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Biomedical subjects

R E Bell

Publications and source records attributed to R E Bell.

At least 19 recordsLinked to original sources
PubMed2006

Observation of instability-induced current redistribution in a spherical-torus plasma.

A motional Stark effect diagnostic has been utilized to reconstruct the parallel current density profile in a spherical-torus plasma for the first time. The measured current profile compares favorably with neoclassical theory when no large-scale magnetohydrodynamic instabilities are present in the plasma. However, a current profile anomaly is observed during saturated interchange-type instability activity. This apparent anomaly can be explained by redistribution of neutral beam injection current drive and represents the first observation of interchange-type instabilities causing such redistribution. The associated current profile modifications contribute to sustaining the central safety factor above unity for over five resistive diffusion times, and similar processes may contribute to improved operational scenarios proposed for ITER.

Journal Article↗
PubMed2006

Active stabilization of the resistive-wall mode in high-beta, low-rotation plasmas.

The resistive-wall mode is actively stabilized in the National Spherical Torus Experiment in high-beta plasmas rotating significantly below the critical rotation speed for passive stability and in the range predicted for the International Thermonuclear Experimental Reactor. Variation of feedback stabilization parameters shows mode excitation or suppression. Stabilization of toroidal mode number unity did not lead to instability of toroidal mode number two. The mode can become unstable by deforming poloidally, an important consideration for stabilization system design.

Journal Article↗
PubMed2006

Observation of plasma toroidal-momentum dissipation by neoclassical toroidal viscosity.

Dissipation of plasma toroidal angular momentum is observed in the National Spherical Torus Experiment due to applied nonaxisymmetric magnetic fields and their plasma-induced increase by resonant field amplification and resistive wall mode destabilization. The measured decrease of the plasma toroidal angular momentum profile is compared to calculations of nonresonant drag torque based on the theory of neoclassical toroidal viscosity. Quantitative agreement between experiment and theory is found when the effect of toroidally trapped particles is included.

Journal Article↗
PubMed2005

Treatment of mycotic aortic aneurysms with endoluminal grafts.

PURPOSE: To report the benefit of endoluminal repair of mycotic aortic aneurysms and highlight the need for a registry. METHODS: Nine patients (five female) were identified over 5 years (1998-2003) as having presumed mycotic aortic aneurysms (12 in total) suitable for endoluminal grafting. A total of nine thoracic and three abdominal were grafted and followed up for a median of 36 months. RESULTS: Six of the aneurysms have resolved and one was converted to an open repair. There was one early death from rupture of a second undiagnosed aneurysm and two late deaths from rupture due to persistent inflammation. Long-term antibiotics have not been mandatory to ensure survival. CONCLUSIONS: Mycotic aortic aneurysms of the thoracic and abdominal aorta do benefit from endoluminal repair, particularly when arising in previously normal aortic tissue. Endoluminal grafting also has a role in the palliation of secondarily infected aortas and so to prove its efficacy in the treatment of all these rare cases a registry is required.

Adult↗
PubMed2004

Endovascular treatment of acute type B aortic dissection.

Intervention is currently reserved in acute aortic dissection for Stanford Type A and for complications of Type B. Endovascular techniques such as fenestration of the intimal flap and stenting of vessel origins have been used to alleviate end-organ ischaemia due to compromised branches. The introduction of stent grafts has offered a realistic alternative to surgery for Type B dissections. Closure of the primary entry tear encourages thrombosis of the false lumen, which is associated with good long-term outcome. Many questions remain unanswered and randomised controlled trials need to be performed to establish the role of stent grafts in uncomplicated Type B dissections, and the use of bare stents to encourage thrombosis of the more distal false lumen. Improvements in the design and engineering of stent grafts may help to establish endoluminal repair as the first line treatment of aortic dissection.

Aortic Dissection↗
PubMed2003

Mid-term results for second-generation thoracic stent grafts.

BACKGROUND: Thoracic stent grafts offer an alternative to open surgery for thoracic aortic disease, but their long-term durability is unknown. This report includes mid-term follow-up for commercially available thoracic devices. METHODS: Data were collected prospectively for a series of endoluminal grafts used to treat thoracic aortic pathology. RESULTS: Between July 1997 and October 2002, 67 patients received thoracic stent grafts. Elective procedures incurred a 30-day mortality rate of 2 per cent (one of 42 patients) and urgent repair 16 per cent (four of 25). Paraplegia affected three (4 per cent) of 67 patients and three patients had a stroke. The median follow-up was 17 (range 2-64) months; four patients were lost. There were six late deaths, two from aneurysm rupture (rupture of a mycotic aneurysm at 5 months and stent migration at 28 months). Other device-related complications comprised three proximal endoleaks, one of which required open surgical correction with removal of the stent graft, and two distal endoleaks, which were successfully treated with distal extension cuffs. CONCLUSION: In the mid term, endoluminal repair of thoracic aortic pathology appears to be a safe alternative to open surgery, but continued surveillance is essential.

Adolescent↗
PubMed2003

Results of urgent and emergency thoracic procedures treated by endoluminal repair.

INTRODUCTION: emergency surgery on the thoracic aorta is associated with a high mortality. Endovascular treatment for these patients may offer a realistic alternative to open surgery. METHOD: between 1997 and 2002 data was collected prospectively on all patients who underwent urgent or emergency endoluminal repair for thoracic aortic pathology. All patients had ruptured or were at risk of rupture, and had been assessed as high risk for open surgery. RESULTS: twenty-four patients required urgent/emergency stent grafts. The median age was 74 (range 17-90). Indications included: trauma (transection in 3 and traumatic dissection in 1), acute symptomatic type B dissection (4), symptomatic degenerative aneurysms (7), false aneurysms associated with infection (6), Takayasu's vasculitis causing rupture of the descending thoracic aorta (1), symptomatic aneurysm associated with chronic dissection (1) and a secondary aorto-oesophageal fistula (1). The 30-day survival was 83.3% (20/24) and the survival at 1 year was 70.8% (17/24). The median follow-up was 13.5 months (range 2-57). The complications included: transient paraplegia (1), non-disabling stroke (1), distal endoleak treated with an extension cuff (1) and a proximal endoleak (1) which required removal of the graft at open surgery. CONCLUSION: endoluminal repair of thoracic aortic disease requiring urgent/emergency treatment has encouraging results with low morbidity and mortality rates compared with open surgery. Long-term follow-up is required to assess the durability of the grafts.

Adolescent↗
PubMed2003

Surgical OGD--a dying art?

INTRODUCTION: Reductions in surgical training and the increases in medical gastroenterology have raised concerns that surgeons may not be adequately trained in upper gastrointestinal (GI) endoscopy. METHOD: To evaluate this problem, a questionnaire was sent to all current surgical specialist registrars (SpRs) in the South Thames East Region. RESULTS: There was an 82% (52/63) response rate. Only 50% (26/52) of trainees had received more than 6 months' training in upper GI endoscopy. 83% (43/52) were in posts which did not provide adequate elective exposure for training. 50% (26/52) were required to provide an emergency service, despite a paucity of experience and less than 50% were able to perform therapeutic injection. In the main, emergency endoscopy is performed with substandard equipment, poor facilities, and untrained staff. CONCLUSIONS: Surgical trainees are poorly trained and do not have the necessary skills to provide an emergency service for upper GI haemorrhage. Emergency endoscopy facilities are severely under resourced.

Acute Disease↗
PubMed2002

Characteristics of the first H-mode discharges in the national spherical torus experiment.

We report observations of the first low-to-high ( L-H) confinement mode transitions in the National Spherical Torus Experiment. The H-mode energy confinement time increased over reference discharges transiently by 100-200%, as high as approximately 100 ms. This confinement time is approximately 2 times higher than predicted by a multimachine scaling. Thus the confinement time of spherical tori has been extended to a record high value, leading to an eventual revision of confinement scalings. Finally, the power threshold for H-mode access is >10x higher than predicted by an international scaling from conventional aspect-ratio tokamaks, which could lead to new understanding of H-mode transition dynamics.

Journal Article↗
PubMed2001

Iliac arterial injuries after endovascular repair of abdominal aortic aneurysms: correlation with iliac curvature and diameter.

PURPOSE: To determine the relationship between iliac arterial tortuosity and cross-sectional area and the occurrence of iliac arterial injuries following transfemoral delivery of endovascular prostheses for repair of abdominal aortic aneurysms. MATERIALS AND METHODS: Iliac arterial curvature values and orthogonal cross-sectional areas were determined from helical computed tomographic (CT) data acquired in 42 patients prior to transfemoral delivery of aortic stent-grafts. The curvature and luminal cross-sectional area orthogonal to the median centerline were quantified every millimeter along the median centerline of the iliac arteries. An indicator of global iliac tortuosity, the iliac tortuosity index, was defined as the sum of the curvature values for all points with a curvature of 0.3 cm(-1) or greater, and cross-sectional area (CSA) was indexed for all points as the mean cross-sectional diameter (D = 2 radical[CSA/pi]). Following stent-graft deployment, helical CT data were analyzed for the presence of iliac arterial dissections independently by two reviewers. RESULTS: Eighteen dissections were detected in 16 patients. The iliac tortuosity index was significantly larger in iliac arteries with dissections (35.5 +/- 20.8 [mean +/- SD]) when compared with both nondissected contralateral iliac arteries in the same patients (26.1 +/- 21.0, P =.001) and iliac arteries in patients without any iliac arterial injury (20 +/- 9, P =.009). The tortuosity index was higher ipsilateral to the primary component delivery in 10 of 11 iliac dissections that developed along the primary component delivery route. CONCLUSION: A high degree of iliac arterial tortuosity appears to impart greater risk for the development of iliac arterial injuries in patients undergoing transfemoral delivery of endovascular devices.

Aged↗
PubMed2001

Ionising radiation (medical exposure) regulations (Northern Ireland) 2000 and their implications for Accident and Emergency (A&E) doctors in training.

With the introduction of the Ionising Radiation (Medical Exposure) Regulations (Northern Ireland) 2000 (IRMER) the medical practitioner faces greater accountability when requesting radiological investigations. The referrer (usually a doctor or dentist) must supply sufficient medical data to justify radiation exposure to a patient. These regulations can lead to criminal prosecution if breached. Our objectives were to identify the level of unjustified requests for plain abdominal radiography among A&E doctors and whether there is a statistically significant difference in the justification of request between doctors of differing experience. We reviewed and prepared statistical analysis of 100 A&E request forms for plain abdominal radiography. Royal College of Radiologist Guidelines were used as a "Gold standard" for justification of the investigation. A&E doctors of less than six months experience are at greater risk of breaching these regulations when requesting plain abdominal films, when compared to more experienced doctors. This is a serious issue which should be addressed at undergraduate and pre-registration level in addition to ongoing audit.

Adolescent↗
PubMed1991

The role of footwear in childhood injuries.

To assess the influence of footwear on injury, we prospectively studied all injured children presenting to the Emergency Department of The Children's Hospital of Philadelphia during February, May, July, and October 1988. Information was collected concerning the type and characteristics of footwear worn and environmental factors. Comparisons were made between those involving and those not involving loss of footing (LOF) during injury. Of the 3015 children studied, LOF occurred in 1075 (35.8%). Overall, significantly more injuries involved LOF in children whose feet were covered (n = 946, 37.0%) than in those who were barefoot (n = 129, 29.1%) at the time of injury (P less than 0.001). However, children wearing low-top sneakers had the lowest rate of LOF (24.0%) of any group. Children wearing rough-sole footwear had LOF significantly less frequently (24.2%) than those wearing smooth-sole footwear (51.8%; P less than 0.001). Rubber-sole footwear was less frequently associated with LOF (n = 488, 28.6%) than were other sole materials (n = 457, 53.8%; P less than 0.001). Our data suggest a potential injury prevention strategy involving utilization of rough-sole footwear.

Accidental Falls↗
PubMed1986

A nonpulmonary complication of high-frequency oscillation.

High-frequency ventilation (HFV) has been suggested as an alternative to standard positive-pressure ventilation with positive end-expiratory pressure (PPV/PEEP) in the treatment of infants with hyaline membrane disease. To assess the relative safety and efficacy of HFV, we compared standard PPV to HFV delivered by oscillation (HFO) and HFV delivered by a flow interrupter (HFFI) in a previously validated preterm baboon model of hyaline membrane disease. At necropsy, the livers of several animals were unexpectedly found to have severe fatty change and/or cytoplasmic vacuolization and edema. There was a strong correlation between use of HFO and the development of liver lesions. The hepatic lesion may reflect decreased cardiac output with a concomitant fall in splenic perfusion and/or alterations in normal intrathoracic pressure that increase resistance in the hepatic vasculature. Although the etiology cannot be determined precisely, these data suggest the potential for nonpulmonary complications of HFV in the immature newborn and mandate further investigation before its widespread clinical application.

Animals↗
PubMed1986

Pulmonary interstitial emphysema treated by high-frequency oscillatory ventilation.

Twenty-seven low birth weight infants who developed pulmonary interstitial emphysema (PIE) and respiratory failure while on conventional ventilation were treated with high-frequency oscillatory ventilation (HFOV). The mean birth weight was 1.2 kg (range 0.55 to 2) with gestational age of 28 wk (range 25 to 34). Ten patients died, six of whom had documented sepsis with shock and were therefore excluded from analysis. All patients showed initial improvement on HFOV. Surviving patients showed continued improvement in oxygenation and ventilation at increasingly lower fraction of inspired oxygen and proximal airway pressure with resolution of PIE, while nonsurvivors progressively developed chronic respiratory insufficiency with continued PIE from which recovery was not possible. Overall survival in nonseptic patients was 80% (16 of 20). We found HFOV to be effective in the treatment of PIE and hypothesize that interstitial airleak is decreased during HFOV because adequate ventilation is provided at lower peak distal airway pressures.

Critical Care↗
PubMed1985

Cardiac defects in a patient with congenital contractural arachnodactyly.

Congenital contractural arachnodactyly (CCA) is a connective tissue disorder sharing many of the clinical manifestations of Marfan's syndrome. The case presented emphasizes that severe cardiac involvement may be manifested in the neonate with CCA, thus altering the more characteristic benign prognosis of CCA.

Contracture↗