BioImpedance Analysis

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Authors - W

Wang, M.; Dickin, F.J.; Williams, R.A.
Title   The grouped node technique as a means of handling large
        electrode surfaces in electrical impedance tomography
Journal Physiological Measurement
        16
         Suppl. 3A
        AUG
Year    1995
Page    A219-A226
Address M Wang
        Univ Manchester
        Inst Sci & Technol
        Dept Chem Engn
        POB 88
        Manchester M60 1QD
        Lancs, England
Serial# 0967-3334
Keys    COMPUTED-TOMOGRAPHY
Abs.    A finite-element method employing a grouped node technique
        as a means of handling large electrode surfaces in
        electrical impedance process tomography is presented. The
        technique groups sets of nodes representing discrete
        boundary electrodes in a two-dimensional finite-element
        mesh into corresponding sets of single nodes via a
        transformation matrix G. The subsequent field solution is
        obtained based on the new boundary conditions in the
        standard way after implementing this procedure. Comparison
        of the resultant boundary voltage profiles from this
        approach against measurements made on laboratory scale
        phantoms are reported.

Ward, L.C.; Cornish, B.; Thomas, B.
Title   Untitled
Journal American Journal of Human Biology
        7
        3
Year    1995
Page    289-290
Address LC Ward
        Univ Queensland
        Brisbane
        Qld, Australia
Serial# 1042-0533
Keys    BIOELECTRICAL IMPEDANCE ANALYSIS; TOTAL-BODY WATER; FLUID

Ward, L.C.; Thomas, B.J.; Cornish, B.H.
Title   Multifrequency impedance in the assessment of body water
        losses during dialysis - Comment
Journal Renal Physiology and Biochemistry
        18
        5
        SEP-OCT
Year    1995
Page    267-268
Address LC Ward
        Univ Queensland
        Dept Biochem
        Brisbane
        Qld 4072, Australia
Serial# 1011-6524

Author   - Ward LC
Author   - Byrne NM
Author   - Rutter K
Author   - Hennoste L
Author   - Hills AP
Author   - Cornish BH
Author   - Thomas BJ
Title    - Reliability of multiple frequency bioelectrical impedance
           analysis: An intermachine comparison.
         - English
         - Article
         - Ward LC, Univ Queensland, Dept Biochem, Brisbane, Qld
           4072, AUSTRALIA
         - The technical reliability (i.e., interinstrument and
           interoperator reliability) of three SEAC-swept frequency
           bioimpedance monitors was assessed for both errors of
           measurement and associated analyses. In addition,
           intraoperator and intrainstrument variability was
           evaluated for repeat measures over a 4-hour period. The
           measured impedance values from a range of resistance-
           capacitance circuits were accurate to within 3% of
           theoretical values over a range of 50-800 ohms. Similarly,
           phase was measured over the range 1 degrees-19 degrees
           with a maximum deviation of 1.3 degrees from the
           theoretical value. The extrapolated impedance at zero
           frequency was equally well determined (+/-3%). However,
           the accuracy of the extrapolated value at infinite
           frequency was decreased, particularly at impedances below
           50 ohms (approaching the lower limit of the measurement
           range of the instrument). The interinstrument/operator
           variation for whole body measurements were recorded on
           human volunteers with biases of less than +/-1% for
           measured impedance values and less than 3% for phase. The
           variation in the extrapolated values of impedance at zero
           and infinite frequencies included variations due to
           operator choice of the analysis parameters but was still
           less than +/-0.5%. (C) 1997 Wiley-Liss, Inc.
Journal - Amer J Hum Biol 1997;9(1):63-72

Watson, S.J.; Smallwood, R.H.; Brown, B.H.; Cherian, P.;
Bardhan, K.D.
Determination of the relationship between the pH and
conductivity of gastric juice
Physiological Measurement
17
1
FEB
1996
21-27
SJ Watson
Royal Hallamshire Hosp
Dept Med Phys & Clin Engn
1 Floor
Glossup Rd
Sheffield S10 2JF
S Yorkshire, England
0967-3334
conductivity; electrical impedance tomography; gastric
acidity; gastric secretion
Studies of gastric secretion were carried out on 14
subjects, some of whom had taken acid secretion inhibitors.
In vitro studies were performed in an attempt to ascertain
the effect of H+ and Na+ ions on conductivity. There is a
strong correlation between intragastric pH and conductivity
for pH < 2, but none of the gastric samples were isotonic.
The measured conductivity of the samples was therefore
considerably lower than predicted for isotonic gastric
juice.

Author   - Wen ZC
Author   - Chen SA
Author   - Chiang CE
Author   - Tai CT
Author   - Lee SH
Author   - Chen YZ
Author   - Yu WC
Author   - Huang JL
Author   - Chang MS
Title    - Temperature and impedance monitoring during radiofrequency
           catheter ablation of slow AV node pathway in patients with
           atrioventricular node reentrant tachycardia.
         - English
         - Article
         - Chen SA, Vet Gen Hosp, Div Cardiol, 201 SEC 2, Shih Pai
           Rd, Taipei, TAIWAN
         - This study was designed to observe the changes of
           temperature and impedance and to find the role of
           temperature control in radiofrequency ablation of slow
           pathways in patients with AN node reentrant tachycardia.
           Power, impedance and temperature were measured during each
           application of radiofrequency energy while the generator
           was operated in the power control mode. A total of 760
           applications were delivered in 76 patients. The success
           rate was 100% without recurrence during a follow-up period
           of 8+/-3 months. The mean catheter tip temperature
           associated with successful ablation was 51.3+/-5.4 degrees
           C (range 45 degrees C to 64 degrees C), and significantly
           higher than the unsuccessful pulses (48.7+/-6.2 degrees C,
           P <0.05). The mean temperature was 49.8+/-3.1 degrees C
           during accelerated junctional rhythm, significantly higher
           than the pulses without this rhythm. The mean temperature
           correlated well with early decrease of impedance (r=0.71,
           P <0.001), and an early decrease of impedance more than 5
           ohms had an 87% positive predictive value for adequate
           tissue heating. These data suggested that, if temperature
           monitoring was available, setting the target temperature
           at about 51 degrees C could achieve adequate tissue
           heating for successful ablation of slow pathway; if not,
           impedance monitoring with an early decrease of impedance
           >5 ohms could predict adequate tissue heating.
Journal - Int J Cardiol 1996 DEC 13;57(3):257-263

White-E-M; Wilson-A-C; Greene-S-A; McCowan-C; Thomas-G-E; Cairns-A-
Y; Ricketts-I-W
Body mass index centile charts to assess fatness of British
children.
Archives of Disease in Childhood 72(1): 38-41
1995
English
Body mass index (BMI) relates weight to height and reflects the
shape of a child, but because of age dependency it has not been
used conventionally for the estimation of fatness in children.
From measurements of Tayside children (n = 34,533) centile charts
were constructed for BMI (wt/ht-2) from the raw data of height and
weight, using Cole's LMS method for normalized growth standards.
These data were compared with the only available European BMI
charts published from data of French children obtained over a
period of 24 years from 1956-79. British children appear to be '
fatter'. Within a subgroup (n = 445) the BMI values were
correlated with estimations of body fat, for boys and girls, from
skinfold thickness (r = 0.8 and 0.81) and bioelectrical impedance (
r = 0.65 and 0.7). The limits of acceptable BMI have yet to be
defined.

Williams, P.A.; Saha, S.
The electrical and dielectric properties of human bone tissue
and their relationship with density and bone mineral content
Annals of Biomedical Engineering
24
2
MAR-APR
1996
222-233
S Saha
Univ Calif Riverside
Marlan & Rosemary Bourns Coll Engn
Riverside, CA 92521 USA
0090-6964
electrical properties; human bone; density; resistance;
capacitance
FLUID-SATURATED BONE; PULSED ELECTROMAGNETIC-FIELDS; BOVINE
FEMORAL BONE; IMPEDANCE TOMOGRAPHY; CORTICAL BONE; FREQUENCY;
CONDUCTIVITY; DIAPHYSIS; PERMITTIVITY; FRACTURES
In this study, we examined the electrical properties of wet
human cortical and cancellous bone tissue from distal tibia
and their relationship to the wet, dry, and ash tissue
densities. The resistivity and specific capacitance of both
cortical and cancellous bone were determined for different
frequencies and directions (orientation). The wet, dry, and
ash tissue densities of the bone samples were measured, and
the ash content was determined. Correlation and regression
analysis was used to examine the possible relationships
among the electrical properties and the tissue densities
for cancellous and cortical bone specimens separately as
well as for all of the bone specimens combined. Highly
significant positive correlations (p < 0.001) were found
between the wet density of bone and the dry and ash
densities. The specific capacitance of the cancellous bone
specimens in all three orthogonal directions showed
significant (p < 0.01) positive correlations with the wet,
dry, and ash densities. In general, the specific
capacitance depended more on density for all bone specimens,
and only a weak relationship was found between the
resistivity of human cortical bone and density.

Wolf, M.; Weigert, A.; Kreymann, G.
Title   Body composition and energy expenditure in thyroidectomized
        patients during short-term hypothyroidism and thyrotropin-
        suppressive thyroxine therapy
Journal European Journal of Endocrinology
        134
        2
        FEB
Year    1996
Page    168-173
Address M Wolf
        Univ Hamburg
        Krankenhaus Eppendorf
        Med Kernklin & Poliklin
        Martinistr 52
        D-20246 Hamburg, Germany
Serial# 0804-4643
Keys    FAT-FREE MASS; BIOELECTRICAL IMPEDANCE ANALYSIS; RESTING
        METABOLIC-RATE; THYROID-HORMONES; WOMEN; MEN
Abs.    Thyroid hormone levels are a major determinant of energy
        balance and are thought to modify body composition by their
        effects on metabolism of lipids, carbohydrate and protein.
        The present study evaluates changes of body composition and
        basal energy expenditure (BEE) in thyroidectomized short-
        term profound hypothyroidism while off all thyroid hormone
        before diagnostic whole-body I-131-imaging and while on
        thyrotrophin-suppressive thyroxine therapy, Basal energy
        expenditure was assessed by indirect calorimetry, and four-
        point body impedance analysis was used to estimate body
        composition. Patients were compared with healthy controls
        matched with respect to sex, age, height and weight,
        Compared to healthy controls the percentages of body water
        and body cell mass were significantly lower while the
        percentage of fat was significantly higher in patients
        during shore-term hypothyroidism. Weight did not change
        significantly when patients were put on thyroxine treatment,
        but body fat (-0.95 +/- 2.25 kg, p < 0.01) decreased while
        body water (+0.94 +/- 1.31kg, p < 0.01) and body cell mass
        (+0.9 +/- 2.5 kg, p < 0.05) increased, With thyroxine
        replacement, body composition was not significantly
        different between patients and controls. Compared to
        healthy controls, BEE was significantly lower in patients
        without thyroxine replacement (5265 +/- 766 kJ/24 h vs 6362
        +/- 992 kJ/24 h; p < 0.001), With thyroxine treatment, BEE
        increased (6492 +/- 967kJ/24 h) but was not significantly
        different from the controls (p > 0.05). Neither body
        composition nor BEE was significantly different in a
        subgroup of thyroxine-treated patients with free
        triiodothyronine or thyroxine values above the normal
        range. In conclusion, both body composition and energy
        expenditure showed significant changes when patients were
        deprived of thyroid hormone. However, no evidence of excess
        metabolic effects of thyroid hormone during thyrotrophin-
        suppressive thyroxine therapy was found.

Author Woltjer, H.H.; Bogaard, H.J.; Scheffer, G.J.;
        Vanderspoel, H.I.; Huybregts, M.A.J.M.; Devries, P.M.J.M.
Title   Standardization of non-invasive impedance cardiography for
        assessment of stroke volume: Comparison with thermodilution
Journal British Journal of Anaesthesia
        77
        6
        DEC
Year    1996
Page    748-752
Address PMJM Devries
        Acad Hosp Vu
        Dept Pulm Med
        POB 7075
        NL-1007 MB Amsterdam, Netherlands
Serial# 0007-0912
Keys    measurement techniques, impedance cardiography; measurement
        techniques, thermodilution; monitoring, stroke volume; model,
        mathematical
        THORACIC ELECTRICAL BIOIMPEDANCE; SYSTOLIC-TIME INTERVALS;
        CARDIAC-OUTPUT; 2 EQUATIONS; DERIVATION; EXERCISE
Abs.    Since its introduction by Kubicek and colleagues, impedance
        cardiography has been suggested as a non-invasive, simple,
        safe and cost-effective method of measuring stroke volume.
        Several controversial reports on its validity have been
        published. Pitfalls of this method included the nature of
        the electrode system and the validity of the equations.
        Therefore, the purpose of this study was to compare two
        different spot electrode arrays and the two most frequently
        used stroke volume equations with each other and with
        thermodilution. In 37 patients, 24-36 h after cardiac
        surgery, we performed simultaneous measurements of stroke
        volume with impedance cardiography (SVIC) and with
        thermodilution (SVTD) SVIC was obtained using the lateral
        spot (LS) electrode array, according to Bernstein, and a
        newly proposed modified semi-circular (MSG) spot electrode
        array. The equations of Kubicek and Sramek-Bernstein were
        used to calculate SVIC. The Sramek-Bernstein equation was
        valid only when the LS array was used; the Kubicek equation
        determined SVTD correctly only when the MSC array was used.
        However, a considerably better correlation and agreement
        (mean difference (2 SD)) was found between SVIC and SVTD
        for the latter (r = 0.90, 0.5 (17.1) ml vs r = 0.64, -4.9
        (31.8) ml for the Sramek-Bernstein equation). We conclude
        that the most valid measurement of stroke volume using
        impedance cardiography was obtained when the MSC array was
        used together with Kubicek's equation.

Wong, K.C.; Xiong, D.W.; Kerr, P.G.; Borovnicar, D.J.;
        Stroud, D.B.; Atkins, R.C.; Strauss, B.J.G.
Title   Kt/V in CAPD by different estimations of V
Journal Kidney International
        48
        2
        AUG
Year    1995
Page    563-569
Address PG Kerr
        Monash Med Ctr
        Dept Nephrol
        Clayton
        Vic 3168, Australia
Serial# 0085-2538
Keys    TOTAL-BODY WATER; BIOELECTRICAL-IMPEDANCE ANALYSIS; DIALYSIS;
        UREA; HEMODIALYSIS; VOLUMES
Abs.    This study compared the measurements of total body water
        (TBW) by 58% body weight (TBW58%), the Watson equation
        (TBWWV) and bioelectric impedance (TBWBIA) with the gold
        standard, Deuterium oxide (TBWD2O) dilution method in
        twenty continuous ambulatory peritoneal dialysis (CAPD)
        patients. TBW volumes were highest when calculated as
        TBW58% (42.6 +/- 9.4 liter) and lowest when calculated from
        TBWWV (34.6 +/- 6.8 liter). TBWBIA underestimated TBW when
        compared to TBWD2O, although the difference was not
        statistically significant (37.1 +/- 9.8 liter and 38.8 +/-
        9.3 liter, respectively). In fact, TBWBIA correlated
        strongly with TBWD2O (r = 0.8, P < 0.0001). These
        discrepancies resulted in significant differences when Kt/V
        week(-1) derived from the four methods were compared. To
        determine the effect of percent fat mass on the estimation
        of TBW by each method, we compared TBW and Kt/V week(-1)
        derived from the four methods in nine CAPD patients who had
        normal percent fat mass (Non-Obese) and 11 CAPD patients
        who had greater than normal % fat mass (Obese). In the Non-
        Obese group, there was close correlation of TBWBIA, TBWWV
        and TBW58% when compared with TBWD2O (r = 0.93, P < 0.001,
        r = 0.89, P < 0.01 and R = 0.86, P < 0.01, respectively).
        Also, Kt/V week(-1) derived from TBWBIA, TBWWV and TBW58%
        correlated strongly with Kt/V week(-1) from TBWD2O (r =
        0.93, P < 0.0005, r = 0.83, P < 0.01 and r = 0.8, P < 0.01,
        respectively). In the Obese patients, the correlations
        between TBWD2O and TBWBIA and TBWWV were only moderate in
        strength (r = 0.67, P = 0.02 and r = 0.61, P = 0.04,
        respectively). There was no significant correlation between
        TBW58% and TBWD2O in the Obese group (r = 0.44, P = NS).
        Kt/V week(-1) derived from TBWBIA; TBWWV and TBW58% had
        only moderate correlation with Kt/V week(-1) from D2O.
        Similar findings in TBW measurements and Kt/V week(-1) were
        obtained in CAPD patients (N = 9) who had normal BMI (< 26
        kg/m(2); termed, Normal Weight) and those who had BMI > 26
        kg/m(2) (N = 11; termed, Overweight; data not shown). Our
        results suggest that the discrepancies in TBW and Kt/V in
        CAPD patients with different body habitus were a result of
        relative body fat mass. Thus, in CAPD patients who were not
        obese, all four methods gave good correlations of TBW and
        Kt/V. Even though TBWBIA had the smallest bias and the best
        correlation with TBWD2O, the wide limits of agreement
        between BIA and D2O dilution suggest that BIA is
        inappropriate at the present time for assessing TBW in CAPD
        patients, especially in the obese. In the case of
        discrepancy in Kt/V and clinical outcome, adequacy of
        dialysis in CAPD patients should be assessed by accurate
        measurement of V using the D2O dilution method.

Woodburn, K.R.; Murtagh, A.; Breslin, P.; Reid, A.W.;
        Leiberman, D.P.; Gilmour, D.G.; Pollock, J.G.
Title   Insonation and impedance analysis in graft surveillance
Journal British Journal of Surgery
        82
        9
        SEP
Year    1995
Page    1222-1225
Address KR Woodburn
        Eastern Gen Hosp
        Dept Surg
        Seafield Rd
        Edinburgh EH6 7LN
        Midlothian, Scotland
Serial# 0007-1323
Keys    FEMORODISTAL GRAFT; EARLY DIAGNOSIS; VEIN; STENOSES; IDENTIFY;
        DUPLEX
Abs.    Seventy consecutive patients with infrainguinal bypass
        grafts entered a 1-year graft surveillance programme
        involving colour duplex scanning, direct graft insonation
        and computer-assisted impedance analysis. Graft patients
        with a positive duplex scan, high frequencies on graft
        insonation or an impedance value above 0.50 subsequently
        underwent arteriography. Sixteen patients were excluded
        before the initial surveillance visit. The 54 remaining
        patients with grafts (30 vein, 24 synthetic) underwent a
        total of 137 surveillance visits, with 21 grafts confirmed
        to be 'at risk'. The sensitivity of an impedance value
        above 0.55 in identifying these grafts was 86 per cent,
        rising to 95 per cent when combined with graft insonation.
        Duplex scanning did not identify any abnormalities in 11
        grafts that were either shown by arteriography to be 'at
        risk' or occluded before arteriography. Impedance
        measurement and graft insonation are simple screening
        techniques with a high sensitivity (when combined), which
        identify 'at risk' infrainguinal grafts. Positive graft
        insonation or an impedance value over 0.55 will identify
        all 'at risk' vein grafts while minimizing the number of
        unnecessary arteriograms.

Woodrow, G.; Oldroyd, B.; Turney, J.H.; Smith, M.A.
Title   Segmental bioelectrical impedance in patients with chronic
        renal failure
Journal Clinical Nutrition
        15
        5
        OCT
Year    1996
Page    275-279
Address G Woodrow
        Univ Leeds
        Gen Infirm
        Renal Unit
        Great George St
        Leeds LS1 3EX
        W Yorkshire, England
Serial# 0261-5614
Keys    TOTAL-BODY WATER; FAT-FREE MASS; BIOIMPEDANCE ANALYSIS;
        HEMODIALYSIS-PATIENTS; WHOLE-BODY; DIALYSIS; FLUID
Abs.    We studied changes in hydration by whole body and segmental
        (arm, leg and trunk) bioelectrical impedance analysis (BIA)
        in patients with chronic renal failure (CRF) undergoing
        haemodialysis and continuous ambulatory peritoneal dialysis
        (CARD). Mean (SD) fluid removal by haemodialysis of 1.38
        (0.81) kg was overestimated by whole body BIA at 1.83
        (1.13) l, P < 0.005. Peritoneal fluid drained from the CARD
        patients of 1.88 (0.36)kg was underestimated by whole body
        BIA at 0.59 (0.35) l, P < 0.0001. Resistance and reactance
        significantly increased for the whole body and all segments
        (except trunk reactance) after haemodialysis. Drainage of
        CARD fluid resulted in smaller Increases in trunk
        resistance and whole body resistance. The increase in trunk
        resistance was less in CARD than haemodialysis patients,
        even though the volume of fluid drained from the peritoneum
        in CARD patients exceeded that removed from the whole body
        during haemodialysis. We conclude that whole body BIA does
        not estimate changes in body fluid with sufficient accuracy
        to be of use in clinical practice. Segmental impedance may
        be a potentially useful method for investigation of
        regional changes in body fluid, though is insensitive to
        changes within the peritoneal cavity.

Author   - Woodrow G
Author   - Oldroyd B
Author   - Turney JH
Author   - Davies PSW
Author   - Day JME
Author   - Smith MA
Title    - Measurement of total body water and urea kinetic modelling
           in peritoneal dialysis.
         - English
         - Article
         - Woodrow G, Univ Leeds, Gen Infirm, Renal Unit, Great
           George St, Leeds LS1 3EX, W Yorkshire, ENGLAND
         - Studies of the effect of Kt/V (urea) on prediction of
           outcome in patients on peritoneal dialysis have shown
           conflicting results. We performed this study to examine
           the effects of the measurement of V by varying techniques
           on the calculation of Kt/V, using body water estimated by
           deuterium oxide dilution (D2O dilution) as the criterion
           method for estimation of V. Studies were performed in 20
           peritoneal dialysis patients. Kt was calculated from 24-
           hour dialysate and urine collections and V estimated by
           D2O dilution, Watson formulae, 58% of body weight,
           bioelectrical impedance (BIA) and 73% of fat-free mass
           estimated by DEXA. V was also measured in 35 healthy
           controls. Hydration, expressed as body water by D2O
           dilution as a percentage of fat-free mass estimated by
           DEXA did not differ between peritoneal dialysis patients
           71.0 (4.9)% and a healthy control group 71.1 (5.0)%. Mean
           Kt/V using D2O dilution was 2.14 (0.36). The other
           techniques resulted in a significantly lower Kt/V; Watson
           equations 2.01 (0.35), p <0.005, BIA 1.93 (0.31), p
           <0.0001, DEXA 2.06 (0.28), p <0.05, 58% body weight 1.83
           (0.38), p <0.0001. Limits of agreement of Kt/V by the
           simpler techniques compared with D2O dilution [mean
           difference of (other techniques - D2O dilution) as % of
           mean values +/- 95% limits of agreement] were Watson
           equation -5.9 +/- 15.3%, BIA -10.1 +/- 15.5%, DEXA -3.4 +/-
           13.5% and 58% body weight -9.9 +/- 23.5%. Differences in
           Kt/V from estimates using D2O dilution were significantly
           negatively correlated with body fat for 58% body weight
           (r=-0.80, p <0.0001) and the Watson formulae (r=-0.49, p
           <0.05) but not for BIA or DEXA. We conclude that
           clinically significant variation in Kt/V may occur due to
           the estimation of V and may account for the uncertainty of
           the value of Kt/V as a predictor of outcome in peritoneal
           dialysis patients. Estimating V by BIA and DEXA did not
           have any benefit over the Watson formulae in terms of
           agreement with D2O dilution, though did avoid systematic
           errors related to body fat. Estimation of V as a fixed
           proportion of body weight is clearly inferior to the other
           techniques.
Journal - Clin Nephrol 1997 JAN;47(1):52-57

Author Woodrow, G.; Oldroyd, B.; Turney, J.H.; Davies, P.S.W.;
        Day, J.M.E.; Smith, M.A.
Title   Four-component model of body composition in chronic renal
        failure comprising dual-energy X-ray absorptiometry and
        measurement of total body water by deuterium oxide dilution
Journal Clinical Science
        91
        6
        DEC
Year    1996
Page    763-769
Address G Woodrow
        Univ Leeds
        Gen Infirm
        Renal Unit
        Great George St
        Leeds LS1 3EX
        W Yorkshire, England
Serial# 0143-5221
Keys    body composition; chronic kidney failure; densitometry; X-ray
        absorptiometry; total body water
        BIOELECTRICAL-IMPEDANCE ANALYSIS; FAT-FREE MASS; HEMODIALYSIS-
        PATIENTS; NEUTRON-ACTIVATION; DIALYSIS PATIENTS; NITROGEN;
        HUMANS; HYDRATION; POTASSIUM; PROTEIN
Abs.    1. Assessment of nutrition in patients with chronic renal
        failure by body composition measurement techniques may be
        affected by variable hydration,
        2. This study aimed to derive a four-component model of
        body composition (consisting of fat, protein, total body
        water and body mineral) from a combination of dual-energy X-
        ray absorptiometry and total body water measured by
        deuterium oxide dilution, allowing assessment of body
        protein stores without the effect of variation in hydration,
        Patients with chronic renal failure on haemodialysis,
        peritoneal dialysis and conservative treatment and a
        control group were studied, Patients with chronic renal
        failure were at an 'ideal' state of hydration on clinical
        assessment.
        3. Hydration was defined by total body water as a
        percentage of fat-free mass measured by dual-energy X-ray
        absorptiometry, and no differences were found between
        chronic renal failure subgroups and control subjects
        (except in the female undialysed chronic renal failure
        subgroup), Hydration was significantly correlated with
        percentage total body fat in the control groups but not in
        patients with chronic renal failure.
        4. Lean tissue measured by dual-energy X-ray absorptiometry
        was significantly reduced in three of the six chronic renal
        failure groups compared with control subjects (male and
        female patients on haemodialysis and female patients on
        peritoneal dialysis), Protein estimated from the four-
        component model failed to detect these abnormalities,
        5. Lean tissue measured by dual-energy X-ray absorptiometry
        in normal subjects strongly correlated with fat-free mass
        measured by total body potassium in normal subjects (male r
        = 0.91; female r = 0.89, both P < 0.0001), The correlation
        of protein estimated from the four-component model with fat-
        free mass measured by total body potassium was far weaker
        in male control subjects (r = 0.51, P<0.05) and not
        significant in female control subjects (r = 0.38, P not
        significant), In the normal subjects protein estimated from
        the four-component model showed a much greater variation
        from protein estimated by total body potassium than did
        protein estimated simply as 27% of dual-energy X-ray
        absorptiometry fat-free mass minus total body mineral.
        6. Hydration in patients with chronic renal failure in whom
        fluid balance is believed to be normal on clinical criteria
        does not differ from that in normal subjects, The combined
        model of dual-energy X-ray absorptiometry and total body
        water is not a useful method for the measurement of body
        protein.