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S Julian

Publications and source records attributed to S Julian.

9 recordsLinked to original sources
PubMed2002

Finite element analysis in spine research.

Finite element analysis is a widely accepted tool used in many industries and research activities. It allows new designs to be thoroughly 'tested' before a prototype is even manufactured, components and systems which cannot readily be experimented upon to be examined, and 'diagnostic' investigations to be undertaken. Finite element models are already making an important contribution to our understanding of the spine and its components. Models are being used to reveal the biomechanical function of the spine and its behaviour when healthy, diseased or damaged. They are also providing support in the design and application of spinal instrumentation. The spine is a very complex structure, and many of the models are simplified and idealized because of the complexity and uncertainty in the geometry, material properties and boundary conditions of these problems. This type of modelling simplification is not peculiar to spinal modelling problems. Indeed, the idealization is often a strength when there is such uncertainty and variation between one individual and another, allowing cause-effect relationships to be isolated and fully explored, and the inherent variability of experimental tests to be eliminated. This paper reviews the development of finite element analysis in spinal modelling. It shows how modelling provides a wealth of information on our physiological performance, reduces our dependence on animal and cadaveric experiments and is an invaluable complement to clinical studies. It also leads to the conclusion that, as computing power and software capabilities increase, it is quite conceivable that in the future it will be possible to generate patient-specific models that could be used for patient assessment and even pre- and inter-operative planning.

Biomechanical Phenomena↗
PubMed2002

Patient-specific spine models. Part 1: Finite element analysis of the lumbar intervertebral disc--a material sensitivity study.

If patient-specific finite element models of the spine could be developed, they would offer enormous opportunities in the diagnosis and management of back problems. Several generic models have been developed in the past, but there has been very little detailed examination of the sensitivity of these models' characteristics to the input parameters. This relationship must be thoroughly understood if representative patient-specific models are to be realized and used with confidence. In particular, the performance of the intervertebral discs are central to any spine model and need detailed investigation first. A generic non-linear model of an intervertebral disc was developed and subjected to compressive, flexion and torsional loading regimes. The effects of both material and geometric non-linearities were investigated for the three loading schemes and the results compared with experimental data. The basic material properties of the fibres, annulus and nucleus were then varied and the effects on the stiffness, annulus bulge and annulus stresses analysed. The results showed that the non-linear geometry assumption had a significant effect on the compression characteristics, whereas the non-linear material option did not. In contrast, the material non-linearity was more important for the flexural and torsional loading schemes. Thus, the inclusion of non-linear material and geometry analysis options in finite element models of intervertebral discs is necessary to predict in vivo load-deflection characteristics accurately. When the influence of the material properties was examined in detail, it was found that the fibre properties did not have a significant effect on the compressive stiffness of the disc but did affect the flexural and torsional stiffnesses by up to +/-20 per cent. All loading modes were sensitive to the annulus properties with stiffnesses varying by up to +/-16 per cent. The model also revealed that for a particular compressive deformation or flexural or torsional rotation, the disc bulge was not sensitive to any of the material properties over the range of properties considered. The annulus stresses did differ significantly as the material properties were varied (up to 70 per cent under a compressive load and 60 per cent during disc flexion).

Compressive Strength↗
PubMed2001

CD4+ T cell-independent vaccination against Pneumocystis carinii in mice.

Host defenses are profoundly compromised in HIV-infected hosts due to progressive depletion of CD4+ T lymphocytes. Moreover, deficient CD4+ T lymphocytes impair vaccination approaches to prevent opportunistic infection. Therefore, we investigated a CD4+ T cell-independent vaccine approach to a prototypic AIDS-defining infection, Pneumocystis carinii (PC) pneumonia. Here, we demonstrate that bone marrow-derived dendritic cells (DCs) expressing the murine CD40 ligand, when pulsed ex vivo by PC antigen, elicited significant titers of anti-PC IgG in CD4-deficient mice. Vaccinated animals demonstrated significant protection from PC infection, and this protection was the result of an effective humoral response, since adoptive transfer of CD4-depleted splenocytes or serum conferred this protection to CD4-deficient mice. Western blot analysis of PC antigen revealed that DC-vaccinated, CD4-deficient mice predominantly reacted to a 55-kDa PC antigen. These studies show promise for advances in CD4-independent vaccination against HIV-related pathogens.

Adoptive Transfer↗
PubMed1989

Rupture of the liver and right hemidiaphragm presenting as right hemothorax.

A young man hit by a car while riding his motorcycle presented with reversible hypotension, a compression fracture of C6, fractures of the left femur and of ribs 9-12 on the right, and right hemothorax. A falsely negative peritoneal lavage delayed laparotomy, which, when done, demonstrated two right diaphragmatic rents with bleeding into the right chest from a severe liver injury. Presentation of this case demonstrates that while peritoneal lavage is an excellent way to exclude intraperitoneal hemorrhage following blunt abdominal trauma, false-negative results may occur in the setting of hemorrhage with diaphragmatic rupture.

Abdominal Injuries↗
PubMed1989

Evaluation of a monoclonal antibody pool for rapid diagnosis of respiratory viral infections.

A pool of monoclonal antibodies (MAbP) was evaluated both as a method of cell culture confirmation and as a rapid diagnostic screen for viral infection in respiratory secretions. The MAbP was used in a two-step fluorescent staining procedure on cells harvested from cultures (phase 1) and on exfoliated nasopharyngeal or tracheal cells (phase 2). Antibodies in the MAbP were directed against respiratory syncytial virus, adenoviruses, parainfluenza virus types 1, 2, and 3, and influenza viruses A and B. Individual antiviral antibody stains were used to identify specific viruses from MAbP-positive specimens. In phase 1 (cell culture confirmation only), 241 respiratory specimens were tested. MAbP sensitivity and specificity were 91 and 94%, respectively. In phase 2, 376 respiratory specimens were evaluated by direct staining of exfoliated cells, and these results were compared with results of cell culture isolation. The sensitivity and specificity of the MAbP used in direct specimen testing were 69 and 97%, respectively. These results indicate that the MAbP is highly specific and fairly sensitive for detection of seven different respiratory viruses in one testing procedure. The MAbP is a rapid screening technique for respiratory secretions and is potentially a cost-effective approach to viral detection.

Adenoviruses, Human↗
PubMedDate not supplied

Unusual presentation of cholelithiasis on T1-weighted MR imaging.

Cholelithiasis usually appears on magnetic resonance as a signal void contrasting with the high signal of surrounding bile. We describe the appearance of two intraluminal gallstones as high-signal areas on a heavily T1-weighted scan and, based on infrared spectroscopic analysis of the stones, believe the fatty-acid content of the stones accounts for this unusual result. Increased focal intraluminal signal on strongly T1-weighted sequences does not, therefore, preclude a diagnosis of cholelithiasis.

Aged↗
PubMedDate not supplied

Subxiphoid pericardial window for pericardial effusive disease.

A subxiphoid pericardial window made in 123 patients allowed drainage and diagnosis of pericardial effusions. In 40 patients with malignancy and effusions, median drainage was 450 ml; cytology was positive in 17 or 36 (47%), and pericardial biopsy showed cancer in 13 (43%) of 30 patients. In 11 patients with malignancy, both cytology of effusions and biopsy of the pericardium were negative. In 83 patients with benign effusions, median drainage was 400 ml. Effusions recurred in 14 of the 123 patients (11%); nine patients in the benign group and five in the malignant group. Five of these 14 underwent thoracotomy (3 to 542 days postoperatively); two underwent median sternotomy and one underwent pericardiocentesis. Two intraoperative deaths resulted from cardiac arrest. Mortality at 30 days was 25% (10/40 patients) in the malignant group and 11% (9/83 patients) in the benign group. No deaths resulted from recurrent effusions. The establishment of a subxiphoid pericardial window allows rapid and safe drainage of pericardial effusions with sampling for cytology and pericardial biopsy. It has minimal morbidity and few recurrent effusions.

Drainage↗
PubMedDate not supplied

[Acute methotrexate poisoning: apropos of 16 cases reported to the Paris Poison Control Center and review of the literature].

16 cases of acute methotrexate (MTX) poisoning were reported to the Paris Poison Control Centre and 62 others were published between 1974 and 1995. Until 1992, MTX was mainly prescribed for neoplastic diseases. Clinical features involve acute renal failure, pancytopenia, and cutaneous or mucous injury. These cases emphasise major risk factors responsible for misuse and overdosage. Since 1992, MTX has been increasingly used in rheumatological or pulmonary diseases (rheumatoid arthritis, steroid-dependent asthma). Most of the overdosages were due to a medical misuse (in the dosage regimen or a misunderstanding of the prescription by nurse, pharmacist or patient). All patients had a bone marrow suppression. The treatment is based especially on early administration of folinic acid rescue.

Acute Disease↗