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Biomedical subjects

G T Smith

Publications and source records attributed to G T Smith.

At least 91 records · Page 5Linked to original sources
PubMed1990

Emergence of alcohol expectancies in childhood: a possible critical period.

Previous investigations with adolescents (aged 12-19) have shown alcohol-related expectancies to develop in childhood prior to significant drinking experience and to covary directly with drinking behavior. To chart the development of alcohol expectancies in children as young as age 6, a procedure was developed to be as independent as possible of age-related variation in reading and language development. This instrument was administered to 114 elementary school children of both genders, distributed across grades 1 to 5. Psychometric analysis provided evidence of the test's reliability and validity. Evaluation of the developmental pattern produced two primary findings: (1) there was an overall trend of increasingly positive expectancies with age; and (2) strikingly, the bulk of the increase was observed in the third and fourth grades. Children's expectancies may be less differentiated than adolescent or adult expectancies. These findings suggest that the precursors for later alcohol use and abuse are formed in childhood and that prevention efforts may need to begin as early as third grade.

Age Factors↗
PubMed1989

Using alcohol expectancies to predict adolescent drinking behavior after one year.

An accumulating literature has shown the influence of childhood experiences associated with alcohol use on later drinking practices. Recent studies have suggested that alcohol-related expectancy may serve as an intervening variable to connect these early experiences with the later, proximal decision to drink when opportunities for actual alcohol consumption arise. Those studies, however, have collected expectancy and drinking data concurrently, whereas the present study for the first time reports on the power of expectancies measured in early adolescents (seventh and eighth grades) to predict self-reported drinking onset and drinking behavior measured a full year later. Results show that five of seven expectancy scores readily discriminated between nonproblem drinkers and those subsequently beginning problem drinking and accounted for a large portion of the variance in a continuous quantity/frequency index and a problem drinking index. The strength of these timelagged relations strengthens the case for inferring that expectancies have causal power on drinking behavior and suggests prevention strategies.

Adolescent↗
PubMed1989

The visual evoked potential in acute primary angle closure glaucoma.

Visual evoked potentials (VEPs) were elicited from 29 patients who had experienced a previous attack of acute primary angle closure glaucoma. The VEPs were shown to be abnormal in at least one of the measures (latency, amplitude, contrast threshold, or slope) in 72.4% of affected eyes, whereas only 41.4% indicated obvious optic nerve damage. It is notable that 48.1% of fellow eyes with no (known) history of acute pressure rise also showed some form of VEP abnormality. The possible pathophysiological mechanisms operating in both affected and fellow eyes are discussed. It is concluded that, despite the presence of possible artefactual influences, the results probably reflect the presence of primary angle closure glaucoma.

Adult↗
PubMed1989

13N ammonia myocardial imaging at rest and with exercise in normal volunteers. Quantification of absolute myocardial perfusion with dynamic positron emission tomography.

Positron emission tomography (PET) was applied to the measurement of myocardial perfusion using the perfusion tracer 13N-labeled ammonia. 13N ammonia was delivered intravenously to 13 healthy volunteers both at rest and during supine bicycle exercise. Dynamic PET imaging was obtained in three cross-sectional planes for 10 minutes commencing with each injection. The left ventricle was divided into eight sectors, and a small region of interest was assigned to the left ventricular blood pool to obtain the arterial input function. The net extraction of 13N ammonia was obtained for each sector by dividing the tissue 13N concentration at 10 minutes by the integral of the input function from the time of injection to 10 minutes. With this approach for calculating net extractions, rest and exercise net extractions were not significantly different from each other. To obviate possible overestimation of the true 13N ammonia input function by contamination by 13N-labeled compounds other than 13N ammonia or by spillover from myocardium into blood pool, the net extractions were calculated using only the first 90 seconds of the blood and tissue time-activity curves. This approach for calculating net extractions yielded significant differences between rest and exercise, with an average ratio of exercise to rest of 1.38 +/- 0.34. Nonetheless, the increase was less than predicted from the average 2.7-2.8-fold increase in double product at peak exercise or the 1.7-fold increase in double product at 1 minute after exercise. However, when the first 90 seconds of dynamic data were fit with a two compartment tracer kinetic model, average perfusion rates of 0.75 +/- 0.43 ml/min/g at rest and 1.50 +/- 0.74 ml/min/g with exercise were obtained. This average increase in perfusion of 2.2-fold corresponded to similar average increases in double product. Thus, the noninvasive technique of PET imaging with 13N ammonia shows promise for future applications in determining absolute flows in patients with coronary artery disease.

Adult↗
PubMed1988

A case of ameloblastic carcinoma with pulmonary metastases.

A case initially thought to be ameloblastoma of the mandible which showed rapid local destruction and was demonstrated to have three pulmonary metastases post mortem 18 months after the first symptoms in the mandible. The diagnosis is now considered to be ameloblastic carcinoma. The difficulties in histological diagnosis and varying classifications of malignant odontogenic tumours is noted.

Aged↗
PubMed1987

The economics of essential drug programmes.

Public health measures are still the most important factor in improving Third World health. However, medicines have an important part to play, and it is now generally agreed that for the very poor populations medicines should be restricted to those on an 'essential drugs list' and should be made available as cheaply as possible. A major problem arises, however, in trying to stop these very cheap supplies 'leaking' back into the private sector, and being sold to the public at high prices. This is particularly true as many countries have a large rich urban elite as well as a much larger poor rural population. It is also important to recognise that research into Third World diseases must be financed by profits on the sale of medicines in advanced countries. A 'cheap drug' policy in rich countries can be very harmful to the long-term health even of the less developed countries.

Developing Countries↗
PubMed1984

Evaluation of enzymic assay for paracetamol: clinical and forensic experiences.

The performance of the enzymic paracetamol assay (Cambridge Life Science, UK) was evaluated for use in clinical and forensic analyses and compared with gas-liquid chromatography and EMIT (Syva) systems. It was found to be precise, accurate and rapid for the analysis of paracetamol in serum, with a possible application for the quantitative screening of post mortem blood.

Journal Article↗
PubMed1984

Error analysis of the double-integral method for calculating brain blood perfusion from inert gas clearance data.

A single-photon dynamic computer-assisted tomograph (DSPECT) has been built and is currently being used to evaluate regional cerebral blood perfusion in patients and volunteers. A computer simulation of the system was created to analyze the effects of data collection, Poisson noise, attenuation compensation, and the reconstruction technique now employed in the DSPECT. Several methods of attenuation compensation were used to generate perfusion images from both ideal and noisy data. The results indicate that the mean perfusion is calculated to within 10.4% accuracy for all perfusion rates in a region of interest if attenuation correction is used. Without attenuation correction, perfusions are underestimated by as much as 27%. The three correctors tested have different effects on the calculated perfusion value, depending on the location of the region of interest in the picture. The algorithm introduces random noise that is proportional to both the random error in the input data and the perfusion rate. Air-curve delay errors result in inaccuracies in the final perfusion picture that are proportional to perfusion rate. Physiological values (0.8-1.5) of the partition coefficient cause overestimation of both gray (0-34%) and white (7-67%) matter perfusion values. Compton scatter and collimator effects were not addressed in this study.

Brain↗
PubMed1984

Anatomic localization of cholecystokinin receptors to the pyloric sphincter.

In an effort to identify target sites within the gastrointestinal (GI) tract through which cholecystokinin (CCK) may exert its gastric inhibitory and satiety effects, the distribution of CCK receptors was mapped in the stomach and small bowel by in vitro radiography utilizing 125I-labeled Bolton-Hunter CCK-33. Specific receptor binding was localized to the circular smooth muscle layer of the pyloric sphincter. Negligible binding was observed in the oblique, circular, or longitudinal muscle layers of other GI levels. Moderate nonspecific binding was associated with mucosal tissue in all gastric sections. The restriction of CCK receptors to the circular smooth muscle of the pyloric sphincter suggests this location as the site through which CCK inhibits gastric emptying. Gastric distension secondary to this inhibition may be the mechanism for CCK-induced satiety.

Animals↗
PubMed1983

Ulceration of the hand secondary to a radial arteriovenous fistula: a model for varicose ulceration.

A patient in whom a radial arteriovenous fistula was constructed in preparation for haemodialysis subsequently developed ulceration on the dorsum of the hand. The lesion failed to heal despite antibiotic treatment, and so the fistula was closed. The lesion healed within three weeks. Subsequent construction of a fistula at the right wrist was followed 12 months later by the development of similar ulceration of the right hand. This complication of arteriovenous fistulas is similar to varicose ulceration of the leg and provides a unique opportunity to study the effects of sustained venous hypertension on the skin.

Arteriovenous Shunt, Surgical↗
PubMed1983

An electrocardiographic model of myocardial ischemic injury.

Previous electrocardiographic models of myocardial ischemic injury have assumed that transmembrane potential changes are uniform throughout a region of ischemia such that injury currents arise exclusively at the boundary between normal and ischemic myocardium. In such models, the distribution and amplitude of ST segment deflections are considered to arise from a polarized surface interfacing normal and ischemic myocardium. This concept in modeling ischemic injury was derived from the application of principles of electric field theory which had been successfully applied previously to ventricular activation in which QRS potentials are considered to arise from polarized surfaces representing the relatively narrow interfaces between depolarized and nondepolarized myocardium. The present paper outlines the limitations of modeling ischemic injury as a polarized surface in terms of the failure of the predictions of such a model to be supported by the experimentally observed: 1) distribution and relative amplitude of epicardial ST segment elevation overlying a region of ischemia; 2) directional changes in epicardial ST segment elevation that occur with changes in the size of an ischemic region; and 3) nonuniform distribution of transmembrane potential changes which occur within a region of ischemia. A new electrocardiographic model of ischemic injury is formulated which accounts for the nonuniform distribution of transmembrane potential changes which occur throughout a region of ischemia. The model accurately describes experimental observations regarding ST segment deflections which had remained inconsistent with previous models.

Coronary Disease↗