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Hahn, G.; Sipinkova, I.; Baisch, F.; Hellige, G.
Changes in the thoracic impedance distribution under different ventilatory conditions
Journal Physiological Measurement
16
Suppl. 3A
AUG
1995
A161-A173
G Hahn
Univ Gottingen
Ctr Anaesthesiol Emergency & Intens Care Med
Dept Anaesthesiol Res
Gottingen, Germany
0967-3334
The present study was performed with the aim of checking the suitability of EIT in imaging regional thoracic impedance variations during lung ventilation under predefined conditions and to compare EIT with established reference techniques. A new technique of functional EIT imaging designed to visualize physiologically relevant information from the sequentially registered series of thoracic impedance distributions. was introduced. Experiments were performed on five spontaneously breathing healthy subjects and on 12 anaesthetized supine pigs. 16 electrodes were placed around the thorax and consecutive transthoracic impedance distributions were measured at a rate of 1 Hz (Sheffield; APT. system mark I, IBEES, Sheffield, UK). Several voluntary breathing manoeuvres were performed in human subjects and the tracings of local impedance were compared with standard spirometry. In animal experiments EIT was applied during artificial ventilation at different ventilation rates and during stepwise passive emptying and filling of either one or both lungs while the respiratory muscles were relaxed. Further, selective blockade of lung regions resulting in regionally reduced ventilation was performed and the capability of EIT to follow and differentiate local ventilatory disturbances was checked by reference techniques (x-ray and staining methods). The experiments revealed an overall agreement between the spirometric and impedance data in all breathing patterns performed. A linear relationship between changes of the air content of the lungs and the regional thoracic impedance was shown (intraindividual correlation coefficient range, 0.986-0.999; n = 12 animals). The functional images of the impedance distribution across the thorax reproduced adequately the typical anatomical characteristics of the pig and the human thorax. The spatial resolution of EIT functional images was sufficient to differentiate lung areas corresponding to approximately 20 ml tissue volume. EIT with the additional evaluation procedure of functional imaging was shown to be a suitable and reliable method of imaging different ventilatory conditions with the potential to become a useful tool for monitoring respiratory function. |
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Hahn, G.; Sipinkova, I.; Baisch, F.; Hellige, G.
Changes in the thoracic impedance distribution under different ventilatory conditions
Journal Physiological Measurement
16
Suppl. 3A
AUG
1995
A161-A173
G Hahn
Univ Gottingen
Ctr Anaesthesiol Emergency & Intens Care Med
Dept Anaesthesiol Res
Gottingen, Germany
0967-3334
The present study was performed with the aim of checking the suitability of EIT in imaging regional thoracic impedance variations during lung ventilation under predefined conditions and to compare EIT with established reference techniques. A new technique of functional EIT imaging designed to visualize physiologically relevant information from the sequentially registered series of thoracic impedance distributions was introduced. Experiments were performed on five spontaneously breathing healthy subjects and on 12 anaesthetized supine pigs. 16 electrodes were placed around the thorax and consecutive transthoracic impedance distributions were measured at a rate of 1 Hz (Sheffield; APT. system mark I, IBEES, Sheffield, UK). Several voluntary breathing manoeuvres were performed in human subjects and the tracings of local impedance were compared with standard spirometry. In animal experiments EIT was applied during artificial ventilation at different ventilation rates and during stepwise passive emptying and filling of either one or both lungs while the respiratory muscles were relaxed. Further, selective blockade of lung regions resulting in regionally reduced ventilation was performed and the capability of EIT to follow and differentiate local ventilatory disturbances was checked by reference techniques (x-ray and staining methods). The experiments revealed an overall agreement between the pirometric and impedance data in all breathing patterns performed. A linear relationship between changes of the air content of the lungs and the regional thoracic impedance was shown (intraindividual correlation coefficient range, 0.986-0.999; n = 12 animals). The functional images of the impedance distribution across the thorax reproduced adequately the typical anatomical characteristics of the pig and the human thorax. The spatial resolution of EIT functional images was sufficient to differentiate lung areas corresponding to approximately 20 ml tissue volume. EIT with the additional evaluation procedure of functional imaging was shown to be a suitable and reliable method of imaging different ventilatory conditions with the potential to become a useful tool for monitoring respiratory function. |
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Hahn, G.; Frerichs, I.; Kleyer, M.; Hellige, G.
Local mechanics of the lung tissue determined by functional EIT
Journal Physiological Measurement
17
Suppl. 4A
NOV
1996
A159-A166
G Hahn
Univ Gottingen
Ctr Anaesthesiol Emergency & Intens Care Med
Dept Anaesthesiol Res
Tl 195
D-37075 Gottingen, Germany
0967-3334
APPLIED POTENTIAL TOMOGRAPHY
A new functional EIT (f-EIT) evaluation technique providing information on the local dynamic behaviour of the lungs is presented. Out of a series of single EIT thoracic images local time courses of the impedance change are extracted. To detect regional differences in the dynamic behaviour of the lung tissue the local time courses at different locations are related to the average time course of the impedance change over the whole thoracic cross section. The time shifts between this reference signal and the signals from separate positions are calculated from the phase information of the complex cross spectra and evaluated in terms of the local phase angle. The computed phaseshifts are imaged over the cross section creating an 'f-EIT phase image' characterizing the local dynamic properties. To relate the observed differences to the proper lung location the resulting images are presented as a combination of the f-EIT ventilation images, which represent the]local amplitude of ventilation and the f-EIT phase images. The new imaging technique was tested in spontaneously breathing humans. Alterations to pulmonary dynamics were induced by changing the body posture of the subjects. The f-EIT phase imaging procedure was shown to identify lung regions with different dynamics and it is expected that this technique will also distinguish pathologically determined alterations. |
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Haines, S.T.; Bussey, H.I.
Diagnosis of deep vein thrombosis
American Journal of Health - System Pharmacy
54
1
JAN 1
1997
66-74
ST Haines
Univ Maryland
Dept Pharm Practice & Sci
Sch Pharm
506 W Fayette St
Room 203
Baltimore, MD 21201 USA
1079-2082
LIGHT-REFLECTION RHEOGRAPHY; HIGH-RISK PATIENTS; VENOUS- THROMBOSIS; IMPEDANCE PLETHYSMOGRAPHY; CONTRAST VENOGRAPHY; SYMPTOMATIC OUTPATIENTS; DOPPLER ULTRASOUND; ULTRASONOGRAPHY; LEG; ACCURACY
The diagnosis of deep vein thrombosis (DVT) is discussed. Accurately diagnosing DVT is critical to making appropriate treatment decisions. Careful patient assessment, combined with objective testing, improves the accuracy of the diagnosis and reduces the Likelihood of inappropriate treatment. Venography remains the reference standard for the diagnosis of DVT but is expensive, invasive, and prone to inducing complications. Ultrasonography has become the most frequently used noninvasive test for symptomatic DWT because it is highly sensitive and specific in the hands of an experienced examiner. impedance plethysmography also has been widely used, but recent studies suggest that it is less sensitive than once believed. The radiolabeled I-125- fibrinogen uptake test is no longer available because of concerns about the transmission of blood-borne pathogens. Current thermographic techniques have relatively high sensitivity but poor specificity for DVT. Magnetic resonance imaging and computed tomography are useful adjunctive tests, but their use is Limited by cost and availability. D-dimer whole-blood testing may prove to be a rapid and convenient means of ruling out the diagnosis of DVT at the bedside, but further study is needed. When used alone, none of the noninvasive methods is sufficiently sensitive for the evaluation of asymptomatic patients. The diagnostic strategy used should be based on whether the patient is symptomatic or asymptomatic, whether the event is a first one or is recurrent, and a careful clinical assessment. Accurate diagnosis of deep vein thrombosis relies on both testing and patient assessment. |
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Hampshire, A.R.; Smallwood, R.H.; Brown, B.H.; Primhak, R.A.
Multifrequency and parametric EIT images of neonatal lungs
Journal Physiological Measurement
16
Suppl. 3A
AUG
1995
A175-A189
AR Hampshire
Royal Hallamshire Hosp
Dept Med Phys & Clin Engn
Sheffield S10 2JF
S Yorkshire, England
0967-3334
The aims of the study were to investigate the problems involved in making multifrequency EIT measurements on neonates and to compare the images obtained with the results from a group of normal adults. The Sheffield electrical impedance tomographic spectroscopy (EITS) system acquires multifrequency data using a set of eight drive and eight receive electrodes. EITS measurements were made on an inhomogenous group of 10 neonates admitted to the special care baby unit for observation and feeding. R/S characteristic frequency, RC and SC parameters were generated using the Cole equation. Comparisons of the parameters were made with data collected from normal adults in another study. We have shown that it is possible to obtain EITS parametric images of neonatal lungs and that there are some differences in Cole parameters between the adult and neonatal groups. |
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Hannan, W.J.; Cowen, S.J.; Plester, C.E.; Fearon, K.C.H.; Debeau, A.
Comparison of bio-impedance spectroscopy and multi-frequency bio-impedance analysis for the assessment of extracellular and total body water in surgical patients
Journal Clinical Science
89
6
DEC
1995
651-658
WJ Hannan
Western Gen Hosp
Dept Med Phys & Med Engn
Edinburgh EH4 2XU
Midlothian, Scotland
0143-5221
bio-impedance; extracellular water; nutrition; total body water
1. Measurements of extracellular and total body water provide useful information on the nutritional status of surgical patients and may be estimated from whole-body bio- impedance measurements at different frequencies.
2. Resistance and reactance were measured at 50 frequencies from 5 kHz to 1 MHz in 29 surgical patients (17 males, 12 ferhales) with a wide range of extracellular to total body water ratios.
3. A fit to the spectrum of reactance versus resistance data gave predicted resistances at frequencies zero and infinity. Values of extracellular and total body water determined by this bio-impedance spectroscopy technique were regressed against values obtained from radioisotope dilution. The standard errors of the estimate were 1.8931 and 3.2591 respectively.
4. Resistance indices (height(2)/resistance) at selected frequencies gave the highest correlations with extracellular and total body water at 5 kHz and 200 kHz respectively, and prediction equations derived from multiple stepwise regressions also showed these to be the optimum frequencies. The standard errors of the estimate for this multi-frequency bio-impedance analysis method were 1.9371 and 2.6061 for extracellular and total body water respectively.
5. To assess the ability of the two methods to measure changes in extracellular and total, body water, reproducibility was assessed from repeat measurements 10 min apart in a subgroup of 15 patients. Bio-impedance spectroscopy gave mean coefficients of variation for extracellular and total body water of 0.9% and 3.0% respectively. For multifrequency bio-impedance analysis the corresponding coefficients of variation were 0.9% and 0.6%.
6. It is concluded that a simple impedance analyser operating at only two frequencies compares favourably with the more complex spectroscopy technique for the determination of extracellular and total body water in surgical patients. |
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Harrison-J-E; McNeill-K-G
Nutritional assessment.
Blood Purification 12(1): 68-72
1994
English
Measurements of body composition are made to assess nutritional status. The measurements used for these studies should be selected on the basis of reliability, as well as simplicity and costs, and reliability depends on the information required. In normal adults simple estimates of fat and lean tissue (LBM), i.e. the anthropometric measurements of weight, height and skin fold thickness, should be sufficient since the proportions, in LBM, of water, protein and bone mineral are relatively constant. Measurements of body water (by isotope dilution or bioelectrical impedance) allow indirect estimates of fat and LBM that are reliable, provided that water is a constant proportion of LBM. In disease states, however, including renal disease, it is well established that the proportion of water in LBM varies from significant water overload to dehydration. In disease, it is important to determine not only total LBM but also the quality of LBM, determining essential body protein as well as body water. Body protein can be measured directly by nuclear techniques. This procedure should be more readily available for the clinical investigation of nutritional status. |
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Hart, F.X.; Toll, R.B.; Berner, N.J.; Bennett, N.H.
The low-frequency dielectric properties of octopus arm muscle measured in vivo
Journal Physics in Medicine and Biology
41
10
OCT
1996
2043-2052
FX Hart
Univ S Sewanee
Dept Phys
Sewanee, TN 37383 USA
0031-9155
ELECTRICAL-IMPEDANCE; SKELETAL-MUSCLE
The conductance and capacitance of octopus arm are measured in vivo over the frequency range 5 Hz to 1 MHz. Measurement of these parameters for a number of electrode separations permits the determination of me variations in tissue conductivity and dielectric constant with frequency. In the range 1-100 kHz the conductivity is independent of the frequency f and the dielectric constant varies as f(-1). These results, in conjunction with those reported previously for frog skeletal muscle, are consistent with the fractal model for the dielectric properties of animal tissue proposed by Dissado. Transformation of the results to complex impedance spectra indicates the presence of a dispersion above 100 kHz. |
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Hebuterne, X.; Hastier, P.; Peroux, J.L.; Zeboudj, N.; Delmont, J.P.; Rampal, P.
Resting energy expenditure in patients with alcoholic chronic pancreatitis
Journal Digestive Diseases and Sciences
41
3
MAR
1996
533-539
X Hebuterne
Hop Larchet
Serv Gastroenterol & Nutr
Ctr Agree Nutr Parentale Domicile
F-06202 Nice 03, France
0163-2116
indirect calorimetry; bioelectric impedance analysis; energy metabolism; resting energy expenditure; fat-free mass; chronic pancreatitis; nutrition NUTRITION; DISEASE; ETHANOL; MASS
The aim of this study was to assess resting energy expenditure in patients with chronic pancreatitis; 33 patients with alcohol-related chronic pancreatitis (group 1: 13 normal weight, group 2: 20 underweight) and 11 undernourished patients without identifiable disease (group 3) were studied. Body composition was determined by bioelectric impedance analysis and energy expenditure by indirect calorimetry. The percentage of body weight occupied by fat-free mass was similar among the three groups (76.4 +/- 1.5%, 78.6 +/- 1.3% and 76.8 +/- 2.1% for groups 1, 2, and 3, respectively). The measured resting energy expenditure (REE) was higher than the predicted EE (Harris and Benedict formula and Cunningham's equation) for the underweight patients with chronic pancreatitis (group 2) (P < 0.05), but not for the two other groups. According to Cunningham's equation, 65% of the group 2 patients were hypermetabolic (REE 110% of predicted EE) versus 23.1% and 20% in groups 1 and 3. When adjusted for fat free mass, REE was significantly (P < 0.01) higher in group 2 (35.0 +/- 0.9 kcal/kg/24 hr) than in the other two groups (30.1 +/- 0.7 kcal/kg/24 hr and 30.8 +/- 1.4 kcal/kg/24 hr in groups 1 and 3, respectively). During chronic pancreatitis, weight loss is accompanied by hypermetabolism, which should be taken into consideration during nutritional support. |
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Hahn, G.; Frerichs, I.; Kleyer, M.; Hellige, G.
Local mechanics of the lung tissue determined by functional EIT
Journal Physiological Measurement
17
Suppl. 4A
NOV
1996
A159-A166
G Hahn
Univ Gottingen
Ctr Anaesthesiol Emergency & Intens Care Med
Dept Anaesthesiol Res
Tl 195
D-37075 Gottingen, Germany
0967-3334
APPLIED POTENTIAL TOMOGRAPHY
A new functional EIT (f-EIT) evaluation technique providing information on the local dynamic behaviour of the lungs is presented. Out of a series of single EIT thoracic images local time courses of the impedance change are extracted. To detect regional differences in the dynamic behaviour of the lung tissue the local time courses at different locations are related to the average time course of the impedance change over the whole thoracic cross section. The time shifts between this reference signal and the signals from separate positions are calculated from the phase information of the complex cross spectra and evaluated in terms of the local phase angle. The computed phaseshifts are imaged over the cross section creating an 'f-EIT phase image' characterizing the local dynamic properties. To relate the observed differences to the proper lung location the resulting images are presented as a combination of the f-EIT ventilation images, which represent the]local amplitude of ventilation and the f-EIT phase images. The new imaging technique was tested in spontaneously breathing humans. Alterations to pulmonary dynamics were induced by changing the body posture of the subjects. The f-EIT phase imaging procedure was shown to identify lung regions with different dynamics and it is expected that this technique will also distinguish pathologically determined alterations. |
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Hendel, H.W.; Gotfredsen, A.; Andersen, T.; Hojgaard, L.; Hilsted, J.
Body composition during weight loss in obese patients estimated by dual energy X-ray absorptiometry and by total body potassium
Journal International Journal of Obesity
20
12
DEC
1996
1111-1119
HW Hendel
Hvidovre Univ Hosp
Dept Clin Physiol & Nucl Med 239
Kettegards Alle 30
Copenhagen, Denmark
0307-0565
DXA; TBK; body composition; obesity; weight loss FAT-FREE MASS; BIOELECTRICAL IMPEDANCE; PHOTON ABSORPTIOMETRY; BONE MASS; DENSITY; DEXA; REDUCTION; ADULTS; INVIVO; DIET
OBJECTIVE: To validate the ability of DXA to measure total body composition before and after weight loss and the composition of the lost body mass.
DESIGN: Cross sectional and follow-up study of body composition before and after a weight loss of 10.6 +/- 6.8 kg.
SUBJECTS: 31 obese subjects with a mean body weight of 105.2 +/- 15.2 kg at baseline, and a mean body weight of 94.6 +/- 16.5 kg at follow-up.
MEASUREMENTS: Body composition was measured by dual X-ray absorptiometry, total body potassium counting, and high precision scales before and after a weight loss.
RESULTS: DXA and the scales showed a strong linear relation (r=1). At baseline, however, DXA underestimated the body weight by a maximum of 3.2 kg because the subjects were too large for the scan table. After weight loss body weight measurements were accurate. Before and after weight loss the linear relations between DXA and TBK for FFM were strong (r=0.92 and 0.93). Bland and Altman plots showed limits of agreement of +/-9 kg before and after weight loss; DXA underestimated FFM in women and overestimated FFM in men. DXA accounted for 80% of the lost body weight. The composition of the lost body mass did not differ from that estimated by TBK (7.6% FFM and 92.4% FM by TBK; 11% FFM and 89% FM by DXA).
CONCLUSION: DXA estimates accurately the body composition and the composition of weight loss in groups of obese subjects. However, the scan table may be too small for patients weighing more than 95 kg. |
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Hendel HW; Gotfredsen A; Hojgaard L; Andersen T; Hilsted J
Change in fat-free mass assessed by bioelectrical impedance, total body potassium and dual energy X-ray absorptiometry during prolonged weight loss.
Scand J Clin Lab Invest 1996 DEC;56(8):671-679
English
Article
Hendel HW, Hvidovre Univ Hosp, Dept Clin Physiol & Nucl
Med 239, Kettegards Alle 30, DK 2650 Copenhagen, DENMARK
A total of 16 obese women (body mass index (BMI) 30-43 kg m(-2)) participated in a weight reduction study. Before and after a weight loss of 11.7 +/- 7.4 kg (mean +/- SD), body composition was assessed by dual energy X-ray absorptiometry (DXA), and total body potassium counting (TBK). These measurements were compared with bioimpedance analysis (BIA) by applying 11 predictive BIA equations published in the literature. Predictive equations for the present study population were developed, with the use of fat-free mass (FFM) as assessed by TBK and DXA as references in multiple regression analysis. The results of the BIA equations varied widely; FFM was generally overestimated by BIA as compared with DXA and TBK before and after weight loss. During weight loss, the FFM did not change, as estimated by DXA (1.3 +/- 2.3 kg, p 0.05) and TBK (0.9 +/- 2.9 kg, p 0.05). The recorded change in impedance (R) was also insignificant. Three BIA equations from the literature, which were not specific for the degree of obesity in the present study group, predicted changes in FFM (from 0.5 +/- 3.6 to 2.4 +/- 4.4 kg, p 0.05) that were comparable with those estimated by the reference methods. Eight equations from the literature, which included equations specific for the degree of obesity in the study group, and the group specific equations developed for the present population predicted significant changes in FFM during weight loss (from 2.3 +/- 3.0 to 5.0 +/- 3.0 kg, p < 0.05). We conclude that in obesity most predictive equations are unable to predict static body composition and are not reproducible for individuals over time. However, a significant or insignificant change in R (without accompanying predictive equations) may be used to indicate whether FFM is lost or preserved in groups of obese subjects. |
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Henneberg KA; Roberge FA
Simulation of propagation in a bundle of skeletal muscle fibers: Modulation effects of passive fibers.
English
Article
Ann Biomed Eng 1997 JAN-FEB;25(1):29-45
Henneberg KA, Univ Montreal, Inst Genie Biomed, CP 6128,
Montreal, PQ H3C 3J7, CANADA
Computer simulations are used to study passive fiber modulation of propagation in a tightly packed bundle of frog skeletal muscle fibers (uniform fiber radius of 50 mu m). With T = 20 degrees C and a uniform nominal interstitial cleft width (d) over bar = 0.35 mu m, about 92% of the active fiber source current (I-ma) enters the passive tissue as a radial load current (I-ep) while the rest flows longitudinally in the cleft between the active and adjacent passive fibers. The conduction velocity of 1.32 m/s was about 30% lower than on an isolated fiber in a Ringer bath, in close agreement with experimental results. The peak-to-peak interstitial potential (phi(epp)) at the active fiber surface was 38 mV, compared to 1.3 mV for the isolated fiber. A uniform increase of d from 0.35 to 1.2 mu m decreased phi(epp) from 38 to 25 mV, increased the velocity from 1.32 to 1.54 m/s, and decreased the maximum rate of rise of the action potential upstroke (V-max) from 512 to 503 V/s. Increasing the phase angle of the passive fiber membrane impedence (Z(m)) increases the phase delay between I-ma and I-ep, thereby increasing phi(epp) which in turn slows down propagation and increases V-max. |
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Hettrick DA; Battocletti JH; Ackmann JJ; Linehan JH; Warltier DC
Effects of physical parameters on the cylindrical model for volume measurement by conductance.
English
Article
Ann Biomed Eng 1997 JAN-FEB;25(1):126-134
Hettrick DA, Med Coll Wisconsin, Med, Dept Anesthesiol,
Room 462C, 8701 Watertown Plank Rd, Milwaukee,WI 53226 USA
Despite its undisputed utility for determining changes in ventricular pressure-volume relationships, the conductance catheter technique has not been proven reliable for measuring absolute volume. This limitation is due to violations of the assumptions inherent in the cylindrical model on which the method is based (i.e., homogeneous electric field and no leakage current). The purpose of this investigation was to relate cylindrical model correction factors to the physical environment of the catheter and to the cylindrical equation. Physical measurements of saline-filled, nonconductive cylinders using a four-electrode conductance catheter were compared with a three-dimensional finite element model of the physical apparatus. These measurements were incorporated into a parallel conductance model to relate physical parameters to corrections in the cylindrical equation for volume measurement. Excellent agreement between measured and modelled data was found Results demonstrated a nonlinear relationship between the field nonhomogeneity correction factor (alpha) and cylinder diameter. The relationship between alpha and diameter was consistent with a theoretical extrapolation of cylinder diameter toward infinity. An inverse relationship between alpha and the parallel conductance volume (V-p) was also clarified. The parallel conductance model was able to demonstrate opposite effects of the physical presence of the catheter body and electrodes, which tended to cancel out any net effect on measured conductance. Results of this investigation and the developed finite element model clarify the nature of the correction terms in the cylindrical model and may lead to greater application of the conductance technique. |
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Hofmann, B.
Penalty methods for the inverse problem in EIT
Journal Physiological Measurement
17
Suppl. 4A
NOV
1996
A73-A76
B Hofmann
Univ Gottingen
Inst Numer & Angew Math
D-37073 Gottingen, Germany
0967-3334
The conductivity profiles arising in medical applications of electrical impedance tomography (EIT) are often of 'blocky' structure, i.e. they are relatively constant inside an organ and are rapidly varying at its boundary. Standard regularisation methods for the inverse problem tend to blur these sharply defined edges. A penalty method is proposed which is especially designed for a better reconstruction of discontinuous conductivity profiles. |
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Holder, D.S.; Hanquan, Y.; Rao, A.
Some practical biological phantoms for calibrating multifrequency electrical impedance tomography
Journal Physiological Measurement
17
Suppl. 4A
NOV
1996
A167-A177
DS Holder
Univ London Univ Coll
Dept Physiol
Gower St
London WC1E 6BT, England
0967-3334
BLOOD; EIT
Three groups of materials have been assessed with a Hewlett-Packard 4284A impedance analyser and Sheffield Mark I electrical impedance tomography (EIT) system for suitability for calibration of multifrequency EIT systems. They were required to be easy to use, stable over several hours, and have complex impedance similar to biological tissue. The groups were: (i) inorganic materials including barium titanate, polystyrene microspheres and fumed silica, all in aqueous suspension; these had phase angles below 1 degrees and so were unsuitable. (ii) Cucumber in KCI solution. Cucumber cortex had a phase angle of 40 degrees at a centre frequency of 50 kHz. Contrast between the cucumber and bathing solution could be selected by varying the KCl concentration. (iii) Polyurethane sponge immersed in packed red cells. The phase angle of packed cells was about 25 degrees at I MHz. Sponge resistivities and permittivities when immersed in packed cells were 5-20% higher than the bathing solution itself, for densities of 2-6.2% w/v. Both the biological materials appear suitable for the intended purpose; system (iii) is inherently more stable, and has capacitance in both bathing medium and test object. If an initial accuracy of greater than about +/-15% is required, direct measurement with an impedance analyser is recommended prior to imaging studies. |
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Holder, D.S.; Rao, A.; Hanquan, Y.
Imaging of physiologically evoked responses by electrical impedance tomography with cortical electrodes in the anaesthetized rabbit
Journal Physiological Measurement
17
Suppl. 4A
NOV
1996
A179-A186
DS Holder
Univ London Univ Coll
Dept Physiol
Gower St
London WC1E 6BT, England
0967-3334
SPREADING DEPRESSION; ANESTHETIZED RAT; ISCHEMIA; SYSTEM; EIT
The purpose of this study was to determine if electrical impedance tomography (EIT) could be used to image impedance changes of several per cent over tens of seconds, known to occur during evoked activity of the cerebral cortex. A ring of 16 electrodes was placed on the exposed superior surface of the brain of anaesthetized rabbits. EIT images were acquired every 15 s using a Sheffield Mark 1 EIT system. During periods of 2.5-3 min of intense photic stimulation of both eyes or electrical stimulation of a forepaw, reproducible impedance decreases of 4.5 +/- 2.7% and 2.7 +/- 2.4% (mean +/- SD) respectively occurred in appropriate cortical areas, with a time course similar to the period of stimulation. They were accompanied by adjacent smaller impedance increases. The decreases are probably due to increased blood flow and temperature; the cause of the adjacent increases may be a shadowing artefact of the reconstruction algorithm or due to physiological shrinkage of the extracellular space. This demonstrates, for the first time, that such small changes may be imaged under optimal conditions. These results are encouraging to the prospect that EIT may eventually be suitable for imaging evoked responses or epilepsy in human subjects. |
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Hu, H.Y.; Kato, Y.
Body composition assessed by bioelectrical impedance analysis (BIA) in patients with Graves' disease before and after treatment
Endocrine Journal
42
4
AUG
1995
545-550
Y Kato
Shimane Med Univ
Dept Med, Div 1
89-1 Enya CHO
Izumo
Shimane 693, Japan
0918-8959
body composition; bioelectrical impedance analysis; body cell mass; extracellular water; free T-4; Graves' disease X-RAY ABSORPTIOMETRY; THYROID-HORMONE; SKELETAL-MUSCLE; FAT; MALNUTRITION; SEGMENTS; WATER
Body composition was assessed by bioelectrical impedance analysis (BIA) in 11 female patients with Graves' disease and in 49 age-matched healthy Japanese women. Patients with Graves' disease were examined in the hyperthyroid state before treatment and in the stable euthyroid state after treatment with antithyroid drugs for 6 to 18 months. Body weight (BW), percent body fat (BF/BW), percent lean body mass (LBM/BW) and percent total body water (TBW/BW) were not statistically different between hyperthyroid Graves' patients and healthy subjects. Percent body cell mass (BCM/BW) was much lower in hyperthyroid Graves' patients than in healthy subjects (mean +/- SEM; 33.9 +/- 2.4% vs. 41.5 +/- 0.5%, P<0.001). Percent ratio of extracellular water to total body water (ECW/TBW) was much greater in hyperthyroid Graves' patients than in healthy subjects (53.9 +/- 3.0% vs. 41.8 +/- 0.5%, P<0.001). These abnormal ratios, BCM/BW and ECW/TBW, were normalized after treatment. Serum free T-4 levels showed a positive correlation with ECW/TBW (r=0.779) and a reverse correlation with BCM/BW (r= -0.760) in all of the patients with Graves' disease examined. These findings indicate that body composition is affected by thyroid hormones and that body composition in hyperthyroid Graves' disease is characterized by decreased BCM associated with increased ECW. |
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Hu, H.Y.; Yamamoto, H.; Sohmiya, M.; Abe, T.; Murakami, Y.; Kato, Y.
Body composition assessed by bioelectrical impedance analysis (BIA) and the correlation with plasma insulin-like growth factor I (IGF-I) in normal Japanese subjects and patients with acromegaly and GH deficiency (vol 41, pg 63, 1994)
Endocrine Journal
43
1
FEB
1996
0918-8959 |
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Hu, H.Y.; Kato, Y.
Body composition assessed by bioelectrical impedance analysis (BIA) in patients with Graves' disease before and after treatment
Endocrine Journal
42
4
AUG
1995
545-550
Y Kato
Shimane Med Univ
Dept Med, Div 1
89-1 Enya CHO
Izumo
Shimane 693, Japan
0918-8959
body composition; bioelectrical impedance analysis; body cell mass; extracellular water; free T-4; Graves' disease X-RAY ABSORPTIOMETRY; THYROID-HORMONE; SKELETAL-MUSCLE; FAT; MALNUTRITION; SEGMENTS; WATER
Body composition was assessed by bioelectrical impedance analysis (BIA) in 11 female patients with Graves' disease and in 49 age-matched healthy Japanese women. Patients with Graves' disease were examined in the hyperthyroid state before treatment and in the stable euthyroid state after treatment with antithyroid drugs for 6 to 18 months. Body weight (BW), percent body fat (BF/BW), percent lean body mass (LBM/BW) and percent total body water (TBW/BW) were not statistically different between hyperthyroid Graves' patients and healthy subjects. Percent body cell mass (BCM/BW) was much lower in hyperthyroid Graves' patients than in healthy subjects (mean +/- SEM; 33.9 +/- 2.4% vs. 41.5 +/- 0.5%, P<0.001). Percent ratio of extracellular water to total body water (ECW/TBW) was much greater in hyperthyroid Graves' patients than in healthy subjects (53.9 +/- 3.0% vs. 41.8 +/- 0.5%, P<0.001). These abnormal ratios, BCM/BW and ECW/TBW, were normalized after treatment. Serum free T-4 levels showed a positive correlation with ECW/TBW (r=0.779) and a reverse correlation with BCM/BW (r= -0.760) in all of the patients with Graves' disease examined. These findings indicate that body composition is affected by thyroid hormones and that body composition in hyperthyroid Graves' disease is characterized by decreased BCM associated with increased ECW. |
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Hughes, T.A.T.; Liu, P.; Griffiths, H.; Wiles, C.M.
The repeatability and variability of electrical impedance tomography indices of pharyngeal transit time in normal adults
Journal Physiological Measurement
16
Suppl. 3A
AUG
1995
A79-A86
TAT Hughes
Univ Wales Coll Med
Dept Med Neurol
Cardiff CF4 4XN
S Glam, Wales
0967-3334
Two electrical impedance tomography (Err) indices of pharyngeal transit time have been repeatedly measured in 20 normal adults. The time course of change in pharyngeal conductivity whilst swallowing 5, 10 and 20 mi boluses was expressed either as a full width at 20% maximum (FW20) or as a full width at 50% maximum (FW50): the latter could be satisfactorily measured more frequently. Mean coefficients of variation for FW20 and FW50 tended to decrease with increasing bolus volume but this was statistically significant only for FW50 in men. FW20 and FW50 were significantly shorter in men than women and increased with increasing age. FW50 was significantly smaller when larger bolus volumes were swallowed. FW50 was significantly shorter when low-conductivity fluid was used and there was an insignificant trend for it to be longer with electrodes in the highest position. The amplitude of the conductivity change recorded was significantly affected by all factors studied apart from age. If EIT is to be used as a technique for monitoring changes in pharyngeal transit time in patients with neurogenic dysphagia, repeat examinations should be performed under the same conditions and, if possible, large bolus volumes should be used. |
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Hughes TAT; Liu P; Griffiths H; Wiles CM
Repeatability of indices of swallowing in healthy adults: Electrical impedance tomography compared with a simple timed test of swallowing.
English
Article
Med Biol Eng Comput 1996 SEP;34(5):366-368
Hughes TAT, Univ Wales Coll Med, Dept Med Neurol, Cardiff
CF4 4XN, S Glam, WALES |
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Huysmans, M.C.D.N.J.M.; Longbottom, C.; Pitts, N.B.; Los, P.; Bruce, P.G.
Impedance spectroscopy of teeth with and without approximal caries lesions - An in vitro study
Journal of Dental Research
75
11
NOV
1996
1871-1878
MCDNJM Huysmans
Univ Nijmegen, Trikon
Inst Dent Clin Res,Dept Cariol & Endodontol
POB 9101
NL-6500 HB Nijmegen, Netherlands
0022-0345
dental caries; caries diagnosis; electrical impedance spectroscopy; diagnostic systems DENTAL ENAMEL; BOVINE ENAMEL; PERMEABILITY; MEMBRANES
Caries diagnosis by the measurement of electrical resistance is hampered by polarization effects when de or single-low-frequency ac currents are used. Electrical impedance spectroscopy, measuring impedance over a large range of frequencies, will provide more detailed information about the electrical characteristics of teeth. It was the aim of this study (a) to characterize the complex impedance behavior of whole extracted teeth, measured at the approximal surface, and (b) to identify parameters of the complex impedance behavior of the teeth which would be useful in distinguishing between degrees of carious involvement. Thirty-nine extracted premolar teeth with 59 unrestored and undamaged (excepting caries) approximal surfaces were selected. The tooth surfaces were divided into three groups according to their macroscopic appearance: sound (group S, n = 16), white- or brown-spot lesion present (group L, n = 33), or cavitated (group C, n = 10). The teeth were inserted into a jig which allowed for counter-electrode contact via a conducting gel. The working electrode consisted of a carbonated fiber material. Electrical impedance measurements were performed over a maximum range of about 1 MHz to 0.1 Hz. We analyzed electrical impedance data by fitting equivalent circuits. Fit was evaluated numerically and visually. The complex impedance spectra divided naturally into three groups which corresponded almost perfectly with the classifications of S, L, and C. The groups differed most in the de resistance. Mean R(dc) for groups S, L, and C were 68 M Omega, 5.9 Mn, and 321 k Omega, respectively. These means were significantly different from each other (log-transformed data, ANOVA, p < 0.001; Tukey multiple comparisons, p < 0.001). It is concluded that the in vitro performance of electrical impedance spectroscopy in differentiating among sound, non-cavitated carious, and cavitated approximal tooth surfaces is excellent. |
