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Biomedical subjects

P J Phillips

Publications and source records attributed to P J Phillips.

At least 19 recordsLinked to original sources
PubMed2001

Reproducibility of DXA: potential impact on serial measurements and misclassification of osteoporosis.

The reproducibility of bone mineral density (BMD) measurements by dual-energy X-ray absorptiometry (DXA), based on 12 successive monthly determinations, was assessed in a group of 24 subjects (23 postmenopausal women, 1 man) using six trained operators. The variability (S2A) was calculated from both duplicate operator measurements and the standard error of estimate from nonparametric regression of the individual subject series. Robust estimates of SA from the 90th percentile of the sampling distribution of variances were calculated for the spine (25 mg/cm2), femur neck (20 mg/cm2) and total femur (15.5 mg/cm2) using the bootstrap technique. The critical difference for a significant decrease (p = 0.05) at the spine, femoral neck and total femur was estimated at 57, 46 and 36 mg/cm2 respectively. Estimation of S2A allowed calculation of the probability that the true BMD, for an observed BMD near the osteoporosis diagnostic threshold (T-score < -2.5), is not misclassified. Analysis of covariance established a significant operator-subject interaction at all sites, but only the total femur was associated with a significant difference between operators. The percentage of body fat was a significant covariate for the spine and total femur regions. ANOVA showed that the greater proportion of variance was instrument-related. The limitations of DXA as an analytical method are discussed.

Absorptiometry, Photon↗
PubMed2001

Computational and performance aspects of PCA-based face-recognition algorithms.

Algorithms based on principal component analysis (PCA) form the basis of numerous studies in the psychological and algorithmic face-recognition literature. PCA is a statistical technique and its incorporation into a face-recognition algorithm requires numerous design decisions. We explicitly state the design decisions by introducing a generic modular PCA-algorithm. This allows us to investigate these decisions, including those not documented in the literature. We experimented with different implementations of each module, and evaluated the different implementations using the September 1996 FERET evaluation protocol (the de facto standard for evaluating face-recognition algorithms). We experimented with (i) changing the illumination normalization procedure; (ii) studying effects on algorithm performance of compressing images with JPEG and wavelet compression algorithms; (iii) varying the number of eigenvectors in the representation; and (iv) changing the similarity measure in the classification process. We performed two experiments. In the first experiment, we obtained performance results on the standard September 1996 FERET large-gallery image sets. In the second experiment, we examined the variability in algorithm performance on different sets of facial images. The study was performed on 100 randomly generated image sets (galleries) of the same size. Our two most significant results are (i) changing the similarity measure produced the greatest change in performance, and (ii) that difference in performance of +/- 10% is needed to distinguish between algorithms.

Algorithms↗
PubMed2000

The clinical role of quantitative ultrasound in assessing fracture risk and bone status.

Quantitative ultrasound (QUS) analysis of calcaneal bone is useful to quantify fracture risk, and in monitoring response to treatment and identifying bone changes associated with disease and medication. However, diagnosis of osteoporosis by QUS measurements remains contentious, but the problems are due to the limitations of the present T-scores rather than the technique. QUS offers the potential for the widespread detection of low bone mass and subsequent management and prevention of fracture.

Absorptiometry, Photon↗
PubMed2000

Traumatic hyphema: a critical review of the scientifically catastrophic history of steroid treatment therefore; and A report of 24 additional cases with no rebleeding after treatment with the Yasuna systemic steroid, no touch PLUS protocol.

PURPOSE: To establish a detailed history of steroid therapy administered either systemically or topically for traumatic hyphema (TH) over the past 40 years. To this literature, we report and add another 24 TH cases treated with the Yasuna systemic steroid No Touch PLUS protocol. METHODS: Review of all reports in Medline since its inception in 1966 and such reports not in Medline but retrievable by successive reference and various alternate sources. Retrospective review of charts of all cases of TH at the University of Florida from 1980-1987. Of 135 cases so retrieved, 24 were found who had received this treatment protocol properly. (Ethical, moral and liability aspects prohibited a formal comparative study of a no medical treatment control group since this is unconscionable and abusive at the present state of knowledge.) RESULTS: The historical review revealed that there is general ignorance of the salutary effect of both topical and systemic steroids in reducing the rebleed rate in TH. This is so marked that at least five experiments reported in the literature are invalidated to a variable degree because all patients, in both the experimental and control groups, had received topical steroids. Further, that the remarkable reduction in the rebleed rates for control groups of theoretically medically untreated TH, from the vicinity of 25% or more to the vicinity of 10-15% appears to be due primarily, if not solely, to this now ubiquitous administration of topical steroids in TH. In addition, in retrospect, there are also a remarkable number (at least 5) of major statistical errors in this literature and another 6 studies of outpatients in which compliance with therapy as outpatients is not even considered. Therefore at least 16 (57%) of the 28 papers reviewed have serious flaws and doubtful or uncertain results or conclusions. Of the 9 papers which lead one to wrongful conclusions, 5 are prejudicial against systemic steroid treatment (and 2 against systemic ACA treatment, and 2 against systemic TXA treatment). All but one of the nine are, as a corollary, prejudicial in favor of non medical treatment of TH. In our 24 cases studied, none suffered a rebleeding episode. CONCLUSIONS: The "continuing controversy" about medical treatment of TH is the direct result of poor science and poor scientific methods in clinical trials. Because no method has yet been devised to determine which traumatic hyphemas will rebleed, but preventing rebleeding is about all that we can do maximize the outcome, we recommend that all patients with TH receive the Yasuna systemic steroids no touch and/or PLUS protocol in addition to current conventional treatment (bed rest, hospitalization for all patients under 18 years of age)

Antifibrinolytic Agents↗
PubMed1999

Asthma and chronic obstructive airway diseases are associated with osteoporosis and fractures: a literature review.

The objective was to assess the association between asthma and/or chronic obstructive airway diseases (COAD), and osteoporosis, and appraise treatments of osteoporosis in these patients. MEDLINE and Excerpta Medica were searched for original research with control groups which tested the above association. One cohort and nine cross-section studies of bone density in patients with asthma and/or COAD were retrieved. These demonstrated clinically important bone density reductions of up to 29% in subjects, dependent upon daily oral corticosteroids, by a variety of measurement techniques, at various bone sites. Bone density reduction has also been less consistently reported in the absence of oral corticosteroids, suggesting that other factors including high-dose inhaled corticosteroids may have a role. Fracture studies. Three studies in oral corticosteroid-dependent asthmatics demonstrated a vertebral fracture prevalence up to 56%, and annual vertebral fracture incidence of up to 42%. The strength of the available evidence is limited, but suggests that patients with asthma and/or COAD are at increased risk of osteoporosis. The evidence of the association between osteoporosis and inhaled corticosteroids is much more limited than for oral corticosteroids. Bisphosphonates are promising agents to maintain and/or promote bone mass in this patient group.

Administration, Inhalation↗
PubMed1999

Barriers to minority participation in the orthopaedic profession. Personal perspectives.

A brief summary of one individual's pathway and the challenges encountered along the road to becoming an orthopaedic surgeon are outlined. Beginning with the decision to pursue a career in medicine, and chronicling the subsequent decisions made along the way, key elements that facilitated this individual's success are reviewed. Some of the difficulties encountered from the perspective of a minority candidate also are discussed and what perhaps may be deemed an indirect pathway to an orthopaedic career. The importance of institutional support, mentorship, and recruitment are essential to facilitate and secure the success of minority candidates.

Career Choice↗
PubMed1998

Public perceptions and self-reported prevalence of osteoporosis in South Australia.

The self-reported prevalence of, and attitudes to and perceptions of, osteoporosis in the South Australian community were assessed using data collected as part of the 1995 South Australian Health Omnibus Survey (household interviews)--a clustered, self-weighting, multistage sample of households in metropolitan and country centers. The self-reported prevalence was 4.8 (95% CI: 3.7-5.8) and 1.4% (95% CI: 0.8-2.0) for women (n = 1531) and men (n = 1485) respectively. For individuals with osteoporosis, calcium was the favored treatment (52%), while 33% of women were on hormone replacement therapy. An appropriate definition of osteoporosis was given by 62% of women and 37% of men. The main risk factors were reported as lack of calcium and age. There was a significant association between knowledge of the definition of osteoporosis and identification of correct risk factors. A high perceived risk of osteoporosis was reported in 23% of women and 7% of men. Osteoporosis risk was assessed as higher in those who did not adopt recognized prevention measures. Perception of risk was not related to the individual's own risk factors. Self-reported prevalence of osteoporosis significantly underestimates the likely true prevalence and general awareness and knowledge is much lower for men than women. The importance of individual risk factors for osteoporosis are not understood by the general community.

Adolescent↗
PubMed1998

Adaptation in patterns of c-fos expression in the brain associated with exposure to either single or repeated social stress in male rats.

Intraspecific confrontation between male rats represents a biologically relevant form of social stress. C-fos expression has been used to map the pattern of neural activation following either a single (acute) or repeated (10 times) exposure of an intruder male to a larger male in the latter's home cage. These conditions induce high levels of aggressive interaction. Sixty minutes after a single defeat, there was intense c-fos expression (quantified using image analysis) in restricted areas of the basal forebrain (including lateral septum, bed nucleus of stria terminalis, lateral preoptic area, lateral hypothalamic area, paraventricular nucleus, and medial and central amygdala) as well as in the autonomic and monoaminergic nuclei of the brainstem (central grey, dorsal and median raphe, locus coeruleus and nucleus of the solitary tract). After the tenth defeat, this pattern was modified despite persistently high levels of aggression. Some areas in the forebrain (bed nucleus of stria terminalis, paraventricular nucleus and medial amygdala) continued to express increased c-fos; others (the septum, lateral hypothalamic area, lateral preoptic area and central amygdala) no longer expressed c-fos. The brainstem response was equally varied: the central grey and the raphe nuclei continued to respond after repeated defeat, whereas the solitary nucleus and locus coeruleus did not. On the other hand, there was no change in the behaviour of intruder rats after repeated defeat. This study shows the pattern of adaptation at a cellular level in the basal forebrain and brainstem to repeated defeat. As in our previous studies of repeated restraint, modulation in the expression of c-fos following repeated stress is highly regionally specific, suggesting that differential neural processing is involved in adaptation to social stress.

Adaptation, Psychological↗
PubMed1998

The design of matching pursuit filters.

This paper presents a new technique for creating efficient and compact models from data, called matching pursuit filters. The design of a matching pursuit filter is based on an adapted wavelet expansion, where the expansion is adapted to both the data and the pattern recognition problem being addressed. This contrasts with most adaptation schemes, where the representation is a function of the data, but not of the problem to be solved. This approach does not decompose the images in the training set individually, but rather determines the expansion by simultaneously decomposing all the images. Because it uses two-dimensional wavelets as the building blocks for the decomposition, the representation is explicitly two-dimensional and is composed of local information. Matching pursuit filters can be trained to detect, recognize, or identify objects and have been applied to recognizing faces and detecting objects in infrared imagery.

Algorithms↗
PubMed1997

Sustained activation of extracellular-signal-regulated kinase 1 (ERK1) is required for the continued expression of cyclin D1 in G1 phase.

In Chinese hamster embryo fibroblasts (IIC9 cells), platelet-derived growth factor (PDGF) stimulated mitogen-activated protein kinase/extracellular-signal-regulated kinase (MAP kinase/ERK) activity, but not that of c-jun N-terminal kinase (JNK), and induced G1 phase progression. ERK1 activation was biphasic and was sustained throughout the G1 phase of the cell cycle. PDGF induced cyclin D1 protein and mRNA levels in a time-dependent manner. Inhibition of PDGF-induced ERK1 activity by the addition of a selective inhibitor of MEK1 (MAP kinase kinase/ERK kinase 1) activation, PD98059, or transfection with a dominant-negative ERK1 (dnERK-) was correlated with growth arrest. In contrast, growth was unaffected by expression of dominant-negative JNK (dnJNK-). Interestingly, addition of PD98059 or dnERK-, but not dnJNK-, resulted in a dramatic decrease in cyclin D1 protein and mRNA levels, concomitant with a decrease in cyclin D1-cyclin-dependent kinase activity. To investigate the importance of sustained ERK1 activation, ERK1 activity was blocked by the addition of PD98059 throughout G1. Addition of PD98059 up to 4 h after PDGF treatment decreased ERK1 activity to the levels found in growth-arrested IIC9 cells. Loss of cyclin D1 mRNA and protein expression was observed within 1 h after inhibition of the second sustained phase of ERK1 activity. Disruption of sustained ERK1 activity also resulted in G1 growth arrest. These data provide evidence for a role for sustained ERK activity in controlling G1 progression through positive regulation of the continued expression of cyclin D1, a protein known to positively regulate G1 progression.

Animals↗
PubMed1997

Initiation of hormone replacement therapy after diagnosis of osteoporosis by bone densitometry.

The effect of osteoporosis, as diagnosed by bone densitometry, on general practitioners' decisions to initiate hormone replacement therapy (HRT) was assessed. Data for the study were collected by questionnaire from 147 women (> 40 years), previously referred for measurement of bone mineral density (BMD) at the proximal forearm. Among the women, at the time of BMD measurement, current and ever use of HRT was 35% and 50% respectively, and 25.2% were osteoporotic on the basis of their BMD level. HRT was more likely to be initiated by women who were told that their BMD was low (ODR 3.4; 95% CI 1.2-9.7); 37% of all women with osteoporosis were using HRT compared with 78% who were taking calcium supplements. Potential reasons for the low HRT prescription may include the nature of the BMD report, patient aversion to HRT and doctors' concern with the long-term side-effects of HRT.

Absorptiometry, Photon↗
PubMed1997

Alternate site testing for HbA1c using the Primus CLC330 GHb analyzer.

OBJECTIVE: To determine whether the Primus high-pressure liquid chromatography (HPLC) is suited to alternate site testing (AST) for HbA1c in a hospital diabetes outpatient clinic. RESEARCH DESIGN AND METHODS: Patients were attending the clinic for routine management of their diabetes. A number of diabetic patients with uremia (n = 11) were also investigated. HbA1c levels were measured in the outpatient setting by the Primus HPLC and in a more limited study the DCA-2000 instrument using the new 6-min assay cartridge. HbA1c measurements were also performed with Pierce affinity minicolumns and a Bio-Rad Variant HPLC. RESULTS: The Primus HPLC assay had low imprecision of 2.3, 1.6, and 1.0% for HbA1c levels of 4.7, 7.3, and 11.1%, respectively, and was not prone to interference by carbamylated hemoglobin as found for the ion-exchange Variant HPLC method. Method comparison studies showed that the bias and proportional error between the Pierce affinity minicolumn procedure (standardized with respect to an external quality control program) and the Primus HPLC (Y) was -0.4 and 1.2% respectively (n = 32). Similarly the bias and proportional error between the Primus and DCA-2000 methods was 0.7 and -2.5%. The Primus was shown to give falsely elevated HbA1c concentrations if the time between sequential injections was > 28 min. CONCLUSIONS: The Primus HPLC has a decided advantage over specialty AST instruments, like the DCA-2000, in not only meeting AST requirements but also allowing rapid automated batch processing of all laboratory HbA1c samples.

Chromatography, Affinity↗