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Caffin, J. Multi-frequency impedance technique |
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Calderwood, J.H. Electrode-skin impedance from a dielectric viewpoint It is well established that the frequency variation of the complex electrode-skin impedance (ESI) (Z) over cap is given by (Z) over cap = K(i omega)(-n), where n has a typical value of about 0.8. It is not easy to find a physical reason for this behaviour. However, many materials exhibit Cole-Davidson (CD) behaviour, so that in the high- frequency (hf) region their impedance has a characteristic, which is almost indistinguishable from that of the ESI. It is therefore possible that the ESI exhibits a behaviour given by the CD equation or one of its variants, but that this has not been detected because experimental measurements have not extended to sufficiently low frequencies. Whatever the ESI behaviour may be at low frequencies, there are theoretical reasons which show that (Z) over cap cannot obey the above equation indefinitely as the frequency is reduced. If the deviation from it at low frequencies were found to be consistent with CD behaviour, then a physical explanation in terms of protonic fluctuations, which has previously been put forward to explain CD behaviour, would be available as a possible explanation of ESI behaviour over the whole frequency range. It is shown that any such deviation would be more likely to be detected if the variation of complex capacitance with frequency, rather than of impedance with frequency, were to be plotted. |
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Cartana, J.; Stock, M.J. Effects of clenbuterol and salbutamol on tissue rubidium uptake in vivo In anesthetized rats, injection of the beta(2)-adrenoceptor (beta(2)-AR) agonist clenbuterol (0.45 mu mol/kg) caused a marked stimulation of (RbCl)-Rb-86 (Rb) uptake by skeletal muscle, but had no effect on other tissues; soleus muscle showed the largest (144% increase) response. Injection of another beta(2)-AR agonist (salbutamol 0.45 mu mol/kg) had no effect on Rb uptake by any tissue except soleus muscle (83%). Both agonists increased body (colonic) temperature to the same extent. A 3-day treatment with salbutamol as a dietary admixture had no effect on body weight, muscle mass, or tissue Rb uptake, whereas the same treatment using clenbuterol produced significant increases in body weight and muscle mass and significant decreases in Rb uptake in three of the four muscle groups studied; Rb uptake in soleus was not affected. In another experiment, the short- term effect of clenbuterol injection on muscle Rb uptake was found to be resistant to a high dose (20 mg/kg) of the selective beta(2)-AR antagonist ICI 118551. It was concluded that the selective effects of short-term administration of clenbuterol on muscle Rb uptake, coupled with its effects over 3 days on Rb uptake and muscle hypertrophy, implicate beta-AR modulation of cation transport (possibly via Na,K-adenosine triphosphatase [ATPase] activity) in the anabolic effects of clenbuterol on muscle protein deposition. Since the stimulation of Rb uptake by clenbuterol was resistant to high doses of a selective beta(2)-AR antagonist and since salbutamol had little or no effect on muscle hypertrophy or Rb uptake, it is suggested that clenbuterol may exert its effects via an atypical beta-AR. Copyright (C) 1995 by W.B. Saunders Company |
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Casas, O.; Rosell, J.; Bragos, R.; Lozano, A.; Riu, P.J. A parallel broadband real-time system for electrical impedance tomography This paper deals with the design, implementation and performance of TIE-4sys, an electrical impedance tomograph. This instrument is a parallel broadband real-time system. It measures impedance using an array of 16 electrodes and reconstructs the images using a weighted back-projection technique. The objective of this development is to enable multifrequency EIT clinical studies to be undertaken. The system is capable of acquiring 25 frames/s and makes multifrequency cardiac-gated images. The frequency range is from 10 kHz to 250 kHz and the signal to noise ratio for the real component is better than 60 dB. |
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Cha, K.; Wilmore, D.W. Segmental vs whole body multifrequency bioimpedance measurements - Reply |
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Cha, K.C.; Chertow, G.M.; Gonzalez, J.; Lazarus, J.M.; Wilmore, D.W. Multifrequency bioelectrical impedance estimates the distribution of body water Multifrequency bioelectrical impedance analysis was used to estimate the ratio of extracellular water (ECW) to total body water in subjects with end-stage renal disease. The body's resistance was measured at frequencies ranging from 1 kHz to 1 MHz. The impedance index (height(2)/resistance) determined at low frequency (5 Mit) correlated most closely with ECW (r = 0.886) using sodium bromide dilution as the standard of comparison. In contrast, the ratio of height squared to resistance determined at high frequency (500 kHz) correlated most closely with total body water (r = 0.974) using deuterium oxide dilution as the standard of comparison. The ratio of resistance at 500 kHz to resistance at 5 kHz was directly correlated (r = 0.767) with the ratio of ECW to total body water. Multifrequency bioelectrical impedance analysis may assist in the evaluation of body water distribution in end-stage renal disease and other clinical disorders of fluid volume and/or distribution. |
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Chassard, D.; Berrada, K.; Bryssine, B.; Guiraud, M.; Bouletreau, P. Influence of body compartments on propofol induction dose in female patients Background: For induction of anaesthesia, drugs such as propofol are commonly administered according to a per weight basis. However, drugs are primarily distributed to the fat-free mass. This study was undertaken to determine the relationship between propofol requirement for induction and body mass determined by bioimpedance analysis (BIA) or by body mass index (BMI). Methods: Twenty-one ASA 1 female patients scheduled for gynaecologic surgery received propofol for induction at 133 mg. min(-1). Stepwise regression analysis was used to describe the relationships between propofol requirement for loss of consciousness and age, body weight, and lean body mass measured by BIA and BMI (independent variables). Results: Loss of consciousness was obtained with a propofol dose (Mean (SEM)) of 2.17+/-0.10 mg . kg(-1). Stepwise analysis showed that propofol requirement (total dose) was not proportional to weight or age but related to lean body mass as determined by BIA and to body mass index (r(2) = 0.447; global P-value <0.007). BMI was the only regressor variable when the propofol dose was expressed in mg. kg(-1) (r(2) = 0.661; P<0.001). Conclusions: Our results indicate that propofol requirements for induction are proportional to the lean body mass rather than total body weight. |
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Chauveau, N.; Ayeva, B.; Rigaud, B.; Morucci, J.P. A multifrequency serial EIT system A multifrequency (1 kHz-1 MHz) serial electrical impedance tomography (EIT) system has been developed. It is based on 16 active electrodes and can be extended up to 32. Each active electrode can be programmed for current driving and for measuring either the injected current or the voltage difference between adjacent electrodes, and includes calibration facilities. Real and imaginary parts of the impedance are obtained by applying a parametric identification method (extended Prony), but other techniques are easily adaptable. Image reconstruction is carried out using the Sheffield filtered back-projection algorithm. Characteristic frequency images are under development and should be of great interest to distinguish between normal and tumorous tissues. |
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Chen, Z.; Lohman, T.G.; Stini, W.A.; Ritenbaugh, C.; Aickin, M. Fat or lean tissue mass: Which one is the major determinant of bone mineral mass in healthy postmenopausal women? The relative importance of fat and lean tissue mass in determining bone mineral mass among postmenopausal women was examined in this 1-year. longitudinal study, Fifty postmenopausal Caucasian women entered the study; 45 of them completed a 1-year follow up. Dual-energy Ii-ray absorptiometry was employed for measuring total and regional bone mineral density (BMD) and bone mineral content (BMC), fat tissue mass (FTM), lean tissue mass (LTM), and body weight. Results from linear regression analysis using the cross-sectional data (n = 50) of the study indicated that LTM explained a larger percentage of variation in bone mineral mass than did FTM. FTM and LTM were found to be moderately correlated (r = 0.55); when FTM was entered in the same predicting regression models, LTM was a significant predictor (p < 0.05) of the total and regional BMC, but not BMD, The percent FIM (and inversely %LTM) was correlated with BMD and BMC, but significant correlation was primarily found only for total body BMD (or BMC), Weight was the best predictor of total body BMD and BMC, Longitudinally (n = 45), annual changes in both FTM and weight were significantly associated with annual changes in regional BMD after adjustment for initial bone mineral values (p < 0.05), We conclude that bone mineral mass is more closely related to LTM than to FTM, while annual changes in regional BMB) are more closely correlated with changes in FTM in healthy postmenopausal women. Meanwhile, increased body weight is significantly associated with increased bone mineral mass. |
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Chertow, G.M.; Lowrie, E.G.; Wilmore, D.W.; Gonzalez, J.; Lew, N.L.; Ling, J.; Leboff, M.S.; Gottlieb, M.N.; Huang, W.; Zebrowski, B.; College, J.; Lazarus, J.M. Nutritional assessment with bioelectrical impedance analysis in maintenance hemodialysis patients Protein energy malnutrition is common among persons with ESRD and contributes substantially to morbidity and mortality, The usual methods of nutritional assessment, such as anthropometry, can be misleading because of altered tissue hydration. Bioelectrical impedance analysis (BIA) has been recommended by some as a practical nutritional assessment tool but has not been validated in patients with ESRD. Thirty-three stable patients on maintenance hemodialysis were evaluated in an ambulatory clinical research center with simultaneous BIA, dual-energy x-ray absorptiometry, and deuterium oxide (D2O) and sodium bromide (NaBr) isotope dilution studies. Standard determinations of total body water (TBW) and body cell mass (BCM) were obtained and compared with values estimated by BIA. Two separate outpatient BIA measurements were also obtained approximately 2 wk before and after the clinical research center evaluation. BCM estimated by BIA was directly correlated (r = 0.92, P < 0.0001) with BCM determined by DEXA and NaBr. TBW estimated by BIA was directly correlated (r = 0.96, P < 0.0001) with TBW determined by deuterium oxide dilution. The reactance to resistance ratio (Xc/R) derived from BIA was inversely correlated (r = -0.73, P < 0.0001) with the extracellular water/TBW ratio determined by NaBr/D2O. Bland-Altman analyses showed that for TEW, BIA was in excellent agreement with D2O dilution. BCM was modestly underestimated by BIA compared with the dual-energy x-ray absorptiometry/NaBr standard and was adjusted by linear regression. The coefficients of variation on repeated BIA measurements were below 4%, demonstrating test-retest reliability. BIA is a valid and reliable method of nutritional assessment in maintenance hemodialysis patients. |
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Author(s): Title: Abstract: |
Chertow-G-M; Lowrie-E-G; Wilmore-D-W; Gonzalez-J; Lew-N-L; Ling-J; Nutritional assessment with bioelectrical impedance analysis in maintenance hemodialysis patients. Protein energy malnutrition is common among persons with ESRD and contributes substantially to morbidity and mortality. The usual methods of nutritional assessment, such as anthropometry, can be misleading because of altered tissue hydration. Bioelectrical impedance analysis (BIA) has been recommended by some as a practical nutritional assessment tool but has not been validated in patients with ESRD. Thirty-three stable patients on maintenance hemodialysis were evaluated in an ambulatory clinical research center with simultaneous BIA, dual-energy x-ray absorptiometry, and deuterium oxide (D-2O) and sodium bromide (NaBr) isotope dilution studies. Standard determinations of total body water (TBW) and body cell mass (BCM) were obtained and compared with values estimated by BIA. Two separate outpatient BIA measurements were also obtained approximately 2 wk before and after the clinical research center evaluation. BCM estimated by BIA was directly correlated (r = 0.92, P lt 0.0001) with BCM determined by DEXA and NaBr. TBW estimated by BIA was directly correlated (r = 0.96, P lt 0.0001) with TBW determined by deuterium oxide dilution. The reactance to resistance ratio (Xc/R) derived from BIA was inversely correlated (r = -0.73, P lt 0.0001) with the extracellular water/ TBW ratio determined by NaBr/D-2O. Bland- Altman analyses showed that for TBW, BIA was in excellent agreement with D-2O dilution. BCM was modestly underestimated by BIA compared with the dual-energy x-ray absorptiometry/NaBr standard and was adjusted by linear regression. The coefficients of variation on repeated BIA measurements were below 4%, demonstrating test-retest reliability. BIA is a valid and reliable method of nutritional assessment in maintenance hemodialysis patients. |
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Chertow, G.M. The ambiguities of predicting total body water and body cell mass with a single frequency (50KHz) measurement of bioimpedance - Response |
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Chumlea, W.C.; Guo, S.S.; Siervogel, R.M. Untitled - Reply |
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Chumlea, W.C.; Guo, S.S.; Vellas, B.; Guigoz, Y. Techniques of assessing muscle mass and function (sarcopenia) for epidemiological studies of the elderly For epidemiological studies, reliable and valid measurements or indices of muscle mass are needed to screen for those elderly persons at risk for sarcopenia, and to determine the prevalence of these conditions on a national level. The methods more suitable for field or epidemiological settings are anthropometry, bioelectrical impedance, and grip strength. These field methods, while reliable, have limited demonstrated validity in their application to the elderly and are restricted by the limited functional capabilities of the elderly, which decrease with age. Epidemiological studies of the elderly need to include sufficient numbers of persons of different ethnic backgrounds, and at the older ages. For an epidemiological study of tire elderly today, one also needs to select the categories of elderly persons to be included in such studies: healthy, sick, very old, handicapped, level of functional status, etc., because relationships among variables can have different statistical and biological associations. Future work should be directed at improving the design and methodology of epidemiological and serial studies so as to maximize the numbers and categories of elderly persons who can be studied. |
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Colquhoun, K.O.; Timms, S.; Fricker, C.R. Detection of Escherichia coli in potable water using direct impedance technology Direct impedance measurement utilizing a medium previously described as being specific for Escherichia coli and which contains trimethylamine N-oxide (TMAO) and glucuronic acid was used to detect E. coli in water samples. The system was compared with the Colilert(R) presence/absence test and the United Kingdom standard membrane filtration technique using membrane lauryl sulphate broth. The impedance method correlated well with both the traditional membrane method (93%) and the Colilert(R) method (93.95%) for a number of different water types. No interference from Citrobacter spp. (as reported in previous studies) was detected in this study although some Salmonella spp. did give false-positive results: The data presented here suggest that the use of direct impedance may offer an alternative to conventional methods for the detection of E. coli in water. |
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Coster, H.G.L.; Chilcott, T.C.; Coster, A.C.F. mpedance spectroscopy of interfaces, membranes and ultrastructures For the past century, impedance spectroscopy has provided a non-invasive means of characterizing the electrical properties of many systems. Even today, it often provides the only non-invasive method for detailed structural-functional studies of these systems. This is especially so of systems in which important processes occur at the molecular level, such as those processes associated with biological and synthetic membranes and interfaces that form between solutions and various solids (e.g. metals and colloid particles). The fundamental concepts of impedance spectroscopy are re-examined and a review is given of the role that impedance pectroscopy has played in the development of our understanding of cellular and synthetic membranes, cell biophysics and ionic systems in general. Special emphasis is given to the problems associated with solution-electrode interfaces, as well as unstirred layers, which can plague measurements on biological systems and have led to much confusion in the past. A description is given of a new computer-controlled, four-terminal digital impedance spectrometer, which provides resolutions in impedance magnitude and phase of 0.002% and 0.001 degrees respectively over a frequency range of 10(-2) to 10(5) Hz and for impedances ranging from 10 to 10(9) Omega. We also describe impedance dispersions in terms of transfer functions which, when plotted along the negative frequency axis, yield ''spectra'' with distinct sharp peaks that identify fundamental frequency constants of the system. This ''control engineering'' form of presentation of impedance spectra demystifies the impedance analyses of these systems. The spectra and changes in these which occur as a result of perturbations to the system can be readily assessed and interpreted. |
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Cugini, P.; Salandri, A.; Petrangeli, C.M.; Capodaglio, P.F.; Giovannini, C. Circadian rhythms in human body composition The study investigates how the human body composition (BC) changes as a function of the day-night cycle. The BC was investigated using bioelectrical impedance analysis (BIA) of 10 clinically healthy subjects (CHS), monitored in supine position (readings at 2-h intervals), avoiding mealtimes, dietary abuses, and bladder and intestinal retention. Time series data were analyzed for their temporal characteristics and circadian rhythm (CR). All the variables of BC (lean body mass, fat body mass, body cell mass, total body water, intracellular and extracellular body water, sodium and potassium exchangeable pool) showed a within-day variability with nighttime crests. Such an oscillatory synchronism corroborates the hypothesis that the rest time plays a fundamental role, via its anabolic effects, in conferring the nocturnal phase to the CR of the human BC. |