Reliability in estimates of body composition of birds: oxygen-18 versus deuterium dilution

Body composition in birds was evaluated indirectly by 18O and 2H dilution. Body composition was determined by whole-body chemical analysis of eight adult roosters (Gallus gallus). In vivo measurements of total body water (TBW) were carried out using doubly labeled water (2H2 18O). Estimated dilution spaces using both the plateau and intercept approaches were compared with the results obtained by carcass lyophilization. Both 18O and 2H slightly overestimated TBW compared with the results obtained by lyophilization, by 2.2%+/-1.9% and 5.7%+/-0.2%, respectively; both differences were statistically significant (P<0.01). The difference between these isotope estimations was significant (P<0.001). However, isotope dilution spaces and TBW were highly correlated. There was a strong inverse relationship between total body fat and TBW percentages (r2=0.98, P<0.0001). The relation between TBW and body protein was significant. Water content in lean body mass (72.8%) obtained in our study was very close to that reported in mammals, demonstrating no fundamental difference in tissue water content between birds and mammals. Estimated body fat and protein values from isotopic dilution did not significantly differ from values obtained by direct chemical analysis (P>0.05), except for body fat in the Pace and Rathbun approach (Table 3). Although estimation of TBW and body composition by isotope dilution is time consuming and expensive, deuterium offers a reliable and low-cost alternative compared with 18O. The advantage of in vivo estimation of TBW with isotopic dilution in combination with the regression approach is that it permits repeated measurements of body composition on the same birds under laboratory and free-living conditions.     

Body composition in mink (Mustela vison) kits during 21-42 days postpartum using estimates of hydrogen isotope dilution and direct carcass analysis

We compared carcass analysis and hydrogen isotope dilution methods to measure total body water (TBW) and body composition in a small altricial carnivore, the mink. Dilution space (D) of mink at 21-42 days of age (n=20), was determined after subcutaneous administration of tritiated water. The same animals were then used to determine TBW and body composition by carcass analysis and to derive predictive empirical relationships between TBW and total body fat, protein and energy. A separate validation set of 27 kits was used to test the accuracy of predicting body composition from TBW. D overestimated TBW by a consistent and predictable 4.1% (R(2)=0.999, P<0.001). Our estimates of fat, protein and energy content, using equations derived from TBW, were not significantly different than those obtained from direct carcass analysis (P>0.980) in either the initial or validation set of mink. TBW was shown to decrease from 81 to 76% and total body protein to increase from 14 to 19% of LBM of the kits from 21 to 42 days of age. Although a rapidly changing hydration state was apparent in neonates, we conclude that when this is taken into account, accurate estimates of body composition can be obtained from hydrogen isotope dilution.     

Evaluation of the deuterium dilution method to estimate body composition in the barnacle goose: accuracy and minimum equilibration time

We examined body composition in barnacle geese (Branta leucopsis) by proximate carcass analysis and by deuterium isotope dilution. We studied the effect of isotope equilibration time on the accuracy of total body water (TBW) estimates and evaluated models to predict fat-free mass (FFM) and fat mass (FM) from different measurements varying in their level of invasiveness. Deuterium enrichment determined at 45, 90, and 180 min after isotope injection did not differ significantly. At all sampling intervals, isotope dilution spaces (TBW(d)) consistently overestimated body water determined by carcass analysis (TBW(c)). However, variance in the deviation from actual TBW was higher at the 45-min sampling interval, whereas variability was the same at 90 and 180 min, indicating that 90 min is sufficient time to allow for adequate equilibration. At 90 min equilibration time, deuterium isotope dilution overestimated TBW(c) by 7.1% +/= 2.6% (P < 0.001, paired t-test, n=20). This overestimate was consistent over the range of TBW studied, and TBW(c) could thus be predicted from TBW(d) (r2=0.976, P<0.001). Variation in TBW(c) and TBW(d) explained, respectively, 99% and 98% of the variation in FFM. FM could be predicted with a relative error of ca. 10% from TBW estimates in combination with body mass (BM). In contrast, BM and external body measurements allowed only poor prediction. Abdominal fat fresh mass was highly correlated to total FM and, if the carcass is available, allows simple means of fat prediction without dissecting the entire specimen.     

Dual-energy X-ray absorptiometry lean soft tissue hydration: independent contributions of intra- and extracellular water

Dual-energy X-ray absorptiometry (DEXA) provides a measure of lean soft tissue (LST). LST hydration, often assumed to be constant, is relevant to several aspects of DEXA body composition estimates. The aims of this study were to develop a theoretical model of LST total body water (TBW) content and to examine hydration effects with empirically derived model coefficients and then to experimentally test the model's prediction that, in healthy adults, LST hydration is not constant but varies as a function of extra- and intracellular water distribution (E/I). The initial phase involved TBW/LST model development and application with empirically derived model coefficients. Model predictions were then tested in a cross-sectional study of 215 healthy adults. LST was measured by DEXA, extracellular water (ECW) by NaBr dilution, intracellular water (ICW) by whole body (40)K counting, and TBW by (2)H(2)O dilution. TBW estimates, calculated as ECW + ICW, were highly correlated with (r = 0.97, SEE = 2.1 kg, P < 0.001) and showed no significant bias compared with TBW measured by (2)H(2)O. Model-predicted TBW/LST was almost identical to experimentally derived values (means +/- SD) in the total group (0.767 vs. 0.764 +/- 0.028). LST hydration was significantly correlated with E/I (total group, r = 0.30, SEE = 0.027, P < 0.001). Although E/I increased with age (men, r = 0.48; women, r = 0.37; both P < 0.001), the association between TBW/LST and age was nonsignificant. Hydration of the DEXA-derived LST compartment is thus not constant but varies predictably with ECW and ICW distribution. This observation has implications for the accuracy of body fat measurements by DEXA and the use of TBW as a means of checking DEXA system calibration.     

A prediction equation for total body water from bioelectrical impedance in Japanese children

Total body water (TBW) measured by isotope dilution techniques can be used to assess body composition safely and accurately in children. Unfortunately, this method is not readily available for most research projects, particularly when working with large groups of people, because the equipment is complicated and highly specialized. Bioelectrical impedance (BI) method is a simple, quick, and inexpensive method for the assessment of total body water (TBW). In Japanese child population, however, a lack of prediction equations is a problem to determine TBW. The purpose of this study was to determine the prediction equation for TBW determination in Japanese children using the isotope dilution technique as the reference method. Seventy Japanese children (39 boys, 31 girls) with ages ranging between 3 and 6 years participated in this study. They were randomly divided into the validation group (26 boys, 20 girls) and cross-validation group (13 boys, 11 girls). In a forward stepwise regression analysis, 96% of the variability in TBW measured by deuterium oxide (D(2)O) dilution could be predicted by the following equation: TBW(kg)=0.149 x Resistance Index (Stature(2)/resistance, cm(2)/Omega)+0.244 x Weight(kg)+0.460 x Age(y)+0.501 x Sex (boy=1, girl=0)+1.628, with a root mean square error (RMSE) of 0.440 kg in the validation group. This equation predicted TBW in the cross-validation group with R(2)=0.946 and a pure error (PE)=0.400 kg TBW. Hence, this equation should be applicable for predicting TBW in Japanese children aged 3-6 y.     

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.     

Consequences of a low litter birth weight phenotype for postnatal lean growth performance and neonatal testicular morphology in the pig

The consequences of a low litter average birth weight phenotype for postnatal growth performance and carcass quality of all progeny, and testicular development in male offspring, were investigated. Using data from 25 sows with one, and 223 sows with two consecutive farrowing events, individual birth weight (BW) was measured and each litter between 9 and 16 total pigs born was classified as low (LBW), medium (MBW) or high (HBW) birth weight: low and high BW being defined as >1 standard deviation below or above, respectively, the population mean for each litter size. Litter average BW was repeatable within sows. At castration, testicular tissue was collected from 40 male pigs in LBW and HBW litters with individual BW close to their litter average BW and used for histomorphometric analysis. LBW piglets had a lower absolute number of germ cells, Sertoli cells and Leydig cells in their testes and a higher brain : testis weight ratio than HBW piglets. Overall, LBW litters had lower placental weight and higher brain : liver, brain : intestine and brain : Semitendinosus muscle weight ratios than MBW and HBW litters. In the nursery and grow–finish (GF) phase, pigs were kept in pens by BW classification (9 HBW, 17 MBW and 10 LBW pens) with 13 males and 13 females per pen. Average daily gain tended to be lower in LBW than HBW litters in lactation (P = 0.06) and throughout the nursery and GF phases (P < 0.01), resulting in an increasing difference in body weight between LBW, MBW and HBW litters (P < 0.05). Average daily feed intake was lower (P < 0.001) in LBW than HBW litters in the nursery and GF phases. Feed utilization efficiency (feed/gain) was similar for LBW and HBW litters in the nursery, but was lower (P < 0.001) in HBW than LBW litters in the GF phase. By design, slaughter weight was similar between BW classifications; however, LBW litters needed 9 more days to reach the same slaughter weight than HBW litters (P < 0.001). BW classification did not affect carcass composition traits. In conclusion, LBW litters showed benchmarks of intrauterine growth retardation, LBW had a negative impact on testicular development and germ and somatic cell populations, and was associated with decreased postnatal growth during all phases of production; however, no measurable effect on carcass composition traits was established.     

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.     

Comparison of different methods of interpretation for the prediction of body water by heavy water dilution method: application in the male goat

Deuterium oxide dilution space (DS) predicted by a 1 or 2 compartment kinetic model was used to estimate total body water in male kids. Empty body water (EBW), total body water at slaughter (TBW) and total body water calculated in the middle of day of injection (TBWM) were predicted with more accuracy by 2 compartment models. Residual standard deviation for EBW, TBW and TBWM estimated from a 2 open compartment model was 939 g, 464 g and 450 g respectively. Measurement of DS provides an accurate method to determine body water content and body composition.     

Can tritiated water-dilution space accurately predict total body water in chukar partridges?

Total body water (TBW) volumes determined from the dilution space of injected tritiated water have consistently overestimated actual water volumes (determined by desiccation to constant mass) in reptiles and mammals, but results for birds are controversial. We investigated potential errors in both the dilution method and the desiccation method in an attempt to resolve this controversy. Tritiated water dilution yielded an accurate measurement of water mass in vitro. However, in vivo, this method yielded a 4.6% overestimate of the amount of water (3.1% of live body mass) in chukar partridges, apparently largely because of loss of tritium from body water to sites of dissociable hydrogens on body solids. An additional source of overestimation (approximately 2% of body mass) was loss of tritium to the solids in blood samples during distillation of blood to obtain pure water for tritium analysis. Measuring tritium activity in plasma samples avoided this problem but required measurement of, and correction for, the dry matter content in plasma. Desiccation to constant mass by lyophilization or oven-drying also overestimated the amount of water actually in the bodies of chukar partridges by 1.4% of body mass, because these values included water adsorbed onto the outside of feathers. When desiccating defeathered carcasses, oven-drying at 70 degrees C yielded TBW values identical to those obtained from lyophilization, but TBW was overestimated (0.5% of body mass) by drying at 100 degrees C due to loss of organic substances as well as water.(ABSTRACT TRUNCATED AT 250 WORDS)     

Prediction of body composition in habitually active middle-aged men.

In 45 physically active men (ages 35-67 yr) who underwent hydrostatic weighing to determine body composition, multiple regression equations were developed for the prediction of body density (D), lean body weight (LBW), fat body weight (FBW), and % fat using selected anthropometric measurements. The prediction accuracy for these parameters using several previously generated anthropometric regression equations was also determined. With equations developed from the present data a substantially higher correlation was obtained between measured and predicted LBW (r = 0.95) than between measured and predicted D (r = 0.85), FBW (r = 0.88), or % fat (r = 0.84). When previously developed equations were applied to the present sample, correlations between measured and predicted values were considerably lower (4-42%) than in the original studies; this reduction was least in the case of LBW. Analysis of previous data indicated that in selected populations total body weight can account for a relatively large fraction of the variance in LBW. LBW may be estimated quite accurately (r greater than or equal to 0.90) in physically active men with one of several regression equations which include total body weight as an independent variable.     

Validation of water flux and body composition in glaucous gulls (Larus hyperboreus)

Water influx rates (WIR) measured with tritiated water dilution were compared with direct measures of water and energy intake in glaucous gulls (Larus hyperboreus). Total body water (TBW) measured isotopically was also compared with TBW determined by body composition analysis (BCA) of the same birds. Seventeen wild gulls were captured and studied in outdoor enclosures at Ny-Alesund, Svalbard, in July 2002. Gulls were hand-fed known quantities of Arctic cod (Boreogadus saida) or given water on the basis of one of four experimental treatments: (A) fasting, (B) fish only, (C) water only, or (D) fish and water. Water and energy content of Arctic cod was also determined. WIR of gulls (after subtracting metabolic water production) in treatments A, B, C, and D were 0, 101 +/- 5, 62 +/- 19, and 122 +/- 21 SD g d(-1), respectively. Measured water intake in each group was 0, 111 +/- 2, 64 +/- 3, and 134 +/- 15 SD g d(-1), respectively. On average, WIR underestimated measured water intake in each group. Errors were lowest but most variable for gulls fed water only (-2.2% +/- 32.8%) compared with gulls fed fish only (-9.0% +/- 5.4%) or fish and water (-9.0% +/- 7.0%). Compared with measured water intake, errors in WIR were relatively low overall (-6.9% +/- 17.4%) and comparable to previous validation studies. The difference in TBW determined by BCA versus isotopic dilution ranged between -1.02% and +8.59% of mass. On average, TBW measured isotopically (632 +/- 24 g kg(-1)) overestimated true body water by a factor of 1.033.     

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.     

Measurement of the body composition of living gray seals by hydrogen isotope dilution

The body composition of living gray seals (Halichoerus grypus) can be accurately predicted from a two-step model that involves measurement of total body water (TBW) by 2H or 3H dilution and application of predictive relationships between body components and TBW that were derived empirically by slaughter chemical analysis. TBW was overestimated by both 2HHO and 3HHO dilution; mean overestimates were 2.8 +/- 0.9% (SE) with 2H and 4.0 +/- 0.6% with 3H. The relationships for prediction of total body fat (TBF), protein (TBP), gross energy (TBGE), and ash (TBA) were as follows: %TBF = 105.1 - 1.47 (%TBW); %TBP = 0.42 (%TBW) - 4.75; TBGE (MJ) = 40.8 (mass in kg) - 48.5 (TBW in kg) - 0.4; and TBA (kg) = 0.1 - 0.008 (mass in kg) + 0.05 (TBW in kg). These relationships are applicable to gray seals of both sexes over a wide range of age and body conditions, and they predict the body composition of gray seals more accurately than the predictive equations derived from ringed seals (Pusa hispida) (Stirling et al., Can. J. Zool. 53: 1021-1027, 1975) and from the equation of Pace and Rathbun (J. Biol. Chem. 158: 685-691, 1945), which has been reported to be generally applicable to mammals.     

Total body water and ECFV measured using bioelectrical impedance analysis and indicator dilution in horses.

The purposes of this study were 1) to determine the compartmentation of body water in horses by using indicator dilution techniques and 2) to simultaneously measure bioelectrical impedance to current flow at impulse current frequencies of 5 and 200 kHz to formulate predictive equations that could be used to estimate total body water (TBW), extracellular fluid volume (ECFV), and intracellular fluid volume (ICFV). Eight horses and ponies weighing from 214 to 636 kg had catheters placed into the left and right jugular veins. Deuterium oxide, sodium thiocyanate, and Evans blue were infused for the measurement of TBW, ECFV, and plasma volume (PV), respectively. Bioelectrical impedance was measured by using a tetrapolar electrode configuration, with electrode pairs secured above the knee and hock. Measured TBW, ECFV, and PV were 0.677 +/- 0.022, 0.253 +/- 0.006, and 0.040 +/- 0.002 l/kg body mass, respectively. Strong linear correlations were determined among measured variables that allowed for the prediction of TBW, ECFV, ICFV, and PV from measures of horse length or height and impedance. It is concluded that bioelectrical impedance analysis (BIA) can be used to improve the predictive accuracy of noninvasive estimates of ECFV and PV in euhydrated horses at rest.     

Hypobaric hypoxia (380 Torr) decreases intracellular and total body water in goats

The effects of prolonged hypoxia on body water distribution was studied in four unanesthetized adult goats (Capra lircus) at sea level and after 16 days in a hypobaric chamber [(380 Torr, 5,500 m, 24 +/- 1 degrees C); arterial PO2 = 27 +/- 2 (SE) Torr]. Total body water (TBW), extracellular fluid volume (ECF), and plasma volume (PV) were determined with 3H2O, [14C]inulin, and indocyanine green dye, respectively. Blood volume (BV) [BV = 100PV/(100 - hematocrit)], erythrocyte volume (RCV) (RCV = BV - PV), and intracellular fluid (ICF) (ICF = TBW - ECF) and interstitial fluid (ISF) (ISF = ECF - PV) volumes were calculated. Hypoxia resulted in increased pulmonary ventilation and arterial pH and decreased arterial PCO2 and PO2 (P less than 0.05). In addition, body mass (-7.1%), TBW (-9.1%), and ICF volume (-14.4%) all decreased, whereas ECF (+11.7%) and ISF (+27.7%) volumes increased (P less than 0.05). The decrease in TBW accounted for 89% of the loss of body mass. Although PV decreased significantly (-15.3%), BV was unchanged because of an offsetting increase in RCV (+39.5%; P less than 0.05). We conclude that, in adult goats, prolonged hypobaric hypoxia results in decreases in TBW volume, ICF volume, and PV, with concomitant increases in ECF and ISF volumes.     

INDICES OF BODY CONDITION AND BODY COMPOSITION IN FEMALE ANTARCTIC FUR SEALS (ARCTOCEPHALUS GAZELLA)

An attempt was made to develop simple, inexpensive, rapid means of determining body composition in Antarctic fur seals ( Arctocephalus gazella ). Measurements of total body water ( TBW ) and total body lipid ( TBL ), obtained by hydrogen isotope dilution, were compared to the results of bioelectrical impedance analysis ( BIA ) and morphometric indices of body condition in 52 adult females. TBW was weakly correlated with BIA measurements of resistance ( v = -0.30, P < 0.03). Conductor volume (length2/resistance) was more highly correlated with TBW ( r = 0.75, P < 0.0001) and the inclusion of mass into the predictive equation improved the correlation further ( r = 0.95, P < 0.0001). A body condition index (mass/length) previously used in pinniped studies was positively correlated to TBL ( r = 0.77, P < 0.0001) validating its use as a relative index of condition. However, body mass alone was highly correlated to TBW ( r = 0.94, P < 0.0001) and appears to provide a simple, rapid means of estimating body composition in adult females. This technique may also be applicable to juvenile male Antarctic fur seals.     

ESTIMATION OF TOTAL BODY WATER IN HARBOR SEALS: HOW USEFUL IS BIOELECTRICAL IMPEDANCE ANALYSIS?

We evaluated bioelectrical impedance analysis (BIA) as a means of rapidly and inexpensively estimating total body water (TBW) of harbor seals ( Phoca vitulina ). Deuterium oxide dilution was used to estimate TBW in 17 adult females and 16 of their pups between birth and late lactation. Isotope dilution was also used to determine TBW in 12 adult males early and 10 of these males late in the breeding season. At the same time, resistance ( Rs ) and reactance ( Xc ) measurements were taken using a tetrapolar, impedance plethysmograph (Model 101 A, RJL Systems). Seals were sedated with diazepam prior to taking BIA measurements. Within-day duplicate Rs measurements on pups and adults, taken 2-240 min apart, differed by an average of 3.0%± 1.4% ( n = 42, CV = 102%). Movement of the seal during BIA measurements caused variability in both Rs and Xc values. BIA measurements were generally poor predictors of TBW. Rs was significantly correlated with TBW in pups only ( Rs = 0.93, P = 0.001, n = 11). Bioelectrical conductor volume (length2/ Rs ) was significantly correlated with TBW only in adult females ( Rs = 0.63, P = 0.02, n = 14). We conclude that BIA is not a reliable method of estimating TBW in wild harbor seals.     

Use of NMR for measurement of total body water and estimation of body fat

A nuclear magnetic resonance (NMR) method is described for quantitatively measuring total body water (TBW) and for estimating the fat content of baboons. The hydrogen associated with water was measured as the amplitude of the free-induction decay voltage following a series of 90 degree radio frequency pulses at the Lamour frequency for hydrogen with a pulse length of 14 microseconds and a peak measuring time of 50 microseconds. TBW was calculated by multiplying the peak amplitude (volts) by the experimentally determined constant for a water standard (g water/V). This NMR method yielded TBW contents similar to those obtained in the same baboons by direct gravimetric procedures. In contrast, the widely used 3H2O-dilution method usually and variably overestimated body water. By providing an accurate measure of body water, this NMR procedure provides a rapid, noninvasive, reasonably accurate way of estimating body fat content.     

Mastalgia and total body water.

Total body water (TBW) was measured early and late in a menstrual cycle in 56 women, 39 of whom had breast pain. The remainder were asymphtomatic controls. Most women did not conform to the traditional view that there is a premenstrual increase in TBW. In some TBW decreased, while in others there was no change from the early cycle measurement. No TBW pattern correlated with any syndromes of breast pain or with any psychoneurotic profile.