Search PubMed⌕ Search

Biomedical subjects

L C Ward

Publications and source records attributed to L C Ward.

At least 55 records · Page 3Linked to original sources
PubMed1998

Prediction of the chemical composition of lamb carcasses from multi-frequency impedance data.

Multi-frequency bioimpedance analysis (MFBIA) was used to determine the impedance, reactance and resistance of 103 lamb carcasses (17.1-34.2 kg) immediately after slaughter and evisceration. Carcasses were halved, frozen and one half subsequently homogenized and analysed for water, crude protein and fat content. Three measures of carcass length were obtained. Diagonal length between the electrodes (right side biceps femoris to left side of neck) explained a greater proportion of the variance in water mass than did estimates of spinal length and was selected for use in the index L2/Z to predict the mass of chemical components in the carcass. Use of impedance (Z) measured at the characteristic frequency (Zc) instead of 50 kHz (Z50) did not improve the power of the model to predict the mass of water, protein or fat in the carcass. While L2/Z50 explained a significant proportion of variation in the masses of body water (r(2) 0.64), protein (r(2) 0.34) and fat (r(2) 0.35), its inclusion in multi-variate indices offered small or no increases in predictive capacity when hot carcass weight (HCW) and a measure of rib fat-depth (GR) were present in the model. Optimized equations were able to account for 65-90% of the variance observed in the weight of chemical components in the carcass. It is concluded that single frequency impedance data do not provide better prediction of carcass composition than can be obtained from measures of HCW and GR. Indices of intracellular water mass derived from impedance at zero frequency and the characteristic frequency explained a similar proportion of the variance in carcass protein mass as did the index L2/Z50.

Animals↗
PubMed1998

Potential errors in the application of mixture theory to multifrequency bioelectrical impedance analysis.

Potential errors in the application of mixture theory to the analysis of multiple-frequency bioelectrical impedance data for the determination of body fluid volumes are assessed. Potential sources of error include: conductive length; tissue fluid resistivity; body density; weight and technical errors of measurement. Inclusion of inaccurate estimates of body density and weight introduce errors of typically < +/- 3% but incorrect assumptions regarding conductive length or fluid resistivities may each incur errors of up to 20%.

Adult↗
PubMed1998

Sources of error in bioimpedance spectroscopy.

Two different makes of bioimpedance spectrometer (UniQuest-SEAC SFB-3 and Xitron 4000B) were used for a series of measurements on volunteers and patients in intensive care. Although each machine was accurate over the frequency range 5 to 500 kHz when bench tested on model resistor-capacitor circuits, significant differences in their recorded impedance parameters appeared when used in vivo, especially on intensive care patients. A series of laboratory tests was performed on each machine simulating the situation in vivo to identify possible reasons for these differences. Whilst stray capacitance in the environment was identified as the major contributor to variability in high-frequency performance, interaction between electrode impedance and lead positioning was also a factor. The observed phase shift with frequency or time delay (Td) used in the Xitron modeling software appears to be the result of a time constant caused by stray capacitance and so is unlikely to have any biological meaning. Significant differences in the in vivo numerical values produced by bioimpedance spectrometers may be attributed to instrument design, data processing and, in particular, the clinical environment.

Adult↗
PubMed1998

Data analysis in multiple-frequency bioelectrical impedance analysis.

The performance of three analytical methods for multiple-frequency bioelectrical impedance analysis (MFBIA) data was assessed. The methods were the established method of Cole and Cole, the newly proposed method of Siconolfi and co-workers and a modification of this procedure. Method performance was assessed from the adequacy of the curve fitting techniques, as judged by the correlation coefficient and standard error of the estimate, and the accuracy of the different methods in determining the theoretical values of impedance parameters describing a set of model electrical circuits. The experimental data were well fitted by all curve-fitting procedures (r = 0.9 with SEE 0.3 to 3.5% or better for most circuit-procedure combinations). Cole-Cole modelling provided the most accurate estimates of circuit impedance values, generally within 1-2% of the theoretical values, followed by the Siconolfi procedure using a sixth-order polynomial regression (1-6% variation). None of the methods, however, accurately estimated circuit parameters when the measured impedances were low (< 20 omega) reflecting the electronic limits of the impedance meter used. These data suggest that Cole-Cole modelling remains the preferred method for the analysis of MFBIA data.

Body Composition↗
PubMed1998

Measurement of social introversion by the MMPI-2.

Psychometric characteristics of the Social Introversion (Si) scale, the Social Discomfort (SOD) scale, and the Si subscales of the MMPI-2 were examined in clinical samples of 122 psychiatric patients and 399 patients with substance-use disorders. The combined Si1 (Shyness/Self-Consciousness) and Si2 (Social Avoidance) subscales correlated highly with SOD and are apparent measures of the social introversion construct. Si3 (Self/Other Alienation) was found to be a measure of the general maladjustment factor of the MMPI-2. Content not included on the Si subscales was divided into a group of items that measures general maladjustment and 2 other item groups that may assess minor constructs related to social introversion. As in previous research, the 3 Si subscales accounted well for variance in Si scores.

Alabama↗
PubMed1998

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 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 (3H2O) 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.

Adipocytes↗
PubMed1997

Evaluation of bioelectrical impedance for prospective nutritional assessment in cystic fibrosis.

We have compared the use of bioelectrical impedance analysis (BIA) with anthropometry for the prediction of changes in total body potassium (TBK) in a group (n = 31) of children with cystic fibrosis. Linear regression analysis showed that TBK was highly correlated (r > 0.93) with height2/impedance, weight, height, and fat-free mass (FFM) estimated from skin-fold measurements. Changes in TBK were also correlated, but less well, with changes in height2/impedance, weight, height, and FFM (r = 0.69, 0.59, 0.44, and 0.40, respectively). The children were divided into two groups: those who had normal accretion of TBK (> 5%/y) and those who had suboptimal accretion of TBK (< 5%/y). Analysis of variance showed that the significant difference in the change in TBK between the groups was detectable by concomitant changes in impedance and weight but not by changes in height, FFM, or weight and height Z scores. The results of this study suggest that serial BIA measures may be useful as a predictor of progressive undernutrition and poor growth in children with cystic fibrosis.

Adolescent↗
PubMed1997

Extraction of electrical characteristics from pixels of multifrequency EIT images.

Computer modelling has shown that electrical characteristics of individual pixels may be extracted from within multiple-frequency electrical impedance tomography (MFEIT) images formed using a reference data set obtained from a purely resistive, homogeneous medium. In some applications it is desirable to extract the electrical characteristics of individual pixels from images where a purely resistive, homogeneous reference data set is not available. One such application of the technique of MFEIT is to allow the acquisition of in vivo images using reference data sets obtained from a non-homogeneous medium with a reactive component. However, the reactive component of the reference data set introduces difficulties with the extraction of the true electrical characteristics from the image pixels. This study was a preliminary investigation of a technique to extract electrical parameters from multifrequency images when the reference data set has a reactive component. Unlike the situation in which a homogeneous, resistive data set is available, it is not possible to obtain the impedance and phase information directly from the image pixel values of the MFEIT images data set, as the phase of the reactive reference is not known. The method reported here to extract the electrical characteristics (the Cole-Cole plot) initially assumes that this phase angle is zero. With this assumption, an impedance spectrum can be directly extracted from the image set. To obtain the true Cole-Cole plot a correction must be applied to account for the inherent rotation of the extracted impedance spectrum about the origin, which is a result of the assumption. This work shows that the angle of rotation associated with the reactive component of the reference data set may be determined using a priori knowledge of the distribution of frequencies of the Cole-Cole plot. Using this angle of rotation, the true Cole-Cole plot can be obtained from the impedance spectrum extracted from the MFEIT image data set. The method was investigated using simulated data, both with and without noise, and also for image data obtained in vitro. The in vitro studies involved 32 logarithmically spaced frequencies from 4 kHz up to 1 MHz and demonstrated that differences between the true characteristics and those of the impedance spectrum were reduced significantly after application of the correction technique. The differences between the extracted parameters and the true values prior to correction were in the range from 16% to 70%. Following application of the correction technique the differences were reduced to less than 5%. The parameters obtained from the Cole-Cole plot may be useful as a characterization of the nature and health of the imaged tissues.

Biometry↗
PubMed1997

Confirmatory factor analyses of the Anxiety and Depression content scales of the MMPI-2.

A sample of 408 patients with substance use disorders was equally divided into derivation and cross-validation samples. All patients had taken the MMPI-2. Exploratory factor analyses of MMPI-2 item data in the derivation sample permitted construction of latent variable measurement models for the Anxiety (ANX) and Depression (DEP) content scales. The 2-factor models for ANX consisted of Trait Anxiety and Worry, and the 3-factor model for DEP contained factors of Trait Depression, Hopelessness, and Self-Depreciation. Confirmatory factor analyses in cross-validation demonstrated a good fit for both models and for their combination in a 5-factor measurement model. Latent variable correlations in the 5-factor model helped explain the high correlation and low discriminant validity of ANX and DEP.

Adult↗
PubMed1997

Psychometric assessment of motives for using cocaine in men with substance use disorders.

A 15-item self-report questionnaire from a previous study of social, coping, and enhancement motives for drinking was reworded to assess motives for using cocaine. Data from 121 cocaine users indicated satisfactory reliabilities for the 3 new 5-item scales, and the fit of a 3-factor structure in confirmatory factor analysis was comparable to that of the earlier study of drinking motives. Removal of 4 items substantially improved the fit to the 3-factor model without reducing reliabilities. Some evidence of validity was inferred from a correlation between reported use of cocaine for coping and a measure of general maladjustment.

Adaptation, Psychological↗
PubMed1997

Validity of quick short forms of the Wechsler Adult Intelligence Scale-Revised with brain-damaged patients.

The validities of 41 short forms of the Wechsler Adult Intelligence Scale-Revised that require 20 minutes or less to give were compared in a sample of 174 brain-damaged patients. Mean errors in predicting Full Scale IQs were computed for each subtest combination, and a short form efficiency index was calculated by correcting mean error for administration time. The three quick abbreviations proposed by Kaufman (1990) proved to be among the more efficient predictors of Full Scale IQ, but a number of other short forms also performed well. The data provide psychometric information for selecting a quick measure of IQ that fits the needs, preferences, and time constraints of the neuropsychologist.

Journal Article↗
PubMed1996

Bioelectrical impedance for monitoring the efficacy of lymphoedema treatment programmes.

The treatment of lymphoedema includes a combination of massage, compression bandaging, and exercise. To date the most common technique of assessing the efficacy of treatment has involved estimating the total limb volume from circumferential measurements at fixed intervals along the limb. This study investigated the application of multiple frequency bioelectrical impedance analysis, MFBIA, to monitor the volume of lymphoedema in the upper limb of patients who developed this disorder following surgery for cancer of the breast. Daily measurements of both circumference and impedance of both the affected and unaffected limbs were recorded for 20 patients throughout their 4 week treatment programmes. Twenty control subjects were also monitored daily over a similar 4 week period. Prior to the commencement of treatment the bioimpedance technique detected a significant (P < 0.01) asymmetry between the two limbs of the control subjects, associated with handedness (P < 0.001). Circumferential estimates of limb volumes in the control group detected no asymmetry. Impedance measures of extracellular fluid showed all of the patients to lie outside the 95% confidence interval determined from the data of the control group. The trends of the impedance measures and the circumferential estimates of volume throughout the 4 week program were found to be significantly different (P < 0.05); MFBIA exhibiting a greater sensitivity in the detection of lymphoedema. The results demonstrate that MFBIA is significantly more sensitive than circumferential measurement both in the early diagnosis of lymphoedema and in monitoring change.

Adult↗
PubMed1996

Clinical, biochemical, hematologic, and radiographic responses in Paget's disease following intravenous pamidronate disodium: a 2-year study.

An intravenous dosage schedule using pamidronate disodium, based on biochemical severity, was used to treat 71 patients with Paget's disease who had no previous bisphosphonate treatment. Disease severity was stratified by fasting hydroxyproline excretion (HypE): Group (Gp) I (mild disease; HypE < 5.0 mumol/LGF) received a total dose of 120 mg; Gp II (moderate; HypE 5.00-9.99) received 180 mg; and Gp III (severe; HypE > or = 10) received 240 mg. Within each group patients were randomly allocated to receive daily 30 mg or 60 mg infusions. Observations for 2 years included pain scores, indices of bone turnover, and radiology of lytic lesions. There was no difference in biochemical responses, or in the percentage of patients with early fever, between the 30 mg and 60 mg daily subgroups; for convenience, 60 mg infusions are recommended. Neutrophils and total white cell counts were both significantly below baseline 4 days after the first infusion; lymphocytes were significantly reduced by day 2; and all three measures had returned to within the reference range by day 6. Remission was assessed at 6 months, when both plasma alkaline phosphatase (ALP) and HypE had reached stable nadirs. Increasing severity was associated with increasing resistance to suppression of HypE at 6 months to within the reference range: Gp I, 87%; Gp II, 44%; and Gp III, 0% (p < 0.0001 by chi-square test). Biochemical relapse at 2 years (defined as ALP 50% above the 6 month level) was also dependent on initial disease severity (Gp I, 6%; GpII, 39%; Gp III, 62%; p < 0.0005 by chi-square test). There was no association between time to relapse and either initial dose or log dose. Radiologic lytic lesions (in 22 patients) were all in remission at 3 months; however, relapse rates at 2 years appeared to be severity-dependent: Gp I, 13%; Gp II, 43%; and Gp III, 57% (n.s. by chi-square test). Remission rates based on a fall to < 50% of pretreatment of either HypE or ALP were more in accord with lytic lesion remission rates than were rates based on HypE falling to within the reference range. Pamidronate produced a significant reduction from baseline in Pagetic bone, Pagetic joint, and unrelated musculoskeletal pain in the first 6 months (p < 0.0001). From 0 months to 2 years the maintenance of improvement in bone pain (p < 0.005) and joint pain (p < 0.05) was significantly better than in unrelated pain. Pamidronate is a safe, welltolerated, and effective treatment for Paget's disease. In spite of larger dosage in severe disease, increasing severity was associated with resistance to normalization of biochemistry and a higher incidence of biochemical and radiological relapse at 2 years. Our current dosage recommendation would be for two 60 mg infusions for mild disease (Gp I); and four 60 mg infusions for moderate disease (Gp II). Severe disease (Gp III) remains a challenge; regardless of dosage, the majority of patients will be in relapse 2 years after a single course of treatment.

Aged↗
PubMed1996

Monitoring of extracellular and total body water during haemodialysis using multifrequency bio-electrical impedance analysis.

Multifrequency bio-electrical impedance analysis (MFBIA) was evaluated as a technique for monitoring changes in extracellular and total body water (ECW and TBW, respectively) of 15 subjects during dialysis. Dilution analysis, using deuterium oxide and sodium bromide, was also performed on each subject before dialysis so that prediction equations for ECW and TBW based on the MFBIA measures could be developed. These prediction equations were then used to estimate water compartment volume changes during dialysis and compared with volumetric measures of the dialysate removed. The results show that MFBIA does not accurately measure ECW and TBW changes during dialysis. The MFBIA measures tend to overestimate the changes and are not sufficiently precise to be clinically useful.

Adult↗
PubMed1996

Evaluation of multiple frequency bioelectrical impedance and Cole-Cole analysis for the assessment of body water volumes in healthy humans.

OBJECTIVE: To assess the application of a Cole-Cole analysis of multiple frequency bioelectrical impedance analysis (MFBIA) measurements to predict total body water (TBW) and extracellular water (ECW) in humans. This technique has previously been shown to produce accurate and reliable estimates in both normal and abnormal animals. DESIGN: The whole body impedance of 60 healthy humans was measured at 496 frequencies (ranging from 4 kHz to 1 MHz) and the impedance at zero frequency, Ro, and at the characteristic frequency, Zc, were determined from the impedance spectrum, (Cole-Cole plot). TBW and ECW were independently determined using deuterium and bromide tracer dilution techniques. SETTING: At the Dunn Clinical Nutrition Centre and The Department of Biochemistry, University of Queensland. SUBJECTS: 60 healthy adult volunteers (27 men and 33 women, aged 18-45 years). RESULTS: The results presented suggest that the swept frequency bioimpedance technique estimates total body water, (SEE = 5.2%), and extracellular water, (SEE = 10%), only slightly better in normal, healthy subjects than a method based on single frequency bioimpedance or anthropometric estimates based on weight, height and gender. CONCLUSIONS: This study has undertaken the most extensive analysis to date of relationships between TBW (and ECW) and individual impedances obtained at different frequencies ( > 400 frequencies), and has shown marginal advantages of using one frequency over another, even if values predicted from theoretical bioimpedance models are used in the estimations. However in situations where there are disturbances of fluid distribution, values predicted from the Cole-Cole analysis of swept frequency bioimpedance measurements could prove to be more useful.

Adolescent↗
PubMed1995

Multiple frequency bioelectrical impedance for the prediction of total body potassium in cystic fibrosis.

The use of multiple frequency bioelectrical impedance analysis (MFBIA) was compared with single frequency bioelectrical impedance analysis (SFBIA) and anthropometry to estimate the size of the body cell mass (BCM) in a paediatric cystic fibrosis population. BCM was independently determined from the accepted gold standard reference of total body potassium (TBK). MFBIA was used to measure the impedance of the body at 248 frequencies from 4 kHz to 1 MHz. Data were analysed using Cole-Cole plots of reactance versus resistance. The limits of agreement procedure was used to determine the reliability and precision of the different techniques to predict values for TBK, in an individual subject. The results indicate that MFBIA with a precision of 12% offers little improvement over single frequency BIA but is better and more accurate than anthropometry for the prediction of TBK in an individual patient.

Journal Article↗
PubMed1995

The use of Cole-Cole plots to compare two multifrequency bioimpedance instruments.

Two commercially available multifrequency bioimpedance spectrometers (Xitron 4000B and SEAC SFB3) were compared by performing measurements on a set of electronic circuits and by studying 14 healthy volunteers. Output data were plotted as reactance versus resistance and fitted with a semi-circle using a least squares fitting program. In tests with six electronic circuits both instruments produced impedance loci that were well described by semicircular Cole-Cole plots, though there were some minor discrepancies using the Xitron instrument at frequencies above 150 kHz. When tested on the volunteers the SEAC instrument gave very good fits (RMSE = 1.5 Omega) to a semi-circle from 5-600 kHz on all volunteers. The Xitron instrument gave excellent fits to the semi-circle between 5 and 55 kHz (RMSE = 0.7 Omega) but above 55 kHz the phase measurements stayed constant or even increased, confirming the anomalous behaviour reported by other authors. The conclusions to be drawn are that the semicircular plots predicted by the Cole-Cole theory give a very good description of multifrequency impedance data recorded by the SEAC SFB3 instrument, on human subjects, for frequencies between 5 and 600 kHz. The Xitron 4000B is not able to reproduce the theoretically expected results in humans above 55 kHz.

Journal Article↗