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Biomedical subjects

J Talbot

Publications and source records attributed to J Talbot.

At least 19 recordsLinked to original sources
PubMed2006

Retinal pigment epithelial changes and choroidal neovascularisation at the edge of posterior staphylomas; a case series and review of the literature.

PURPOSE: To report five myopic patients who presented with a variety of changes at the edge of posterior staphyloma. METHODS: Retrospective, observational case series. The clinical and angiographic records of five patients who showed changes at the edge of posterior staphyloma were reviewed. One of these patients had been referred querying macular dystrophy. RESULTS: On fundus examination, three patients showed retinal pigment epithelial (RPE) changes at the edge of the staphyloma and two showed RPE atrophy with surrounding haemorrhages. Fluorescein angiography revealed areas of hyperfluorescence at the point of change of curvature of the staphyloma suggestive of RPE atrophy in all patients. In two patients, a choroidal neovascular membrane was seen. Indocyanine green angiogram carried out in one patient showed the presence of an occult choroidal neovascular membrane with preservation of the adjacent choriocapillaris. CONCLUSION: This case series illustrates the variety of changes that can occur at the edge of posterior staphylomas, which ranged from RPE disturbance to choroidal neovascular membrane formation. In one of the patients, these changes were mistaken for macular dystrophy. Our observations also support the hypothesis that chorioretinal changes occur at the edge of staphylomas and may predispose to choroidal neovasularisation.

Adolescent↗
PubMed2005

Convection in vibrated annular granular beds.

The response to vibration of a granular bed, consisting of a standard cylindrical geometry but with the addition of a dissipative cylindrical inner wall, has been investigated both experimentally (using positron emission particle tracking) and numerically (using hard sphere molecular dynamics simulation). The packing fraction profiles and granular temperature distributions (in both vertical and horizontal directions) were determined as a function of height and distance from the axis. The two sets of results were in reasonable agreement. The molecular dynamics simulations were used to explore the behavior of the granular bed in the inner wall-outer wall coefficient of restitution phase space. It was observed that one could control the direction of the toroidal convection rolls by manipulating the relative dissipation at the inner and outer walls via the coefficients of restitution, and with several layers of grains it was seen that double convection rolls could also be formed, a result that was subsequently confirmed experimentally.

Journal Article↗
PubMed2005

Boltzmann equation for a granular capped rectangle in a thermalized bath of hard disks.

By using the Boltzmann approach, we study the steady-state dynamics of a granular capped rectangle placed in a two-dimensional bath of thermalized hard disks. Hard core collisions are assumed elastic between disks and inelastic between the capped rectangle and the disks, with a normal coefficient of restitution alpha < 1. Assuming a Gaussian ansatz for the probability distribution functions, we obtain analytical expressions for the granular temperatures. We show the absence of equipartition and investigate both the role of the anisotropy of the capped rectangle and of the relative ratio of the bath particles to the linear sizes of the capped rectangle. In addition, we investigate a model of a capped rectangle with two normal coefficients of restitution for collisions along the straight and curved surfaces of the capped rectangle. In this case one observes equipartition for a nontrivial ratio of the normal coefficient of restitutions.

Journal Article↗
PubMed2005

Oral fluorescein angiography with the scanning laser ophthalmoscope in diabetic retinopathy: a case controlled comparison with intravenous fluorescein angiography.

AIM: To compare the performance of oral fundus fluorescein angiography with a confocal scanning laser ophthalmoscope (SLO) with intravenous fundus fluorescein angiography (IVFFA) with a fundus camera in the assessment of sight-threatening diabetic retinopathy. PATIENTS AND METHODS: A total of 25 patients undergoing IVFFA to investigate their diabetic retinopathy were recruited. Participants returned 1 week later and an oral angiogram with the SLO was performed. Six facets of the oral and intravenous angiograms were scored and compared: visualization of the foveal avascular zone (FAZ); branch retinal identification; macular leakage; identification of microaneurysms in areas of macular leakage; peripheral nonperfusion, and leakage from neovascular complexes. RESULTS: Compared to IVFFA, the FAZ was unreliably visualized with oral angiography (Kappa 0.1, 95% CI 0-0.3). In contrast, macular leakage (Kappa 0.78, 95%, CI 0.72-0.83), identification of microaneurysms in areas of macular leakage (Kappa 0.78, 95%, CI 0.72-0.83), and neovascular complexes (Kappa 1.0) were reliably seen. Analysis of the visualization of peripheral nonperfusion was complicated by the finding that profuse dye leakage from neovascular complexes obscured the view of the peripheral retina. If the five angiograms in which this occurred were excluded, oral angiography identified 23 of the 24 eyes in which significant nonperfusion was found on IVFFA. CONCLUSION: Oral angiography with the SLO can provide high-quality angiograms that allow judgments to be made about the presence of treatable diabetic maculopathy, proliferative diabetic retinopathy, and peripheral nonperfusion. In the presence of coexisting macular oedema, it proved to be an unreliable technique with which to investigate foveal ischaemia.

Administration, Oral↗
PubMed2004

Thermalization of an anisotropic granular particle.

We investigate the dynamics of a needle in a two-dimensional bath composed of thermalized point particles. Collisions between the needle and points are inelastic and characterized by a normal restitution coefficient alpha<1. By using the Enskog-Boltzmann equation, we obtain analytical expressions for the translational and rotational granular temperatures of the needle and show that these are, in general, different from the bath temperature. The translational temperature always exceeds the rotational one, though the difference decreases with increasing moment of inertia. The predictions of the theory are in very good agreement with numerical simulations of the model.

Anisotropy↗
PubMed2003

Analysis of Mycobacterium avium complex isolates from blood samples of AIDS patients by pulsed-field gel electrophoresis.

A molecular analysis of the first Mycobacterium avium complex (MAC) blood isolates from 177 patients from 10 Canadian cities revealed that each cluster of indistinguishable strains consisted of isolates from epidemiologically unrelated patients in the same city or region. This study supports the premise that acquisition of MAC from a common environmental source occasionally occurs.

Acquired Immunodeficiency Syndrome↗
PubMed2002

Wall-enhanced convection in vibrofluidized granular systems.

An event-driven molecular dynamics simulation of inelastic hard spheres contained in a cylinder and subject to strong vibration reproduces accurately experimental results [R. D. Wildman et al., Phys. Rev. Lett. 86, 3304 (2001)] for a system of vibrofluidized glass beads. In particular, we are able to obtain the velocity field and the density and temperature profiles observed experimentally. In addition, we show that the appearance of convection rolls is strongly influenced by the value of the sidewall-particle restitution coefficient. Suggestions for observing more complex convection patterns are proposed.

Journal Article↗
PubMed2001

Postsanatorium pattern of antituberculous drug resistance in the Canadian-born population of western Canada: effect of outpatient care and immigration.

Concurrent with the shift in tuberculosis case management from sanatorium to outpatient setting was a shift in the continent of origin (Europe to Asia) of most new immigrants to CANADA: To assess the impact of these two events on antituberculous drug resistance in the Canadian-born population, the authors reviewed the results of six drug resistance surveys conducted in the two westernmost provinces of Canada between 1963 and 1994. Survey data were complemented by new molecular diagnostic and contact tracing data collected over 5 years (1994--1998) in one of the three large urban centers of the region. Over the time spanned by the surveys, there was no increase in the proportion of all Canadian-born tuberculosis cases who relapsed or the proportion of all Canadian-born relapsed cases who were drug resistant (approximately 12--13%). In addition, the prevalence of primary drug resistance among Canadian-born cases did not increase; rates consistently averaged between 2% and 5% despite a doubling of primary resistance rates among foreign-born cases. Molecular diagnostic and contact tracing data strongly supported the survey findings. The authors concluded that outpatient care and immigration have thus far had no measurable impact on the pattern of antituberculous drug resistance in the Canadian-born population of western CANADA:

Adolescent↗
PubMed2000

Invasive pneumococcal infections in Canadian children, 1991-1998: implications for new vaccination strategies. Canadian Paediatric Society/Laboratory Centre for Disease Control Immunization Monitoring Program, Active (IMPACT).

We reviewed 2040 consecutive cases of invasive pneumococcal infection that were seen at 11 pediatric centers across Canada during 1991-1998 to determine if such infections could be prevented by new conjugate vaccines. Isolates from 1528 cases were serotyped. Most cases (61.5%) occurred in patients aged >2 years. Underlying medical conditions were present in 23.2% of case patients. Serotypes in the 7-valent conjugate vaccine matched isolates as follows: 85.8% of tested isolates from children aged 6 months to 5 years, but significantly fewer isolates in younger and older children; 72.9% of isolates from non-healthy children, but 83.9% of isolates from previously healthy children; and 95.4% of isolates with high-level penicillin resistance, but only 72.7% of those with intermediate-level resistance. Significant natural variation in the proportion of isolates matching 7-valent vaccines occurred from year to year and among centers. New conjugate vaccines have great potential but their effectiveness and limitations require ongoing study.

Bacteremia↗
PubMed2000

Enzyme I of the phosphoenolpyruvate:sugar phosphotransferase system. In vitro intragenic complementation: the roles of Arg126 in phosphoryl transfer and the C-terminal domain in dimerization.

Enzyme I mutants of the Salmonella typhimurium phosphoenolpyruvate:sugar phosphotransferase system (PTS), which show in vitro intragenic complementation, have been identified as Arg126Cys (strain SB1690 ptsI34), Gly356Ser (strain SB1681 ptsI16), and Arg375Cys (strain SB1476 ptsI17). The mutation Arg126Cys is in the N-terminal HPr-binding domain, and complements Gly356Ser and Arg375Cys enzyme I mutations located in the C-terminal phosphoenolpyruvate(PEP)-binding domain. Complementation results in the formation of unstable heterodimers. None of the mutations alters the K(m) for HPr, which is phosphorylated by enzyme I. Arg126 is a conserved residue; the Arg126Cys mutation gives a V(max) of 0.04% wild-type, establishing a role in phosphoryl transfer. The Gly356Ser and Arg375Cys mutations reduce enzyme I V(max) to 4 and 2%, respectively, and for both, the PEP K(m) is increased from 0.1 to 3 mM. It is concluded that this activity was from the monomer, rather than the dimer normally found in assays of wild-type. In the presence of Arg126Cys enzyme, V(max) for Gly356Ser and Arg375Cys enzymes I increased 6- and 2-fold, respectively; the K(m) for PEP decreased to <10 microM, but the K(m) became dependent upon the stability of the heterodimer in the assay. Gly356 is conserved in enzyme I and pyruvate phosphate dikinase, which is a homologue of enzyme I, and this residue is part of a conserved sequence in the subunit interaction site. Gly356Ser mutation impairs enzyme I dimerization. The mutation Arg375Cys also impairs dimerization, but the equivalent residue in pyruvate phosphate dikinase is not associated with the subunit interaction site. A 37 000 Da, C-terminal domain of enzyme I has been expressed and purified; it dimerizes and complements Gly356Ser and Arg375Cys enzymes I proving that the association/dissociation properties of enzyme I are a function of the C-terminal domain.

Amino Acid Sequence↗
PubMed2000

Identification and characterization of the human and mouse SLC19A3 gene: a novel member of the reduced folate family of micronutrient transporter genes.

We report here the isolation, characterization, and chromosomal localization of the genes encoding the human and corresponding murine orthologue of solute carrier family 19A member 3 (SLC19A3). Human SLC19A3 encodes a 496-amino-acid residue protein with a predicted molecular weight of 56 kDa that shares sequence similarity to both SLC19A1 (reduced folate transporter (RFC-1)) and SLC19A2 (high affinity thiamine transporter (THTR-1)). Like the SLC19A1 and SLC19A2 proteins, SLC19A3 contains 12 putative transmembrane domains. The human SLC19A3 gene is widely expressed, with the most abundant expression observed in placenta, kidney, and liver, and has been mapped to chromosome 2q37. The murine SLC19A3 gene maps to central chromosome 1 in the region defined as a seizure susceptibility locus in the DBA/2J mouse strain. This article describes the identification of SLC19A3, a gene encoding a novel solute transporter, and establishes murine SLC19A3 as a candidate gene for seizures in the DBA/2J mouse.

Amino Acid Sequence↗
PubMed2000

Effects of body orientation, load and vibration on sensing position and movement at the human elbow joint.

Experiments were carried out to study the ability of human subjects to match the position of their forearms relative to the horizontal. The normal, arms-in-front position with the hands aligned and little forward flexion at the shoulder was called the reference position. When the arms were rotated to the side, one arm was raised, or both arms were raised, matching ability deteriorated compared with the reference position, when expressed as an increase in the standard deviation of matching errors. It was concluded that particular significance was assigned by the brain to the arms-in-front position, with the hands in their normal working space. Increases in errors were also observed when the reference arm was made weightless or its weight was increased by means of an adjustable load. This suggested that lifting the arm against gravity provided additional positional information. In a second experiment, dependence of the illusion of muscle lengthening evoked by vibration was tested after two different forms of muscle conditioning, a co-contraction of elbow muscles with the arm held flexed or with it held extended. The speed of the illusory extension of flexor muscles during their vibration increased three-fold after flexion conditioning compared with extension conditioning. Since after flexion conditioning, muscle spindles in flexor muscles are expected to be more sensitive to vibration than after extension conditioning, this observation provides additional support for the view that muscle spindles make an important contribution to kinaesthesia at the elbow joint.

Adult↗
PubMed2000

Mobility of adsorbed proteins: a Brownian dynamics study.

We simulate the adsorption of lysozyme on a solid surface, using Brownian dynamics simulations. A protein molecule is represented as a uniformly charged sphere and interacts with other molecules through screened Coulombic and double-layer forces. The simulation starts from an empty surface and attempts are made to introduce additional proteins at a fixed time interval that is inversely proportional to the bulk protein concentration. We examine the effect of ionic strength and bulk protein concentration on the adsorption kinetics over a range of surface coverages. The structure of the adsorbed layer is examined through snapshots of the configurations and quantitatively with the radial distribution function. We extract the surface diffusion coefficient from the mean square displacement. At high ionic strengths the Coulombic interaction is effectively shielded, leading to increased surface coverage. This effect is quantified with an effective particle radius. Clustering of the adsorbed molecules is promoted by high ionic strength and low bulk concentrations. We find that lateral protein mobility decreases with increasing surface coverage. The observed trends are consistent with previous theoretical and experimental studies.

Adsorption↗
PubMed2000

Evaluation of a pilot project to use computers in a rural general practice term.

In 1998, the Department of General Practice (Faculty of Medicine and Dentistry, University of Western Australia) ran a pilot project to use computers in a sixth year rural general practice term. Students were provided with a laptop computer to take into rural and remote areas throughout Western Australia during their 4-week clinical attachment. An email mailing list was set up for course participants to share experiences and complete set learning activities specifically related to rural general practice. An evaluation of this pilot project found that students felt less isolated on rural attachments, course outcomes were improved and rural preceptors were more involved in the programme. The development of a teaching and learning programme that involves the use of computers in rural general practice for undergraduate students has the potential to improve the quality of their medical education.

Education, Distance↗
PubMed2000

Alternative Curricular Options in Rural Networks (ACORNS): impact of early rural clinical exposure in the University of West Australia medical course.

The aim of this study was to assess the impact of a 4-day rural placement in Western Australia on the interest of fourth year medical students in a career in rural general practice. Students undertaking their Alternative Curricular Options in Rural Networks attachment (ACORNS) completed pre- and post-questionnaires examining their expectations, experiences of, and attitudes to rural general practice. Of the 103 students who participated, 81% expressed an interest in a rural career after the placement, whereas prior to this experience only 48% had been interested. The students also recorded a wide range of learning experiences, both clinical and procedural, and expressed positive attitudes to the variety of experiences and the role of the rural GP. The study concluded that early exposure to rural general practice enhances students' interest in a potential rural practice career and provides them with a broad range of experiences. The role of rural practitioners as role models for students needs to be acknowledged and reinforced.

Attitude of Health Personnel↗
PubMed2000

Adsorption-desorption model and its application to vibrated granular materials.

We investigate both analytically and by numerical simulation the kinetics of a microscopic model of hard rods adsorbing on a linear substrate, a model that is relevant for compaction of granular materials. The computer simulations use an event-driven algorithm that is particularly efficient at very long times. For a small, but finite desorption rate, the system reaches an equilibrium state very slowly, and the long-time kinetics display three successive regimes: an algebraic one where the density varies as 1/t, a logarithmic one where the density varies as 1/ln(t), followed by a terminal exponential approach. The characteristic relaxation time of the final regime, though incorrectly predicted by mean field arguments, can be obtained with a systematic gap-distribution approach. The density fluctuations at equilibrium are also investigated, and the associated time-dependent correlation function exhibits a power law regime followed by a final exponential decay. Finally, we show that denser particle packings can be obtained by varying the desorption rate during the process.

Adsorption↗
PubMed1999

Molecular analysis of the genetic variation among penicillin-susceptible and penicillin-resistant Streptococcus pneumoniae serotypes in Canada.

Few studies have examined the genetic relatedness within and between serotypes of Streptococcus pneumoniae. Penicillin-susceptible S. pneumoniae (PSSP) isolates (n=170) and penicillin-resistant S. pneumoniae (PRSP) isolates (n=48) belonging to 13 different serotypes from across Canada were studied to further understand the molecular epidemiology of S. pneumoniae. PRSP of serotypes 6B, 14, and 19F appeared to be novel clones, differentiated by pulsed-field gel electrophoresis from the recognized international penicillin-resistant clones belonging to these serotypes. In addition, not all PRSP strains shared similar genetic backgrounds with PSSP strains of the same serotype, suggesting that in Canada, certain PRSP strains have emerged from new unique lineages of PRSP. Although there was significant heterogeneity among S. pneumoniae of different serotypes, certain serotypes (3, 7F, and 22F) appeared to be more clonally related despite having originated from different geographic regions.

Cluster Analysis↗