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Biomedical subjects

G C Miller

Publications and source records attributed to G C Miller.

At least 19 recordsLinked to original sources
PubMed2004

Understanding the tropospheric transport and fate of agricultural pesticides.

Many field monitoring studies have indicated the substantial role of the troposphere as both a sink and transport medium for pesticides. At the same time, this is the least studied and understood environmental compartment in regards to pesticide fate. Although the fundamental principles behind volatilization and tropospheric reactivity are well understood, it is becoming increasingly apparent that the ability to quantitatively measure flux and reaction rates in the air will continue to pose problems for researchers. To date, most deterministic models that try to simulate real world conditions generally fail to provide tropospherically relevant flux and reaction rates because it is virtually impossible to scale down all possible interactions occurring in a near-infinite reservoir. Better field methods for determining flux are emerging and more ambient air monitoring studies are being conducted. This growing database of information, together with an understanding of physicochemical properties and use of expert systems, has increased the predictive capability for estimating volatilization flux of pesticides. Unfortunately, there are very limited environmental data on the tropospheric reaction rates of pesticides, and more experimental studies using semivolatile to low-volatility pesticides or their more volatile homologues are required to validate existing structure-activity relationship (SAR) model predictions. The development of new analytical strategies using elevated temperatures for assessing semivolatile to low-volatility pesticide reaction rates and products may provide an alternative approach to the need for controlled environmental temperature data. Recent international workshops organized by the Health Council of The Netherlands for developing uniform approaches for assessing exposure risks to pesticides in air exemplify efforts to synchronize flux with environmental fate information for determining human health and ecological risks. When more detailed pesticide information is desired, especially in high-use agricultural areas, where exposure to humans and nontarget ecological communities is a major concern, field flux measurements and downwind monitoring, together with experimental fate studies, should be considered. The integration of models, empirical testing, and real world monitoring will provide the ultimate safety net needed for assessing exposure risks to airborne pesticides.

Atmosphere↗
PubMed2003

Predictors of the prevalence of bacterial STI among young disadvantaged Indigenous people in north Queensland, Australia.

OBJECTIVE: To identify sexually transmitted infections in rural and remote Indigenous communities in north eastern Australia and examine factors that may influence prevalence. METHODS: A cross sectional survey of 26 Aboriginal and Torres Strait Islander communities in northern Queensland was carried out. 3313 people (2862 Indigenous) aged 15 years and over resident in participating communities during the period March 1998 to December 2000. The main outcome measures were community and population prevalence of chlamydia and gonorrhoea and independently associated risk factors. RESULTS: A total of 238 cases of chlamydia, 66 cases of gonorrhoea, and 37 cases of co-infection were detected among Indigenous participants. Prevalence of chlamydia and/or gonorrhoea ranged from 23.0% among 15-19 year olds to 3.5% among those 40 years and older. In the adjusted analysis younger age, female sex, lower socioeconomic status, the use of alcohol and tobacco, and the structure of community health services were independently associated with a higher prevalence of bacterial STI. CONCLUSION: This study highlights the need for improved STI control in north Queensland Indigenous communities through strategies to improve the reach and accessibility of primary healthcare services.

Adolescent↗
PubMed2000

Use of stable tracer studies to evaluate pesticide photolysis at elevated temperatures.

New methods were developed to determine photolysis rates of medium-weight pesticides in the gas phase using elevated air temperatures and solid-phase microextraction (SPME). A 57-L glass chamber was constructed that utilized collimated xenon arc irradiation that could heat chamber air to increase the amount of pesticide in the gas phase. Gas-phase photolysis rates were determined at various air temperatures by comparing the rate of loss of each of the tested pesticides to a photochemically stable tracer, hexachlorobenzene. Interval sampling of gas-phase constituents was performed using SPME immediately followed by GC-ECD or GC-MSD analysis. The two pesticides under examination were the dinitroaniline herbicide trifluralin and the organophosphorus insecticide chlorpyrifos. The gas-phase photolysis for trifluralin was found to be rapid with half-lives of 22-24 min corrected for sunlight. These results were comparable to photochemical lifetime estimates from other investigators under sunlight conditions. Elevating temperatures from 60 to 80 degrees C did not affect photolysis rates, and these rates could be extrapolated to environmental temperatures. From 60 to 80 degrees C, gas-phase chlorpyrifos photolysis lifetimes were observed to range from 1.4 to 2.2 h corrected for sunlight and will thus be important together with hydroxyl radical reactions for removing this substance from the atmosphere. At these elevated temperatures, pesticides and tracer compounds were found to be substantially in the gas phase, and possible effects on reaction rates from wall interactions were minimized.

Chromatography, Gas↗
PubMed2000

Reactivity of certain organophosphorus insecticides toward hydroxyl radicals at elevated air temperatures.

Methods were developed to determine OH reaction rates for medium-weight organophosphorus pesticides in the gas phase. A 57-L chamber was constructed that utilized xenon arc irradiation (>290 nm) to photolyze the OH precursor, methyl nitrite. Experiments were performed at elevated temperatures ranging from 60 to 80 degrees C to minimize wall sorption. Solid-phase microextraction (SPME) sampling of the gas phase was employed to assess the simultaneous rate of loss of the pesticides in relation to the rate of loss of two reference substances with known OH rate constants. An internal gas-phase standard (hexachlorobenzene), relatively stable to hydroxyl radicals, was used to assess other processes, which included dilution and wall sorption. The relative reaction rates of the organophosphorus insecticides, diazinon and chlorpyrifos, when compared to reference compounds, were unaffected by various air temperatures between 60 and 80 degrees C. Although both insecticides were expected to react at similar rates on the basis of structural activity model predictions, diazinon reacted 3 times more rapidly than chlorpyrifos and gave estimated environmental OH half-lives of 0.5 and 1.4 h, respectively. The degree of sorption onto the chamber walls was minimal and similar for each of the compounds examined. Experimental gas-phase determinations at elevated temperatures may provide important information that can be used when in the assessment of the potential of airborne pesticide risks to nontarget and ecologically sensitive areas.

Hot Temperature↗
PubMed1998

Analysing potential harm in Australian general practice: an incident-monitoring study.

OBJECTIVE: To collect data on incidents of potential or actual harm to general practice patients and to evaluate the possible causes of these incidents. DESIGN: An observational study of incidents of potential harm based on a modified critical incidents technique. A non-random sample of general practitioners (GPs) anonymously submitted incident reports contemporaneously. SETTING AND PARTICIPANTS: Australian general practices between October 1993 and June 1995. During the study period, 324 GPs participated at some time. MAIN OUTCOME MEASURES: GP-reported free-text descriptions of incidents and structured responses for preventability, potential for harm, immediate consequences, predicted long-term outcomes, type of incident, contributing factors, mitigating factors, and additional resource use. RESULTS: 805 incidents were reported--76% were preventable; 27% had potential for severe harm. No long term harm was predicted for 66% of incidents. Incidents could relate to pharmacological management (51 per 100 incidents), nonpharmacological management (42 per 100 incidents), diagnosis (34 per 100 incidents) or equipment (5 per 100 incidents). The most common contributory factors were poor communication between patients and healthcare professionals and actions of others (23 per 100 incidents each) and errors in judgement (22 per 100 incidents). CONCLUSION: Human error and preventable system problems were identified. The incident monitoring technique provided useful data which could be applied to incident prevention strategies.

Adolescent↗
PubMed1997

Collecting data on potentially harmful events: a method for monitoring incidents in general practice.

OBJECTIVE: The prediction and subsequent prevention of errors, which are an integral element of human behaviour, require an understanding of their cause. The incident monitoring technique was developed in the study of aviation errors in the Second World War and has been applied more recently in the field of anaesthetics. This pilot study represents one of the first attempts to apply the incident monitoring technique in the general practice environment. METHOD: A total of 297 GPs across Australia anonymously reported details of unintended events which harmed or could have harmed the patient. Reports were contemporaneously recorded on prepared forms which allowed a free text description of the incident, and structured responses for contributing and mitigating factors, immediate and long-term out-comes, additional costs etc. RESULTS AND DISCUSSION: The first 500 reports were analysed using both of qualitative and quantitative methods and a brief overview of results is presented. The methodological issues arising in the application of this technique to such a large, widely spread profession, in which episodes of care are not necessarily confined to a single consultation, are discussed. This study demonstrated that the incident monitoring technique can be successfully applied in general practice and that the resulting information can facilitate the identification of common factors contributing to such events and allow the development of preventive interventions.

Australia↗
PubMed1995

A new drug classification for computer systems: the ATC extension code.

During the testing of the Read Clinical Codes in general practice medical records in Australia, it became apparent that the pharmaceutical section of the codes was not applicable in a country with different brand names, pack sizes and forms. For pharmacoepidemiological studies, structured classification of both morbidity and pharmaceuticals is required for meaningful analysis. The search for a suitable pharmaceutical classification proved fruitless. While the Australian Government has recently adopted the Anatomical Therapeutic Chemical (ATC) Classification as the national standard, this only classifies drugs to the generic level. None of the extended coding systems used in hospital pharmacies, by community pharmacists, or by Government are hierarchically structured. The extension code we have developed, is an analytical algorithm comprising independent fields for: dosage; strength; manufacturer and brand; and pack size. The codes within each field are also structured in a hierarchical manner. The result is an extension code of 21 digits, each digit or group of digits having a meaning. The structure of this classification will allow analysis of any aspect of the drug prescribed. This system is designed for computerised entry of text and transparent coding of the data--not for manual coding on paper nor manual code entry to the computer.

Algorithms↗
PubMed1994

The adventitia and atherogenesis: removal initiates intimal proliferation in the rabbit which regresses on generation of a 'neoadventitia'.

Removal of the carotid artery adventitia from rabbits induced the formation of an intimal hyperplastic lesion. In rabbits fed a normal diet, the lesion (measured as the intimal:medial ratio) was maximal by day 14 (0.456 +/- 0.079, n = 5, P < 0.01) and thereafter, regressed towards control dimensions (0.037 +/- 0.003, n = 14) by day 28 (0.080 +/- 0.025, n = 7, P = 0.14). In rabbits fed a high cholesterol diet, the lesion was again maximal by day 14 (0.376 +/- 0.056, n = 8, P < 0.01). Although some regression was seen, the lesion persisted to day 42 (0.272 +/- 0.052, n = 8, P < 0.01). Electron microscopy and immunocytochemistry showed two types of lesion, (a) smooth muscle cell predominant on normal diet and, (b) macrophage predominant on high cholesterol diet. Smooth muscle cell predominant lesions underwent almost complete regression, whereas macrophage predominant lesions persisted. We propose that lesion formation may be initiated following the development of arterial wall hypoxia, secondary to excision of the adventitial vasa vasorum. Furthermore, we have devised a novel method to restore a highly vascular 'neoadventitia' to an artery whose adventitia has previously been removed, using loosely placed PVC tubing. We suggest this 'neoadventitia' was able to inhibit the formation of an intimal hyperplastic lesion and to promote regression of an already established lesion by restoring arterial wall oxygenation.

Animals↗
PubMed1992

Photoactivation of hypericin generates singlet oxygen in mitochondria and inhibits succinoxidase.

Photosensitized inhibition of mitochondrial succinoxidase by hypericin was measured in vitro and found to be drug-dose, light-dose, and wavelength dependent. Singlet oxygen generation, monitored using the singlet oxygen trap tetramethylethylene, and oxygen consumption in isolated mitochondria sensitized by hypericin were also light-dose and wavelength dependent. Unequivocal evidence for the generation of singlet oxygen was obtained using kinetic isotope ratios of products from the reaction between singlet oxygen and geminally deuterated tetramethylethylene. An action spectrum for the inhibition of succinoxidase was measured at wavelengths between 400 and 700 nm and found to parallel the recorded visible absorption spectrum of hypericin in isolated mitochondria. The greatest singlet oxygen generation, oxygen consumption, and succinoxidase inhibition occurred with white light or 600 nm irradiation. These data are consistent with a type II singlet-oxygen-mediated mechanism for hypericin induced photosensitized inhibition of mitochondrial succinoxidase.

Animals↗
PubMed1990

Epidemic oral ulceration in largemouth bass (Micropterus salmoides) associated with the leech Myzobdella lugubris.

An epidemic of severe ulcerations of the tongue and buccal cavity was documented in subadult and adult largemouth bass (Micropterus salmoides) from Currituck Sound, North Carolina (USA). Other external clinical signs were not present. Between November 1986 and May 1987, reports from fishermen indicated that as many as 90% of large (greater than 300 mm total length) bass were affected. Older fish were the most commonly involved. The leech, Myzobdella lugubris (= Illinobdella moorei), was consistently present on or near the lesions. Lesions were heavily infected with several different bacteria that were apparently secondary invaders. Stressful (high) salinity or an interruption in the normal migratory cycle of the parasite are suggested as possible causes for this condition in these bass.

Animals↗
PubMed1989

Isolation, characterization and determination of trace organic impurities in FD&C red no. 40.

The unsulfonated aromatic amine 4-nitro-p-cresidine (2-methoxy-5-methyl-4-nitrobenzenamine) was identified as an impurity in the regulated color additive FD&C Red. No. 40. The compound was isolated from the water-soluble color by extraction with chloroform, followed by transfer of the free amines to acid solution and subsequent separation by reversed-phase high-performance liquid chromatography. The 4-nitro-p-cresidine was collected and then identified by gas chromatography-mass spectrometry. The levels of 4-nitro-p-cresidine as well as p-cresidine and aniline were determined in commercial batches of FD&C Red. No. 40.

Aniline Compounds↗
PubMed1986

Microcephaly, short stature, and developmental delay associated with a chemotactic defect and transient hypogammaglobulinaemia in two brothers.

Two brothers presented with unusual facial features, microcephaly, developmental delay, and severe postnatal growth retardation. They both developed eczema in infancy and have had recurrent infections. Additional physical findings in both boys included hypogonadism, flexion contractures, hypoplastic patellae, and scoliosis. Their facial similarity was striking with sloping foreheads, beaked noses, large, protruding ears, and micrognathia. Low levels of serum gammaglobulins and defective chemotaxis were present in both boys in infancy. The hypogammaglobulinaemia was transient and improved, reaching normal levels by 3 1/2 years and 15 months, respectively. Defective chemotaxis and recurrent infections have persisted to the present. Both parents were normal. The mode of inheritance was not clear, as both X linked and autosomal recessive patterns were possible. Although patients with congenital malformations who also had immunodeficiency have previously been reported, immune system abnormalities, especially those of a transient nature, may frequently go unrecognised.

Abnormalities, Multiple↗
PubMed1985

Factory fixation of an arc curve into brachial coronary artery catheters of the manipulative type: a new curve for Sones' type catheters.

Advantage was found in factory fixing an approximation of the curve that has long been hand-formed at the tableside by angiographers using the manipulative type brachial-coronary technique. It consists of a 7 cm arc of a circle of 10 cm diameter. Used in 68 different patients, it was found to definitely facilitate and speed selective cannulation of the coronary artery ostia as compared to previous curves.

Adult↗