 0.95, SEE 1.33 liters. The BISICW prediction of the dilution-determined ICW wasr = 0.87, SEE 1.69 liters. The BIS ICWprediction of the TBK-determined ICW for the 73 subjects wasr = 0.85, SEE = 2.22 liters. Theseresults add further support to the validity of the Hanai theory, theequation used, and the conclusion that ECW and ICW volume can bepredicted by an approach based solely on fundamental principles.

     

Contribution of genetic and environmental factors to variation in body compartments--a twin study in adults

This study aimed at analyzing the contribution of genetic and environmental factors on phenotypic variation of various traits of body composition. Subjects were 30 same-sexed pairs of twins including 20 monozygous (MZ) and 10 dizygous (DZ) pairs, aged 19-62 years. Zygosity was determined by DNA typing and morphological diagnosis. Body composition parameters (fat mass FM, lean body mass LBM, body cell mass BCM, extracellular mass ECM, total body water TBW, extracellular water ECW, and intracellular water ICW) were estimated by tetrapolar bioelectrical impedance analysis. Potential environmental factors influencing body composition (number of children, sporting activity and smoking behaviour) were determined by questionnaires. Heritabilities for traits of body composition were calculated by use of the twin method. Intraclass correlation is > 0.80 for the variation of LBM, BCM, ECM, TBW, ECW, and ICW in both MZ and DZ twins. Estimated heritability (h2) for FM, LBM, BCM, ECW, TBW, ECW, and ICW is 65%, 77%, 79%, 83%, 76%, 68%, and 82%, respectively. The h2 values for FM and LBM are consistent with those reported in other twin studies. For BCM, ECM, ECW and ICW, no comparative h2 estimates exist. Within-pair differences in body compartments do not change with increasing age in MZ and DZ twin pairs (p > 0.05). Stepwise multiple regression analyses indicate that zygosity, age, sex, number of children, sporting level and smoking behaviour do not significantly predict within-pair differences for weight, BMI, FM, LBM, TBW, ECW and ICW (each, p > 0.05). In contrast, sex and the number of children explain together 27% of observed within-pair differences for BCM. Zygosity is the only significant predictor of within-pair differences for ECM and height, explaining 20% (p = 0.008) and 36% of variance, respectively (p < 0.0001). Results indicate that genetic factors exert stronger influences on body composition than the considered environmental traits.     

Assessment of body cell mass at bedside in critically ill patients

Critical illness affects body composition profoundly, especially body cell mass (BCM). BCM loss reflects lean tissue wasting and could be a nutritional marker in critically ill patients. However, BCM assessment with usual isotopic or tracer methods is impractical in intensive care units (ICUs). We aimed to modelize the BCM of critically ill patients using variables available at bedside. Fat-free mass (FFM), bone mineral (Mo), and extracellular water (ECW) of 49 critically ill patients were measured prospectively by dual-energy X-ray absorptiometry and multifrequency bioimpedance. BCM was estimated according to the four-compartment cellular level: BCM = FFM - (ECW/0.98) - (0.73 × Mo). Variables that might influence the BCM were assessed, and multivariable analysis using fractional polynomials was conducted to determine the relations between BCM and these data. Bootstrap resampling was then used to estimate the most stable model predicting BCM. BCM was 22.7 ± 5.4 kg. The most frequent model included height (cm), leg circumference (cm), weight shift (Δ) between ICU admission and body composition assessment (kg), and trunk length (cm) as a linear function: BCM (kg) = 0.266 × height + 0.287 × leg circumference + 0.305 × Δweight - 0.406 × trunk length - 13.52. The fraction of variance explained by this model (adjusted r(2)) was 46%. Including bioelectrical impedance analysis variables in the model did not improve BCM prediction. In summary, our results suggest that BCM can be estimated at bedside, with an error lower than ±20% in 90% subjects, on the basis of static (height, trunk length), less stable (leg circumference), and dynamic biometric variables (Δweight) for critically ill patients.     

Measurement of nutritional status in simulated microgravity by bioelectrical impedance spectroscopy.

The potential of bioelectrical impedance spectroscopy (BIS) for assessing nutritional status in spaceflight was tested in two head-down-tilt bed-rest studies. BIS-predicted extracellular water (ECW), intracellular water (ICW), and total body water (TBW) measured using knee-elbow electrode placement were compared with deuterium and bromide dilution (DIL) volumes in healthy, 19- to 45-yr-old subjects. BIS was accurate during 44 h of head-down tilt with mean differences (BIS - DIL) of 0-0.1 kg for ECW, 0.3-0.5 for ICW, and 0.4-0.6 kg for TBW (n = 28). At 44 h, BIS followed the within-individual change in body water compartments with a relative prediction error (standard error of the estimate/baseline volume) of 2.0-3.6% of water space. In the second study, BIS did not detect an acute decrease (-1.41 +/- 0.91 kg) in ICW secondary to 48 h of a protein-free, 800 kcal/day diet (n = 18). BIS's insensitivity to ICW losses may be because they were predominantly (65%) localized to the trunk and/or because there was a general failure of BIS to measure ICW independently of ECW and TBW. BIS may have potential for measuring nutritional status during spaceflight, but its limitations in precision and insensitivity to acute ICW changes warrant further validation studies.     

New equations for estimating body cell mass from bioimpedance parallel models in healthy older Germans

The objectives of this study were to assess for elderly Germans the validity of existing equations for predicting body cell mass (BCM) and to develop from single- and multifrequency bioimpedance (SFBIA, MFBIA) models new prediction equations. In a data-splitting approach, validation and cross-validation were performed in 160 healthy elderly (60- to 90-yr) subjects. BCM was determined using a tetrapolar bioimpedance analyzer (800 microA; 4 fixed frequencies: 1, 5, 50, and 100 kHz; electrodes placed to hand, wrist, ankle, and foot) and whole body (40)K counting as a reference method. New prediction equations were derived by multiple stepwise regression analysis. The Bland-Altman procedure was used for methods comparison. Relative to whole body counting, the manufacturer's equation overestimated BCM by 9% in men (P < 0.0001, paired t-test) and 4% in women (P = 0.002). Compared with the manufacturer's equation, the newly derived equations (r = 0.92, RMSE = 6-9%) improved accuracy (pure error = 13 vs. 7-8%) and reduced bias and limits of agreement. SFBIA and MFBIA equations did not differ in precision or accuracy. We conclude that the newly derived equations improved BCM estimates in the elderly compared with existing equations. There was no advantage of MFBIA over SFBIA equations.     

Dual X-ray absorptiometry model for characterizing water in the human forearm using multiple frequency bioimpedance analysis

The purpose of this study was to develop a method for measuring intracellular (ICW) and extracellular water (ECW) in the human forearm using multiple frequency bioimpedance analysis (MFBIA). The approach was (i) to measure whole-body and forearm fat-free mass using dual X-ray absorptiometry (DXA); (ii) to use these measurements to estimate the fat-free mass (FFM) resistivity in both the forearm and in the whole body; and (iii) to use the ratio of these FFM resistivities to estimate the resistivity in the ICW and ECW compartments of the forearm. To first demonstrate the accuracy of the DXA software in differentiating lean body mass from fat and bone within a volume of tissue, ex-vivo bovine muscle tissue samples (n = 3) were used to approximate the physical properties of the human forearm. It was found that although the human whole-body software overestimates FFM, it was slightly underestimated by the small animal software. Using this technique, DXA measures of FFM were obtained from human volunteers (n = 11; age = 20 +/- 5 years; height = 170 +/- 12 cm; mass = 64 +/- 16 kg). These measures were used in conjunction with MFBIA measures of impedance of the whole body and of the forearm to determine the resistivities of the ICW and ECW compartments of the forearm, namely 375.8 +/- 25.2 ohms cm and 55.6 +/- 3.7 ohms cm, respectively. These were used in MFBIA equations to calculate the ICW, ECW, and total arm water (TAW) volumes of the human forearm. The calculated TAW and the ECW (+/- SD) volume fraction (667.29 +/- 200.15 mL and 0.169 +/- 0.039 mL, respectively) were in agreement with literature values. MFBIA results were compared with those obtained using nuclear magnetic resonance relaxometry (NMRR). MFBIA was performed on 15 subjects before and after an intense maximal handgrip exercise to estimate changes in water volume in muscle. Following exercise, the total and intracellular water of the forearm increased on average by 8% +/- 3% and 10% +/- 4% (mean +/- SD), respectively. In 5 healthy volunteers, MFBIA and NMRR were performed before and after a similar exercise of the forearm muscle. The changes with exercise of intracellular and total arm water volumes as measured by MFBIA were estimated. The percent increases in total water were found to be 9.4% +/- 4.2% and 9.4% +/- 2.6% and in intracellular water were found to be 10.6% +/- 4.6% and 12.0% +/- 2.8% (mean +/- SD) for NMRR and MFBIA, respectively. The results show that the exercise-induced changes in ICW and TAW determined with the MFBIA model are consistent with those observed with NMRR and radiotracer literature.     

Effect of subclinical hypothyroidism on body fluid compartments.

OBJECTIVE: The present study was aimed to assess the effects of subclinical hypothyroidism on body composition (BC). SUBJECTS: Thirty-one women (age: 37 +/- 9.9 years) with a wide range of body mass index (BMI) were studied. Subclinical hypothyroidism was defined by a basal TSH > or = 4 mU/L and/or TRH stimulated peak > or = 30 mU/L. MEASUREMENTS: For each subject, weight, height, BMI, multifrequency bioelectrical impedance spectroscopy (BIS) and D2O and NaBr dilution tests were performed to assessed total body water (TBW) and extracellular water (ECW). Thyroid function (basal and TRH stimulated TSH, free T3, and free T4) were determined from fasting blood samples for all subjects. Total body dual energy X-ray absorptiometry (DXA) were used to measure fat mass (FM) and lean mass (Lean). RESULTS: The results of BIS were compared with the TBW and ECW estimated by the dilution techniques on the same individuals. The correlation was R2 = 0.65 for impedance at 5 kHz and ECW by NaBr and R2 = 0.72 for impedance at 100 kHz and TBW by D2O. Intracellular water (ICW) was calculated as differences between TBW and ECW measured by dilution methods. Percent of ECW and ICW were related to BMI (ANOVA, p < 0.001). No difference in TBW, body water distribution and body composition related to thyroid function was demonstrated. CONCLUSIONS: In our patients affected with subclinical hypothyroidism, with or without obesity, only obesity appeared related to TBW, ECW and ICW; the subclinical hypothyroidism, on the contrary, had no effect on compartments of body fluids. Bioimpedance is a valid tool to assess body fluid distribution in subclinical hypothyroidism.     

Electrical admittance for filling of the heart during lower body negative pressure in humans.

To evaluate whether electrical admittance of intracellular water is applicable for monitoring filling of the heart, we determined the difference in intracellular water in the thorax (Thorax(ICW)), measured as the reciprocal value of the electrical impedance for the thorax at 1.5 and 100 kHz during lower body negative pressure (LBNP) in humans. Changes in Thorax(ICW) were compared with positron emission tomography-determined C(15)O-labeled erythrocytes over the heart. During -40 mmHg LBNP, the blood volume of the heart decreased by 21 +/- 3% as the erythrocyte volume was reduced by 20 +/- 2% and the plasma volume declined by 26 +/- 2% (P < 0.01; n = 8). Over the heart region, LBNP was also associated with a decrease in the technetium-labeled erythrocyte activity by 26 +/- 4% and, conversely, an increase over the lower leg by 92 +/- 5% (P < 0.01; n = 6). For 15 subjects, LBNP increased thoracic impedance by 3.3 +/- 0.3 Omega (1.5 kHz) and 3.0 +/- 0.4 Omega (100 kHz), whereas leg impedance decreased by 9.0 +/- 3.3 Omega (1.5 kHz) and 6.1 +/- 3 Omega (100 kHz; P < 0.01). Thorax(ICW) was reduced by 7.1 +/- 1.9 S. 10(-4) (P < 0.01) and intracellular water in the leg tended to increase (from 37.8 +/- 4.6 to 40.9 +/- 5.0 S. 10(-4); P = 0.08). The correlation between Thorax(ICW) and heart erythrocyte volume was 0.84 (P < 0.05). The results suggest that thoracic electrical admittance of intracellular water can be applied to evaluate changes in blood volume of the heart during LBNP in humans.     

New bioimpedance model accurately predicts lower limb muscle volume: validation by magnetic resonance imaging

Conventional bioimpedance analysis (BIA) methods now simplify the representation of lower limb geometry and electrical properties for body composition estimation. In the present study, a three-dimensional model of the lower limb was assembled by segmentation of magnetic resonance cross-sectional images (MRI) for adipose tissue, skeletal muscle, and bone. An electrical network was then associated with this model. BIA and MRI measurements were made in six lean subjects (3 men and 3 women, age 32.2 +/- 6.9 yr). Assuming 0.85 S/m for the longitudinal conductivity of the muscle, the model predicted in the examined subjects an impedance profile that conformed well to the BIA impedance profile; predicted and measured resistances were similar (261.3 +/- 7.7 vs. 249 +/- 9 Omega; P = not significant). The resistance profile provided, through a simpler model, muscle area estimates along the lower limb and total leg muscle volume (mean 4,534 cm(3) for men and 4,071 cm(3) for women) with a mean of the absolute value of relative error with respect to MRI of 6.2 +/- 3.9. The new approach suggests that BIA can reasonably estimate the distribution and volume of muscles in the lower extremities of lean subjects.     

Changes in tissue water content measured with multiple-frequency bioimpedance and metabolism measured with 31P-MRS during progressive forearm exercise.

Multiple-frequency bioimpedance analysis (MFBIA) has been used to determine the cellular water composition in the human body. It is noninvasive and has demonstrated good correlations with other invasive measures of tissue water. However, the ability of this method to study transient changes in tissue water in specific muscle groups has not been explored. In this study, MFBIA was used to assess changes in forearm intracellular water (ICW), extracellular water (ECW), and total water (TW) in seven healthy volunteers during and after a progressive wrist flexion exercise protocol. In an identical trial, (31)P magnetic resonance spectroscopy ((31)P-MRS) was used to assess changes in intracellular pH and phosphocreatine (PCr). At the completion of exercise, forearm ICW increased 12.6% (SD 0.07, P = 0.003), TW increased 10.1% (SD 0.06, P = 0.005), and no significant changes were recorded for ECW. A significant correlation was found between the changes in intracellular pH and changes in ICW during exercise (r = -0.84, P = 0.018). With the use of regression analysis, average changes in P(i), PCr, and pH were found to predict changes in ICW (R(2) = 0.98, P = 0.005). In conclusion, MFBIA was sensitive enough to measure transient changes in the exercising forearm muscle. The changes seen were consistent with the hypothesis that intracellular acidification and PCr hydrolysis are important mediators of cellular osmolality and therefore may be responsible for the increased volume of water in the intracellular space that is often recorded after short-term high-intensity exercise.     

Metabolically active portion of fat-free mass: a cellular body composition level modeling analysis

The proportion of fat-free mass (FFM) as body cell mass (BCM) is highly related to whole body resting energy expenditure. However, the magnitude of BCM/FFM may have been underestimated in previous studies. This is because Moore's equation [BCM (kg) = 0.00833 x total body potassium (in mmol)], which was used to predict BCM, underestimates BCM by approximately 11%. The aims of the present study were to develop a theoretical BCM/FFM model at the cellular level and to explore the influences of sex, age, and adiposity on the BCM/FFM. Subjects were 112 adults who had the following measurements: total body water by (2)H(2)O or (3)H(2)O dilution; extracellular water by NaBr dilution; total body nitrogen by in vivo neutron activation analysis; and bone mineral by dual-energy X-ray absorptiometry. FFM was calculated using a multicomponent model and BCM as the difference between FFM and the sum of extracellular fluid and solids. The developed theoretical model revealed that the proportion of BCM to FFM is mainly determined by water distribution (i.e., E/I, the ratio of extracellular to intracellular water). A significant correlation (r = 0.90, P < 0.001) was present between measured and model-predicted BCM/FFM for all subjects pooled. Measured BCM/FFM [mean (SD)] was 0.584 +/- 0.041 and 0.529 +/- 0.041 for adult men and women (P < 0.001), respectively. A multiple linear regression model showed that there are independent significant associations of sex, age, and fat mass with BCM/FFM.     

Validation of tetrapolar bioelectrical impedance method to assess human body composition

This study was conducted to validate the relationship between bioelectrical conductance (ht2/R) and densitometrically determined fat-free mass, and to compare the prediction errors of body fatness derived from the tetrapolar impedance method and skinfold thicknesses, relative to hydrodensitometry. One-hundred and fourteen male and female subjects, aged 18-50 yr, with a wide range of fat-free mass (34-96 kg) and percent body fat (4-41%), participated. For males, densitometrically determined fat-free mass was correlated highly (r = 0.979), with fat-free mass predicted from tetrapolar conductance measures using an equation developed for males in a previous study. For females, the correlation between measured fat-free mass and values predicted from the combined (previous and present male data) equation for men also was strong (r = 0.954). The regression coefficients in the male and female regression equations were not significantly different. Relative to hydrodensitometry, the impedance method had a lower predictive error or standard error of the estimates of estimating body fatness than did a standard anthropometric technique (2.7 vs. 3.9%). Therefore this study establishes the validity and reliability of the tetrapolar impedance method for use in assessment of body composition in healthy humans.     

Body cell mass: model development and validation at the cellular level of body composition

Existing models to estimate the metabolically active body cell mass (BCM) component in vivo remain incompletely developed. The classic Moore model is based on an assumed BCM potassium content of 120 mmol/kg. Our objectives were to develop an improved total body potassium (TBK)-independent BCM prediction model on the basis of an earlier model (Cohn SH, Vaswani AN, Yasumura S, Yuen K, and Ellis KJ. J Lab Clin Med 105: 305-311, 1985), to apply this improved model in subjects to explore the sex and age dependence of the TBK/BCM ratio, to develop a new TBK/BCM model on the basis of physiological associations between TBK and total body water (TBW) at the cellular level of body composition, and to fit this new model with available reference data. Subjects were 112 healthy adults who had the following components measured: TBW by 2H2O or 3H2O, extracellular water by NaBr, total body nitrogen by in vivo neutron activation, bone mineral by dual-energy X-ray absorptiometry, and TBK by whole body counting. Human reference data were collected from earlier published reports. The improved Cohn model-derived TBK/BCM ratio was (mean +/- SD) 109.0 +/- 10.9 mmol/kg and was not significantly related to sex and age. A simplified version of the new TBK-TBW model provided a TBK/BCM ratio almost identical (109.1 mmol/kg) to that derived by the improved Cohn model. The TBK-BCM prediction formula derived from the improved and new models [BCM (kg) = 1/109 x TBK (mmol); or BCM = 0.0092 x TBK] gives BCM estimates approximately 11% higher than the classic Moore model (BCM = 0.0083 x TBK) formulated on rough tissue composition estimates. The present analyses provide a physiologically based, improved, and validated TBK-BCM prediction formula that should prove useful in body composition and metabolism research.     

Increased extracellular water compartment, relative to intracellular water compartment, after weight reduction.

The hydration of fat free mass (FFM) and extracellular (ECW) and intracellular water (ICW) compartments were studied in 30 obese premenopausal women before and after a 3-mo weight-reduction program and again after a 9-mo weight-maintenance program. Body fat was determined by a four-compartment model. Total body water and ECW were determined by deuterium dilution and bromide dilution, respectively. After the weight-reduction period, mean weight loss was 12.8 kg, and body fat was reduced on average by 10.9 kg. During weight maintenance, changes in body mass and body fat were not significant. Before weight reduction, mean ECW/ICW ratio was relatively high (0.78 +/- 0.10). During the the study, total body water and ICW did not change significantly. ECW did not change significantly after weight reduction, but 12 mo after the start ECW was significantly increased by 1 liter. The ECW/ICW ratio increased to 0.87 +/- 0.12 (month 12). The hydration of the FFM increased from 74 +/- 1 to 77 +/- 2% during the weight reduction and remained elevated during weight maintenance. In conclusion, the ECW/ICW ratio and the hydration of the FFM, did not normalize during weight reduction and weight maintenance.     

Human hydrometry: comparison of multifrequency bioelectrical impedance with 2H2O and bromine dilution

The traditionalmethod of assessing total body water (TBW), extracellular water (ECW),and intracellular water (ICW) has been the use of isotopes, on thebasis of the dilution principle. Although the development ofbioelectrical impedance techniques has eliminated many of themeasurement constraints associated with the dilution methods, thedegree of interchangeability between the two methods remains uncertain.We used multifrequency bioelectrical impedance spectroscopy (BIS),²H₂Odilution, and bromine dilution to assess TBW, ECW, and ICW in 469 healthy subjects (248 males, 221 females) aged 3-29 yr. We foundthat the TBW, ECW, and ICW estimates for the BIS and dilution methodswere significantly correlated(r² = 0.80-0.96, P < 0.0001, SE ofthe estimate = 2.3-2.7 liters). On the basis of population, theconstants used in the BIS analysis could be adjusted so that the meandifferences with the dilution methods would become zero. The SD valuesfor the mean differences between the dilution and BIS methods, however,remained significant for both males and females: TBW (±2.1-2.8liters), ECW (±1.4-1.6 liters), and ICW (2.0-3.1 liters).To improve the accuracy of the BIS measurement for an individual withinthe age range we have examined, further refinement of the constantsused in the BIS analysis is needed.

     

The validity of multifrequency bioelectrical impedance measures to detect changes in the hydration status of wrestlers during acute dehydration and rehydration

The objective of this study was to examine the validity of multifrequency direct segmental bioelectrical impedance analysis (DSM-BIA) measures to detect changes in the hydration status of wrestlers after they underwent 3% acute dehydration and a 2-hour rehydration period. Fifty-six National Collegiate Athletic Association wrestlers: (mean ± SEM); age 19.5 ± 0.2 years, height 1.73 ± 0.01 m, and body mass (BM) 82.5 ± 2.3 kg were tested in euhydrated, dehydrated (-3.5%), and 2-hour rehydration conditions using DSM-BIA to detect the changes in hydration status. The hydration status was quantified by measuring the changes in plasma osmolality (P(osm)), urine osmolality (Uosm), urine specific gravity (U(sg)), BM, and weighted segmental impedance at frequencies of 5, 20, 50, 100, and 500 kHz. Weighted segmental impedance significantly increased after a 3.5% reduction in the body weight for all the 5 frequencies evaluated, but it did not return to baseline at 2-hour rehydration. P(osm) (303 ± 0.6 mOsm·L(-1)), Uosm (617 ± 47 mOsm·L(-1)), and U(sg) (1.017 ± 0.001) all significantly increased at postdehydration and returned to baseline at 2-hour rehydration. Estimations of extracellular water were significantly different throughout the trial, but there were no significant changes in the estimations of the total body water or intracellular water. The results of this study demonstrate the potential use of DSM-BIA as a field measure to assess the hydration status of wrestlers for the purpose of minimal weight certification before the competitive season. When employing DSM-BIA to assess the hydration status, the results indicated that the changes in weighted segmental impedance at the frequencies evaluated (5, 20, 50, 100, and 500 kHz) are sensitive to acute changes in dehydration but lag behind changes in the standard physiological (plasma and urinary) markers of hydration status after a 2-hour rehydration period.     

Equation for estimating total body water by bioelectrical impedance measurements in Japanese subjects]

This article reports a study in which the equation for total body water (TBW) estimated from deuterium (2H2O)-dilution method and bioelectrical impedance measurement (BIM) is described. Subjects were 60 healthy males aged 30 +/- 18.3 yr (18-74) and 31 healthy females aged 37 +/- 17.5 yr (19-70). Total body water determined by the analysis of the dilution of orally ingested deuterium oxide (1g2H2O, 99.75 atom % excess/kg body weight) in urine. Bioelectrical impedance was measured for each subjects in a supine position using an electrical impedance analyzer (500 microA, 50kHz, T-1988K, Toyo Physical Inc.) with a four electrodes (Y-250, Nihon Kohden). The mean values of total body water and the impedance in males and females subjects were 34.1 +/- 4.27 l and 25.7 +/- 2.42 l, 567 +/- 28.5 omega and 562 +/- 32.5 omega, respectively. Height squared divided by resistance (Ht2/R) correlated well with TBW as measured by 2H2 O, r = 0.530 (p less than 0.001) in males and r = 0.782 (p less than 0.001) in females. The best-fitting regression equation to predict TBW comprised Ht2/R(X1) and body weight (X2) (R = 0.915, SEE = 1.70 l in males and R = 0.834, SEE = 1.28 l in females). Equations were provided with BIM instrument for the prediction of TBW: for males TBW, l = 0.1983X1 + 0.4004X2 - 0.7938 and for females TBW, l = 0.3536X1 + 0.1269X2 + 3.3417. These results suggest that bioelectrical impedance measurement is a useful measure of total body water in Japanese subjects.     

Use of bioelectrical impedance spectroscopy to provide a measure of body composition in sows

The ability to accurately estimate fat mass and fat-free mass (FFM) has the potential to improve the way in which sow body condition can be managed in a breeding herd. Bioelectrical impedance spectroscopy (BIS) has been evaluated as a practical technique for assessment of body composition in several livestock species, but similar work is lacking in sows. Bioelectrical impedance uses population-specific algorithms that require values for the apparent resistivities of body fluids and body proportion factors. This study comprised three major aims: (i) to derive apparent resistivity coefficients for extracellular water (ECW) and intracellular water (ICW) required for validation of BIS predictions of total body water (TBW) in live sows against standard reference tracer dilution methods; (ii) to develop predictions of TBW to body composition prediction algorithms, namely FFM, by developing a body geometry correction factor (Kb) and (iii) to compare the BIS predictions of FFM against existing impedance predictors and published prediction equations for use in sows, based on physical measurements of back-fat depth and BW (P2-based predictors). Whole body impedance measurements and the determination of TBW by deuterium dilution and ECW by bromide dilution were performed on 40 Large White x Landrace sows. Mean apparent resistivity coefficients of body fluids were 431.1 Ω.cm for ECW and 1827.8 Ω.cm for ICW. Using these coefficients, TBW and ECW were over-estimated by 6.5 and 3.3%, respectively, compared to measured reference values, although these differences were not statistically different (P > 0.05). Mean Kb was 1.09 ± 0.14. Fat-free mass predictions were 194.9 kg, which equates to 60.9% of total sow weight, and 183.0 kg for BIS and the deuterium dilution method, respectively. Mean differences between the predicted and measured FFM values ranged from − 8.2 to 32.7%, but were not statistically different (P > 0.05). Method validation (leave-one-out procedure) revealed that mean differences between predicted and measured values were not statistically significant (P > 0.05). Of the impedance-based predictors, equivalence testing revealed that BIS displayed the lowest test bias of 11.9 kg (8.2%), although the P2-based prediction equations exhibited the lowest bias and percentage equivalence, with narrow limits of agreement. Results indicate although differences between mean predicted and measured values were not significantly different, relatively wide limits of agreement suggest BIS as an impractical option for assessing body composition in individual sows compared to the use of existing prediction equations based on BW and back fat.