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Biomedical subjects

James Foster

Publications and source records attributed to James Foster.

12 recordsLinked to original sources
PubMed2006

Randomized pilot study to disseminate caries-control services in dentist offices.

BACKGROUND: To determine whether education and financial incentives increased dentists' delivery of fluoride varnish and sealants to at risk children covered by capitation dental insurance in Washington state (U.S.). METHODS: In 1999, 53 dental offices in Washington Dental Service's capitation dental plan were invited to participate in the study, and consenting offices were randomized to intervention (n = 9) and control (n = 10) groups. Offices recruited 689 capitation children aged 6-14 and at risk for caries, who were followed for 2 years. Intervention offices received provider education and fee-for-service reimbursement for delivering fluoride varnish and sealants. Insurance records were used to calculate office service rates for fluoride, sealants, and restorations. Parents completed mail surveys after follow-up to measure their children's dental utilization, dental satisfaction, dental fear and oral health status. Regression models estimated differences in service rates between intervention and control offices, and compared survey measures between groups. RESULTS: Nineteen offices (34%) consented to participate in the study. Fluoride and sealant rates were greater in the intervention offices than the control offices, but the differences were not statistically significant. Restoration rates were lower in the intervention offices than the control offices. Parents in the intervention group reported their children had less dental fear than control group parents. CONCLUSION: Due to low dentist participation the study lacked power to detect an intervention effect on dentists' delivery of caries-control services. The intervention may have reduced children's dental fear.

Journal Article↗
PubMed2006

Relaxed neighbor joining: a fast distance-based phylogenetic tree construction method.

Our ability to construct very large phylogenetic trees is becoming more important as vast amounts of sequence data are becoming readily available. Neighbor joining (NJ) is a widely used distance-based phylogenetic tree construction method that has historically been considered fast, but it is prohibitively slow for building trees from increasingly large datasets. We developed a fast variant of NJ called relaxed neighbor joining (RNJ) and performed experiments to measure the speed improvement over NJ. Since repeated runs of the RNJ algorithm generate a superset of the trees that repeated NJ runs generate, we also assessed tree quality. RNJ is dramatically faster than NJ, and the quality of resulting trees is very similar for the two algorithms. The results indicate that RNJ is a reasonable alternative to NJ and that it is especially well suited for uses that involve large numbers of taxa or highly repetitive procedures such as bootstrapping.

Algorithms↗
PubMed2006

Beyond the aortic bifurcation: branched endovascular grafts for thoracoabdominal and aortoiliac aneurysms.

OBJECTIVES: To evaluate the use of novel technology to treat complex aortic aneurysms involving branches that provide critical end-organ blood supply. METHODS: A prospective study was conducted in patients with thoracoabdominal, suprarenal, or common iliac aneurysms (TAA, SRA, or CIA) at high risk for open surgical repair. An endovascular graft using the Zenith platform was customized to fit patient anatomy (TAA or SRA) and combined with Jomed balloon-expandable stent-grafts. Prefabricated hypogastric branches were used with a Zenith abdominal aortic aneurysm (AAA) or Fluency self-expanding fenestrated device in conjunction with a self-expanding stent-graft. Analyses were conducted in accordance with the endovascular aneurysm reporting standards document. Follow-up studies occurred at discharge, 1, 6, and 12 months, and included computed tomography and duplex ultrasound scans, and flat plate radiography. RESULTS: Fifty patients were treated (9 TAA, 20 SRA, 21 CIA). The mean aneurysm size was 7.6 cm (TAA), 7.2 cm (SRA), and 6.1 cm AAA size associated with a mean CIA size of 3.8 cm. Bilateral CIA aneurysms were present in 86% (18/21) of patients with CIA aneurysms. Perioperative mortality was 2% (1/50) and resulted from a myocardial infarction after a planned conduit and iliac endarterectomy required for device access. Five late deaths occurred (2 TAA, 2 SRA, 1 CIA), three of which (2 TAA, 1 SRA) were aneurysm related. Failure to access internal iliac arteries occurred in three cases, and two late hypogastric branch thromboses occurred. No visceral branches were lost acutely or occluded during follow-up. Sac shrinkage (>5 mm) was noted in 65% of patients at 6 months and in all patients (10/10) by 12 months. There were no ruptures or conversions, but nine patients required secondary interventions. CONCLUSIONS: Branch vessel technology has made it technically feasible to preserve critical end-organ perfusion in the setting of CIA, SRA, and TAA aneurysms. The relatively low acute mortality rate and lack of short-term branch vessel loss are encouraging and merit further investigation. These advances have the potential to markedly diminish the complications associated with conventional management of complex aneurysms.

Angioplasty↗
PubMed2006

Ovine prion protein variant A(136)R(154)L(168)Q(171) increases resistance to experimental challenge with bovine spongiform encephalopathy agent.

Susceptibility and incubation periods of transmissible spongiform encephalopathies, such as scrapie in sheep, are modulated by the PrP gene. The standard model of association between ovine PrP genetics and classical scrapie susceptibility is based on PrP genotypes with respect to codons 136, 154 and 171, e.g. alanine-arginine-glutamine (ARQ). It is demonstrated here that a proline to leucine substitution in codon 168 of the ovine PrP protein gene is associated with increased resistance to experimental bovine spongiform encephalopathy (BSE) inoculation. The ARL(168)Q PrP allele was found in heterozygous ARP(168)Q/ARL(168)Q sheep that have so far survived intravenous BSE challenge three times longer than BSE-challenged homozygous ARP(168)Q/ARP(168)Q sheep, which develop disease in around 700 days. In contrast, the L141F polymorphism does not appear to be associated with susceptibility to intravenous BSE challenge.

Alleles↗
PubMed2003

Collecting, shipping, storing, and imaging snow crystals and ice grains with low-temperature scanning electron microscopy.

Methods to collect, transport, and store samples of snow and ice have been developed that enable detailed observations of these samples with a technique known as low-temperature scanning electron microscopy (LTSEM). This technique increases the resolution and ease with which samples of snow and ice can be observed, studied, and photographed. Samples are easily collected in the field and have been shipped to the electron microscopy laboratory by common air carrier from distances as far as 5,000 miles. Delicate specimens of snow crystals and ice grains survive the shipment procedures and have been stored for as long as 3 years without undergoing any structural changes. The samples are not subjected to the melting or sublimation artifacts. LTSEM allows individual crystals to be observed for several hours with no detectable changes. Furthermore, the instrument permits recording of photographs containing the parallax information necessary for three-dimensional imaging of the true shapes of snowflakes, snow crystals, snow clusters, ice grains, and interspersed air spaces. This study presents detailed descriptions of the procedures that have been used successfully in the field and the laboratory to collect, ship, store, and image snow crystals and ice grains.

Cold Temperature↗
PubMed2002

Transmission of prion diseases by blood transfusion.

Attempts to detect infectivity in the blood of humans and animals affected with transmissible spongiform encephalopathies (TSEs or prion diseases) have often been inconclusive because of the limitations of cross-species bioassays and the small volumes of blood that can be injected by the intracerebral route. A model has been developed for the experimental study of TSE transmission by blood transfusion using sheep experimentally infected with bovine spongiform encephalopathy (BSE) or natural scrapie as donors and susceptible scrapie-free sheep as recipients. Donors and recipients of the same species greatly increase the sensitivity of the bioassay and in sheep large volumes of blood can be injected by the intravenous (i.v.) route. Transmission of BSE to a single animal using this approach was reported recently. This study confirms this result with a second transmission of BSE and four new cases of transmission of natural scrapie. Positive transmissions occurred with blood taken at pre-clinical and clinical stages of infection. Initial studies indicate that following such infection by the i.v. route, deposition of the abnormal prion protein isoform, PrP(Sc), in peripheral tissues may be much more limited than is seen following oral infection. These results confirm the risks of TSE infection via blood products and suggest that the measures taken to restrict the use of blood in the UK have been fully justified.

Animals↗
PubMed2002

Strain characterization of natural sheep scrapie and comparison with BSE.

Scrapie was transmitted to mice from ten sheep, collected in the UK between 1985 and 1994. As in previous natural scrapie transmissions, the results varied between scrapie sources in terms of the incidence of disease, incubation periods and neuropathology in challenged mice. This contrasted with the uniformity seen in transmissions of BSE to mice. The scrapie and BSE isolates were characterized further by serial passage in mice. Different TSE strains were isolated from each source according to the Sinc or PrP genotype of the mouse used for passage. The same two mouse-passaged strains, 301C and 301V, were isolated from each of three BSE sources. Despite the variation seen in the primary transmissions of scrapie, relatively few mouse-passaged scrapie strains were isolated and these were distinct from the BSE-derived strains. The ME7 scrapie strain, which has often been isolated from independent sheep sources in the past, was identified in isolates from four of the sheep. However, a new distinct strain, 221C, was derived from a further four scrapie sheep. These results suggest that there is agent strain variation in natural scrapie in sheep and that the spectrum of strains present may have changed over the last 20 years. The tested sample is too small to come to any conclusions about whether the BSE strain is present in sheep, but the study provides a framework for further more extensive studies.

Animals↗
PubMed2001

Partial dissociation of PrP(Sc) deposition and vacuolation in the brains of scrapie and BSE experimentally affected goats.

The diagnosis of transmissible spongiform encephalopathies (TSEs) depends on the detection of vacuolation in brain sections taken from affected individuals and/or the identification of the disease-associated isoform of the PrP (prion) protein (PrP(Sc)). During the course of an investigation, goats clinically affected following experimental infection with three different sources of TSE (SSBP/1, CH1641 and BSE) developed widespread vacuolar degeneration in the brain. With BSE, PrP(Sc) was clearly recognized in affected goat brain by immunocytochemistry (icc) and Western blotting, but in contrast the experimental scrapie sources SSBP/1 and CH1641 showed almost no or very little PrP(Sc) by icc. Western blot analysis of PrP(Sc) from BSE-affected and SSBP/1-affected goat brain showed that the protein was present in brain affected by both TSE sources, but could not be used to determine how much protein was present. It became clear that PrP(Sc) and vacuolation could be partially dissociated following challenge with two of the three TSE sources. Subtle differences in glycosylation patterns between BSE- and SSBP/1-associated PrP protein isoforms could also be recognized, although these experimentally generated results should not be regarded as a BSE/scrapie differential test. However, our study warns that the reliance on PrP(Sc) determination by icc alone as a means by which to diagnose TSE infection may generate false negative results.

Animals↗
PubMedDate not supplied

Irregular snow crystals: structural features as revealed by low temperature scanning electron microscopy.

For nearly 50 years, investigators using light microscopy have vaguely alluded to a unique type of snow crystal that has become known as an irregular snow crystal. However, the limited resolution and depth-of-field of the light microscope has prevented investigators from characterizing these crystals. In this study, a field-emission scanning electron microscope, equipped with a cold stage, was used to document the structural features, physical associations, and atmospheric metamorphosis of irregular snow crystals. The crystals appear as irregular hexagons, measuring 60 to 90 mm across, when viewed from the a-axis. Their length (c-axis) rarely exceeds the diameter. The irregular crystals are occasionally found as secondary particles on other larger forms of snow crystals; however, they most frequently occur in aggregates consisting of more than 100 irregular crystals. In the aggregates, the irregular crystals have their axes oriented parallel to one another and, collectively, tend to form columnar structures. Occasionally, these columnar structures exhibit rounded faces along one side, suggesting atmospheric metamorphoses during formation and descent. In extreme cases of metamorphoses, the aggregates would be difficult to distinguish from graupel. Frost, consisting of irregular crystals, has also been encountered, suggesting that atmospheric conditions that favor their growth can also occur terrestrially.

Journal Article↗
PubMedDate not supplied

Rime and graupel: description and characterization as revealed by low-temperature scanning electron microscopy.

Snow crystals, which form by vapor deposition, occasionally come in contact with supercooled cloud droplets during their formation and descent. When this occurs, the droplets adhere and freeze to the snow crystals in a process known as accretion. During the early stages of accretion, discrete snow crystals exhibiting frozen cloud droplets are referred to as rime. If this process continues, the snow crystal may become completely engulfed in frozen cloud droplets. The resulting particle is known as graupel. Light microscopic investigations have studied rime and graupel for nearly 100 years. However, the limiting resolution and depth of field associated with the light microscope have prevented detailed descriptions of the microscopic cloud droplets and the three-dimensional topography of the rime and graupel particles. This study uses low-temperature scanning electron microscopy to characterize the frozen precipitates that are commonly known as rime and graupel. Rime, consisting of frozen cloud droplets, is observed on all types of snow crystals including needles, columns, plates, and dendrites. The droplets, which vary in size from 10 to 100 microm, frequently accumulate along one face of a single snow crystal, but are found more randomly distributed on aggregations consisting of two or more snow crystals (snowflakes). The early stages of riming are characterized by the presence of frozen cloud droplets that appear as a layer of flattened hemispheres on the surface of the snow crystal. As this process continues, the cloud droplets appear more sinuous and elongate as they contact and freeze to the rimed crystals. The advanced stages of this process result in graupel, a particle 1 to 3 mm across, composed of hundreds of frozen cloud droplets interspersed with considerable air spaces; the original snow crystal is no longer discernible. This study increases our knowledge about the process and characteristics of riming and suggests that the initial appearance of the flattened hemispheres may result from impact of the leading face of the snow crystal with cloud droplets. The elongated and sinuous configurations of frozen cloud droplets that are encountered on the more advanced stages suggest that aerodynamic forces propel cloud droplets to the trailing face of the descending crystal where they make contact and freeze.

Journal Article↗
PubMedDate not supplied

Use of low-temperature scanning electron microscopy to compare and characterize three classes of snow cover.

This study, which uses low-temperature scanning electron microscopy (LTSEM), systematically sampled and characterized snow crystals that were collected from three unique classes of snow cover: prairie, taiga, and alpine. These classes, which were defined in previous field studies, result from exposure to unique climatic variables relating to wind, precipitation, and air temperature. Snow samples were taken at 10 cm depth intervals from the walls of freshly excavated snow pits. The depth of the snow pits for the prairie, taiga, and alpine covers were 28, 81, and 110 cm, respectively. Visual examination revealed that the prairie snow cover consisted of two distinct layers whereas the taiga and alpine covers had four distinct layers. Visual measurements were able to establish the range of crystal sizes that occurred in each layer, the temperature within the pit, and the snow density. The LTSEM observations revealed the detailed structures of the types of crystals that occurred in the snow covers, and documented the metamorphosis that transpired in the descending layers. Briefly, the top layers from two of the snow covers consisted of freshly fallen snow crystals that could be readily distinguished as plates and columns (prairie) or graupel (taiga). Alternatively, the top layer in the alpine cover consisted of older dendritic crystal fragments that had undergone early metamorphosis, that is, they had lost their sharp edges and had begun to show signs of joining or bonding with neighboring crystals. A unique layer, known as sun crust, was found in the prairie snow cover; however, successive samplings from all three snow covers showed similar stages of metamorphism that led to the formation of depth hoar crystals. These changes included the gradual development of large, three-dimensional crystals having clearly defined flat faces, sharp edges, internal depressions, and facets. The study, which indicates that LTSEM can be used to enhance visual data by systematically characterizing snow crystals that are collected at remote locations, is important for understanding the physics of snowpacks and the metamorphosis that leads to potential avalanche situations. In addition, the metamorphosis of snow crystals must be considered when microwave radiometry is used to estimate the snow water equivalent in the winter snowpack, because large snow crystals more effectively scatter passive microwave radiation than small crystals.

Journal Article↗