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Biomedical subjects

A N Wilson

Publications and source records attributed to A N Wilson.

At least 19 recordsLinked to original sources
PubMed2006

Probing shell structure and shape changes in neutron-rich sulfur isotopes through transient-field g-factor measurements on fast radioactive beams of 38S and 40S.

The shell structure underlying shape changes in neutron-rich nuclei near N = 28 has been investigated by a novel application of the transient-field technique to measure the first-excited-state g factors in 38S and 40S produced as fast radioactive beams. There is a fine balance between proton and neutron contributions to the magnetic moments in both nuclei. The g factor of deformed 40S does not resemble that of a conventional collective nucleus because spin contributions are more important than usual.

Journal Article↗
PubMed2005

Excitation energies of superdeformed States in 196Pb: towards a systematic study of the second well in Pb isotopes.

The excitation energy of the lowest-energy superdeformed band in 196Pb is established using the techniques of time-correlated gamma-ray spectroscopy. Together with previous measurements on 192Pb and 194Pb, this result allows superdeformed excitation energies, binding energies, and two-proton and two-neutron separation energies to be studied systematically, providing stringent tests for current nuclear models. The results are examined for evidence of a "superdeformed shell gap."

Journal Article↗
PubMed2003

Direct decays from superdeformed states in 192Pb observed using time-correlated gamma-ray spectroscopy.

Correlations of decays above and below isomeric states in the normally deformed minimum of 192Pb have been used to identify discrete transitions in the decay of the superdeformed (SD) band. The data establish the absolute excitation energy of the lowest observed SD level as 4.425 MeV. Extrapolation to the bandhead indicates that the excitation energy of the superdeformed well in 192Pb is 0.5 MeV lower than in the heavier isotope 194Pb. The results confirm the trend to decreasing excitation energy with decreasing neutron number predicted by both a macroscopic Strutinsky method approach and microscopic mean field calculations.

Journal Article↗
PubMed2003

Bone turnover markers in serum and periodontal microenvironments.

BACKGROUND: Periodontitis is characterized by altered bone turnover, but local measurements are difficult. OBJECTIVES: The objective of this study was to develop a method to measure multiple markers of bone turnover from single samples collected at various bone surfaces of the periodontium, and to test the ratios of these markers against more traditional serum and gingival crevicular fluid (GCF) samples. MATERIALS AND METHODS: Fourteen subjects with untreated periodontitis were recruited for sampling serum, GCF (from sites > or = 5 mm probing depth that bled on probing) and washes of periodontal bone surfaces (adjacent interproximal, vestibular cortical and trabecular bone) with a novel irrigating device. All samples were analyzed for osteocalcin (OC, bone turnover marker; RIA), cross-linked N-telopeptide of type I collagen (NTx, bone resorption marker; ELISA) and albumin (Alb, serum protein; ELISA). Results were reported as ratios: OC/NTx to determine relative bone turnover, and OC/Alb or NTx/Alb to determine local OC or NTx production. RESULTS: The OC/NTx ratio was significantly higher (p < or = 0.05) in serum vs. GCF (OC undetectable), interproximal bone and cortical vestibular bone, but significantly lower than in trabecular vestibular bone. The OC/Alb ratio for serum was also statistically lower than for vestibular trabecular bone. The NTx/Alb ratio for serum was statistically lower than for GCF and all the bone wash test sites. The results indicated considerable local production of both OC and NTx. CONCLUSIONS: This system demonstrated that multiple markers of bone turnover can be harvested by irrigation from periodontal bone microenvironments. Bone turnover profiles from periodontal bone surfaces and GCF differed from systemic bone turnover profiles (serum) and may be valuable in tracking site-specific responses to disease or treatment.

Adult↗
PubMed2001

Linear polarization measurement of interband transitions in superdeformed 190hg: model-independent evidence for octupole vibrational structures.

The linear polarization of gamma rays between excited and yrast superdeformed (SD) states in 190Hg was measured using the four-element CLOVER detectors of the EUROBALL IV gamma-ray spectrometer. This measurement shows in a model-independent way that the interband transitions which compete with the highly collective in-band quadrupole transitions are largely enhanced electric dipoles. Not only do these results represent the first measurement of the multipolarity of transitions between different SD states, but they also provide strong evidence for the interpretation of the structures in the SD minimum of the A approximately 190 region in terms of octupole excitations.

Journal Article↗
PubMed1997

Impaired cardioplegic delivery and the loss of cardioprotection: a role for preconditioning.

We have previously shown that, while ischemic preconditioning and cardioplegia afford similar protection against injury during ischemia and reperfusion, this protection is not additive. However, it is not known whether the same applies when the delivery of cardioplegia is suboptimal, such as may occur in the case of a coronary stenosis. To investigate the protective effect of cardioplegia v preconditioning when the delivery of cardioplegia is impaired, isolated rat hearts were subjected to 40 min of global ischemia followed by 40 min of reperfusion. Seven groups of hearts (1 g wet wt) were studied (n = 8/group): Group 1: controls with unprotected ischemia (no intervention): Group 2: in which only 0.2 ml of the St Thomas' cardioplegic solution was administered (2 min) prior to ischemia: group 3: in which the volume of cardioplegic solution was increased to 0.5 ml: Group 4: received 1.0 ml of cardioplegia: Group 5: received 2.0 ml of cardioplegia: Group 6: were subjected to ischemic preconditioning (3 min ischemia, 3 min reperfusion, 5 min ischemia, 5 min reperfusion) prior to ischemia: and Group 7: in which ischemic preconditioning and cardioplegia (1.0 ml) were used in combination. The mean postischemic recovery of left ventricular developed pressure (LVDP), expressed as a percentage of its pre-ischemic value, was 33 +/- 3% in the control group: this was significantly improved (P < 0.05) in hearts receiving 2.0 ml of cardioplegia (59 +/- 5%), whereas volumes of 0.2, 0.5 or 1.0 ml of cardioplegia afforded no significant protection (recoveries of LVDP were 32 +/- 6%, 37 +/- 5% and 37 +/- 5%, respectively). Preconditioning alone and the combination of preconditioning plus 1.0 ml of cardioplegia afforded similar protection (57 +/- 3%, and 58 +/- 3%, P < 0.05 v controls). At the end of reperfusion, left ventricular end-diastolic pressure (LVEDP) was substantially increased in control hearts (57 +/- 3 mmHg): it was decreased in the groups receiving 2.0 ml of cardioplegic solution (40 +/- 5 mmHg; P < 0.05 v control group), but not in the group receiving 0.2, 0.5 or 1.0 ml of cardioplegic solution (59 +/- 4, 55 +/- 3 and 54 +/- 4 mmHg, respectively). Again, preconditioning alone or preconditioning plus 1.0 ml of cardioplegia afforded similar good protection (39 +/- 1 mmHg and 37 +/- 2 mmHg, respectively). A similar pattern was observed for the post-ischemic recovery of coronary flow. Under conditions where the delivery of cardioplegia is impaired (< 2.0 ml/g myocardium) preconditioning alone or preconditioning in combination with cardioplegia is more protective that cardioplegia alone. These results may be of clinical interest because most patients undergoing surgery for ischemic heart disease suffer from severe coronary artery lesions that may prevent the delivery of sufficient cardioplegic solution to ensure maximum protection.

Animals↗
PubMed1997

Clinical, motor, and biological correlates of depressive disorders after focal subcortical lesions.

The authors studied depression after focal subcortical lesions (SCLs) in 45 highly selected subjects. Secondary major depression (secondary MD) occurred in 20.0%, depressive disorder NOS (secondary DDNOS) in 4.4%, and secondary dysthymia in 0.0%. secondary MD after SCLs was associated with pallidal lesions (88.9%) and dystonia without geste antagonistique; subjects with secondary DDNOS had nigrotegmental lesions and parkinsonism. Depressive severity after SCLs correlated positively with severity of parkinsonism and dystonia. Pallidal lesions disrupting neurotransmitter systems and pallidothalamic and parietal input to the frontal lobe may lead to secondary MD, whereas nigrotegmental lesions may predispose to secondary MD forme fruste (secondary DDNOS) through disruption of mesocortical frontal or nigrostriatal dopamine tracts. Patients should be closely followed over several years for depression after such lesions, especially when accompanied by parkinsonism or dystonia without geste antagonistique.

Brain Diseases↗
PubMed1997

Major depression after left posterior globus pallidus lesions.

We studied subjects with focal subcortical lesions (SCLs) and investigated the frequency of pallidal lesions in secondary major depression (secondary MD) presenting after but not before lesion onset. Forty-five subjects were selected for focal subcortical lesions (SCLs) from 10,000 hospital magnetic resonance imaging (MRI) films. SCLs were ascertained by neuroradiologic criteria. Major depression was ascertained by DSM-III, -III-R, and -IV criteria. We compared subjects with secondary MD to SCL subjects lacking life histories of mood disorders and investigated the lesion distribution among pallidal subregions evident on MRI. We further tested an association between pallidal lesions and secondary MD. Pallidal lesions were present in eight (89%) of nine subjects with secondary MD and 13 (59%) of 22 controls. Left posterior pallidal lesions occurred in four (44%) of the nine subjects with secondary MD and two (9%) of the 22 controls (one-tailed Fisher's exact test p = 0.043). Demographic and other factors did not differ between subjects with secondary MD and controls (using Fisher's exact test or Mann-Whitney U test as statistically appropriate). These data, of small sample size and requiring confirmation, suggest the possibility that abnormal pallidal function may contribute to depressive pathophysiology, perhaps by influencing basal ganglia-thalamocortical mood circuits. Left-lateralized circuits in the posterior pallidum may be of particular relevance. The left pallidal association is compatible with previous findings in poststroke depression. Patients with left pallidal lesions may deserve close monitoring for secondary MD after subcortical lesions.

Aged↗
PubMed1994

Adenosine is not the sole vasodilator released on exposure of isolated guinea-pig hearts to histamine and isoprenaline.

1. The role of adenosine in the control of coronary vessel tone was studied using two guinea-pig hearts in series. Vasodilatory mediator(s) released by the donor heart were assayed by the recipient heart. 2. Adenosine deaminase reduced the activity of vasodilatory mediator(s) released by histamine and isoprenaline by 58.0 +/- 14.4% and 80.5 +/- 5.9% respectively; responses to exogenous adenosine were abolished. 3. Adenosine deaminase added to the donor perfusate supplying the recipient heart caused a significant increase in basal perfusion pressure. 4. Our results suggest adenosine is not the sole mediator of vasodilation in stressed hearts and additionally unstressed hearts appear to release a basal vasodilatory level of adenosine.

Acetylcholine↗
PubMed1994

Local control of soft tissue sarcoma of the extremity: the experience of a multidisciplinary sarcoma group with definitive surgery and radiotherapy.

Data gathered on 62 patients with soft tissue sarcoma of an extremity, treated in entirety by an experienced multidisciplinary sarcoma group, were analysed. With a philosophy of emphasising attainment of histologically negative margins at carefully planned limb sparing surgery, combined with either pre-operative or postoperative radiation therapy, a crude local control rate of 95% (59 of 62 patients) at a minimum of 24 months follow-up was obtained. Of 9 patients with microscopically positive margins after definitive surgery, 8 had undergone maximal resection compatible with preservation of function. One of these 9 failed locally, indicating that radiation therapy is effective in eradicating microscopic disease in this tumour. The excellent local control obtained with limb-sparing surgery in this series justifies early referral of patients with these uncommon cancers to an experienced multidisciplinary unit. 26 patients (42%) failed systemically at a minimum of 24 months follow-up, and 19 (30.6%) died of their disease, confirming the need for effective systemic therapy in soft tissue sarcoma. Tumours greater than 10 cm in diameter had a greater risk of systemic relapse.

Adolescent↗
PubMed1994

Does endogenous adenosine have a role in the cardiac responses to isoprenaline and in the rapid fade of the inotropic response of perfused heart?

The role of endogenous adenosine during the beta-adrenoceptor responses to isoprenaline of guinea-pig isolated cardiac preparations was examined. Insignificant effects of adenosine deaminase (0.3 U.mL-1) on cumulative concentration--response curves for isoprenaline on isolated left and right atria and papillary muscles indicated a negligible depressant effect of endogenous adenosine during these responses. The increase in force of contraction to an infusion of isoprenaline (14 nM) in perfused spontaneously beating hearts rapidly waned while the infusion continued, whereas the increase in rate of contraction remained constant throughout the infusion. The degree of fade was less in paced preparations (5 Hz), indicating that it was only in part due to the rate increase exerting some mechanical constraint on the force of contraction. The P1-purinoceptor antagonist 8-phenyltheophylline (12 microM) and adenosine deaminase (0.3 U.mL-1) did not enhance the peak responses to the isoprenaline infusion. The fade of the inotropic response in both spontaneous and paced hearts was also not attenuated by the presence of 8-phenyltheophylline or adenosine deaminase. The fade was not, therefore, due to release of endogenous adenosine exerting a depressant effect. Whether this declining inotropic response represents a form of rapid desensitization remains to be determined.

Adenosine↗
PubMed1994

The finite element analysis of stress in the periodontal ligament when subject to vertical orthodontic forces.

In the past, vertical intrusive movement of teeth has been considered difficult and most routine clinical vertical movement of teeth has been confined to extrusion. It has been suggested that attempts at intrusion may result in an increased incidence of root resorption and also in occasional devitalization. The displacement and resulting stress fields associated with such treatment can be successfully studied using the finite element method. In the case being considered initial movements are known to be small; therefore, the assumption in the study that the material behaves linear-elastically is considered to be reasonable. This study of vertical tooth movement demonstrated that the maximum cervical margin stress in the periodontal ligament was 0.0046 N/mm2, whilst the highest apical stress was 0.00205 N/mm2 when intrusive and extrusive forces of 1 Newton were applied to the buccal surface of the crown of a tooth model. These stresses were evaluated in the light of previous studies and found to be within the suggested clinical optimum level. However, the periodontal stress distribution following orthodontic loading within this three-dimensional finite element model was found to be highly complex.

Cuspid↗
PubMed1992

Stresses induced by edgewise appliances in the periodontal ligament--a finite element study.

The quantification of stress in the periodontal ligament is an important concept, as stress in this tissue is transmitted to the alveolus, with subsequent bone remodelling and tooth movement. A number of clinical studies have suggested figures for such an optimal stress range. This study makes use of a finite element technique to determine the stress induced in the periodontal ligament in three dimensions when a maxillary canine tooth is subjected to an orthodontic force similar to that produced by an edgewise appliance. The maximum stress induced at the cervical margin of the periodontal ligament was 0.072 N/mm2, while the maximum stress induced at the level of the apical foramen was 0.0038 N/mm2. These results are discussed in the light of known clinical experience and compared with the stresses produced in the periodontal ligament by other orthodontic forces. The findings would suggest that even with 'perfect' edgewise mechanics it would be difficult to obtain canine movement by pure translation or 'bodily movement.'

Alveolar Process↗
PubMed1992

Prostaglandin D2 production and identification of prostaglandin H synthase within canine mast cell granule.

We have identified the presence of functional prostaglandin H synthase (PGH synthase, E.C. 1.14.99.1, or cyclooxygenase) within canine mast cell granules by demonstrating the generation of prostaglandin (PG) D2 from isolated and purified granules incubated with substrate as arachidonic acid or stimulated with calcium ionophore, A23187. This confirms the presence of both enzyme and substrate within the granule. Localization of PGH synthase to the granule was confirmed by immunoblotting of the pure granule preparation and by immunocytochemistry using the whole cell. In functional studies, colchicine, a microtubule polymerization inhibitor, caused a fall of up to 70%, both in the amount of histamine released and in the amount of PGD2 generated. This suggests either that functional PGH synthase is closely associated and coactivated with granules or that there is an independent association of this enzyme with the microtubule system. Release of the preformed and newly formed mediators of the mast cell appear to be closely linked, and prevention of degranulation may therefore attenuate the effects of both classes of mediators.

Animals↗
PubMed1991

A stress analysis of the periodontal ligament under various orthodontic loadings.

The accurate modelling of teeth under orthodontic load in the laboratory has many shortcomings in that it has not been possible to integrate methods, such as three-dimensional models, photo-elastic stress analysis, laser holographic interferometry, and animal studies, to give comprehensive and repeatable results. In this study, using a three-dimensional finite element model of a human maxillary canine tooth, the maximum principal stresses in the periodontal ligament produced by various orthodontic forces were determined. 1 Newton tipping forces produced stresses at the cervical margin of the periodontal ligament as high as 0.196 N/mm2 and apical stresses up to -0.034 N/mm2, while rotatory forces of two equal, but opposing forces of 0.5 Newton at the cervical margin of the crown produced cervical margin stresses ranging between -0.035 and 0.051 N/mm2, and apical stresses of between 0.0018 and 0.0027 N/mm2. These stresses are examined and discussed in relation to previous clinical, laboratory, and histological studies.

Computer Simulation↗
PubMed1991

A finite element study of canine retraction with a palatal spring.

The use of a removable appliance to retract a maxillary canine tooth into a first premolar extraction space is one of the most commonly performed orthodontic procedures. However, unwanted movements may occur, including excessive tipping, rotation, and flaring of the tooth. The present investigation by the use of a finite element model quantifies some of the initial stresses produced within the periodontal ligament when two obliquely directed forces are applied to a maxillary canine tooth. In simulating the action of a removable appliance it attempts to relate the stress patterns to the nature of the subsequent tooth movement.

Cuspid↗
PubMed1990

Three-dimensional analysis of orthodontic tooth movement.

A three-dimensional finite element model was used to investigate the biomechanical response of an upper canine tooth. The physical model was developed from ceramic replicas and X-rays, and consisted of cancellous and cortical bone, the periodontal ligament, dentine and pulp chamber. Horizontal forces were applied at the tip of the crown and at the cervical margin and a rotational force was applied at the cervical margin of the tooth crown. The resulting displacements and stress field for each load case are presented with particular emphasis being placed on the response of the periodontal ligament. The investigation shows that quantitative information on initial tooth movement can be accurately predicted and used to evaluate the response of orthodontic treatment.

Biomechanical Phenomena↗