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Biomedical subjects

R Barker

Publications and source records attributed to R Barker.

At least 37 records · Page 2Linked to original sources
PubMed1998

Respiratory insufficiency due to high anterior cervical cord infarction.

OBJECTS AND METHODS: Respiratory dysfunction may occur as a result of lesions in the upper cervical spinal cord disturbing the descending pathways subserving automatic and volitional ventilatory control. Four patients are described who presented with acute respiratory insufficiency caused by infarction of the anterior portion of the upper cervical cord due to presumed anterior spinal artery occlusion. RESULTS: Two patients presented after respiratory arrests; they were ventilated and there was no automatic or volitional respiratory effort. Both had signs of an extensive anterior spinal cord lesion at the C2 level and this was confirmed by MRI. One patient presented with a C4 infarction and required ventilation for three months. Ventilatory recovery was characterised by the development of an automatic respiratory pattern. The fourth patient required ventilation for two months after infarction at the C3 level. On attempted weaning he had prolonged periods of hypoventilation and apnoea during inattention and sleep indicating impairment of automatic respiratory control. CONCLUSION: Infarction of the spinal cord at high cervical levels may be due to fibrocartilaginous embolism and involvement of the descending respiratory pathways may occur. Extensive lesions at C1/2 cause complete interruption of descending respiratory control leading to apnoea. Partial lesions at C3/4 cause selective interruption of automatic or voluntary pathways and give rise to characteristic respiratory patterns. The prognosis depends on the level and extent of the lesion.

Adult↗
PubMed1997

Hypnosis and event-related potential correlates of error processing in a stroop-type paradigm: a test of the frontal hypothesis.

A model of frontal inhibition in hypnosis was elucidated by examining with cortical evoked potentials error negativity and positivity in 23 low versus medium/high hypnotisables during a perceptual task which included trials with conflicting stimulus information. In susceptible subjects the number of correct responses was found to be smaller for trials with incongruent stimulus information with hypnosis when compared with baseline. While the early negative wave to incorrect responses tended to be higher in susceptible subjects, this wave was no longer followed by a late positivity, posited to reflect a failure to process further the error-related information. The results with hypnosis are interpreted as a failure of context updating without a global deficit in supervisory attention.

Adult↗
PubMed1997

Population change between 1986 and 1996 in Australia: population numbers, components of change and age profiles.

"This paper represents a preliminary analysis of the release of 1996 Census-based ERP [estimates of resident population] by examining regional population shifts and components of population change in Australia between 1986 and 1996.... With particular reference to Queensland, this paper also examines changes in the age profiles of regional populations over the decade to June 1996. Changes in the population structure of Queensland's growth regions are compared with those of regions experiencing population decline."

Age Distribution↗
PubMed1995

Patient entries in the electronic medical record: an interactive interview used in primary care.

We describe the development, implementation, and use of a computer-administered patient interview, the Health History Interview, by over 300 new patients in a primary care practice at Boston's Beth Israel Hospital. The interview has been well accepted by patients and rated positively by providers. It electronically captures clinical information directly from patients for use during their initial encounter with a provider. It facilitates aggregate analysis of clinical data for quality improvement efforts, such as aiming preventive medicine interventions at identified problem areas within the clinic. Expectations management has been an important task throughout the project. Increasing use of the interview beyond the 30-40% of new patients who have taken it will require greater communication with patients, greater convenience to patients and providers, and more evidence of the clinical, administrative, and research benefits of the technique. Most important, full implementation will require fundamental changes in physician practice habits and patterns of communication between patients and the health care system, as well as clearly demonstrated cost-benefit improvements through the use of these tools.

Adult↗
PubMed1994

Ibotenic acid lesions of the striatum reduce drug-induced rotation in the 6-hydroxydopamine-lesioned rat.

Lesions of the dopaminergic nigrostriatal tract produce a range of motor and sensorimotor deficits. One of the simplest and most reliable is the rotational response of the animal following activation with drugs that stimulate the dopaminergic network, most notably amphetamine and apomorphine. Consequently, the rotation test has been extensively used in assessing the success of treatments designed to restore dopaminergic function, including neural transplants. The present study investigates whether rotation induced by 6-hydroxydopamine lesions of the nigrostriatal bundle in rats is modified by additional lesions in the neostriatum. It was found that apomorphine-induced rotation can be reduced by ibotenic acid lesions of the dopamine-deafferented striatum, and that the extent of the reduction was proportional to the size of the lesions. In contrast, such lesions produced a non-significant reduction in amphetamine-induced rotation, although the correlation between the extent of the reduction and the size of the lesion was again apparent. Since the pattern of change was similar in direction, albeit smaller in magnitude, than the previously reported effects of intrastriatal transplantation in rats with similar nigrostriatal lesions, rotation tests alone do not provide an unequivocal test of graft survival and function.

Amphetamine↗
PubMed1993

Immunohistochemical identification of rat adrenal cortical tissue in situ, in vitro, and in intracerebral adrenal grafts.

We have used a polyclonal antibody to the biosynthetic adrenocortical enzyme, 3-beta-hydroxysteroid dehydrogenase, to demonstrate rat adrenal cortical tissue in situ, in vitro, and in intracerebral adrenal suspension grafts. This technique provides a means of identifying the degree to which adrenal medulla grafts are in practice contaminated by adrenal cortical cells and allows analysis of the extent to which the presence of cortical cells influences the viability, differentiation, and functional efficacy of intracerebral adrenal grafts.

3-Hydroxysteroid Dehydrogenases↗
PubMed1993

A selective tachykinin receptor agonist promotes differentiation but not survival of rat chromaffin cells in vitro.

Rat chromaffin cells display phenotypic plasticity postnatally. In the presence of glucocorticoids, they retain a chromaffin cell phenotype, whilst in the presence of nerve growth factor and the absence of glucocorticoids they adopt a sympathetic neuronal phenotype. The tachykinins have some of the characteristics of a neurotrophic factor and are present in the form of a substance P afferent input in the rat adrenal medulla. We investigated the effects of stable NK1 and NK2 tachykinin receptor agonists, Ava[L-Pro,N-Me-Leu-10]SP7-11 (GR73632) and [Lys-3,Gly-8,R-Lac-Leu-9]NKA3-10 (GR64349), respectively, on the survival and phenotype of P5-7 rat chromaffin cells in vitro. GR73632 promoted neurite outgrowth, characteristic of the sympathetic neuronal phenotype, in the absence of NGF and glucocorticoids, but was without effect on survival after 2 weeks in culture. GR64349 was without effect.

Adrenal Glands↗
PubMed1993

Comparison of the pharmacokinetics and pharmacodynamics of the aldose reductase inhibitors, AL03152 (RS), AL03802 (R), and AL03803 (S).

The pharmacokinetics of AL03152 (RS) and its enantiomers, AL03802 (R) and AL03803 (S), were studied in the Sprague-Dawley rat following intravenous bolus administration. The enantiomers had differing pharmacokinetic profiles, while the racemic compound exhibited pharmacokinetic parameters approximating the mean values of the individual enantiomers. The total clearance (CLT) values of the two enantiomers were similar, but the intrinsic clearance (Cl(int)) was much greater for the S-enantiomer than for the R-enantiomer. The volume of distribution (Vss) for AL03802 (R) was threefold greater than that for AL03803 (S). The stereoselectivity in Vss could not be totally accounted for by the slight difference in serum protein binding of the isomers and resulted in a difference in the half-lives of the enantiomers. Only the R-isomer exhibited a persistent terminal elimination phase, consistent with more extensive tissue binding than the S-isomer. AL03152 enantiomers were equivalent in potency assessed from in vitro IC50 values toward rat lens aldose reductase and rat kidney L-hexonate dehydrogenase and lens EC50 values in diabetic rats.

Aldehyde Reductase↗
PubMed1993

Interstate migration to south east Queensland: an analysis.

"There is increasing evidence that south east Queensland is emerging as the growth centre of Australia during the 1990s as a result of an accelerating redistribution of Australia's population.... This paper highlights the magnitude and characteristics of internal migration impacting on Queensland and south east Queensland based on an examination of migration data from the 1991 Census. In addition, some more recent data on the level and distribution of migration are presented."

Australia↗
PubMed1992

Substance P and multiple sclerosis.

Multiple sclerosis is an inflammatory disease which affects the white matter of the central nervous system (CNS). The aetiology of this condition is unknown but it is generally believed to represent an autoimmunological response to a component of myelin triggered by an environmental factor, in a genetically susceptible individual. The natural history of the disease, in terms of clinical disability, is unpredictable, and the factors responsible unknown. Substance P is an undecapeptide that acts as a neurotransmitter in the CNS and as a regulator of immune responses. The recent discovery of substance P immunoreactive astrocytes in multiple sclerosis plaques raises the possibility that this peptide may be important both in the development of plaques and in governing the natural history of the disease.

Autoimmunity↗
PubMed1992

Pharmacokinetics and efficacy of structurally related spirohydantoin and spirosuccinimide aldose reductase inhibitors.

1. Six potent aldose reductase inhibitors (ARI), three spirohydantoin (I to III) and three spirosuccinimide (IV to VI) compounds, showed similar IC50 activities in vitro for the inhibition of rat lens aldose reductase, but their ED50 values in diabetic rats varied as much as 20-fold in the lens and 50-fold in the sciatic nerve tissue. Pharmacokinetic studies were undertaken to investigate these findings. Structure-pharmacokinetic relationships were studied following i.v. administration to cynomolgus monkeys. 2. The clearance (CL) of each spirosuccinimide ARI was faster (greater than 5 times) than that of the corresponding spirohydantoin compound. In both series the CL values of the C(4) methyl and methoxy analogues were 4-fold greater than those for the unsubstituted compounds, although the CL values of the methoxy and methyl derivatives in the same series were not significantly different. 3. The volumes of distribution (Vss) of the spirohydantoins were about one-half those of the corresponding spirosuccinimides, and the Vss values of the parent compounds of both ARI series did not differ dramatically from those of their methyl and methoxy analogues. 4. All six compounds were eliminated from plasma in a biexponential fashion. The half-lives (lambda 1 and lambda 2) of the spirohydantoin compounds were much longer than those of the corresponding spirosuccinimide compounds, and the unsubstituted compounds had longer half-lives than their methyl and methoxy derivatives. The longest lambda 1 and lambda 2 half-lives were observed for imirestat, while two of the spirosuccinimides had the shortest half-lives. 5. These results indicate that the relationships observed between the in vitro and in vivo activities of the six ARI can be attributed to structurally dependent differences in metabolic clearance.

Administration, Oral↗
PubMed1991

Spontaneous pneumothorax: marker gas technique for predicting outcome of manual aspiration.

OBJECTIVE: To determine whether in a patient with spontaneous pneumothorax the presence or absence of a pleural leak can be shown at the time of manual aspiration by use of a marker gas. Also, to find out if the technique can predict whether manual aspiration will be successful, hence avoiding the need for intercostal tube drainage. DESIGN: Prospective study of 25 episodes of pneumothorax during which patients breathed air from a Douglas bag that contained chlorofluorocarbon gases from a metered dose inhaler while the pneumothorax was aspirated. SETTING: Medical unit of a district general hospital. PATIENTS: 22 patients who presented over nine months with acute pneumothorax. MAIN OUTCOME MEASURES: Presence or absence of chlorofluorocarbon marker gases in the aspirate. Presence or absence of sustained re-expansion of the affected lung in the chest radiograph. RESULTS: Marker gas was detected in the aspirate from 16 out of 25 pneumothoraces. Of these, 13 required intercostal tube drainage because of failure of the lung to re-expand. Marker gas was not detected in nine cases, and in all of these cases manual aspiration resulted in sustained re-expansion of the lung. CONCLUSIONS: The presence or absence of a pleural leak during manual aspiration of spontaneous pneumothorax can be shown by using this technique. The absence of marker gas in the aspirate implies that manual aspiration will be successful, whereas its presence predicts, in most cases, either failure of manual aspiration to expand the lung or early re-collapse of the lung.

Acute Disease↗