Biomedical subjects

D F Percy

Publications and source records attributed to D F Percy.

8 recordsLinked to original sources

PubMed2001

Mixed multivariate generalized linear models for assessing lower-limb arterial stenoses.

Experiments and observational studies often involve gathering information on several response variables, enabling us to model their dependence on observable predictor variables. Despite associations between the response variables, they are often analysed separately using general and generalized linear models. This paper investigates applications of multivariate regression analysis to improve the accuracy of predictions and decisions, in the specific context of diagnosing arterial stenoses in human legs. Two basic models are developed for this application, using (i) four binary responses and (ii) a mixture of two binary and two normal responses. The results clearly demonstrate the potential advantages offered by this approach.

Arterial Occlusive Diseases↗

PubMed1994

Occupational hydrocarbon exposure and diabetic nephropathy.

Exposure to hydrocarbons has been implicated in the pathogenesis of glomerulonephritis but its role in the development of diabetic nephropathy remains unknown. Three groups of patients with Type 1 diabetes of over 10 years duration were studied. Group 1 comprised 45 patients (23 F) with no diabetic nephropathy (urinary albumin excretion (AER) < 30 mg 24 h-1), group 2 comprised 37 patients (17 F) with incipient diabetic nephropathy (AER between 30-300 mg 24 h-1), and group 3 comprised 31 patients (15 F) with overt diabetic nephropathy (AER > 300 mg 24 h-1). The groups were comparable for age, sex, duration of diabetes, recent glycaemic control, social class, and residential area. Patients were assessed blindly by a validated questionnaire and interview for hydrocarbon exposure, consumption of tobacco, analgesic agents, and alcohol. Exposure scores to hydrocarbons derived from the questionnaire were significantly higher in patients with incipient and overt diabetic nephropathy with smoking adjusted odds ratios of 3.6 and 5.2, respectively. The consumption of alcohol, analgesic agents, tobacco, and smoking habits were similar in the three groups. In conclusion, hydrocarbon exposure may be a key environmental factor in the development of diabetic nephropathy in patients with Type 1 diabetes.

Adult↗

PubMed1993

Multivariate analysis of cholesterol distribution for monitoring the risk of coronary heart disease.

The screening of people for potential coronary heart disease and the monitoring of subjects considered at risk have been performed for some time by measuring total serum cholesterol and its constituent lipoproteins. However, these measurements vary substantially within subjects, making such assessments imprecise. It has been suggested that greater consistency can be achieved by analysing the joint distribution of the individual lipoproteins or of transformed variables derived from them. In this paper we present the results of a laboratory experiment to investigate these ideas with a view to improving current methods of monitoring patients at risk. Nested, random-effects, multivariate analysis of variance and the log-ratio analysis of compositions are used to include information on all three lipoproteins simultaneously, and ratios of generalized variances are used to assess and compare the different response variables. The multivariate approach is seen to be far superior to the usual methods. Recommendations are made for routine monitoring and the practical implications are discussed.

Analysis of Variance↗

PubMed1993

Renal impairment with chronic hydrocarbon exposure.

Occupational hydrocarbon exposure is believed by some investigators to play an important role in the development of several non-neoplastic renal diseases. In view of the continuing debate in this area of nephrology we adopted a cross-sectional approach by investigating the prevalence of clinical or sub-clinical renal dysfunction in subjects chronically exposed to hydrocarbons at their work site. Three groups of healthy men working in different and separate areas of a major car manufacturing plant in the North-west of England participated in the study. Group 1 comprised 112 paint sprayers with exposure to paint-based hydrocarbons, group 2 comprised 101 volunteers working in the transmission area of the plant with exposure to petroleum-based mineral oils, and group 3 comprised 92 automated press operators with minimal background exposure to lubricants who acted as internal controls. Early markers of renal dysfunction such as serum creatinine, urinary total protein, albumin, transferrin, retinol binding protein, N-acetyl-glucosaminidase, gamma-glutamyl transferase, and leucine-amino-peptidase excretion were measured. Upper reference values of the parameters measured were derived from 105 comparable laboratory based controls with no occupational exposure to hydrocarbons or heavy metals. Group 1 had a significantly higher prevalence of elevated serum creatinine than the other groups and a higher prevalence of abnormal urinary total protein, N-acetyl-glucosaminidase, gamma-glutamyl transferase, and leucine-amino-peptidase excretion than groups 2 and 3. Group 2 had normal serum creatinine but a significantly higher prevalence of abnormal urinary total protein, transferrin, retinol binding protein, N-acetyl-glucosaminidase, and leucine-amino-peptidase excretion than group 3. Serum albumin was similar in all groups. There was some clustering of abnormal findings but the markers of renal dysfunction used in the study identified 37 individuals in group 1 and 31 subjects in group 2 with at least one abnormal parameter, compared to only five individuals in internal controls. This difference between the two target groups and group 3 was highly significant (p < 0.001). Subjects with chronic paint exposure had renal impairment and tubular dysfunction. Tubular dysfunction was also prominent with petroleum oil exposure. We therefore conclude that chronic hydrocarbon exposure may be associated with clinical and sub-clinical renal dysfunction. We advocate careful monitoring of workers exposure to hydrocarbons and for more effective preventive measures.

Adult↗

PubMed1992

Detection of bone marrow abnormalities in patients with Hodgkin's disease by T1 mapping of MR images of lumbar vertebral bone marrow.

Pixel by pixel T1 mapping of MR images has been used in conjunction with image analysis techniques to study the lumbar vertebral bone marrow of 20 patients with refractory or relapsed Hodgkin's disease prior to salvage chemotherapy, or high dose chemotherapy with autologous bone marrow rescue. Compared to 18 age matched controls, seven patients had significantly abnormal lumbar vertebral marrow T1 histograms with median, 5% and 95% centile T1 values that lay outside a three dimensional 95% probability region obtained for the normals. Six of these patients had increased areas of high T1 consistent with bone marrow involvement with lymphoma; although, only in two of them had Hodgkin's disease been detected by bilateral iliac crest bone marrow biopsy. Post-treatment studies were performed in four patients who had abnormal areas of high T1 in the lumbar vertebral bone marrow. All showed normalisation of the T1 histogram, with a reduction of T1 values to within the normal range as defined by the studies of age matched controls. T1 mapping of bone marrow offers potential for detecting bone marrow infiltrates in patients with lymphoma, and also for the assessment of treatment response.

Adult↗

PubMed1992

Blocked arteries and multivariate regression.

Ultrasound blood flow waveforms may be used in the diagnosis of arterial occlusive disease in human legs. We develop a statistical model to predict disease severity, conditional on the ultrasound data and some training data. It belongs to the class of models known as seemingly unrelated regressions, for which the Bayesian predictive density function cannot be evaluated analytically. Allowing for missing components of response vectors in the training data, we describe a first-order approximation to the predictive density, based on a Bayes estimate of the precision matrix. This approximation is then used to generate cross-validated predictions of disease severity in a set of 31 patients. We conclude with a discussion of the results.

Arterial Occlusive Diseases↗

PubMed1992

Primary glomerulonephritis and hydrocarbon exposure: a case-control study and literature review.

A case-control study was undertaken to investigate the possible role of chronic hydrocarbon exposure and tobacco and alcohol consumption in the causation of primary glomerulonephritis. Exposure to hydrocarbons and the consumption of tobacco and alcohol were assessed blindly by telephone interview and questionnaire in 55 patients with end-stage renal disease due to biopsy-proven primary glomerulonephritis in whom there had been no evidence of systemic disease. This was compared with 55 normal subjects matched for age, sex, social class and residential area and a comparable internal control group of 45 patients with end-stage renal disease secondary to systemic disease, diabetic nephropathy or chronic pyelonephritis. Hydrocarbon exposure scores derived from the results of the questionnaires were significantly higher (p < 0.001) in the patients with primary glomerulonephritis than in the normal subjects and the internal control group. Moreover, more detailed assessment of the type of hydrocarbon exposure showed significantly greater exposure of patients with glomerulonephritis to petroleum products (p < 0.001), greasing/degreasing agents (p < 0.01) and paints/glue (p < 0.05), and a resulting estimated relative risk of developing glomerulonephritis with each type of hydrocarbon exposure of 15.5, 5.3 and 2.0. Those patients with heavy hydrocarbon exposure (hydrocarbon score > 25,000) had a significantly higher serum creatinine at presentation than those with mild to moderate exposure, suggestive of more advanced renal disease. However, there was no significant difference in tobacco and alcohol consumption among subjects in different groups. We conclude that occupational exposure to hydrocarbon is likely to play a role in the pathogenesis of primary glomerulonephritis and that the risk of developing glomerulonephritis is greatest in those subjects exposed to petroleum products.

Adult↗

PubMed1991

The quantitative study of lumbar vertebral bone marrow using T1 mapping and image analysis techniques: methodology and preliminary results.

A method of quantifying lumbar vertebral bone marrow using pixel by pixel T1 mapping of spin echo magnetic resonance images is described. The accuracy and precision of the relaxation time measurements is confirmed by studies with the EEC Concerted Research Project, test object no. 5. The T1 data from all the pixels sampled from lumbar vertebral marrow are displayed as a histogram. By "thresholding" relative to normal control data the spatial distribution of high or low T1 pixels can be demonstrated. The approach is superior to that of the conventional region of interest method for quantifying and analysing relaxation time data, and allows tissue heterogeneity to be studied. Studies in patients with aplastic anaemia and acute leukaemia have been performed.

Adult↗