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Biomedical subjects

K W Thomas

Publications and source records attributed to K W Thomas.

At least 37 records · Page 2Linked to original sources
PubMed1980

Hypogammaglobulinaemia in foals: prevalence on Victorian studs and simple methods for detection and correction in the field.

The prevalence of hypogammaglobulinaemia in 82 young foals was determined. Twelve foals were considered clinically abnormal at birth and ten died within two weeks. All of these foals were hypogammaglobulinaemic. Seven (10%) of the other 70 apparently normal foals were hypogammaglobulinaemic despite having suckled normally. Three of these foals developed significant disease and one died at one month of age. Rapid detection of foals with low serum immunoglobulin levels was achieved by adapting the zinc sulphate turbidity test to partially evacuated blood collection tubes. This permitted test to be conducted on the stud or in the veterinarian's own laboratory. Plasma concentrated twofold by a freeze thaw technique was administered intravenously to supplement the immunoglobulin levels of two colostrum deprived foals. The simplicity of the concentration procedure eliminated the need for laboratory preparation of equine immunoglobulin.

Agammaglobulinemia↗
PubMed1976

Manganese levels and the morphology of the epiphyseal plate in broilers with slipped tendons.

Manganese deficiency in chickens results in perosis and a higher incidence of slipped tendon. Perosis is associated with a disorganization of the epiphyseal growth plates and changes in the chemical composition of the cartilage matrix. Male broilers with slipped tendons were selected from a commercial broiler farm over a 9 week growing period. Their growth rates, epiphyseal cartilage histology and tissue manganese concentrations were examined and compared with (a) normal broilers from the same farm, and (b) similar broilers raised on control and manganese deficient diets. Field broilers with slipped tendons showed no evidence of abnormality in the histological appearance of the proximal tibial growth plate at any of the ages examined. The manganese content of liver and epiphyseal cartilage from field broilers showing slipped tendon was comparable with that present in tissue from normal broilers wither from the field or raised on a chemically defined diey supplemented with managese. The slightly retared growth rate seen in the field broilers was attributed to feeding problems associated with the lameness condition. These results provide conclusive evidence that slipped tendon in field broilers is not dur to a manganese deficiency in the tissues, nor does it appear to be associated with abnormal proliferation of the chondrocytes in the epiphyseal plate.

Animals↗
PubMed1976

Official statistics and blindness in Hong Kong.

WHO designated 1976 as the year for the prevention of blindness and attention is drawn to the prevalence rate and causes of blindness in Hong Kong. The former as released by WHO is as high as 1392 per 100,000 and the latter tends to suggest Vitamin A deficiency is still an important cause here. This article reviews all the official statistics on blindness published in Hong Kong over the past twenty years and seeks to suggest an appropriate prevalence rate for Hong Kong and demonstrate the changing pattern of causes of blindness in Hong Kong. It concludes that Hong Kong should adopt a statistical definition and classification of blindness accepted internationally and suggests that in the presentation of statistics, the misleading factor of present inclusion of past events should be avoided.

Adolescent↗
PubMedDate not supplied

Population-based dietary intakes and tap water concentrations for selected elements in the EPA region V National Human Exposure Assessment Survey (NHEXAS).

A National Human Exposure Assessment Survey (NHEXAS) field study was performed in U.S. Environmental Protection Agency (EPA) Region V, providing population-based exposure distribution data for selected elements in several personal, environmental, and biological media. Population distributions are reported for the 11 elements that were measured in water and dietary samples. Dietary intakes and home tap water concentrations of lead, arsenic, and cadmium were further examined for intermedia associations, for differences between dietary exposure for adults and children, and to estimate the proportion of the population above health-based reference values (dietary) or regulatory action levels or maximum contaminant levels (water). Water lead and arsenic concentrations were significantly associated with dietary intake. Intake of all elements was higher from solid foods than from liquid foods (including drinking water). Dietary intakes of Pb, As, and Cd were greater than those calculated for intake from home tap water or inhalation on a microg/day basis. Median dietary intakes for the Region V population for Pb, As, and Cd were 0.10, 0.13, and 0.19 microg/kg bw/day, respectively. While Pb, As, and Cd concentrations in the foods consumed by 0 to 6-year-old children were similar to or lower than those for adults, dietary intakes calculated on a body weight basis were 1.5 to 2.5 times higher for young children. Intrapersonal intake differences accounted for most of the variance in short-term (daily) dietary intakes for Pb and As, while interpersonal differences accounted for more of the intake variance for Cd. Only small percentages of the population exceeded health-based intake reference values or concentrations equal to regulatory levels in water for Pb, As, and Cd.

Adolescent↗
PubMedDate not supplied

Sampling design, response rates, and analysis weights for the National Human Exposure Assessment Survey (NHEXAS) in EPA region 5.

For the Phase I field test of the National Human Exposure Assessment Survey (NHEXAS) in U.S. Environmental Protection Agency (EPA) Region 5, this paper presents the survey sampling design, the response rates achieved, and the sample weighting procedure implemented to compensate for unit nonresponse. To enable statistically defensible inferences to the entire region, a sample of about 250 members of the household population in EPA Region 5 was selected using a stratified multistage probability-based survey sampling design. Sample selection proceeded in four nested stages: (1) sample counties; (2) area segments based on Census blocks within sample counties; (3) housing units (HUs) within sample segments; and (4) individual participants within sample households. Each fourth-stage sample member was asked to participate in 6 days of exposure monitoring. A subsample of participants was asked to participate in two rounds of longitudinal follow-up data collection. Approximately 70% of all sample households participated in household screening interviews in which rosters of household members were developed. Over 70% of the sample subjects selected from these households completed the Baseline Questionnaire regarding their demographic characteristics and potential for exposures. And, over 75% of these sample members went on to complete at least the core environmental monitoring, including personal exposures to volatile organic compounds (VOCs) and tap water concentrations of metals. The sample weighting procedures used the data collected in the screening interviews for all household members to fit logistic models for nonresponse in the later phases of the study. Moreover, the statistical analysis weights were poststratified to 1994 State population projections obtained from the Bureau of the Census to ensure consistency with other statistics for the Region.

Adolescent↗
PubMedDate not supplied

Design strategy for assessing multi-pathway exposure for children: the Minnesota Children's Pesticide Exposure Study (MNCPES).

Although children are exposed to a variety of environmental hazards, including pesticides, there is a scarcity of information available to estimate exposures realistically. This article reports on one of the first attempts to measure multi-pathway pesticide exposures in a population-based sample of urban and non-urban children. A design strategy was developed to assess multi-pathway pesticide exposures in children using personal exposure measurements in combination with complimentary measurements of biological markers of exposure, concentrations in relevant environmental media, and time spent in important microenvironments and participating in exposure-related activities. Sample collection and analysis emphasized measurement of three insecticides (i.e., chlorpyrifos, diazinon, and malathion) and one herbicide (i.e., atrazine). These compounds were selected because of their frequent use, presence in multiple environmental media, expected population exposures, and related hazard/toxicity. The study was conducted during the summer of 1997 in Minnesota and involved a stratified sample of households with children ages 3-12 years. Participants resided in either (a) the cities of Minneapolis and St. Paul (urban households), or (b) Rice and Goodhue Counties just south of the metropolitan area (non-urban households). Results from a residential inventory documenting storage and use of products containing the target pesticides were used to preferentially select households where children were likely to have higher exposures. The study successfully obtained pesticide exposure data for 102 children, including measurements of personal exposures (air, hand rinse, duplicate diet), environmental concentrations (residential indoor/outdoor air, drinking water, residential surfaces, soil), activity patterns (obtained by questionnaire, diary, videotaping), and internal dose (metabolites in urine).

Biomarkers↗
PubMedDate not supplied

Measurement of multi-pollutant and multi-pathway exposures in a probability-based sample of children: practical strategies for effective field studies.

The purpose of this manuscript is to describe the practical strategies developed for the implementation of the Minnesota Children's Pesticide Exposure Study (MNCPES), which is one of the first probability-based samples of multi-pathway and multi-pesticide exposures in children. The primary objective of MNCPES was to characterize children's exposure to selected pesticides through a combination of questionnaires, personal exposure measurements (i.e., air, duplicate diet, hand rinse), and complementary monitoring of biological samples (i.e., pesticide metabolites in urine), environmental samples (i.e., residential indoor/outdoor air, drinking water, dust on residential surfaces, soil), and children's activity patterns. A cross-sectional design employing a stratified random sample was used to identify homes with age-eligible children and screen residences to facilitate oversampling of households with higher potential exposures. Numerous techniques were employed in the study, including in-person contact by locally based interviewers, brief and highly focused home visits, graduated subject incentives, and training of parents and children to assist in sample collection. It is not feasible to quantify increases in rates of subject recruitment, retention, or compliance that resulted from the techniques employed in this study. Nevertheless, results indicate that the total package of implemented procedures was instrumental in obtaining a high percentage of valid samples for targeted households and environmental media.

Adolescent↗
PubMedDate not supplied

The challenge of assessing children's residential exposure to pesticides.

In implementing the Food Quality Protection Act (FQPA) the U.S. Environmental Protection Agency (USEPA) has adopted a policy that the exposure factors and models used to assess and predict exposure to pesticides should generally be conservative. Some elements of exposure assessments for FQPA are screening level--they are both uncertain and conservative. If more realistic assessments are to be conducted, then research is required to reduce uncertainty associated with the factors and models used in the exposure assessments. To develop the strategy for conducting this research, critical exposure pathways and factors were identified, and the quality and quantity of data associated with default assumptions for exposure factors were evaluated. Then, based on our current understanding of the pathways that are potentially most important and most uncertain, significant research requirements were identified and prioritized to improve the data available and assumptions used to assess children's aggregate exposure to pesticides. Based on the results of these efforts, four priority research areas were identified: (1) pesticide use patterns in microenvironments where children spend time, (2) temporal and spatial distribution of pesticides following application in a residential setting, (3) dermal and nondietary ingestion exposure assessment methods and exposure factors, (4) dietary exposure assessment methods and exposure factors for infants and young children. The National Exposure Research Laboratory (NERL) research strategy in support of FQPA is designed to address these priority research needs.

Administration, Cutaneous↗
PubMedDate not supplied

A device for sampling of human alveolar breath for the measurement of expired volatile organic compounds.

This report describes the development of a portable spirometer capable of collecting primarily alveolar breath into 1.8-L canisters for subsequent gas chromatographic/mass spectrometric (GC/MS) analysis. Based on CO2 measurements, greater than 97% of the breath collected is alveolar in origin. Sample collection takes place in approximately two minutes. Clean air for inhalation is provided by two organic vapor respirator cartridges. Studies of the breakthrough volume of test compounds at both the 5- and 50-micrograms/m3 levels indicate that each cartridge filter can be used to sample over 300 L of air and that this volume is not altered by intermittent use and storage of the filter for up to five days. In experiments designed to mimic human breathing, recoveries of test compounds through the device at the 5-mu/m3 level ranged from 87 to 112%. Essentially no volatile organic compound (VOC) memory (i.e., adsorption carryover by the device) was measured at the 50-micrograms/m3 level. The data suggest that the device can be used successfully for organic compounds with volatilities greater than that of p-dichlorobenzene.

Air Pollutants↗
PubMedDate not supplied

A canister-based method for collection and GC/MS analysis of volatile organic compounds in human breath.

A method previously used for collection and analysis of volatile organic compounds (VOCs) in human whole breath was modified to encompass compounds with higher vapor pressures. A VOC spirometer was designed for field studies of environmentally exposed populations with breath concentrations in the microgram/m3 (ppb) range. The VOC spirometer was configured for sample collection and GC/MS analysis of breath samples using stainless steel canisters. Recoveries of 17 analytes in synthetic breath through the spirometer at 4 and 21 degrees C were generally above 80% except for n-dodecane which demonstrated poor recoveries at the lower temperature. The maximum sample volume available for analysis during recovery studies with natural breath was 100 mL because of copious quantities of CO2 present. Decay curves showing the breath elimination of 1,1,1-trichloroethane and benzene from a man after exposure to consumer products demonstrates the utility of the method.

Breath Tests↗
PubMedDate not supplied

Evaluation of internet-based clinical decision support systems.

BACKGROUND: Scientifically based clinical guidelines have become increasingly used to educate physicians and improve quality of care. While individual guidelines are potentially useful, repeated studies have shown that guidelines are ineffective in changing physician behavior. The Internet has evolved as a potentially useful tool for guideline education, dissemination, and implementation because of its open standards and its ability to provide concise, relevant clinical information at the location and time of need. OBJECTIVE: Our objective was to develop and test decision support systems (DSS) based on clinical guidelines which could be delivered over the Internet for two disease models: asthma and tuberculosis (TB) preventive therapy. METHODS: Using open standards of HTML and CGI, we developed an acute asthma severity assessment DSS and a preventative tuberculosis treatment DSS based on content from national guidelines that are recognized as standards of care. Both DSS's are published on the Internet and operate through a decision algorithm developed from the parent guidelines with clinical information provided by the user at the point of clinical care. We tested the effectiveness of each DSS in influencing physician decisions using clinical scenario testing. RESULTS: We first validated the asthma algorithm by comparing asthma experts' decisions with the decisions reached by nonpulmonary nurses using the computerized DSS. Using the DSS, nurses scored the same as experts (89% vs. 88%; p = NS). Using the same scenario test instrument, we next compared internal medicine residents using the DSS with residents using a printed version of the National Asthma Education Program-2 guidelines. Residents using the computerized DSS scored significantly better than residents using the paper-based guidelines (92% vs. 84%; p <0.002). We similarly compared residents using the computerized TB DSS to residents using a printed reference card; the residents using the computerized DSS scored significantly better (95.8% vs. 56.6% correct; p<0.001). CONCLUSIONS: Previous work has shown that guidelines disseminated through traditional educational interventions have minimal impact on physician behavior. Although computerized DSS have been effective in altering physician behavior, many of these systems are not widely available. We have developed two clinical DSS's based on national guidelines and published them on the Internet. Both systems improved physician compliance with national guidelines when tested in clinical scenarios. By providing information that is coupled to relevant activity, we expect that these widely available DSS's will serve as effective educational tools to positively impact physician behavior.

Asthma↗
PubMedDate not supplied

The identification of polar organic compounds found in consumer products and their toxicological properties.

Exposure to volatile organic compounds (VOCs) in the indoor environment has received substantial research attention in the past several years, with the goal of better understanding the impact of such exposures on human health and well-being. Many VOCs can arise from consumer products used within the indoor environment. The VOCs emitted from five representative consumer products were collected onto Tenax-GC and subjected to thermal desorption and analysis by gas chromatography, in combination with low-resolution mass spectrometry (MS), high-resolution MS, and matrix-isolation Fourier transform infrared spectroscopy for structural characterization. An emphasis was placed on the polar organic compounds often used to provide fragrance in these products. The structures of a number of these compounds were confirmed, and an electronic literature search was carried out on them to determine any known toxic properties. The search revealed that many of the VOCs possess toxic properties when studied at acute, relatively high-level exposures. In addition, toxic effects were reported for a few of the chemicals, such as benzaldehyde, alpha-terpineol, benzyl acetate, and ethanol, at relatively low dose levels of 9-14 mg/kg. In general, the data were unclear as to the effect of chronic, low-level exposures. The widespread use of such chemicals suggests that the health effects of chronic exposures need to be determined. Validated analytical methods for the quantitative characterization of polar organic compounds at low concentrations will be required to make such work possible.

Air Pollution, Indoor↗
PubMedDate not supplied

Identification of 1,3-butadiene, benzene, and other volatile organics from wok oil emissions.

As part of a program to determine the underlying factors responsible for genotoxicity and perhaps lung cancer risk in Chinese women, we qualitatively identified the volatile components emitted during the heating of cooking oils to 265 degrees C. 1,3-Butadiene, benzene, and a series of aldehydes, olefins, and saturated hydrocarbons were elucidated in vapors from Chinese rapeseed oil. On a relative basis, the intensity of 1,3-butadiene vapors from this were 15.7-, 6.3-, and 1.4-fold greater than in the vapors from peanut, soybean, and Canola oils, respectively. Thus, the Chinese rapeseed oil yielded a higher emission rate of 1,3-butadiene than the other three oils investigated. The benzene formation rate followed a similar trend, i.e., its intensity in Chinese rapeseed oil was 14-, 6.6-, and 1.7-fold greater than in vapors from peanut, soybean, and Canola oils, respectively.

Arachis↗
PubMedDate not supplied

Temporal variability of benzene exposures for residents in several New Jersey homes with attached garages or tobacco smoke.

The U.S. Environmental Protection Agency's (EPA) previous TEAM studies of personal exposure to VOCs for 700 residents in several U.S. cities found that indoor air concentrations were often higher than outdoor levels. Several potential sources of benzene exposure were identified, including environmental tobacco smoke and materials or activities associated with attached garages. Indoor, personal, and outdoor monitoring was conducted at eleven New Jersey homes over multiple 12-hr monitoring periods. One study objective was to assess the impact of attached garages on human exposure to benzene and the variability of benzene exposure across time. Benzene was also measured in several homes inhabited by smokers and in homes without known combustion sources for comparative purposes. At homes with a garage or environmental tobacco smoke, mean indoor and personal benzene concentrations were two to five times higher than outdoor levels at all but one home. Mean personal exposures ranged from 8 to 31 micrograms/m3. Indoor/outdoor ratios were calculated and ranged from 0.8 to 11. Benzene levels in the four garages ranged from 3 to 196 micrograms/m3 and usually were higher than either indoor living areas or personal levels. Multi-zone air exchange rates were measured, and benzene source strengths in each zone were estimated. Garage source strength estimates for benzene ranged from 310 to 52,000 micrograms/h. The mass transfer of benzene from sources in the garage to home living areas was also large in three of the homes, ranging from 730 to 26,000 micrograms/h. Materials or activities in the garage were a source of benzene exposure for the residents in these three homes. Large temporal variations (factors of 2 to 30) were observed in indoor and personal benzene concentrations, indoor/outdoor ratios, and source strengths over the six or ten monitoring periods at each home. Changes in outdoor air benzene levels were an underlying factor in changing exposure levels, with indoor sources further elevating indoor air levels and personal exposures.

Air Pollution, Indoor↗
PubMedDate not supplied

Particle Total Exposure Assessment Methodology (PTEAM) study: distributions of aerosol and elemental concentrations in personal, indoor, and outdoor air samples in a southern California community.

Particle concentrations were measured for a probability-based sample of 178 nonsmoking individuals aged 10 or older residing in Riverside, California, in the fall of 1990. Two 12-hr personal-exposure PM10 samples were obtained for each participant, along with fixed-location PM10 and PM2.5 indoor and outdoor air samples at their residences. The particle samples were also analyzed via X-ray fluorescence (XRF) to determine elemental concentrations for selected elements, including some toxic metals, crustal elements, and combustion- and industrial-source related elements. About 25% of the target population was estimated to have 24-hr personal exposures to PM10 that exceeded the national ambient air concentration standard of 150 micrograms/m3. The daytime personal exposure levels (median of 130 micrograms/m3) tended to exceed both indoor and outdoor levels by about 50%; nighttime personal exposure levels were lower and were only slightly higher than nighttime indoor levels. Several possible reasons for the elevated daytime personal PM10 levels (relative to indoor levels) are considered. Certain activities such as house cleaning and smoking were found to be associated with elevated personal exposure levels.

Aerosols↗