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Biomedical subjects

S M Wright

Publications and source records attributed to S M Wright.

At least 73 records · Page 4Linked to original sources
PubMed1997

Outcomes of acute myocardial infarction in the Department of Veterans Affairs: does regionalization of health care work?

OBJECTIVES: This study examines the association between the regional availability of cardiac technology and outcomes of care for patients admitted to Department of Veterans Affairs (VA) hospitals. Patients using the VA regional medical system initially are admitted to a hospital with or without the on-site availability of technology-intensive cardiac services. METHODS: The authors identified male veterans (n = 24,229) discharged from VA hospitals with a primary diagnosis of acute myocardial infarction (AMI) from January 1, 1988 through December 31, 1990. Analyses of mortality up to 2 years after AMI and the use of cardiac procedures were stratified by the type of VA hospitals to which patients initially were admitted. Logistic regression models adjusted for age, race, marital status, hospitalization in previous year, comorbidities, cardiac complications coded, and year of AMI. RESULTS: Adjusted mortality was significantly higher for patients initially admitted to hospitals without on-site cardiac technology at: 2 days (odds ratio [OR] 0.70; 95% confidence interval [CI] 0.62-0.81), 90 days (OR 0.78; 95% CI 0.73-0.85); 1 year (OR 0.87, 95% CI 0.81-0.93); and 2 years (OR 0.86, 95% CI 0.81-0.92) compared with hospitals with on-site cardiac technology (ie, coronary angioplasty and cardiac surgery facilities). Patients initially admitted to hospitals without on-site cardiac technology also were less likely to undergo cardiac procedures than patients admitted to hospitals with on-site cardiac technology. CONCLUSIONS: The regional distribution of cardiac technology may restrict patient access to technology-intensive services and to "equally good medical care." Policies that promote regionalization of medical services should consider carefully the distribution of benefits and burdens to patients.

Cardiology Service, Hospital↗
PubMed1997

Where do elderly veterans obtain care for acute myocardial infarction: Department of Veterans Affairs or Medicare?

OBJECTIVE: To examine Department of Veterans Affairs (VA) and Medicare hospitalizations for elderly veterans with acute myocardial infarction (AMI), their use of cardiac procedures in both systems, and patient mortality. DATA SOURCES: Merging of inpatient discharge abstracts obtained from VA Patient Treatment Files (PTF) and Medicare MedPAR Part A files. STUDY DESIGN: A retrospective cohort study of male veterans 65 years or older who were prior users of the VA medical system (veteran-users) and who were initially admitted to a VA or Medicare hospital with a primary diagnosis of AMI at some time from January 1, 1988 through December 31, 1990 (N = 25,312). We examined the use of cardiac catheterization, coronary bypass surgery, and percutaneous transluminal coronary angioplasty in the 90 days after initial admission for AMI in both VA and Medicare systems, and survival at 30 days, 90 days, and one year. Other key measures included patient age, race, marital status, comorbidities, cardiac complications, prior utilization, and the availability of cardiac technology at the admitting hospital. PRINCIPAL FINDINGS: More than half of veteran-users (54 percent) were initially hospitalized in a Medicare hospital when they suffered an AMI. These Medicare index patients were more likely to receive cardiac catheterization (OR 1.24, 95% C.I. 1.17-1.32), coronary bypass surgery (OR 2.01, 95% C.I. 1.83-2.20), and percutaneous transluminal coronary angioplasty (OR 2.56, 95% C.I. 2.30-2.85) than VA index patients. Small proportions of patients crossed over between systems of care for catheterization procedures (VA to Medicare = 3.3%, and Medicare to VA = 5.1%). Many VA index patients crossed over to Medicare hospitals to obtain bypass surgery (27.6 percent) or coronary angioplasty (12.1 percent). Mortality was not significantly different between veteran-users who were initially admitted to VA versus Medicare hospitals. CONCLUSIONS: Dual-system utilization highlights the need to look at both systems of care when evaluating access, costs, and quality either in VA or in Medicare systems. Policy changes that affect access to and utilization of one system may lead to unpredictable results in the other.

Aged↗
PubMed1995

Design of matching networks for low noise preamplifiers.

This paper discusses matching networks that minimize inductive coupling between the antennas within an array while simultaneously insuring minimum noise contributions from preamplifiers. Typical low noise preamplifier designs require a strong mismatch between the source impedance and the amplifier input impedance (reflection coefficient close to one) to achieve optimal noise performance. This is in contrast to the familiar impedance match known from communication theory where input and source impedances have complex conjugate values for maximizing the power transfer from source to amplifier. The high input reflection coefficient of low noise amplifiers can be exploited to reduce antenna currents by using lossless impedance transformations to create a high impedance at the coil terminals while simultaneously maintaining a low noise figure for the amplifier. The networks presented here constitute an improvement over previous work because they give additional freedoms regarding the values of the network components and the amplifier input impedance. The technique has been formalized and coded in MathCad, making the design of realizable networks a simple process.

Magnetic Resonance Imaging↗
PubMed1994

Evidence for interspecies transmission and reassortment of influenza A viruses in pigs in southern China.

The Asian/57, Hong Kong/68, and Russian/77 pandemics of this century appeared or reappeared in China. Interspecies transmission and genetic reassortment of influenza viruses have been implicated in the origin of these human pandemic influenza viruses. Pigs have been suspected to be the "mixing vessel" where reassortment occurs. To investigate this possibility, 104 porcine influenza viruses collected at random from Southern China from 1976 to 1982, including 32 H3N2 isolates and 72 H1N1 isolates, were studied using dot blot hybridization, partial sequencing, and phylogenetic analysis. There were 29 of 32 H3N2 isolates characteristic of viruses originally derived from humans; the other 3 isolates were reassortants containing genes from porcine and human influenza viruses. Phylogenetic analyses of the polymerase B1 (PB1) genes showed that interspecies transmission from humans to pigs has happened multiple times in pigs in Southern China. All 72 H1N1 isolates were of porcine origin characteristic of classical porcine H1N1 influenza virus. Analysis of 624 genes of porcine influenza viruses from Southern China failed to detect any evidence for avian influenza virus genes. This contrasts to what is currently found in Europe, where the majority of porcine influenza virus isolates are of avian origin.

Animals↗
PubMed1994

Racial variation in cardiac procedure use and survival following acute myocardial infarction in the Department of Veterans Affairs.

OBJECTIVE: To examine whether blacks admitted to Veterans Affairs Medical Centers (VAMCs) with an acute myocardial infarction (AMI) are less likely than whites to undergo cardiac catheterization or coronary revascularization procedures and to determine the impact of these differences on patient survival. DESIGN: A retrospective observational study of inpatient discharge abstracts from the Veterans Health Administration (VHA). SETTING: All one hundred fifty-eight acute care hospitals in the VHA. PATIENT POPULATION: Male veterans (n = 33,641) discharge from VAMCs with an International Classification of Diseases, Ninth Revision, Clinical Modification code for AMI from January 1, 1988, to December 31, 1990. INTERVENTION: None. MAIN OUTCOME MEASURES: The use of cardiac catheterization, coronary angioplasty, and/or bypass surgery in the 90 days after admission for AMI, and survival at 30 days, 1 year, and 2 years. MAIN RESULTS: Adjusting for patient and hospital characteristics, blacks with an AMI were 33% less likely than whites to undergo cardiac catheterization, 42% less likely to receive coronary angioplasty, and 54% less likely to receive coronary bypass surgery. Among patients who underwent catheterization, blacks were also less likely than whites to have a subsequent cardiac revascularization procedure. Adjusted 30-day survival for blacks was significantly greater than for whites. One- and 2-year survival rates after AMI were not significantly different between blacks and whites. CONCLUSIONS: In a health care system designed to provide equivalent availability of care to all eligible patients, blacks received substantially fewer cardiac procedures after AMI than whites. Despite undergoing fewer interventional procedures, blacks had better short-term and equivalent intermediate survival rates compared with whites.

Black or African American↗
PubMed1994

A four-channel time domain multiplexer: a cost-effective alternative to multiple receivers.

The concept of simultaneous image acquisition as originally conceived by Hyde has been implemented by Roemer et al. using a multiple receiver system. This article describes an alternative technique that uses time domain multiplexing (TDM) to acquire simultaneous images using a single receiver channel. This method requires few modifications to the existing receiver and has been shown to be equivalent to a true four channel receiver in most applications. The multiplexing technique was implemented and tested on a standard commercial scanner that has also been equipped with a four channel receiver. Signal-to-noise results demonstrate that four independent images can be multiplexed through a single receiver channel with no degradation in image quality. Additionally, spine images that were obtained from a normal volunteer with both a multiplexed single channel receiver and a true four channel receiver system are presented.

Cost-Benefit Analysis↗
PubMed1993

Wild ducks are the reservoir for only a limited number of influenza A subtypes.

Analysis of cloacal samples collected from 12,321 wild ducks in Alberta, Canada, from 1976 to 1990 showed influenza A infections to be seasonal, with prevalences increasing as the population became increasingly more dense. Viruses with 3 haemagglutinin (H3, H4, and H6) and 3 neuraminidase subtypes (N2, N6, and N8) were found consistently to infect both adult and juvenile ducks each year, indicating that wild ducks may be a reservoir for these viruses. In contrast, viruses with 7 haemagglutinin (H2, H5, H7, H8, H9, H11, and H12) and 3 neuraminidase subtypes (N1, N3, and N4) were not found for prolonged periods during the study; when they were found, they primarily infected juveniles at moderate levels. Whilst wild ducks appear to perpetuate some influenza A viruses, they apparently do not act as a reservoir for all such viruses.

Age Factors↗
PubMed1993

MR flow measurement using RF phase gradients in receiver coil arrays.

Radio frequency (RF) phase gradients in the receiver coil field pattern can encode flow velocity information in magnetic resonance (MR) images in the form of phase variations. These phase variations are not readily observed in MR images because they are relatively small compared to phase variations caused by static magnetic field (B0) inhomogeneities, susceptibility variations, and other sources. However, the phase contributions from these other sources are independent of the receiver coil. Therefore, the RF phase gradient encoded flow information can be recovered by subtracting images obtained simultaneously using arrays of independent receiver coils and a multiple channel receiver. This flow velocity information can be extracted retrospectively from standard imaging sequences, including flow-compensated sequences. No additional time is required for the flow study as the flow measurements are made using sequences chosen for optimal imaging, and the images from each coil are obtained simultaneously. Initial results indicate that sufficient sensitivity is obtained to make flow measurements in the range of velocities commonly found in the carotid arteries and other major vessels. In principle, the method works with only two receiver coils. However, additional elements provide additional phase measurements that can be used to increase accuracy, remove ambiguities in flow direction or velocity calculations, and increase the region over which velocity measurements can be accurately made.

Artifacts↗
PubMed1993

Influenza--a model of an emerging virus disease.

Influenza A viruses continue to emerge from the aquatic avian reservoir and cause pandemics. Phylogenetic analysis of the nucleotide sequence of all eight influenza A virus RNA segments indicate that all of the influenza viruses in mammalian hosts originate from the avian gene pool. In contrast to the rapid progressive changes in both the nucleotide and amino acid sequences of mammalian virus gene lineages, avian virus genes show far less variation and, in most cases, appear to be in evolutionary stasis. There are periodic exchanges of influenza virus genes or whole viruses between species giving rise to pandemics of diseases in humans, lower animals and birds. The periodic emergence of influenza viruses in mammalian species has been illustrated by the appearance of a new influenza virus in horses in northern China in 1989. Phylogenetic analysis of classical H1N1, avian-like H1N1 and human H3N2 viruses circulating in Italian pigs reveals that genetic reassortment is taking place between avian- and human-like viruses in the European pig population. These studies provide evidence supporting the possibility that pigs serve as a mixing vessel for reassortment between influenza viruses in mammalian and avian hosts and raise the question of whether the next pandemic of influenza will emerge in Europe!

Animals↗
PubMed1993

Sorbitol content of selected oral liquids.

OBJECTIVE: Excipients in pharmaceuticals usually are considered inert, and may be overlooked in the differential diagnosis of diarrhea. Sorbitol-containing medicinal liquids are capable of inducing osmotic diarrhea. We reviewed the oral liquids in our formulary to determine their sorbitol content and to evaluate the availability of this information. DESIGN: The oral liquids stocked by our hospital were determined through a computer search and manual inspection of the pharmacy storeroom. Three common sources of drug information were consulted to determine each product's sorbitol content: manufacturers' product information, American Hospital Formulary Service (AHFS) Drug Information 91, and Facts and Comparisons Drug Information. We then contacted each manufacturer by mail or telephone to verify the information. SETTING: The study was conducted at the University of Cincinnati Hospital, a tertiary-care, teaching hospital. RESULTS: A total of 129 products (98 chemical entities) were reviewed. Fifty-four (42 percent) of the products examined contained sorbitol. The frequency of sorbitol presence by liquid type was: solutions (33 percent), suspensions (43 percent), syrups (59 percent), elixirs (43 percent), concentrates (67 percent), drops (33 percent), tinctures (0 percent), and emulsions (0 percent). The percentage of listings indicating the presence of sorbitol was: manufacturer's product information (79 percent), Facts and Comparisons (52 percent), and AHFS Drug Information 91 (13 percent). Only three of the 54 products had the exact sorbitol content stated in any source.

Administration, Oral↗
PubMed1992

Interspecies transmission and reassortment of influenza A viruses in pigs and turkeys in the United States.

Genetic reassortment between influenza A viruses in humans and in animals and birds has been implicated in the appearance of new pandemics of human influenza. To determine whether such reassortment has occurred in the United States, the authors compared the genetic origins of gene segments of 73 swine influenza virus isolates (1976-1990), representing 11 states, and 11 turkey virus isolates (1980-1989), representing eight states. The host origin of gene segments encoding the internal proteins of H1N1 swine and turkey influenza viruses was identified by developing a dot-blot assay. All gene segments of swine influenza viruses were characteristic of influenza virus genes from that species, indicating that pigs may not be frequent participants in interspecies genetic exchange and reassortment of influenza viruses in the United States. In contrast, 73% of the turkey influenza virus isolates contained genes of swine origin. One turkey isolate was a reassortant having three genes characteristic of avian influenza virus and three of swine origin. These findings document a high degree of genetic exchange and reassortment of influenza A viruses in domestic turkeys in the United States. The molecular biologic techniques used by the authors should aid future epidemiologic studies of influenza pandemics.

Animals↗
PubMed1992

Prosthetic assessment in the treatment of denture hyperplasia.

The removal of denture-induced trauma is important in the treatment of denture hyperplasia and in the prevention of its redevelopment in susceptible patients. A simple approach to the assessment of dentures is described, which highlights potentially damaging areas of the borders and the fitting surface.

Dental Occlusion↗
PubMed1991

Reproductive health: knowledge, attitudes and needs of adolescents.

OBJECTIVE: To determine the knowledge and attitudes of adolescents with respect to reproductive health, with particular emphasis on their knowledge of the symptoms and transmission of sexually transmitted diseases (STDs), preventive strategies and sources of information. DESIGN: Questionnaire survey of a stratified random sample of Year 10 students followed by group interviews with volunteers from the sample. SETTING: The study was carried out in 33 Victorian secondary schools. PARTICIPANTS: The questionnaire was administered to a stratified random sample of 1351 Year 10 students. Group interviews were conducted with 533 volunteers from the sample. MEASUREMENTS AND MAIN RESULTS: Considerable gaps were identified in knowledge of STDs and their short-term and long-term effects on reproductive health. An STD Knowledge Score was constructed based on responses to 46 items. The mean score for the full sample was 22.7 (49.3% correct) with a standard deviation of 6.4. As a group, country students scored better than city students (mean, 23.8 v. 22.2, t = 3.97, P less than 0.001) and females better than males (mean, 23.5 v. 21.9, t = 4.21, P less than 0.001). Medical practitioners were rarely identified as a source of preventive advice. CONCLUSION: The deficiencies identified in knowledge about reproductive health suggest that young people need better access to health information. Schools and the medical profession need to work together both to provide information and to help young people develop the confidence to use available information sources.

Adolescent↗
PubMed1991

Arrays of mutually coupled receiver coils: theory and application.

Specialized receiver coils having a small sensitive region can provide an improvement in SNR for MR imaging and spectroscopy, at the expense of limiting the usable field of view. This work presents a technique for designing coil arrays that allows the size and location of the sensitive region to be selected remotely. Only one element of the coil array is directly connected to the receiver, allowing flexibility in system design and implementation. A method is presented for the analysis and design of mutually coupled coil arrays of any number of elements of arbitrary shape. The analysis includes mutual coupling effects between primary coils, to allow multiple primary coils to be used simultaneously. A controller system allows remote selection of the sensitive region and automatically matches the impedance of the array to the preamplifier. Results obtained using a mutually coupled coil array designed for spine imaging are shown.

Equipment Design↗
PubMed1991

Dextran magnetite as a liver contrast agent.

The superparamagnetic particle dextran magnetite was studied as a liver tumor contrast agent for magnetic resonance imaging (MRI). The effects of dextran magnetite on the longitudinal (T1) and transverse (T2) relaxation times in liver, spleen, and an implanted rat liver tumor were measured at 0.47 T (IBM/Bruker PC-20 relaxometer) over the dose range of 23 to 69 mumol Fe/kg. Dextran magnetite substantially reduced the T2 of the liver and spleen, but not of the tumor, thereby providing a basis for improved tumor imaging. The T1 of the tumor was not affected following injection of dextran magnetite in the dose range studied, while the spleen T1 was reduced substantially more than the T1 of the liver. Histological studies using the iron reaction for Prussian blue clearly showed dextran magnetite in the liver and spleen, but not in the tumor. While dextran magnetite was sequestered in macrophages in both liver and spleen, the distribution in the liver was more diffuse (70 microns average particle separation) than that in the spleen (25 microns separation). The lack of a T1 effect in the liver is consistent with the fact that a majority of the water in the tissue cannot diffuse to the relaxational centers on the time scale of the liver's intrinsic T1 (280 ms). In the spleen, however, the dextran magnetite is more densely packed in the red pulp allowing a significant fraction of the water to be relaxed by a T1 mechanism. Spin-echo images of the implanted tumor (mammary adenocarcinoma. R3230AC) in the livers of Fischer 344 rats were obtained at 0.50 T (Siemens Magnetom). The tumor-to-liver contrast was improved for both T1 and T2-weighted spin-echo images after intravenous injection of the dextran magnetite contrast agent. The contrast determined from these images agreed with that predicted by the measured T1 and the T2 (Hahn spin-echo) values. In addition, gradient-echo T2-weighted images with good contrast were obtained in a much shorter imaging time than was needed for T2-weighted spin-echo images. These results demonstrate that the MRI contrast enhancement observed with dextran magnetite is based on its selective uptake and distribution in the macrophages in the liver and spleen and that this agent has substantial potential as a superparamagnetic MR contrast agent.

Adenocarcinoma↗