Biomedical subjects

David Williams

Publications and source records attributed to David Williams.

At least 37 records · Page 2Linked to original sources

PubMed2006

Predictors of exercise compliance in individuals with Gulf War veterans illnesses: Department of Veterans Affairs Cooperative Study 470.

Although the health benefits of exercise for individuals with Persian Gulf War veterans illnesses (GWVI) are documented, many of these individuals do not exercise regularly enough to obtain benefits. The purpose of this study was to investigate factors predicting exercise compliance among individuals with GWVI in a multicenter, randomized, clinical trial. Participants were 1,092 veterans who reported at least two of the following cardinal symptoms of GWVI: (1) fatigue, (2) musculoskeletal pain, and (3) cognitive problems. Participants received exercise alone or exercise and cognitive-behavioral therapy. The overall level of compliance was relatively low during the exercise treatment phase (46.2%) and decreased by one-half during the follow-up period (23.0%). Predictors of compliance during treatment included less pain and greater age, motivation, and body mass index. Predictors of compliance during the follow-up period included less pain and greater age. The results highlight factors that affect adoption and maintenance of physical activity in a population with GWVI.

Adult↗

PubMed2006

New interests in magnesium.

After decades of developing strategies to minimise the corrosion of metallic biomaterials, there is now increasing interest in using an intentionally corrodible alloy in a number of critical medical device applications. This article examines the rationale for using magnesium alloys in cardiovascular and orthopaedic devices.

Absorbable Implants↗

PubMed2006

Quantum dots in medical technology.

During the past few years, the rapidly emerging technology of quantum dots has started to have an impact on the techniques of molecular and cellular imaging in medicine. Their advantages are examined here.

Diagnostic Imaging↗

PubMed2006

A registry for tissue engineering clinical trials.

Because tissue engineering products and processes are now being transferred from laboratory research into clinical applications, questions are being raised about what is the scope of an optimal clinical trial in this sector. A registry for these clinical trials is currently being established.

Clinical Trials as Topic↗

PubMed2006

Microgravity effects on fine motor skills: tying surgical knots during parabolic flight.

INTRODUCTION: The health provider on a space exploration mission cannot evacuate a patient to Earth. Contingency plans for medical intervention must be designed for autonomy. This study measured the effect of microgravity on performance of fine motor skills such as basic surgical tasks. METHODS: Eight subjects, six with medical and two with non-medical backgrounds, were evaluated during parabolic microgravity flights aboard NASA's KC-135. We evaluated their skill in tying surgical knots on simulated skin made of silicone using standard techniques for minimally invasive surgery. LabView software was developed to archive forces applied to the laparoscopic tool handles during knot-tying. Studies were controlled for medication (ScopeDex) and the aircraft environment. RESULTS: All participants completed the tests successfully. The data indicated that increased force was applied to the instruments and knot quality decreased during flight compared with ground control sessions. CONCLUSION: Specific metrics of surgical task performance are essential in developing education modules for providers of medical care during exploration-class missions.

Adult↗

PubMed2006

Material surfaces and MRSA.

It appears that our hospitals are facing serious threats from antibiotic-resistant bacteria, especially meticillin-resistant Staphylococcus aureus (MRSA). In this article, some of the new materials related solutions to these threats are discussed

Adamantane↗

PubMed2005

Crystal structures of protein phosphatase-1 bound to motuporin and dihydromicrocystin-LA: elucidation of the mechanism of enzyme inhibition by cyanobacterial toxins.

The microcystins and nodularins are tumour promoting hepatotoxins that are responsible for global adverse human health effects and wildlife fatalities in countries where drinking water supplies contain cyanobacteria. The toxins function by inhibiting broad specificity Ser/Thr protein phosphatases in the host cells, thereby disrupting signal transduction pathways. A previous crystal structure of a microcystin bound to the catalytic subunit of protein phosphatase-1 (PP-1c) showed distinct changes in the active site region when compared with protein phosphatase-1 structures bound to other toxins. We have elucidated the crystal structures of the cyanotoxins, motuporin (nodularin-V) and dihydromicrocystin-LA bound to human protein phosphatase-1c (gamma isoform). The atomic structures of these complexes reveal the structural basis for inhibition of protein phosphatases by these toxins. Comparisons of the structures of the cyanobacterial toxin:phosphatase complexes explain the biochemical mechanism by which microcystins but not nodularins permanently modify their protein phosphatase targets by covalent addition to an active site cysteine residue.

Bacterial Toxins↗

PubMed2005

Radiofrequency ablation of chondroblastoma using a multi-tined expandable electrode system: initial results.

The standard treatment for chondroblastoma is surgery, which can be difficult and disabling due to its apo- or epiphyseal location. Radiofrequency (RF) ablation potentially offers a minimally invasive alternative. The often large size of chondroblastomas can make treatment with plain electrode systems difficult or impossible. This article describes the preliminary experience of RF treatment of chondroblastomas with a multi-tined expandable RF electrode system. Four cases of CT guided RF treatment are described. The tumour was successfully treated in all cases. In two cases, complications occurred; infraction of a subarticular chondroblastoma in one case and cartilage and bone damage in the unaffected compartment of a knee joint in the other. Radiofrequency treatment near a joint surface threatens the integrity of cartilage and therefore long-term joint function. In weight-bearing areas, the lack of bone replacement in successfully treated lesions contributes to the risk of mechanical failure. Multi-tined expandable electrode systems allow the treatment of large chondroblastomas. In weight-bearing joints and lesions near to the articular cartilage, there is a risk of cartilage damage and mechanical weakening of the bone. In lesions without these caveats, RF ablation appears promising. The potential risks and benefits need to be evaluated for each case individually.

Adolescent↗

PubMed2005

Specifying race-ethnic differences in risk for psychiatric disorder in a USA national sample.

BACKGROUND: Epidemiological studies have found lower than expected prevalence of psychiatric disorders among disadvantaged race-ethnic minority groups in the USA. Recent research shows that this is due entirely to reduced lifetime risk of disorders, as opposed to persistence. Specification of race-ethnic differences with respect to clinical and social characteristics can help identify the protective factors that lead to lower lifetime risk among disadvantaged minority groups. METHOD: Data on 5424 Hispanics, non-Hispanic Blacks, and non-Hispanic Whites came from the National Comorbidity Survey Replication, a nationally representative survey conducted with the World Mental Health version of the Composite International Diagnostic Interview. Race-ethnic differences in risk of disorders were compared across specific diagnoses, ages of onset, cohorts and levels of education. RESULTS: Both minority groups had lower risk for common internalizing disorders: depression, generalized anxiety disorder, and social phobia. In addition, Hispanics had lower risk for dysthymia, oppositional-defiant disorder and attention deficit hyperactivity disorder; non-Hispanic Blacks had lower risk for panic disorder, substance use disorders and early-onset impulse control disorders. Lower risk among Hispanics, relative to non-Hispanic Whites, was found only among the younger cohort (age<or=43 years). Lower risk among minorities was more pronounced at lower levels of education. CONCLUSION: The pattern of race-ethnic differences in risk for psychiatric disorders suggests the presence of protective factors that originate in childhood and have generalized effects on internalizing disorders. For Hispanics, but not for non-Hispanic Blacks, the influence of these protective factors has emerged only recently.

Adolescent↗

PubMed2005

Basal ganglia local field potential activity: character and functional significance in the human.

Functional neurosurgery in patients with movement disorders has provided a unique opportunity to record directly form the human basal ganglia (BG) and to thereby further our understanding of these 'dark basements of the mind.' Two possibilities exist: either single unit and local field potential (LFP) recordings can be made intra-operatively through microelectrodes, or LFPs may be recorded directly from the deep brain stimulation electrode in the peri-operative period. The LFPs so recorded in the BG of patients are pleomorphic, oscillatory, focal and the product of synchronised current changes in local neuronal elements. They are presently most simply classified by frequency into activities at <8, 8-30 and >60 Hz, although such a schema is unlikely to capture the full complexity of rhythmic synchronisation with respect to behavioural and disease dependency. The best characterised group of LFP oscillations is that at 8-30 Hz. This activity is prominent in the subthalamic nucleus and globus pallidus of Parkinsonian patients withdrawn from their dopaminergic medication. Dopaminergic treatments, behaviourally relevant stimuli and voluntary movement suppress it. The available evidence points to the 8-30 Hz activity being essentially antikinetic in character and inversely related to motor processing. Its exaggeration may therefore contribute to the bradykinesia of Parkinson's disease.

Action Potentials↗

PubMed2005

Patterns of AFLP variation in a core subset of cultivated hexaploid oat germplasm.

Many core collections have been developed from large collections of crop germplasm, but most of these have not been characterized, particularly using molecular techniques, for germplasm management and utilization. We have attempted to characterize a structured sample representing a world collection of 11,622 cultivated hexaploid oat accessions in the hope of understanding the genetic structure of the world collection. The amplified fragment length polymorphism (AFLP) technique was applied to screen 670 accessions representing 79 countries and one group of uncertain origin. For each accession, 170 AFLP polymorphic bands detected by five AFLP primer pairs were scored. Analyses of the AFLP data showed the effectiveness of the stratified sampling applied in capturing country-wise AFLP variation. The frequencies of polymorphic bands ranged from 0.11 to 0.99, with an average of 0.72. The majority (89.9%) of the AFLP variation resided within accessions of each country, and only 6.2% of the AFLP differences existed among accessions of major geographic regions. Accessions from the Mediterranean region were the most distinct, while those from Russia and the USA were the most diverse. The two distinct groups that were observed were separated largely on the basis of common oat and red oat. Red oat was genetically more diverse than its common and hull-less counterparts, and hull-less oat was more related to common oat than red oat. Landrace and non-landrace accessions displayed similar AFLP variation patterns. These patterns are significant for understanding the domestication of cultivated oat and are useful in classifying the intraspecific diversity of oat germplasm, developing specific core subsets of the oat collection, and exploring new sources of genes for oat improvement.

Avena↗

PubMed2005

Latitudinal characteristics of below- and above-ground biomass of Typha: a modelling approach.

BACKGROUND AND AIMS: The latitudinal differences in the growth characteristics of Typha are largely unknown, although a number of studies have pointed out the effects of climate on the growth and productivity of Typha. Therefore, a dynamic growth model was developed for Typha to examine the effects of latitudinal changes in temperature and radiation on partitioning of the total biomass during the growing season into rhizomes, roots, flowering and vegetative shoots, and inflorescences. METHODS: After validating the model with data from growth studies of Typha found in past literature, it was used to investigate the dynamics of above- and below-ground biomasses at three latitudes: 30 degrees, 40 degrees and 50 degrees. KEY RESULTS: Regardless of the initial rhizome biomass, both above- and below-ground biomass values converged to a latitude-specific equilibrium produced by the balance between the total production and respiration and mortality losses. Above-ground biomass was high from 10 degrees to 35 degrees latitude with sufficient radiation, despite high metabolic losses; however, it decreased markedly at higher latitudes due to a low photosynthetic rate. Below-ground biomass, on the other hand, increased with latitude up to 40 degrees due to decreasing metabolic losses, and then markedly decreased at higher latitudes. Above-ground biomass was enhanced with an increasing number of cohorts regardless of latitude. However, although more cohorts resulted in a larger below-ground biomass at low latitudes, the largest below-ground biomass was provided by a smaller number of cohorts at high latitudes. This difference is due to low production rates of late-season cohorts in high latitudes, compared with consumption for shooting and establishing foliage. CONCLUSIONS: The model could be used to predict the potential growth of Typha in given conditions over a wide range of latitudes and is useful for practical applications such as wetland management or wastewater treatment systems using Typha.

Biomass↗

PubMed2005

Surface plasmon fluorescence measurements of human chorionic gonadotrophin: role of antibody orientation in obtaining enhanced sensitivity and limit of detection.

This paper describes the determination of limits of detection (LODs) of interactions between an antigen, human chorionic gonadotrophin (hCG), and antibodies, anti-alpha-hCG and anti-beta-hCG, using a sandwich assay by surface plasmon field-enhanced fluorescence spectroscopy (SPFS). Randomly biotinylated antibodies were adsorbed onto a structured self-assembled monolayer (SAM)-streptavidin matrix, tethered to gold via a SAM consisting of biotinylated thiol molecules interspersed with hydroxyalkanethiol molecules. The influence of the concentration of biotinylated thiol on the binding of biotinylated antibody and its functionality, in terms of its ability to bind to the hCG antigen, was studied. This allowed determination of the optimum biotin-thiol mole fraction in the mixed thiol solution and consequently in the SAM, to maximize binding of hCG of the streptavidin-bound antibody. SPFS studies of the binding of a secondary fluorescently labeled antibody to hCG immobilized on the optimized SAM-streptavidin-antibody layer showed that a LOD of hCG of 2 mIU mL(-1) (4 x 10(-12) mol L(-1)) could be realized. The system was further optimized by using a more oriented and organized surface by adsorbing monobiotinylated Fab-hCG in place of the whole antibody. A LOD of 0.3 mIU mL(-1) (6 x 10(-13) mol L(-1)) was achieved for this system. This work illustrates the importance of antibody orientation, both on the planar surface and in terms of position of binding site, in maximizing sensor sensitivity.

Antibodies↗

PubMed2005

Different functional loops between cerebral cortex and the subthalmic area in Parkinson's disease.

We investigate the extent to which functional circuits coupling cortical and subthalamic activity are multiple and segregated by frequency in untreated Parkinson's disease (PD). To this end, we recorded EEG and local field potentials (LFPs) from macroelectrodes inserted into the subthalamic nucleus area (SA) in nine awake patients following functional neurosurgery for PD. Patients were studied after overnight withdrawal of medication. Coherence between EEG and SA LFPs was apparent in the theta (3-7 Hz), alpha (8-13 Hz), lower beta (14-20 Hz) and upper beta (21-32 Hz) bands, although activity in the alpha and upper beta bands dominated. Theta coherence predominantly involved mesial and lateral areas, alpha and lower beta coherence the mesial and ipsilateral motor areas, and upper beta coherence the midline cortex. SA LFPs led EEG in the theta band. In contrast, EEG led the depth LFP in the lower and upper beta bands. SA LFP activity in the alpha band could either lead or lag EEG. Thus there are several functional sub-loops between the subthalamic area and cerebral cortical motor regions, distinguished by their frequency, cortical topography and temporal relationships. Tuning to distinct frequencies may provide a means of marking and segregating related processing, over and above any anatomical segregation of processing streams.

Brain Mapping↗

PubMed2005

Submandibular gland transfer for prevention of xerostomia after radiation therapy: swallowing outcomes.

OBJECTIVE: To assess swallowing outcomes in patients with oropharyngeal carcinoma in relation to the Seikaly-Jha procedure for submandibular gland transfer (SJP). The SJP has recently been described as beneficial in the prevention of xerostomia induced by radiation therapy in patients with head and neck cancer. DESIGN: Inception cohort. SETTING: University-affiliated primary care center. PATIENTS: A phase 2 clinical trial was conducted from February 1, 1999, through February 28, 2002, to evaluate SJP in patients with head and neck cancer. During that period, a consecutive sample of 51 patients who underwent surgical resection and reconstruction with a radial forearm free flap for oropharyngeal carcinoma were referred for functional assessment of swallowing after completion of adjuvant radiation therapy. At 6 months after surgery, swallowing assessments for 24 patients were available. INTERVENTION: The cohort of 24 patients included 13 who had preservation of 1 submandibular gland (SJP group) and 11 who did not (control group). MAIN OUTCOME MEASURES: Quantitative and qualitative aspects of swallowing were obtained to determine whether patients in the SJP group performed more optimally than those in the control group. RESULTS: Baseline and stimulated salivary flow rates were significantly different between groups. Patients in the SJP group were able to move the bolus through the oral cavity and into the pharynx faster than those in the control group. In addition, patients in the SJP group swallowed less often per bolus than patients in the control group. The complete swallowing sequence was twice as long in controls. CONCLUSIONS: The SJP for submandibular gland transfer appears to be beneficial in promoting more time-efficient swallowing behaviors. This efficiency has implications for the overall well-being and nutritional status of patients with head and neck cancer.

Adult↗

PubMed2005

Is sphincter electromyography a helpful investigation in the diagnosis of multiple system atrophy? A retrospective study with pathological diagnosis.

Sphincter electromyography (spEMG) is often used as an ancillary test when multiple system atrophy (MSA) is suspected. Our aim was to determine the clinical features associated with spEMG being performed, the influence of the result on the final clinical diagnosis, and its utility as a clinical investigation. A retrospective audit of all cases in the Queen Square Brain Bank between 1989 and 2002 was performed. The clinical features and diagnostic accuracy were compared between patients in whom spEMG was performed and those in whom it was not. From 845 sets of complete clinical records, we identified 37 (4.4%) cases that had been investigated with spEMG. Thirty of these cases had a pathological diagnosis of MSA. Of these 30, 24 had abnormal spEMGs, 5 had a borderline result, and only 1 had a normal spEMG. Sixty-six cases had pathologically proven MSA but no spEMG. Those investigated with spEMG were younger at disease onset (P < 0.001), more frequently male (P = 0.03), and more likely to have had other investigations performed. They had a greater incidence of pyramidal tract signs at final clinical diagnosis, and the final clinical diagnostic accuracy was higher (P = 0.04). Due to the retrospective nature of the study, balanced populations for calculation of sensitivity and specificity were not available. In this selected series of pathologically confirmed cases, investigation with spEMG was one of several factors associated with improved clinical diagnostic accuracy. A normal spEMG is unlikely in pathologically proven MSA, at least in cases with a mean symptom duration of more than 5 years when the test is performed.

Adult↗

PubMed2005

Quantitative assessment of ventricular function in sickle cell disease: effect of long-term erythrocytapheresis.

BACKGROUND: Previous studies on cardiac function in patients with sickle cell disease (SCD) demonstrated abnormalities of systolic and diastolic function including elevated left ventricular myocardial performance index (LVMPI) on chronic transfusion protocols. LVMPI has been validated as a useful and easy non-invasive measure of overall cardiac function. Up to now, there are no reported studies on cardiac function in patients with SCD maintained on long-term erythrocytapheresis (LTE). PROCEDURES: We recorded LVMPI in 22 patients with SCD aged 3-20 years and we compared the results between non-transfused patients (NT-SCD) and patients on LTE (T-SCD). RESULTS: Males with SCD had higher mean LVMPI than females (P = 0.04). There were significant differences among T-SCD, severe NT-SCD, and mild NT-SCD patients with respect to hemoglobin (Hb) levels (P = .003) and TR velocity (P = .03). T-SCD patients showed elevated LVMPI compared to NT-SCD patients with severe and mild disease (P = 0.002). Pair-wise comparisons demonstrated that T-SCD patients had LVMPI that was significantly higher than NT-SCD (mild) patients (P = 0.01). CONCLUSIONS: Our study demonstrates that patients SCD on LTE have cardiac dysfunction based on elevated LVMPI. This may be a reflection of the global severity of disease. Our findings merit further investigation with serial monitoring of LVMPI on a larger number of patients with SCD.

Adolescent↗

PubMed2005

Ion transport blockers inhibit human rhinovirus 2 release.

Picornavirus replication causes leakage of cytoplasmic K+ and an influx of Na+ and Ca2+. In this study, we have explored the possibility that a blockade of Ca2+ and Na+ influx would reduce rhinovirus production and/or release. The Ca2+-channel blockers, verapamil and diltiazem, as well as the blocker of Na+/H+ exchange and the epithelial Na+ channel, EIPA, inhibited both virus production and release. The effect on virus release was more pronounced than the effect on production, thus raising the possibility that rhinovirus release may serve as a target for antiviral agents. Unexpectedly, our results also showed that the antiviral activity of the Ca2+-channel blockers was not due to the block of Ca2+ influx. Similarly, the antiviral activity of EIPA appeared to be unrelated to the blockade of cellular Na+/H+ exchanger or the epithelial Na+ channel. Potential alternative mechanisms of the antiviral activity of these compounds are discussed.

Calcium↗