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Biomedical subjects

R Turner

Publications and source records attributed to R Turner.

At least 109 records · Page 6Linked to original sources
PubMed1998

Effect of pH on element release from dental casting alloys.

STATEMENT OF PROBLEM: Dental casting alloys are subjected to transient acidity in the oral environment, yet most studies have not investigated the effects of these transient environments on elemental release from alloys. Elemental release is important because it plays a significant role in alloy biocompatibility. PURPOSE: It was hypothesized that acidic environments would increase elemental release from dental alloys during exposure and after the acidic environment was removed. This hypothesis was based on the known increase in release of nickel from nickel-based alloys in an acidic environment. MATERIAL AND METHODS: High-noble, noble, and base metal casting alloys were exposed for 30 minutes to solutions with pH ranging from 1 to 7. Elemental release of representative elements was measured by means of atomic absorption spectrometry during the exposure and in the week after the exposure. This release was compared with elemental release in the week before the exposure. RESULTS: High-noble and noble alloys were resistant to acidic environments. A pH of 4 did not increase elemental release during or after exposure. A pH 1 environment slightly elevated release of Ag, Cu, and Pd in some alloys. However, a Ni-based alloy released large amounts of Ni during the acidic exposure of pH 1 or 4, and more importantly, in the week after the exposure as well. Increased time of exposure to acid did not alter elemental release from noble or high-noble alloys, but markedly increased release from the Ni-based alloy. CONCLUSIONS: Transient exposure of casting alloys to an acidic oral environment is likely to significantly increase elemental release from Ni-based alloys, but not from high-noble or noble alloys.

Analysis of Variance↗
PubMed1998

The outcome of tendon transfers for C6-spared quadriplegics.

The purpose of this study was to review retrospectively and evaluate a uniform group of C6-spared quadriplegics who had similar surgical procedures. Eight patients undergoing 12 procedures were reviewed at an average of 3.8 years follow-up. There were three bilateral procedures. All patients had extensor carpi radialis longus to flexor digitorum profundus and brachioradialis to flexor pollicis longus transfers to improve grip strength and key pinch. All patients reported subjective improvements in quality of life, activities of daily living and patient-centred goals. There were six excellent and two good results. Objective improvements included mild improvements in key pinch and grip strength.

Activities of Daily Living↗
PubMed1998

Blood oxygenation level dependent signal time courses during prolonged visual stimulation.

Previous functional magnetic resonance imaging (MRI) studies using extended visual stimulation have reported disparate results. Two studies have shown that blood oxygen level dependent (BOLD) contrast decays over time which is cited as evidence of recoupling between oxygen utilisation and cerebral blood flow during stimulus presentation. These findings have serious implications for the design of functional MRI experiments because they raise the possibility that BOLD contrast may not accurately reflect neuronal activity. Another study reported no decay of BOLD contrast. These studies used different visual stimuli and imaging techniques. We have performed a series of experiments, using different MRI techniques (echo-planar imaging and fast low angle shot) and two different visual stimuli to assess which of these factors may explain the previous results. In all of our experiments the signal time course from areas of significant activation remained largely elevated throughout the duration of stimulation and this is not affected by the imaging method used. Our data, in accordance with that of Bandettini et al., suggest that recoupling between blood flow and oxygen extraction is not a general phenomenon in the human brain when visual stimuli are presented for an extended time.

Adult↗
PubMed1998

Right parietal cortex is involved in the perception of sound movement in humans.

Changes in the delay (phase) and amplitude of sound at the ears are cues for the analysis of sound movement. The detection of these cues depends on the convergence of the inputs to each ear, a process that first occurs in the brainstem. The conscious perception of these cues is likely to involve higher centers. Using novel stimuli that produce different perceptions of movement in the presence of identical phase and amplitude modulation components, we have demonstrated human brain areas that are active specifically during the perception of sound movement. Both functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) demonstrated the involvement of the right parietal cortex in sound movement perception with these stimuli.

Acoustic Stimulation↗
PubMed1998

Mitochondrial DNA deletions in human skin reflect photo- rather than chronologic aging.

We have examined the use of mitochondrial DNA (mtDNA) as a molecular marker to study the relation between chronologic aging and photoageing in human skin. Using a 3-primer quantitative polymerase chain reaction method we have studied changes in the ratio of the 4977 bp deleted to wild-type mtDNA in relation to sun exposure and chronologic age of human skin. Based on previous studies, samples showing greater than 1% deleted mtDNA were classed as abnormal. There was a significant increase in the incidence of high levels (i.e., >1%) of the 4977 bp deleted mtDNA in sun-exposed sites (27%, 27 of 100) compared with sun-protected sites (1.1%, one of 90) (Fisher's exact test, p < 0.0001). There appeared to be no relation between the frequency of the mtDNA deletion and age. Analysis of split skin samples showed that most deletions (93%, n = 27) were confined to the dermal rather than the epidermal component, and in keeping with this deletions were found in three of six primary cultures of fibroblasts from sun-exposed sites. Deletions were not seen in the epidermal component of several epidermal tumors nor were deletions seen in fibroblasts cultured from an individual with Werner's syndrome. We propose that deletions or mutations of mitochondrial DNA may be useful as a marker of cumulative ultraviolet radiation exposure.

Adolescent↗
PubMed1998

Melanocortin 1 receptor variants in an Irish population.

The identification of an association between variants in the human melanocortin 1 receptor (MC1R) gene and red hair and fair skin, as well as the relation between variants of this gene and coat color in animals, suggests that the MC1R is an integral control point in the normal pigmentation phenotype. In order to further define the contribution of MC1R variants to pigmentation in a normal population, we have looked for alterations in this gene in series of individuals from a general Irish population, in whom there is a preponderance of individuals with fair skin type. Seventy-five per cent contained a variant in the MC1R gene, with 30% containing two variants. The Arg151Cys, Arg160Trp, and Asp294His variants were significantly associated with red hair (p = 0.0015, p < 0.001, and p < 0.005, respectively). Importantly, no individuals harboring two of these three variants did not have red hair, although some red-haired individuals only showed one alteration. The same three variants were also over-represented in individuals with light skin type as assessed using a modified Fitzpatrick scale. Despite these associations many subjects with dark hair/darker skin type harbored MC1R variants, but there was no evidence of any particular association of variants with the darker phenotype. The Asp294His variant was similarly associated with red hair in a Dutch population, but was infrequent in red-headed subjects from Sweden. The Asp294His variant was also significantly associated with nonmelanoma skin cancer in a U.K. population. The results show that the Arg151Cys, Arg160Trp, and Asp294His variants are of key significance in determining the pigmentary phenotype and response to ultraviolet radiation, and suggest that in many cases the red-haired component and in some cases fair skin type are inherited as a Mendelian recessive.

Adult↗
PubMed1998

Status of total quality management in Australian public health organisations.

Research suggests that there is some confusion among quality improvement managers about the differences between quality management and traditional quality assurance. This lack of understanding would appear to be the same among rural and urban health staff, although there is a higher percentage of staff engaged in multidisciplinary activities in the rural health services. Education of staff and commitment from top management would seem to be the factors inhibiting the health industry from incorporating quality management into their cultures.

Australia↗
PubMed1998

The functional anatomy of attention to visual motion. A functional MRI study.

Attention can enhance or modulate neural responses to stimuli at early and late stages of sensory processing. We were interested in the modulatory effect of attention to visual motion on cortical responses as measured by functional MRI. Subjects were scanned during repeated presentations of identical stimuli (visual motion) while only the attentional component of the task was varied. Enhanced haemodynamic responses during attentive conditions defined an occipitoparietofrontal system, including sensory and association areas, as well as the medial thalamus and superior colliculus. Attentional modulation was not restricted to extrastriate areas (including V3a and the V5 complex) but was also evident, to a lesser degree, in early visual areas close to the calcarine fissure (V1/V2 border). Attention-related enhancement of cortical responsiveness is discussed in terms of data that implicate modulatory short-term changes in synaptic efficacy and reciprocal connections between striate, extrastriate, parietal and frontal areas. Given the similarity of our attentional network to that controlling eye movements, the results of this study are in accord with theories linking oculomotor control and attention.

Attention↗
PubMed1998

Transmetacarpal intramedullary K-wire fixation of proximal phalangeal fractures.

The management of unstable phalangeal fractures has been associated with significant morbidity. Percutaneous transmetacarpal intramedullary Kirschner wire fixation of proximal phalangeal fractures has been described as a useful technique. We present a retrospective review of 35 digits in 24 patients with unstable fractures of the proximal phalanx treated using this technique between 1985 and 1995. Outcome measures, including radiological adequacy of reduction, total active range of motion, development of joint contracture, grip strength, and digital grip strength, were assessed. Good or excellent results were obtained in 76% of fractures (19 of 25) that were treated and followed. Thirty-two percent of digits (8 of 25) treated developed a proximal interphalangeal joint flexion contracture. Flexion contracture averaged 18.1 deg at the involved joints. Seven secondary procedures were required in 6 patients. Major complications noted during the study included loss of reduction with rotational deformity in four digits, and one nonunion. The use of skeletal traction devices was associated with three of the major complications observed. These devices should not be used concurrently on or adjacent to any digit treated by intramedullary pinning. We conclude that transmetacarpal axial Kirschner wire fixation is a technically simple method of treating unstable proximal phalangeal fractures, and good or excellent results can be obtained in the majority of appropriately selected patients.

Adolescent↗
PubMed1998

Microelectrode-guided pallidotomy: technical approach and its application in medically intractable Parkinson's disease.

OBJECT: The authors describe the microelectrode recording and stimulation techniques used for localizing the caudal sensorimotor portion of the globus pallidus internus (GPi) and nearby structures (internal capsule and optic tract) in patients undergoing GPi pallidotomy. METHODS: Localization is achieved by developing a topographic map of the abovementioned structures based on the physiological characteristics of neurons in the basal ganglia and the microexcitable properties of the internal capsule and optic tract. The location of the caudal GPi can be determined by "form fitting" the physiological map on relevant planes of a stereotactic atlas. A sensorimotor map can be developed by assessing neuronal responses to passive manipulation or active movement of the limbs and orofacial structures. The internal capsule and optic tract, respectively, can be identified by the presence of stimulation-evoked movement or the patient's report of flashes or speckles of light that occur coincident with stimulation. The optic tract may also be located by identifying the neural response to flashes of light. The anatomical/physiological map is used to guide lesion placement within the sensorimotor portion of the pallidum while sparing nearby structures, for example, the external globus pallidus, nucleus basalis, optic tract, and internal capsule. The lesion location and size predicted by using physiological recording together with thin-slice high-resolution magnetic resonance imaging reconstructions of the lesion were confirmed in one patient on histological studies. CONCLUSIONS: These data provide important information concerning target identification for ablative or deep brain stimulation procedures in idiopathic Parkinson's disease and other movement disorders.

Antiparkinson Agents↗
PubMed1998

Evaluation of the biliary tree during laparoscopic cholecystectomy: laparoscopic ultrasound versus intraoperative cholangiography: a prospective study of 150 cases.

From November 1994 to March 1996, 150 patients treated by laparoscopic cholecystectomy were included in a prospective study, to compare intraoperative cholangiography (IOC) and laparoscopic ultrasonography (LU). The biliary tree was successively explored by these two methods in the routine detection of common bile duct stones. The feasibility of LU was 100%. Cholangiography was performed only in 125 cases (83%). The time taken for LU was significantly shorter (11.6 vs. 17.6 minutes, p = 0.0001). In this study, common bile duct stones were found in 14 cases (9%). For their detection, results were comparable to LU and IOC. For LU, sensitivity was 80% and specificity 99%; and for IOC, 78 and 97%, respectively. Both examinations combined had a 100% sensitivity and specificity. Laparoscopic ultrasonography failed to recognize the intrapancreatic part of the common bile duct in 25 cases (17%) and did not show anatomic abnormalities detected by IOC. It did, however, detect other unsuspected intraabdominal abnormalities. Although LU is safe, repeatable, and noninvasive, a considerable learning curve is necessary to optimize its efficacy. Comparison of relative cost must be undertaken.

Adult↗
PubMed1997

UKPDS 25: autoantibodies to islet-cell cytoplasm and glutamic acid decarboxylase for prediction of insulin requirement in type 2 diabetes. UK Prospective Diabetes Study Group.

BACKGROUND: Autoantibodies to islet-cell cytoplasm (ICA) and glutamic acid decarboxylase (GADA) can occur in apparently typical, non-insulin dependent diabetes mellitus (type 2). We investigated whether the presence of either or both antibodies characterises a subtype of diabetes and provides better prediction of requirement for insulin therapy by 6 years' follow-up than clinical variables. METHODS: We measured ICA and GADA at diagnosis of diabetes in a representative population of 3672 white patients with type 2 diabetes, aged between 25 and 65 years. The phenotype was assessed by age of onset, body-mass index, percentage haemoglobin A1c (HbA1c), and islet beta-cell function. We investigated the need for insulin therapy among 1538 patients not assigned insulin and followed up for 6 years from diagnosis. FINDINGS: The proportion of patients with ICA and GADA decreased with increasing age at diagnosis (from 33 [21%] of 157 patients aged 25-34 [corrected] to 66 [4%] of 1769 aged 55-65 for ICA; from 53 [34%] to 122 [7%] for GADA). Among patients younger than 35 at diagnosis, those with ICA or GADA had lower body-mass index than those without (mean 24.9 [SD 6.0] vs 31.7 [7.3] kg/m2; p < 0.0001 and had higher percentage of HbA1c (9.7 vs 8.7%, p < 0.05). 94% of patients with ICA and 84% of those with GADA required insulin therapy by 6 years, compared with 14% of those without the antibodies (p < 0.0001). Among patients older than 55 at diagnosis, the difference between those with and without antibodies in body-mass index was smaller (27.2 [5.4] vs 28.6 [4.8] kg/m2, p < 0.001); 44% of those with ICA, 34% of those with GADA, and 5% with neither antibody required insulin therapy by 6 years (p < 0.0001). Among patients older than 45 years, body-mass index and HbA1c provided little predictive information for insulin requirement, whereas the positive predictive values of GADA (> or = 60 U/L) alone, or both GADA (> or = 20 U/L) and ICA (> 5 U/L), for insulin therapy were 52% and 68%. INTERPRETATION: Among young adults with type 2 diabetes, the phenotype of those with ICA or GADA antibodies was similar to that of classic juvenile-onset insulin-dependent diabetes, and either phenotype or antibodies predicted insulin requirement. In older adults, the phenotype was closer to that of patients without antibodies and only the presence of antibodies predicted an increased likelihood of insulin requirement.

Adult↗
PubMed1997

Dopaminergic neurons intrinsic to the primate striatum.

Intrinsic, striatal tyrosine hydroxylase-immunoreactive (TH-i) cells have received little consideration. In this study we have characterized these neurons and their regulatory response to nigrostriatal dopaminergic deafferentation. TH-i cells were observed in the striatum of both control and 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine (MPTP)-treated monkeys; TH-i cell counts, however, were 3.5-fold higher in the striatum of MPTP-lesioned monkeys. To establish the dopaminergic nature of the TH-i cells, sections were double-labeled with antibodies to dopamine transporter (DAT). Immunofluorescence studies demonstrated that nearly all TH-i cells were double-labeled with DAT, suggesting that they contain the machinery to be functional dopaminergic neurons. Two types of TH-i cells were identified in the striatum: small, aspiny, bipolar cells with varicose dendrites and larger spiny, multipolar cells. The aspiny cells, which were more prevalent, corresponded morphologically to the GABAergic interneurons of the striatum. Double-label immunofluorescence studies using antibodies to TH and glutamate decarboxylase (GAD67), the synthetic enzyme for GABA, showed that 99% of the TH-i cells were GAD67-positive. Very few (<1%) of the TH-i cells, however, were immunoreactive for the calcium-binding proteins calbindin and parvalbumin. In summary, these results demonstrate that the dopaminergic cell population of the striatum responds to dopamine denervation by increasing in number, apparently to compensate for loss of extrinsic dopaminergic innervation. Moreover, this population of cells corresponds largely with the intrinsic GABAergic cells of the striatum. This study also suggests that the adult primate striatum does retain some intrinsic capacity to compensate for dopaminergic cell loss.

Animals↗
PubMed1997

Lateral geniculate activations can be detected using intersubject averaging and fMRI.

Applications of fMRI in functional brain imaging are mainly confined to single subject designs, prohibiting the assessment of subject or group by condition interactions (i.e., differential activations) or areas of conjoint activation. In this paper a framework for fMRI group designs, using statistical parametric mapping, is introduced. It is generally believed that intersubject averaging, which requires spatial normalization and smoothing, will decrease the effective spatial resolution of fMRI or its sensitivity. A subcortical activation of the lateral geniculate nucleus (LGN) was therefore chosen to demonstrate the feasibility and power of intersubject averaging in the context of fMRI. Seven volunteers were studied, while looking at a blank screen or radially moving dots. LGN activation was demonstrated in all single subject analyses and in the group analysis.

Adult↗
PubMed1997

Simultaneous measurement of DeltaR2 and DeltaR2* in cat brain during hypoxia and hypercapnia.

One of the most important issues in blood-oxygen-level-dependent (BOLD)-based brain functional magnetic resonance imaging is the understanding of the vascular structures that are responsible for the signal changes observed. The T2*-related signal changes observed during variations in susceptibility-induced magnetic field gradients are a function both of non-refocusable mechanisms, such as diffusion, and of refocusable effects such as field inhomogeneities. Conversely, T2-related signal changes are only a function of non-refocusable effects. It has been suggested that T2-weighted images could be less sensitive to blood susceptibility changes in a macrovascular environment than T2*-weighted images and could thus be more accurate in identifying the "activation" of the parenchyma rather than "draining vein" effects. In this study we use hypoxia and hypercapnia challenges in cats to provide a change in blood deoxyhemoglobin concentration (as a model for classic BOLD changes and not as a model for neuronal activation). A combined gradient echo and spin echo echo-planar-imaging (EPI) pulse sequence was used to map DeltaR2 (i.e., Delta(1/T2)) and DeltaR2* (i.e., Delta(1/T2*)) changes during the challenges. Our experiments demonstrate that: (i) the acquisition of T2-weighted EPI data does not in itself differentiate signal changes in the parenchyma from those occurring in regions around larger vessels, but that (ii) the simultaneous acquisition of T2- and T2*-weighted images could be useful in identifying microvascular regions in gray matter by analyzing the ratio DeltaR2/DeltaR2*. This value seems independent of the degree of deoxyhemoglobin concentration change, but is related to properties of the vascular environment. We suggest a possible application of the results to the study of brain function in humans.

Animals↗
PubMed1997

Characterizing the relationship between BOLD contrast and regional cerebral blood flow measurements by varying the stimulus presentation rate.

This paper investigates the relationship between the blood oxygenation level dependent (BOLD) contrast effect and regional cerebral blood flow using the techniques of functional MRI (fMRI) and positron emission tomography (PET). A passive listening paradigm with parametric variation in word presentation rate was used to investigate the rate dependency of both BOLD contrast fMRI and H215O PET in primary auditory cortex. We attempted to equate the stimulus presentation acoustic environments by using prerecorded echoplanar imaging sounds during the PET paradigm. We show that there is a linear relationship between word presentation rate and cerebral blood flow in primary auditory cortex, whereas the relationship between BOLD contrast and stimulus presentation rate is highly nonlinear, showing a saturable effect. Two possible explanations for our results are discussed: a nonlinearity in the relationship between BOLD contrast and deoxyhemoglobin concentration or a nonlinear rate dependency of the physiological mechanisms causing changes in deoxyhemoglobin concentration.

Adult↗