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Biomedical subjects

C W Walker

Publications and source records attributed to C W Walker.

53 records · Page 3Linked to original sources
PubMed1990

Radiologic manifestations of adult tuberculosis.

Adult pulmonary tuberculosis commonly presents with radiographic findings of upper lobe cavitary opacities, in which case the correct diagnosis is usually suspected. However, other radiographic presentations of this disease in the adult include intrathoracic adenopathy, pleural effusion, lower lobe consolidation, a miliary pattern, and a solitary nodule. In these latter cases, tuberculosis may not be considered in the differential diagnosis. This article discusses the protean manifestations of adult pulmonary tuberculosis.

Adult↗
PubMed1990

A rapid technique for detection of resistance to chloramphenicol in Streptococcus pneumoniae and comparison with minimum inhibitory concentration and disk-diffusion methods.

Fifty-two strains of Streptococcus pneumoniae were examined for production of chloramphenicol acetyltransferase (CAT) by a rapid technique based upon induction of enzyme activity and chemical assay. This method was compared with one measuring the minimum inhibitory concentration (MIC) by agar dilution and a diffusion test with disks containing 10 micrograms, 30 micrograms and 50 micrograms of chloramphenicol. The MIC for 13 chloramphenicol-resistant strains was 16 mg/L and for 39 sensitive strains less than or equal to 4 mg/L. The chemical assay clearly distinguished resistant from sensitive strains; it was technically simple and provided results within 90 min. The distinction between sensitive and resistant bacteria in the disk diffusion assay was clearer with 10-micrograms than with 30-microgram and 50-micrograms disks. However, the chemical CAT assay, with enzyme induction, is recommended when a rapid result is required.

Bacteriological Techniques↗
PubMed1989

Pulmonary embolism: chest radiographic abnormalities.

The value of chest radiography in the diagnosis of pulmonary embolism has been investigated extensively. Although the chest radiograph seldom permits one to say whether embolism is or is not present, it is still an essential component in the evaluation of the patient with suspected pulmonary embolism. This article stresses the radiographic abnormalities that occur with pulmonary embolism and defines the role of the chest radiograph for evaluation of this disorder.

Humans↗
PubMed1989

Complications from extravasated retroperitoneal barium: case report and review of the literature.

Extravasation of barium into the retroperitoneum is an uncommon complication of radiologic examinations of the gastrointestinal tract. It may occur during evaluation of either the upper or lower tract. A case is presented in which the result was abscess formation, a potential delayed complication of duodenal perforation and retroperitoneal extravasation of barium. In this case, medical treatment was successful.

Abscess↗
PubMed1989

Bronchogenic cysts.

Bronchogenic cysts are relatively uncommon congenital lesions. They may be detected on routine radiography in asymptomatic patients or may present with various manifestations, some of which may be life-threatening. Age at diagnosis ranges from infancy to late adulthood, with asymptomatic lesions occurring more often in older children and adults. Cysts may be located in subcarinal, paratracheal, hilar, paraesophageal and intrapulmonary sites. The chest radiograph is the primary diagnostic study, with computed tomographic scans of the chest providing more definitive evaluation. Despite some controversy, surgery is considered the treatment of choice, even in the asymptomatic patient.

Bronchogenic Cyst↗
PubMed1988

The reliability of methods for detecting chloramphenicol resistance in Haemophilus influenzae.

Eighty-eight strains of Haemophilus influenzae were examined for resistance to chloramphenicol by various techniques. Methods compared were a rapid chemical assay for chloramphenicol acetyltransferase (CAT), an agar dilution minimum inhibitory concentration (MIC) method, disc diffusion tests with 10, 30, and 50 micrograms discs, and a microbiological technique for detecting CAT. Fifty-eight chloramphenicol-sensitive strains had MICs less than or equal to 0.5 mg/l, while 30 resistant strains had MICs greater than or equal to 4 mg/l. The chemical CAT assay clearly distinguished resistant from sensitive strains, was simple to perform and provided results within 30 min. By disc diffusion, the lower the disc content the clearer the distinction between sensitive and resistant populations. Difficulties were encountered in interpretating the microbiological CAT assays as some sensitive strains appeared resistant. The chemical CAT assay is recommended for use when a rapid result is required. Rare chloramphenicol-resistant, CAT-negative strains have been described in the USA and these strains would only be detected by a disc diffusion or MIC test.

Chloramphenicol O-Acetyltransferase↗
PubMed1988

Haemorrhagic colitis: detection of verotoxin producing Escherichia coli O157 in a clinical microbiology laboratory.

Faeces (n = 1319) were examined over three months for the presence of non-sorbitol fermenting, verotoxin producing Escherichia coli (serotype O157). Seven isolates were found, four from patients with bloodstained diarrhoea and three from patients with no evidence of blood in the faeces. Screening of all faecal samples with specific O157 antiserum for non-sorbitol fermenting organisms and agglutination was an important adjunct to clinical and microscopic findings and helped detect cases of verotoxin producing E coli which might otherwise have been missed.

Bacterial Toxins↗
PubMed1988

Effect of a 1.5 Tesla magnetic field on Greenfield filters in vitro and in dogs.

The authors have tested four Greenfield filters for deflection in a 1.5 Tesla magnetic field and found large variations in the amount of deflection among filters. They also placed two filters in dogs and checked the filter for migration by taking radiographs before and after magnetic resonance imaging (MRI) scans. They found no evidence of migration. They conclude that, while most Greenfield filters respond to a magnetic field, the chance of migration of a filter because of an MRI scan is small. Therefore, MRI scanning of patients with Greenfield filters has little risk.

Animals↗
PubMed1987

Determination of polyamines in digestive and reproductive tissues of adult Asterias vulgaris (Echinodermata: Asteroidea).

1. The polyamines spermine, spermidine and putrescine were extracted from tissues of Asterias vulgaris and quantitated using thin layer chromatography. 2. In the pyloric caeca, mean (+/- SE) levels of spermine, spermidine and putrescine were 138(15), 86(24) and 415(77) nmol/g wet wt tissue, respectively. In the testes, levels were 95(12), 13(6) and less than 6 nmol/g wet wt. In the ovaries, levels were 105(9), 11(0.8) and 15(8) nmol/g wet wt. 3. High levels of polyamines in the pyloric caeca may be related to secretion or excretion in this tissue. 4. We hypothesize that polyamines will be important in the regulation of cellular activity in these tissues during the annual reproductive cycle.

Animals↗
PubMed1984

An ultrastructural study of relationships between the ovarian haemal system, follicle cells, and primary oocytes in the sea star, Asterias rubens. Implications for oocyte nutrition.

The genital haemal sinus, present throughout the gonad wall of sea stars, is supposed to be the site of ultimate accumulation of nutrients for the germinal epithelium. Early vitellogenic pear-shaped oocytes are attached to this sinus by stalk-like processes. The ultrastructure of this association and of the oocyte-follicle cell complex is described with emphasis on mechanisms involved in oocyte nutrition. The genital haemal sinus, and sometimes portions of the surrounding genital coelomic sinus, contain a fine granular ground substance and amoeboid cells. Material similar to the haemal ground substance also fills vacuities in the inner basal laminae of the haemal sinus and intervenes between this layer and adjacent germinal and follicle cells in the ovarian lumen. Vitellogenesis is first detectable as numerous vacuoles accumulate within the oocyte-stalk near the haemal sinus; they contain flocculent material and often fuse with adjacent lysosome-like vacuoles. As vitellogenesis proceeds, oocytes develop complex and tenuous connections with the haemal sinus. These consist of a network of pseudopodia that interdigitate with thin sheet-like extensions of follicle cells. These cells are attached to the oolemma by microfilamentous processes and contain regularly arranged concentrations of glycogen granules and well developed rough endoplasmic reticulum. It is concluded, that follicle cells provide each oocyte with a compartmentalized microenvironment within the ovarian lumen, that such compartments are intimately associated with the nutrient laden haemal sinus, and that nutritive and vitellogenic substances, derived extragonadally and stored temporarily in the ovarian wall, can pass through the oocyte-stalk.

Animals↗
PubMedDate not supplied

Radiographic and orthopedic evaluation of wrist trauma.

This paper was written to enable radiologists to contribute more usefully to the diagnosis and treatment of various wrist injuries. All imaging modalities are discussed to equip the radiologist for his difficult task. We present a systematic approach to the evaluation of wrist trauma patients beginning with initial plain films and proceeding through more invasive or sophisticated studies in order to achieve a definitive diagnosis. Toward this end a flow chart has been developed as a quick reference source. The authors have then described the anatomy and kinematics of the wrist to further the radiologist's understanding of the forces involved and the injuries produced by trauma. From this foundation individual injuries are then discussed together with the best methods of making the proper diagnosis of each. Criteria for adequate treatment of various injuries are also presented.

Fractures, Bone↗
PubMedDate not supplied

Exposure to ultraviolet radiation (290-400 nm) causes oxidative stress, DNA damage, and expression of p53/p73 in laboratory experiments on embryos of the spotted salamander, Ambystoma maculatum.

Developing embryos of the spotted salamander, Ambystoma maculatum, exposed to ultraviolet radiation (UVR; 290-400 nm) in the laboratory show a significant sensitivity to UVB (290-320 nm) radiation. Embryos in laboratory experiments exhibited significant DNA damage during exposures to UVR despite a significant increase in the production of the protective pigment melanin in response to UVR exposure. DNA damage occurs as a result of both the direct effects of exposure to UVR, and the indirect effects are mediated by the production of reduced oxygen intermediates. The production of reactive oxygen species initiates the expression of p53/p73 that leads to either DNA repair or apoptosis. When similar experiments are conducted on salamander embryos exposed to solar UVR in vernal pools, the embryos show significantly less sensitivity and higher survivorship. The differences between laboratory and field experiments are a result of the attenuation of UVR caused by the accumulation of dissolved organic carbon within the pools of these wooded areas. These findings suggest that northeastern populations of spotted salamanders are sensitive to UVR but are not significantly affected by present-day irradiances of UVR in the field. These results do suggest that continued decreases in stratospheric ozone over temperate latitudes have the potential to affect spotted salamanders in their natural habitats.

Ambystoma↗
PubMedDate not supplied

Correct placement of epidural steroid injections: fluoroscopic guidance and contrast administration.

We prospectively evaluated 316 caudal-approach epidural steroid injections given by staff radiologists and residents in our department over a 1-year period. Needle placement was checked with fluoroscopy and corrected if necessary. When the needle tip was within the sacral canal, nonionic contrast material was injected. If epidural contrast was not observed, the needle tip was repositioned. Of 111 procedures performed by physicians who had given fewer than 10 epidural steroid injections, 53 (47.7%) resulted in correct nonfluoroscopically directed placement of the needle. For physicians who had performed between 10 and 50 such procedures, 62 (53.4%) of 116 had correct nonfluoroscopically directed placement. For staff physicians, 55 (61.7%) of 89 placements were correct. Even when the sacral hiatus was easily palpated and a staff physician was confident that he or she was within the epidural space, fluoroscopy revealed incorrect placement 14.2% of the time (seven of 49 procedures). In addition, when the needle was positioned within the sacral canal and no blood was evident on Valsalva maneuver or aspiration, the injection was venous in 29 of 316 procedures (9.2%). The presence of blood on the needle stylus was not a reliable indicator of venous placement of the needle. Our findings indicate that fluoroscopy is essential for correct placement of epidural steroid injection. Contrast administration is necessary to avoid venous injection of steroids.

Adult↗
PubMedDate not supplied

Interventional musculoskeletal radiology.

Interventional procedures constitute a significant proportion of musculoskeletal radiology. Percutaneous needle biopsy is the ultimate diagnostic technique for the evaluation of musculoskeletal neoplasms and infections. The procedure is accurate, rapid, and safe. It is ideally suited for the diagnosis of metastatic disease and round cell neoplasms. Several needle procedures have been used for the diagnosis and treatment of low back pain. Diskography is primarily a diagnostic test used to determine the symptomatic disk level when multilevel disk disease is present and also to diagnose internal disk disruption. Nerve block with local anesthetic is also used to locate the symptomatic level in patients with multilevel abnormalities. Epidural steroid injection is a therapeutic procedure that commonly is used in patients with low back pain and has been shown to be most effective in patients with disk herniation. Facet joint injection with local anesthetic and steroid is performed to diagnose and treat the facet syndrome. Other needle procedures in the musculoskeletal system include sacroiliac joint aspiration and injection, prosthetic joint aspiration to evaluate potential infection, distention arthrography, and injections of the coccyx for coccydynia.

Adrenal Cortex Hormones↗