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Biomedical subjects

J M Stevens

Publications and source records attributed to J M Stevens.

At least 145 records · Page 8Linked to original sources
PubMed1989

Catechol estrogen formation in MCF-7 cell culture and effects of bromoestrogen inhibitors.

Agonist and antagonist activities have been reported for several catechol estrogens given exogenously. Since the metabolic clearance rate for catechol estrogens in the body is very rapid, catechol estrogens produced at other tissues will have minimal effect on breast tissue. Information of the extent of catechol estrogen formation within cells is critical in assessing the overall importance of these estrogen metabolites. Investigations of the conversion of estrogens to catechol estrogens were performed in the MCF-7 human mammary carcinoma cell culture system. Reverse-phase high-performance liquid chromatography (HPLC) analysis demonstrated that very little metabolism of estradiol occurs after 48 h, with only small amounts of estrone, 2-hydroxyestradiol, 2-hydroxyestrone, and estriol being observed. The total amount of 2-hydroxyestrogen products formed from 1 microM estradiol was 406.2 pmol (SD = 60.9) per 3 x 10(7) cells in 48 h. Similar results were obtained using the simpler radiometric assay for estrogen 2-hydroxylase, which measures the release of 3H2O from [2(-3)H]estradiol. The effects of inhibitors of estrogen 2-hydroxylase were also examined in MCF-7 cells. 2-Bromoestradiol, 4-bromoestradiol, and 2,4-dibromoestradiol effectively block estrogen 2-hydroxylase in a dose-dependent manner in MCF-7 cultures, with ED50 of approximately 1 microM for each inhibitor. Furthermore, these bromoestrogens bind poorly to estrogen receptors in MCF-7 cells and do not alter cell growth. Thus, in MCF-7 mammary cell cultures, metabolism of estradiol occurs to only a minor degree, and it is unlikely that the levels of catechol estrogens would reach physiologically relevant concentrations in the intact breast cancer cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Breast Neoplasms↗
PubMed1989

Clinical diagnosis from digital displays: preliminary findings of the St Mary's Evaluation Project.

Image quality is a fundamental issue in the introduction of picture archiving and communications systems (PACS), and one that has hitherto been eclipsed by other aspects of the considerable technological challenge facing scientists and manufacturers involved in its development. We conducted a formal evaluation of clinical radiological diagnosis from a commercially available PACS viewing station, using subperiosteal resorbtion in renal osteodystrophy as the test pathological diagnosis, with receiver operating characteristic (ROC) analysis of the results. We conclude that the displayed, digitised images were inferior to film using the apparatus tested and believe that careful, objective clinical evaluation of such systems is of paramount important.

Chronic Kidney Disease-Mineral and Bone Disorder↗
PubMed1989

Outpatient myelography: an acceptable and cost-effective technique.

Sixty-five patients with stable low back pain had their lumbar myelography performed as outpatients, staying in the department for 1 h after the examination. The incidence of post-myelogram headache was similar to that reported for inpatients. No serious after-effects occurred in the study group. The vast majority of patients preferred to be at home following the study. It is concluded that outpatient myelography is safe, less expensive and preferred by the patients.

Adult↗
PubMed1989

Relative safety of intravenous digital subtraction angiography over other methods of carotid angiography and impact on clinical management of cerebrovascular disease.

Data from a multicentre survey based on three London teaching hospitals on the relative safety and clinical utility of intravenous carotid digital subtraction angiography (DSA) over intra-arterial DSA and conventional carotid angiography are presented. The incidence of stroke during intra-arterial DSA was 0.7% (n = 538) and during conventional angiography was 0.8% (n = 780). The incidence of stroke during intravenous DSA was zero (n = 3710). When it constituted the initial investigation, intravenous DSA achieved a 93.8% replacement value over intra-arterial studies as a whole (n = 474) and 89% replacement value for patients having carotid endarterectomy (n = 99). It was also noted that the installation of DSA equipment at one unit coincided with a sixfold increase in the number of carotid angiographic examinations and an almost threefold increase in carotid endarterectomies.

Angiography, Digital Subtraction↗
PubMed1988

Acute effects of the aldehyde dehydrogenase inhibitors, disulfiram, pargyline and cyanamide, on circulating ketone body levels in the rat.

Acetonemia is generally associated with the ketogenic states of fasting and diabetes. Disulfiram (DS), an inhibitor of aldehyde dehydrogenase (AlDH) that is used as an alcohol deterrent drug, is also known to elevate blood acetone in humans, but in the absence of a commensurate increase in its metabolic precursor, acetoacetate. We reexamined the effects of DS and other AlDH inhibitors on circulating ketone body levels in male rats of Sprague-Dawley descent and again demonstrated a 6- and 16-fold increase in blood acetone along with normal levels of acetoacetate at 6 and 24 hr after DS. Pargyline, another inhibitor of AlDH, maintained normal blood acetone levels in the presence of reduced acetoacetate levels. A third inhibitor of AlDH, cyanamide, administered to fasted and nonfasted rats, elevated blood acetone levels 10-fold over controls, with, however, a commensurate 5- and 7-fold increase in blood acetoacetate levels. The threshold values for the cyanamide-induced elevation of blood acetone and acetoacetate were equivalent, i.e. approximately 0.25 mmol/kg body weight (i.p.). The elevation of acetoacetate and the inhibition of hepatic catalase activity by cyanamide are not mechanistically linked, since 3-amino-1,2,4-triazole, another inhibitor of catalase, elevated blood acetone but not acetoacetate levels. These findings suggest that DS-induced acetonemia is due to inhibition of acetone metabolism, whereas enhanced acetone formation through acetoacetate contributes significantly to cyanamide-induced acetonemia.

3-Hydroxybutyric Acid↗
PubMed1988

A model for capacity planning of a comprehensive integrated information system for hospitals and clinics.

Appropriate system sizing is essential to ensuring a reasonable computer response time for end users. A model is discussed that describes the type and number of interactions between user terminals and printers and the central processor for a comprehensive, integrated medical information system. The system modeled includes support to inpatient and outpatient order entry and results reporting for clinical services; registration; admission, disposition, and transfer; patient appointing; pharmacy, clinical laboratory, and radiology; medical record management; and electronic messages. Originally developed for use in benchmark testing of comprehensive systems designed for military hospitals and clinics, the model has been generalized to be applicable to other systems and settings. Results are presented for a routine busy day in a 200-bed teaching hospital providing extensive outpatient services, and a large free-standing clinic. The model results can be applied to several facets of system planning, including sizing of the central processor and communications network, determining the optimal number of storage devices and user devices, and fine tuning the user interface.

Ambulatory Care Information Systems↗
PubMed1987

Some dynamic factors in compressive deformity of the cervical spinal cord.

An investigation into the relative elastic and non-elastic components of compressive deformity of the cervical spinal cord has been made. Sixteen patients were examined by computed myelography with the neck flexed and extended, and one fresh specimen of a human spinal cord was studied under reversible transverse compression with the specimen in a stretched and shortened state. In conditions of transverse compression cord tissue undergoes an alteration in viscoelastic properties, manifesting itself as reduced expansion of the compressed segment as the cord shortens, which in some cases is independent of whether the agent is seen to actually contact the cord. The presence of degenerative changes in cord substance probably accentuates this alteration in mechanical properties.

Aged↗
PubMed1987

Percutaneous insertion of the spinal end of a cysto-peritoneal shunt as definitive treatment to relieve cord compression from a spinal arachnoid cyst.

A case of myelopathy with both intradural and extradural spinal arachnoid cysts is reported treated by cysto-peritoneal shunt, the spinal end of which was inserted percutaneously under fluoroscopic control. The site of drainage was determined by findings at computed myelography. The case illustrates the value of the latter in demonstrating the pathological bio-mechanics producing myelopathy in this condition.

Adult↗
PubMed1986

Computed tomography in cervical spondylotic myelopathy and radiculopathy: visualisation of structures, myelographic comparison, cord measurements and clinical utility.

Sixty-nine patients with cervical spondylotic myelopathy (CSM), radiculopathy (CSR), or both (CSMR) were studied with computed tomography (CT). Computer-assisted myelography (CAM) accurately determines the site and nature of spondylotic protrusions and provides good visualisation of the subarachnoid space and cord deformities even in areas with dilute metrizamide. However, excessive vertebral movement and bulging ligamenta flava with their effects on cord deformity, so easily visualised in myelograms, are completely or partially missed. In the assessment of CSM, metrizamide myelography (MM) followed by CAM should be performed, particularly when the myelographic images are unsatisfactory due to contrast dilution or blockage, when cord compression cannot be ascertained with MM and when cord atrophy is suspected. In CSR, the diagnostic information from MM and CAM is comparable. The diagnostic criteria in CAM are, however, less direct and since MM is adequate in uncomplicated cases, CAM is generally not necessary. The APD, APD/TD ratio, area and circularity are sensitive indices of cord deformity and the first two should be used more often to assist visual assessment of cord deformity. The relation between cord parameters and treatment response is better reflected in CSM cases managed conservatively and the results suggest that the degree of cord deformity is helpful in determining the outcome and hence the choice between surgical and conservative treatment. In plain CT, the osteophytes and calcified discs are adequately visualised and canal dimensions measured with accuracy, but the cervical cord and roots cannot be properly assessed and the diagnosis of CSM or CSR cannot be ascertained. At present, its role in cervical spondylosis is therefore limited.

Humans↗
PubMed1986

Computer-assisted myelography in cervical spondylotic myelopathy and radiculopathy. Clinical correlations and pathogenetic mechanisms.

A total of 53 patients with cervical spondylotic myelopathy and/or radiculopathy were studied with computer-assisted myelography following metrizamide myelography. Cervical cord deformities resulting from spondylotic protrusions were classified into four groups. The A shape (anterior central concavity) is the commonest and is often associated clinically with bilateral anterolateral and posterior column deficits. In the B shape (lateral deformity on one side), unilateral anterolateral column and root signs, usually mild, predominate. The symptomatology of the C shape (lateral deformity on both sides) and the D shape (flattened anterior surface) is bilateral, although not often symmetrical, and includes anterolateral and posterior column disturbances and root signs. Radiculopathy may, however, occur in the absence of cord deformity if the spondylotic lesion is close to or inside the intervertebral foramen. As there is some relationship between cord shapes and symptomatology, the decision as to whether a particular deformity is responsible for the clinical presentation may be made with more confidence. Moreover, the degree of cord deformity correlates well with the severity of symptomatology. Those with mild deformity had relatively few or mild cord signs, whereas in those with severe deformity cord signs were numerous and severe. Certain observations on cord deformity in vivo support the view that compression is an important pathogenetic mechanism in cervical spondylotic myelopathy. Most patients had anterior cord compression and the anterolateral signs were more frequent and marked. Severity of cord signs is associated with the degree of compression. Removal of the compression is followed by re-expansion of the cord and clinical improvement. In a small number of cases where cord compression by osteophytic protrusion was mild, and where clinical improvement followed the removal of the protrusion, the theory of cord traction and friction appears to apply. The contribution of other mechanical factors and of ischaemia to cord damage is also discussed.

Adult↗
PubMed1986

The spinal cord in rheumatoid arthritis with clinical myelopathy: a computed myelographic study.

Thirty one patients with suspected myelopathy due to rheumatoid arthritis were examined by plain radiography and 27 had computed myelography. Clinical features and radiological findings were compared. Deformity of the spinal cord could occur in the absence of combined anterior and posterior compression and correlated closely with clinical features only when considered in combination with skeletal and adjacent soft tissue abnormalities. The best surgical results were achieved by transoral odontoidectomy.

Adult↗
PubMed1986

Transoral decompression and posterior fusion for rheumatoid atlanto-axial subluxation.

Cervical myelopathy is an uncommon but potentially fatal complication of rheumatoid atlanto-axial subluxation. Computerised myelotomography with three-dimensional reconstruction shows that rheumatoid pannus, together with the odontoid peg, contributes significantly to anterior cervico-medullary compression. These findings were the basis for treatment by transoral anterior decompression and posterior occipitocervical fusion, which removes both bony and soft-tissue causes of compression and allows early mobilisation without major external fixation. We report encouraging results from this combined approach in 14 patients who had progressive neurological deterioration.

Adult↗
PubMed1985

Aspects of the anatomy of the cerebellum on computed tomography.

The salient features of the normal CT anatomy of the various lobules of the cerebellar hemispheres and vermis are described. The subdivisions of the vermis were found to be most constant. The surface appearance of the hemisphere lobules was also relatively constant; however, at CT these fissures are imaged at depth and this constancy is not reflected in CT images because folia cross the depths of the major sulci from one lobule to the other in a highly variable manner. The flocculus has been confused with the anterior angle of the cerebellum, and the cerebellar tonsils with the biventral lobule.

Cerebellum↗
PubMed1985

Morphology and measurements of the cervical spinal cord in computer-assisted myelography.

Thirty-six control subjects had computer assisted myelography (CAM) using the EMI CT 5005 scanner. The normal cervical cord is elliptical, more circular at the upper and lower ends and flatter in the mid-segments. Asymptomatic cord deformities, usually mild, were present in nine subjects (25%). Four measurements, namely, sagittal diameter (APD), transverse diameter (TD), area (a) and circumference (c) were made and two more parameters calculated i.e. APD/TD ratio and circularity (= 4 pi a/c2). These control values form the basis of qualitative and quantitative assessment of cord deformity. When cord measurements are to be used, control values should be obtained for each scanner and procedures should be standardized.

Adult↗