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Biomedical subjects

S Preston

Publications and source records attributed to S Preston.

At least 19 recordsLinked to original sources
PubMed2002

Predicting arsenic solubility in contaminated soils using isotopic dilution techniques.

An isotopic dilution assay was developed to measure radiolabile As concentration in a diverse range of soils (pH 3.30-7.62; % C = 1.00-6.55). Soils amended with 50 mg of As kg(-1) (as Na2HAsO4 x 7H2O) were incubated for over 800 d in an aerated "microcosm" experiment. After 818 d, radiolabile As ranged from 27 to 57% of total applied As and showed a pH-dependent increase above pH 6. The radiolabile assay was also applied to three sets of soils historically contaminated with sewage sludge or mine-spoil. Results reflected the various geochemical forms in which the arsenic was present. On soils from a sewage disposal facility, radiolabile arsenate ranged from 3 to 60% of total As; mean lability was lower than in the equivalent pH range of the microcosm soils, suggesting occlusion of As into calcium phosphate compounds in the sludge-amended soils. In soils from mining areas in the U.K. and Malaysia, radiolabile As accounted for 0.44-19% of total As. The lowest levels of lability were associated with extremely large As concentrations, up to 17,000 mg kg(-1), from arsenopyrite. Soil pore water was extracted from the microcosm experiment and speciated using "GEOCHEM". The solid<==>solution equilibria of As in the microcosm soils was described by a simple model based on competition between HAsO4(2-) and HPO4(2-) for "labile" adsorption sites.

Arsenic↗
PubMed2001

Use of bacterial biosensors to interpret the toxicity and mixture toxicity of herbicides in freshwater.

The dose response relationship between seven commonly used herbicides and four luminescence-based bacterial biosensors was characterised. As herbicide concentration increased the light emitted by the test organism declined in a concentration dependent manner. These dose responses were used to compare the predicted vs. observed response of a biosensor in the presence of multiple contaminants. For the majority of herbicide interactions, the relationship was not additive but primarily antagonistic and sometimes synergistic. These biosensors provide a sensitive test and are able to screen a large volume and wide range of samples with relative rapidity and ease of interpretation. In this study biosensor technology has been successfully applied to interpret the interactive effects of herbicides in freshwater environments.

Bacteria↗
PubMed2001

Soil solution extraction techniques for microbial ecotoxicity testing: a comparative evaluation.

The suitability of two different techniques (centrifugation and Rhizon sampler) for obtaining the interstitial pore water of soil (soil solution), integral to the ecotoxicity assessment of metal contaminated soil, were investigated by combining chemical analyses and a luminescence-based microbial biosensor. Two different techniques, centrifugation and Rhizon sampler, were used to extract the soil solution from Insch (a loamy sand) and Boyndie (a sandy loam) soils, which had been amended with different concentrations of Zn and Cd. The concentrations of dissolved organic carbon (DOC), major anions (F- , CI-, NO3, SO4(2-)) and major cations (K+, Mg2+, Ca2+) in the soil solutions varied depending on the extraction technique used. Overall, the concentrations of Zn and Cd were significantly higher in the soil solution extracted using the centrifugation technique compared with that extracted using the Rhizon sampler technique. Furthermore, the differences observed between the two extraction techniques depended on the type of soil from which the solution was being extracted. The luminescence-based biosensor Escherichia coli HB101 pUCD607 was shown to respond to the free metal concentrations in the soil solutions and showed that different toxicities were associated with each soil, depending on the technique used to extract the soil solution. This study highlights the need to characterise the type of extraction technique used to obtain the soil solution for ecotoxicity testing in order that a representative ecotoxicity assessment can be carried out.

Biological Assay↗
PubMed2000

Measuring symptom change in patients with Parkinson's disease.

BACKGROUND: The 39-item Parkinson's disease questionnaire (PDQ-39) is more sensitive to functional change than other measures of health and disability. AIM: To determine the ability of this scale to change over time and the concurrent validity of some of its subscales. METHODS: We assessed a cohort of 67 Parkinson's patients for 18 months, using the PDQ-39, the GHQ-28 general health questionnaire and the Office of Population and Census Surveys disability instrument. RESULTS: The Office of Population and Census Surveys disability instrument and GHQ-28 recorded no significant change, but the PDQ-39 showed marked changes in levels of functioning. We also analysed changes on the PDQ-39 subscales as well as concurrent validity data for several subscales. This showed concurrent validity with the Beck depression and anxiety inventories, the Barthel index and the Royal Postgraduate Medical School severity scale. There was a high level of concurrent validity for all comparisons except for the Barthel index. CONCLUSION: The PDQ-39 is a sensitive tool for monitoring change in patients with Parkinson's disease. It has high levels of concurrent validity with established measures of mood and motor function.

Activities of Daily Living↗
PubMed1997

The leukocyte/neuron cell surface antigen OX2 binds to a ligand on macrophages.

The OX2 membrane glycoprotein contains two immunoglobulin superfamily (IgSF) domains and seems likely to interact with other cell surface proteins. A soluble chimeric protein with the two IgSF domains of OX2 engineered onto domains 3 + 4 of rat CD4 antigen was expressed. To detect possible weak interactions, the chimeric protein was coupled to fluorescent covaspheres to provide a highly avid display of OX2. The OX2 covaspheres bound macrophages but not other cell types. The specificity of the interaction was demonstrated by blocking with Fab fragments of the OX2 monoclonal antibody (mAb). A new mAb, MRC OX88, was raised against macrophages which also blocked the interaction and presumably recognizes the ligand. The epitope for the MRC OX2 mAb and a site for ligand binding were mapped to domain 1 by site-directed mutagenesis. The OX2 antigen is present on thymocytes, some lymphocytes, neurons and endothelial cells; thus, it has the potential to mediate interactions between these cell types and macrophages.

Amino Acid Sequence↗
PubMed1997

The use of administrative data to risk-stratify asthmatic patients.

In this article, a simple methodology to risk-stratify asthmatics is presented and validated. Such a model can be used to identify those high risk and more severely ill asthmatics who could benefit the most from case management and increased educational efforts. Using logistic regression, the model was created to predict the probability of an asthma-related admission among all asthmatics who were members of a large HMO during calendar year 1994 (N = 54,573). The model used data from pharmacy, laboratory, and specialist claims, as well as encounter and demographic data available in U.S. Healthcare's administrative database. A member's prior asthma-specific utilization patterns, pharmaceutically determined severity of illness, and length of enrollment in the managed care organization had the most influence on the equation. A cross-validation of the model confirms how administrative data can be used to accurately risk-stratify those with a chronic disease. Finally, some additional research possibilities associated with the identification of high risk subscribers using only administrative data are outlined.

Adult↗
PubMed1996

Health plan satisfaction and risk of disenrollment among social/HMO and fee-for-service recipients.

Health plan satisfaction among the elderly is affected by multiple individual and locational factors. We used a general behavioral framework of predisposing, enabling, and service use factors to produce adjusted satisfaction scores. These then were included in a logistic analysis to determine the effect of satisfaction on continued membership in social health maintenance organizations (S/HMOs) or continued participation in fee-for-service care. S/HMO members, after one year in the plan, generally reported satisfaction scores comparable to Medicare beneficiaries in fee-for-service care. Satisfaction with perceived physician quality and interpersonal relationships with the providers reduced the risk of disenrollment. Functional impairment reduced the likelihood of disenrollment, but this effect varied by community. Being impaired was protective in communities with established HMOs. In markets where HMOs were emerging or where intensive HMO competition was beginning, disability increased the likelihood of changing current coverage. S/HMO membership, after adjusting for the market area's general disenrollment propensities, had varying effects. Being a newly formed plan was not a consistent predictor of higher disenrollment rates.

Aged↗
PubMed1996

Clinical hypertension in Native Americans: a comparison of 1987 and 1992 rates from ambulatory care data.

THE AUTHORS EXAMINED THE PREVALENCE of clinically diagnosed hypertension among all American Indian and Alaska Native outpatients served in Indian Health Service (IHS) facilities in fiscal year 1992, and compared these rates with a similar analysis done in 1987. In this report they provided data on that analysis as well as on the association between hypertension and diabetes. The 1992 overall estimated age-adjusted prevalence of clinically diagnosed hypertension in adults older than age 15 was 10.4%, compared with 10.9% in 1987, a small but significant decrease. Considerable variation exists in hypertension prevalence rates in American Indian communities as analyzed by IHS service area. This report represents an attempt to use ambulatory patient care data to demonstrate a means for ongoing surveillance of a chronic disease for the entire service population of the IHS. This comprehensive data set represents approximately 60% of the entire U.S. American Indian and Alaska Native population. Based on the ongoing nature of this ambulatory patient care data system, this model for hypertension surveillance permits a unique opportunity for longitudinal evaluation of quality improvement efforts for the American Indian and Alaska Native populations served by the IHS.

Adolescent↗
PubMed1995

A sensitive assay for detecting low-affinity interactions at the cell surface reveals no additional ligands for the adhesion pair rat CD2 and CD48.

The ligand for the T cell antigen CD2 is CD48 in rodents, but CD58 in humans. The extracellular parts of these three antigens are structurally related in that all contain two immunoglobulin superfamily (IgSF) domains. There have been reports of alternative ligands for CD2 in the human, but not so far in rodents. We describe the analysis of ligands for rat CD2 and CD48 using fluorescent beads capable of displaying a high ligand density and detecting low-affinity interactions like that of CD2 with CD48 (Kd = 60-90 microM). Monovalent chimeric proteins containing the two IgSF domains of rat CD48 or CD2 and domains 3 and 4 of rat CD4 (CD4d3+4) were anchored to fluorescent covaspheres via a CD4 monoclonal antibody (mAb) with the CD48 or CD2 domains available for ligand binding. Multivalent CD48-CD4d3+4 covaspheres gave strong specific binding to rat CD2 expressed on the surface of transfected Jurkat cells. CD48-CD4d3+4 was compared with CD48-IgG and CD48-IgM as tools for detecting binding at the cell surface. Soluble divalent CD48-IgG and decavalent CD48-IgM bound to soluble CD2 with a Koff of around 10(-3) s-1 as determined using a BIAcore biosensor. However, binding to cells by CD48-IgG and CD48-IgM was only detectable when they were immobilized on covaspheres and represented no increase in sensitivity over CD48-CD4 covaspheres when tested for binding to cells expressing high and low levels of CD2. CD48-CD4d3+4 covaspheres only bound to rat cells expressing CD2. In the reverse orientation, bindign of CD2-CD4d3+4 covaspheres was dependent on expression of CD48. Pre-incubation of cells with CD2 or CD48 mAb abolished all binding of CD48-CD4d3+4 or CD2-CD4d3+4, respectively. The data provide no evidence for an alternative ligand for rat CD2 or CD48.

Animals↗
PubMed1995

Mating in the monogamous male: behavioral consequences.

In monogamous mammals, males typically show selective affiliation with a single mate, high levels of paternal care, and aggression towards conspecifics to protect male and offspring. We have previously described how selective aggression and affiliation increase after mating in the male prairie vole, Microtus ochrogaster. The current studies further explored the behavioral changes that follow mating in the male of this species. The first set of experiments tested males on several behavioral measures after 24 h of either mating, social (but not sexual) exposure, or no social contact. After 24 h of mating, but not after the other two conditions, aggression and affiliation (partner preference) increased as previously reported. In addition, mated animals showed increased exploration of the open arms of a plus maze, consistent with decreased fearfulness. There were no group differences in paternal behavior (which was high in all three conditions) or analgesia (assessed by tail flick latency). To determine the minimum amount of mating necessary for the induction of aggression, males were tested in a resident-intruder paradigm after 1,6, or 24 h of mating. Although 1 h of mating was associated with a transient increase in the frequency of threats and attacks, the full spectrum of enduring aggression was observed only in the males given 24 h of mating. In a final experiment, the behavioral consequences of mating were studied in males of the closely related montane vole (Microtus montanus) which does not pair bond. Males of this nonmonogamous vole species did not show increased aggression, partner preference, or alterations in plus maze exploration following 24 h of mating. These results demonstrate the importance of prolonged mating for the induction of pair bonding in the monogamous male and they suggest that increases in aggression and affiliation are associated with decreased fearfulness in pair bonded males.

Aggression↗
PubMed1994

Screening of snake venoms for neurotoxic and myotoxic effects using simple in vitro preparations from rodents and chicks.

Eight snake venoms designated by the WHO as International Reference Venoms, and one additional venom were assessed for neurotoxic and myotoxic effects in vitro using the chick biventer cervicis and the rat and mouse phrenic nerve-diaphragm preparations. The objective was to determine whether any of the preparations could be used to detect evidence of neurotoxic or myotoxic activity prior to a more detailed examination. Bungarus multicinctus venom at concentrations above 1 microgram ml-1 selectively blocked neuromuscular transmission, with no direct effect on muscle fibres. Naja naja kaouthia and Notechis scutatus venoms selectively blocked neuromuscular transmission at low concentrations, but at higher concentrations both venoms caused direct effects on skeletal muscle resulting in contractures, loss of tension following direct stimulation and a loss in sensitivity to elevated [K+]0. Vipera russelli (Thailand) venom also blocked neuromuscular transmission but it was less potent than the venoms of B. multicinctus, N. n. kaouthia and N. scutatus. It also caused contractures in the chick biventer cervicis muscle. The venoms of Echis carinatus (Iran and Mali), Crotalus atrox, Bothrops atrox asper and Trimeresurus flavoviridis had limited neuromuscular blocking activity, and most of these venoms blocked [K+]0 and cholinoceptor stimulation in the chick muscle. Although both chick and rodent muscles allowed the assessment of neurotoxic and myotoxic activity, the chick biventer cervicis was simpler and more robust in use than either of the rodent phrenic nerve-diaphragm preparations. We propose that the chick biventer cervicis muscle could be used as a standard preparation for the screening of snake venoms for neurotoxic and myotoxic effects, and that it may be possible to use this preparation as a means to check that antivenoms can neutralize neurotoxic and direct myotoxic actions of venoms.

Animals↗
PubMed1993

Trends in Medicaid nursing home reimbursement: 1978-89.

Medicaid nursing home reimbursement is of concern because of implications for nursing home expenditures. This article presents data on State Medicaid nursing home reimbursement methods, ratesetting methods, and average per diem rates, refining earlier data and updating through 1989. A trend in the early 1980s toward adopting prospective systems played out by the end of the decade. There were trends, however, toward casemix methods, which may increase access for high-need patients, and toward cost-center limits on nursing, which may provide incentives to lower quality care. Analysis supports previous findings that prospective systems allow greater control over increases in rates.

Data Collection↗
PubMed1993

A comparison of S/HMO disenrollees and continuing members.

Four Social/Health Maintenance Organization demonstration projects had disenrollment rates of about 8.6% annually during the first 36 months. This study compares those who disenrolled to those who remained S/HMO members. The analysis found that S/HMOs sponsored by HMOs had lower disenrollment than S/HMOs sponsored by long-term care organizations. The major reasons for disenrollment were dissatisfaction with physician services and premium costs. Having other insurance, not living alone, having inadequate information upon enrollment, having no physical impairments or health problems, and no use of hospital or chronic care were found to be positive predictors of disenrollment. Switching from the S/HMO to another HMO rather than to fee-for-service was associated with having no health problems, having no other health insurance, living alone, and being married.

Aged↗