Bioelectrical impedance analysis for the estimation of body composition in rats

Bioelectrical impedance analysis (BIA) was used to assess body composition in rats fed on either standard laboratory diet or on a high-fat diet designed to induce obesity. Bioelectrical impedance analysis predictions of total body water and thus fat-free mass (FFM) for the group mean values were generally within 5% of the measured values by tritiated water ((H2O)-H-3) dilution. The limits of agreement for the procedure were, however, large, approximately +/-25%, limiting the applicability of the technique for measurement of body composition in individual animals.

Evaluation of multifrequency bioelectrical impedance data for predicting lean tissue mass in beef cattle

Multifrequency bioimpedance analysis has the potential to provide a non-invasive technique for determining body composition in live cattle. A bioimpedance meter developed for use in clinical medicine was adapted and evaluated in 2 experiments using a total of 31 cattle. Prediction equations were obtained for total body water, extracellular body water, intracellular body water, carcass water and carcass protein. There were strong correlations between the results obtained through chemical markers and bioimpedance analysis when determined in cattle that had a wide range of liveweights and conditions. The r(2) values obtained were 0.87 and 0.91 for total body water and extracellular body water respectively. Bioimpedance also correlated with carcass water, measured by chemical analysis (r(2) = 0.72), but less well with carcass protein (r(2) = 0.46). These correlations were improved by inclusion of liveweight and sex as variables in multiple regression analysis. However, the resultant equations were poor predictors of protein and water content in the carcasses of a group of small underfed beef cattle, that had a narrow range of liveweights. In this case, although there was no statistical difference between the predicted and measured values overall, bioimpedance analysis did not detect the differences in carcass protein between the 2 groups that were apparent following chemical analysis. Further work is required to determine the sensitivity of the technique in small underfed cattle, and its potential use in heavier well fed cattle close to slaughter weight.

Bioimpedance spectrometry in the determination of body water compartments: Accuracy and clinical significance

Bioelectrical impedance analysis (BIA) offers the potential for a simple, portable and relatively inexpensive technique for the in vivo measurement of total body water (TBW). The potential of BIA as a technique of body composition analysis is even greater when one considers that body water can be used as a surrogate measure of lean body mass. However, BIA has not found universal acceptance even with the introduction of multi-frequency BIA (MFBIA) which, potentially, may improve the predictive accuracy of the measurement. There are a number of reasons for this lack of acceptance, although perhaps the major reason is that no single algorithm has been developed which can be applied to all subject groups. This may be due, in part, to the commonly used wrist-to-ankle protocol which is not indicated by the basic theory of bioimpedance, where the body is considered as five interconnecting cylinders. Several workers have suggested the use of segmental BIA measurements to provide a protocol more in keeping with basic theory. However, there are other difficulties associated with the application of BIA, such as effects of hydration and ion status, posture and fluid distribution. A further putative advantage of MFBIA is the independent assessment not only of TBW but also of the extracellular fluid volume (ECW), hence heralding the possibility of,being able to assess the fluid distribution between these compartments. Results of studies in this area have been, to date, mixed. Whereas strong relationships of impedance values at low frequencies with ECW, and at high frequencies with TBW, have been reported, changes in impedance are not always well correlated with changes in the size of the fluid compartments (assessed by alternative and more direct means) in pathological conditions. Furthermore, the theoretical advantages of Cole-Cole modelling over selected frequency prediction have not always been apparent. This review will consider the principles, methodology and applications of BIA. The principles and methodology will,be considered in relation to the basic theory of BIA and difficulties experienced in its application. The relative merits of single and multiple frequency BIA will be addressed, with particular attention to the latter's role in the assessment of compartmental fluid volumes. (C) 1998 Elsevier Science Ltd. All rights reserved.

Effects of geological inhomogeneity on high Rayleigh number steady state heat and mass transfer in fluid-saturated porous media heated from below

A parametric study is carried out to investigate how geological inhomogeneity affects the pore-fluid convective flow field, the temperature distribution, and the mass concentration distribution in a fluid-saturated porous medium. The related numerical results have demonstrated that (1) the effects of both medium permeability inhomogeneity and medium thermal conductivity inhomogeneity are significant on the pore-fluid convective flow and the species concentration distribution in the porous medium; (2) the effect of medium thermal conductivity inhomogeneity is dramatic on the temperature distribution in the porous medium, but the effect of medium permeability inhomogeneity on the temperature distribution may be considerable, depending on the Rayleigh number involved in the analysis; (3) if the coupling effect between pore-fluid flow and mass transport is weak, the effect of the Lewis number is negligible on the pore-fluid convective flow and temperature distribution, hut it is significant on the species concentration distribution in the medium.

High-resolution bulk density images, using calibrated X-ray radiography of impregnated soil slices

Bulk density of undisturbed soil samples can be measured using computed tomography (CT) techniques with a spatial resolution of about 1 mm. However, this technique may not be readily accessible. On the other hand, x-ray radiographs have only been considered as qualitative images to describe morphological features. A calibration procedure was set up to generate two-dimensional, high-resolution bulk density images from x-ray radiographs made with a conventional x-ray diffraction apparatus. Test bricks were made to assess the accuracy of the method. Slices of impregnated soil samples were made using hardsetting seedbeds that had been gamma scanned at 5-mm depth increments in a previous study. The calibration procedure involved three stages: (i) calibration of the image grey levels in terms of glass thickness using a staircase made from glass cover slips, (ii) measurement of ratio between the soil and resin mass attenuation coefficients and the glass mass attenuation coefficient, using compacted bricks of known thickness and bulk density, and (iii) image correction accounting for the heterogeneity of the irradiation field. The procedure was simple, rapid, and the equipment was easily accessible. The accuracy of the bulk density determination was good (mean relative error 0.015), The bulk density images showed a good spatial resolution, so that many structural details could be observed. The depth functions were consistent with both the global shrinkage and the gamma probe data previously obtained. The suggested method would be easily applied to the new fuzzy set approach of soil structure, which requires generation of bulk density images. Also, it would be an invaluable tool for studies requiring high-resolution bulk density measurement, such as studies on soil surface crusts.

Electrical impedance particle size method (Coulter Counter) detects the large fat globules in poorly homogenised UHT processed milk

The large fat globules that can be present in UHT milk due to inadequate homogenisation cause a cream layer to form that limits the shelf life of UHT milk. Four different particle size measurement techniques were used to measure the size of fat globules in poorly homogenised UHT milk processed in a UHT pilot plant. The thickness of the cream layer that formed during storage was negatively correlated with homogenisation pressure. It was positively correlated with the mass mean diameter and the percentage volume of particles between 1.5 and 2 mu m diameter, as determined by laser light scattering using the Malvern Mastersizer. Also, the thickness of the cream layer was positively correlated with the volume mode diameter and the percentage volume of particles between 1.5 and 2 mu m diameter, as determined by electrical impedance using the Coulter Counter. The cream layer thickness did not correlate significantly with the Coulter Counter measurements of volume mean diameter, or volume percentages of particles between 2 and 5 mu m or 5 and 10 mu m diameter. Spectroturbidimetry (Emulsion Quality Analyser) and light microscopy analyses were found to be unsuitable for assessing the size of the fat particles. This study suggests that the fat globule size distribution as determined by the electrical impedance method (Coulter Counter) is the most useful for determining the efficiency of homogenisation and therefore for predicting the stability of the fat emulsion in UHT milk during storage.

Speciation of arsenic metabolites in the urine of occupational workers and experimental rats using an optimised hydride cold-trapping method

A hydride cold-trapping technique was developed and optimised for the measurement of urinary arsenic metabolites. The analytical precision of the method was found to be 6.1, 4.0 and 4.8% (n = 5) for inorganic arsenic (As-i), monomethylarsonate (MMA) and dimethylarsinate (DMA), respectively, with recoveries close to 100%, The detection limits were 1.0, 1.3 and 3 ng for As-i, MMA and DMA, respectively. The method was then used to analyse urine samples obtained from three groups of workers for occupational exposure in three companies where copper chrome arsenate was used for timber treatment. The results were compared with those for a normal control group of laboratory workers. Arsenic and its metabolites were also measured in experimental rats given 5 mg As kg(-1) body mass by oral gavage in the form of sodium arsenite, calcium arsenite or sodium arsenate. Occupational workers showed a significantly higher excretion of As-i, Up to two fold increases of urinary As-i excretion in rats compared with control rats were also observed in animals dosed with various forms of arsenicals. The method is suitable for the measurement of arsenic metabolites in urine of both humans and experimental animals.

Measurement and state preparation via ion trap quantum computing

We investigate in detail the effects of a QND vibrational number measurement made on single ions in a recently proposed measurement scheme for the vibrational state of a register of ions in a linear rf trap [C. D'HELON and G. J. MILBURN, Phys Rev. A 54, 5141 (1996)]. The performance of a measurement shows some interesting patterns which are closely related to searching.

Geochemical mass-balance and oxygen-isotope constrains on silcrete formation and its paleoclimatic implications in Southern Australia

Two geographically distinct silcrete associations are present in southern Australia, inland and eastern; these were sampled in central South Australia and central Victoria, respectively, At each site, both silicified and immediately adjacent unsilicified parent material were collected. Analytical data from these pairs were used to construct isocons, assuming Zr immobility, and to calculate the volume change and amount of silica introduced during silicification, These results, together with whole-rock oxygen isotope compositions, were used to determine the delta(18)O of th, introduced silica, The results show that the eastern silcretes in central Victoria are probably linked genetically to the associated basalts, weathering of which supplied the introduced silica, This conclusion is based on the close spatial connection between the two, as well as the substantial amount of introduced silica in the silcretes (greater than in the inland silcretes), resulting in volume increases in some eastern silcretes, Oxygen isotopic calculations for the silcretes indicate that the silica precipitated from groundwaters at temperatures slightly higher than present conditions. Silcrete formation apparently occurred during the Miocene and Pliocene (basalts in Victoria younger than Pliocene lack associated silcrete) and may reflect the much wetter climate in southeastern Australia at that time. The inland silcretes of central South Australia can be divided into pedogenic (the most common) and groundwater varieties. The pedogenic silcretes, which show typical soil features like columnar and nodular textures, contain moderate amounts of introduced silica that precipitated by evaporation from saline groundwaters, For the groundwater silcretes, which have massive textures and formed at or close to the water table, insufficient data are available to determine the mode of formation. The inland pedogenic silcretes have probably been farming from the Eocene-Miocene to the present, implying that conditions of seasonally high evaporation have occurred in central Australia during this time period. Thus silcrete formation depends on a complex interplay between climate and silica supply, and it is impossible to generalize that the presence of silcrete is indicative of a particular climate. Likewise, the elemental composition of silcretes, particularly Ti content, is not necessarily of climatic significance, Nevertheless, detailed geochemical and oxygen isotopic studies of a silcrete and its parent material can elucidate the mechanisms of silcrete formation, and if evaporation is indicated as a major factor in silcrete formation, then the climate at the time was likely to have been at least seasonally arid.

Measurement of grain boundary composition for X52 pipeline steel

Analytical electron microscopy was used to measure the composition of grain boundaries (GBs) and interconstituent boundaries (IBs) of X52 pipeline steel using specimens about 40-60 nm in thickness. All elements of interest were examined with the exception of carbon. With this caveat; there was no segregation at proeutectoid ferrite GBs. This indicated that the commonly expected species S and P are not responsible for preferential corrosion of GBs during intergranular stress corrosion cracking of pipeline steels. Manganese was the only species measured to segregate at the IBs. Manganese segregated to the IBs between proeutectoid ferrite and pearlitic cementite, and desegregated from IBs between proeutectoid ferrite and pearlitic ferrite. The pearlitic cementite was Mn rich. There was no Mn segregation at the IBs between pearlitic ferrite and pearlitic cementite. The pattern of Mn segregation could be explained in terms of diffusion in the process zone ahead of the pearlite during the austenite to pearlite transformation and diffusion in the IBs between the proeutectoid ferrite and pearlite. (C) 1998 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.