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Biomedical subjects

A J Fox

Publications and source records attributed to A J Fox.

At least 109 records · Page 6Linked to original sources
PubMed1997

The risks and benefits of carotid endarterectomy in patients with near occlusion of the carotid artery. North American Symptomatic Carotid Endarterectomy Trial (NASCET) Group.

Some believe that carotid endarterectomy (CEA) for carotid near occlusion is a necessary emergency procedure while others call it dangerous. We used the North American Symptomatic Carotid Endarterectomy Trial (NASCET) data to perform an observational study to examine the safety and benefit of CEA for carotid near occlusion. We divided the data of 659 patients into stenosis groups: 70 to 79%, 80 to 89%, 90 to 94%, and near occlusion. The 106 carotid-near-occlusion patients were subdivided into those with a string-like lumen (n = 29) and those without a string-like lumen (n = 77). Of the 48 patients with near occlusion treated with CEA, 3 (6.3%) had perioperative strokes, similar to the 70-94% stenosis group. Only 1 of 58 patients (1.7%) with near occlusion treated medically had a stroke in the first month, suggesting that CEA is not needed on an emergency basis in this circumstance. For medically treated patients, the 1-year risk of stroke increases with escalating degrees of carotid stenosis, where the risk is 35.1% for patients with 90-94% stenosis. For patients with near occlusion, the 1-year stroke risk diminishes to 11.1%, which approximates the risk for patients with 70-89% stenosis. A comparison of treatment differences indicates that surgery reduces the risk of stroke at 1 year by approximately one-half (p < 0.001), regardless of the degree of stenosis or the subcategory of carotid near occlusion (p = 0.89). Our data suggest that CEA is beneficial for near occlusion and not more dangerous than in patients with 70-94% stenosis, provided that the procedure is performed by an experienced surgeon with a low complication rate.

Arterial Occlusive Diseases↗
PubMed1997

Use of a C-arm system to generate true three-dimensional computed rotational angiograms: preliminary in vitro and in vivo results.

PURPOSE: To evaluate the potential use of a C-arm mounted X-ray image intensifier (XRII) system to generate three-dimensional computed rotational angiograms during interventional neuroradiologic procedures. METHODS: A clinical angiographic system was modified to allow collection of sufficient views during selective intraarterial contrast injections for CT reconstruction of a 15 x 15 x 15-cm3 volume. Image intensifier distortion and C-arm instabilities were corrected by using image-based techniques. The impact of the pulsatile nature of the vessels during image data acquisition and of the presence of bone on the 3-D reconstructions was investigated by generating 3-D reconstructions of an anesthetized 20-kg pig and of a human skull phantom. RESULTS: A sequence of images sufficient for 3-D reconstruction was acquired in less than 5 seconds. Image intensifier distortion and C-arm instabilities were corrected to subpixel accuracy (0.035 mm and 0.07 mm, respectively). Both the intracranial vessels of the pig and the small, high-contrast structures in the skull were reconstructed with negligible artifacts. CONCLUSIONS: Using a C-arm mounted XRII system, computed rotational angiography can provide true 3-D images of diagnostic quality.

Animals↗
PubMed1997

Bilateral anterior ischemic optic neuropathy as a presentation of Takayasu's disease.

Takayasu's disease is an arteritis with a predilection for the proximal branches of the aortic arch. Chronic retinal hypoxic changes and ischemic ocular inflammation, resulting from cervical vascular occlusion, have been described extensively. Anterior ischemic optic neuropathy has rarely been reported in this condition, and only in conjunction with other ophthalmic findings. Here we present the case of a patient who developed bilateral anterior ischemic optic neuropathy in the absence of other eye findings, and was subsequently found to have an aortic arch syndrome compatible with Takayasu's disease.

Anti-Inflammatory Agents↗
PubMed1996

Comparative study of three PCR assays with antigenaemia and serology for the diagnosis of HCMV infection in thoracic transplant recipients.

Three PCR assays were evaluated for the detection of human cytomegalovirus (HCMV) infection in heart and lung transplant recipients in comparison with HCMV antigenaemia and serology assay. Polymorphonuclear leucocyte (PMNL) samples taken at regular intervals after transplantation were tested for HCMV DNA using primer sets homologous to the glycoprotein B (gp58), major immediate early (IE1), and structural phosphoprotein (pp150) regions. The detection of HCMV infection at various times after transplantation showed all three primer sets to have a sensitivity of 100% and a specificity of 92.3% for the detection of HCMV infection although overall the gp58 primer set was found to be significantly more frequently associated with a positive PCR result than the IE1 (P = 0.0228) and pp150 (P = 0.0015) primer sets. The positive PCR result had a positive predictive value of 27.8% for HCMV disease. Detection of HCMV infection was first by the PCR assay, and significantly before the HCMV antigenaemia assay. Of nine patients who received antiviral therapy while PCR positive, only one patient cleared HCMV DNA from PMNLs during treatment but became positive again 17 days later. Quantitative PCR methodologies may improve the predictive value of PCR for HCMV disease and its value for monitoring antiviral therapy.

Antigens, Viral↗
PubMed1996

Geometric characterization of stenosed human carotid arteries.

RATIONALE AND OBJECTIVES: The geometry of stenosed carotid bifurcations was analyzed to determine average representations for several stenosis grades. METHODS: Film angiograms of 62 patients with internal carotid artery stenoses were digitized. Residual lumen boundaries were manually outlined. The outlines were processed with a computer to extract geometric measurements. The measurements were grouped according to stenosis grade and used to create average representations. RESULTS: Accuracy and precision of the outlining technique were +/- 0.020 common carotid diameters (CCD) and +/- 0.025 CCD, respectively. Maximum narrowing of the internal carotid artery occurred at 0.3 CCD +/- 1.5 (mean +/- standard deviation) distal to the flow divider. The region of significant narrowing extended axially 1.2 CCD +/- 1.0. Poststenotic dilatations were observed, with enlargement of 1.3 +/- 0.7 times the normal diameter of the distal internal carotid artery. A tendency toward smaller bifurcation angles with increasing stenosis severity was observed. CONCLUSION: Three-dimensional geometric models could be created for carotid bifurcations that were disease free (normal) and of arbitrary stenosis grade.

Aged↗
PubMed1996

The application of genotyping techniques to the epidemiological analysis of Campylobacter jejuni.

Campylobacter jejuni serogroup reference strains and collections of sporadic and outbreak-associated isolates were examined for restriction fragment length polymorphisms (RFLPs), using C. jejuni random chromosomal and 16S rRNA gene probes. A collection of 48 Penner (HS) and 14 Lior (HL) serogroup reference strains, plus 10 clinical isolates, generated 35 RFLP and 26 ribotype patterns. In combination the two loci generated 48 distinct genotypes. Both probes were able to differentiate between certain random isolates of the same HS/HL serogroups but greater discrimination was obtained with RFLP than with ribotyping. Genotyping distinguished accurately between related and unrelated strains when applied to several outbreaks. Genotypic analysis of C. jejuni by restriction fragment length polymorphisms is a valuable technique for epidemiological typing. Chromosomal variation detected by the two unlinked probe loci provides some information about the genetic relationship between isolates.

Campylobacter Infections↗
PubMed1996

Bradykinin-evoked sensitization of airway sensory nerves: a mechanism for ACE-inhibitor cough.

Cough accompanied by an increased sensitivity of the cough reflex is the most common symptom of inflammatory airway disease. This symptom is also frequently reported in patients receiving angiotensin-converting enzyme (ACE) inhibitors as therapy for heart failure or hypertension, although the underlying mechanism is unknown. We have investigated the possibility that the inflammatory peptide bradykinin, normally degraded by ACE, causes sensitization of airway sensory nerves and an enhancement of the cough reflex in conscious guinea pigs. Treatment of guinea pigs for two weeks with captopril led to an increased cough response to inhaled citric acid, which was prevented by concomitant treatment with the bradykinin receptor antagonist icatibant. A similar icatibant-sensitive enhancement of citric acid-evoked cough was seen in untreated animals after prior inhalation of bradykinin, although cough evoked by hypertonic saline was unaffected. In electrophysiological studies performed in vitro, responses of single vagal C fibers to capsaicin, applied to receptive fields of single-fiber units in the trachea, were also markedly increased after perfusion with bradykinin, whereas A delta fiber responses to hypertonic saline were unaffected. These results indicate that bradykinin-evoked sensitization of airway sensory nerves may underlie the pathogenesis of ACE-inhibitor cough. Bradykinin receptor antagonists may be of benefit in treating chronic cough seen with this and other inflammatory conditions.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1996

Conjugate meningococcal serogroup A and C vaccine: reactogenicity and immunogenicity in United Kingdom infants.

The reactogenicity and immunogenicity of a serogroup A and C meningococcal polysaccharide-CRM197 conjugate vaccine was evaluated in 58 infants who received three doses at 2, 3, and 4 months of age. The conjugate vaccine produced few systemic side effects, and local reactions were significantly less common than those produced by the routine vaccinations. The prevaccination geometric mean titers (GMTs) of A and C polysaccharide antibodies were, respectively, 2.8 and 0.6 microg/mL, rising to 21.5 and 38.5 microg/mL by 1 month after the third dose (age 5 months) and falling to 3.1 and 2.2 mircog/mL by 14 months of age. Prevaccination serum bactericidal titers against 2 serogroup C meningococci strains were <1/4 in 49 of 52 infants, rising to a GMT of 1/3082 at 1 month after the third dose and falling by age 14 months to a GMT of 1/10. Thus, this meningococcal conjugate vaccine proved to be safe and immunogenic, inducing high levels of anti-C polysaccharide antibodies that were bactericidal in young infants.

Antibodies, Bacterial↗
PubMed1996

A novel polymerase chain reaction assay for the detection and speciation of thermophilic Campylobacter spp.

A novel PCR amplification method is described which is specific for the thermophilic, enteropathogenic species Campylobacter jejuni, Camp. coli and Camp. upsaliensis. Rapid, accurate speciation of amplified strains is possible on the basis of restriction fragment length polymorphisms of PCR products digested with three restriction enzymes, AluI, DdeI and DraI. The sensitivity of detection is 25 cfu in water, and 2 x 10(3) cfu in full cream milk. An epidemiological application of the assay in detecting non-culturable campylobacters from a contaminated potable water supply is described.

Campylobacter↗
PubMed1996

Antigenic diversity of meningococcal outer membrane protein PorA has implications for epidemiological analysis and vaccine design.

The currently used serological subtyping scheme for the pathogen Neisseria meningitidis is not comprehensive, a proportion of isolates are reported as not subtypeable (NST), and few isolates are fully characterized with two subtypes for each strain. To establish the reasons for this and to assess the effectiveness of DNA-based subtyping schemes, dot blot hybridization and nucleotide sequence analyses were used to characterize the genes encoding antigenic variants of the meningococcal subtyping antigen, the PorA protein. A total of 233 strains, including 174 serologically NST and 59 partially or completely subtyped meningococcal strains, were surveyed. The NST isolates were chosen to be temporally and geographically representative of NST strains, isolated in England and Wales, and submitted to the Meningococcal Reference Unit in the period 1989 to 1991. The DNA-based analyses demonstrated that all of the strains examined possessed a porA gene. Some of these strains were serologically NST because of a lack of monoclonal antibodies against certain PorA epitopes; in other cases, strains expressed minor variants of known PorA epitopes that did not react with monoclonal antibodies in serological assays. Lack of expression remained a possible explanation for serological typing failure in some cases. These findings have important implications for epidemiological analysis and vaccine design and demonstrate the need for genetic characterization, rather than phenotypic characterization using monoclonal antibodies, for the identification of meningococcal strains.

Amino Acid Sequence↗
PubMed1996

Carotid endartectomy trials.

For endarterectomy for symptomatic carotid artery stenosis, there is strong evidence that has been universally accepted and put forward by the North American Symptomatic Carotid Endarterectomy Trial (NASCET), with corroboration from the European Carotid Surgery Trials Collaborative Group, that patients with severe stenosis have an extremely high risk for stroke without carotid endarterectomy and a low risk with it. We are awaiting for NASCET information regarding the lower limit of percent stenosis for which patients with symptoms should be considered for surgery.

Angiography↗
PubMed1996

Duplex and color Doppler flow sonography of occlusion and near occlusion of the carotid artery.

PURPOSE: To determine whether color Doppler flow imaging with the use of slow-flow sensitivity improves sensitivity and specificity in the differentiation of occlusion and near occlusion of the internal carotid artery. METHODS: Color Doppler and duplex sonography were performed in symptomatic patients who had angiographically confirmed occlusion and/or near occlusion of the internal carotid artery. The study consisted of two phases: in the first, we assessed the usefulness of color Doppler flow imaging by retrospectively reviewing the records of 35 patients with 36 angiographically confirmed occlusions or near occlusions of the internal carotid artery who were examined with color Doppler flow imaging at our institution during a period of 4 years; in the second phase, we incorporated color Doppler sonography into the routine scanning protocols of 39 patients with 41 occluded or nearly occluded internal carotid arteries seen over a period of 2 1/2 years. RESULTS: Overall, color Doppler imaging correctly showed all 34 of the near occlusions (sensitivity, 100%) and 36 of the 43 occlusions (specificity, 84%). Seven patients with angiographically confirmed occlusion had sonographic findings that suggested near occlusion. In the first phase, eight near occlusions were misinterpreted as occlusions with conventional duplex sonography, but were correctly shown with color Doppler flow imaging. In the second phase, sensitivity increased from 50% to 100% (18 or 18) because of better detection of the nearly occluded lumen. This was at the expense of a decrease in specificity (from 100% to 78%). owing to identification of apparent flow in the internal carotid artery on color Doppler flow images in five of 23 occlusions. CONCLUSION: Because of its ability to depict slow flow, color Doppler imaging with slow-flow sensitivity is superior to conventional duplex sonography for the noninvasive discrimination of occlusion from near occlusion of the internal carotid artery.

Arterial Occlusive Diseases↗
PubMed1996

The role of angiography in the assessment of atherosclerotic disease. Assessment of the carotid bifurcation.

Paralleling recent developments in noninvasive vascular imaging of the carotid bifurcation, there have been several randomized therapeutic trials for carotid stenosis to identify which patients should receive treatment. Studies involved in neuroimaging have sought ways to evaluate carotid artery stenosis without standard angiography, whereas those involved in therapeutic decisions for patients with carotid stenosis have attempted to verify the use of carotid endartectomy and determine which patients benefit most from treatment. The methods of measurement for carotid stenosis, duplex ultrasound measurement comparisons, magnetic resonance angiography and computed tomographic angiography, and standard radiographic angiography are discussed.

Angiography↗
PubMed1996

Interobserver variability in angiographic measurement and morphologic characterization of intracranial aneurysms: a report from the International Study of Unruptured Intracranial Aneurysms.

PURPOSE: To determine the variability in assessment of the principal inherent characteristics of intracranial aneurysms through the evaluation of interobserver variability for material with uniform quality. METHODS: Blinded interpretations of a single set of cerebral arteriograms of 55 aneurysms were evaluated by several statistical approaches. RESULTS: Excellent correlations were found for the detection and measurement of aneurysms after adjusting for geometric distortion caused by magnification. Progressively decreasing correspondence was found for factors that characterized morphology, including, in order, determination of margins, assessment of accessory appendages, and identification of a neck. DISCUSSION: Correction for geometric distortion was the most critical factor that influenced uniform measurement of size. Standards for measurement and morphologic characteristics were subsequently established for use in the International Study of Unruptured Intracranial Aneurysms.

Adult↗