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Biomedical subjects

M J Collins

Publications and source records attributed to M J Collins.

At least 37 records · Page 2Linked to original sources
PubMed1999

Hydroxyproline interference during the gas chromatographic analysis of D/L aspartic acid in human dentine.

The proportion of D- to L-enantiomers of aspartic acid in metabolically isolated proteins has been used by forensic scientists to estimate age at death. We have demonstrated the interference of a derivative of hydroxyproline (N-TFA isopropyl Hyp ester) with the N-TFA isopropyl L-Aspartic (Asp) acid ester during gas chromatography of amino acids. This has serious implications for the accurate quantification of the D- to L-Asp ratio extracted from collagenous proteins. Having demonstrated the potential for this co-elution in amino acid standards, acid-soluble dentine proteins and non-mineralised collagen, we argue that this problem can be overcome either by high resolution separation or by analysis of the (Hyp-poor) non-collagenous protein fraction.

Aspartic Acid↗
PubMed1999

Metastatic esophageal carcinoma to the orbit.

PURPOSE: To report a case of esophageal adenocarcinoma and areas of gastric differentiation in the esophagus (Barrett esophagus) metastatic to the orbit. METHODS: A 47-year-old man with a history of esophageal carcinoma developed turgescence around his left eye. He underwent a biopsy and histologic examination of a left orbital mass. RESULTS: Histopathology of the orbital tumor was consistent with metastatic adenocarcinoma from the esophagus. CONCLUSIONS: This metastatic adenocarcinoma to the orbit likely arose in Barrett esophagus.

Adenocarcinoma↗
PubMed1997

Personal ultraviolet radiation exposure of workers in a welding environment.

The personal ultraviolet radiation exposure levels of a group of welders and nearby workers were estimated using a photosensitive polymer film, polysulphone. The polysulphone film was attached to the inner and outer surfaces of eye protection, the workers' clothing, and also placed throughout the work area. The estimated average ocular exposures (inside the helmets) for welders and boiler-makers were between four and five times the maximum permissible exposure (MPE) limit, and the estimated exposures at the spectacles of nonwelders were around 9 times MPE. Body exposures (at the clothing surface) for welders were estimated to be around 3000 times MPE and for nonwelders around 13 times MPE. The ambient ultraviolet radiation levels in the factory were found to exceed the MPE by an average of 5.5 times, even in nonwelding areas. The results suggest that welders require additional ocular protection to supplement conventional welding helmets, and any exposed skin areas of workers in this environment should also be protected.

Case-Control Studies↗
PubMed1997

Angles of entry of ultraviolet radiation into welding helmets.

To investigate the angles of entry of ultraviolet (UV) radiation into welding helmets, a UV detector was placed in the eye socket of a head form that was then fitted with a range of welding helmets. The head form was exposed to a collimated beam of UV radiation from various orientations, and the amount of infiltration was measured. Radiation was found to be reflected from the filter plate and into the detector (eye) after entering through (1) an opening between the edge of the shield and the side of the face, and (2) an opening between the top edge of the shield and the top of the head. These results have significance for UV exposure when welding is performed in highly reflective and enclosed situations, and for the design of welding helmets.

Environmental Monitoring↗
PubMed1997

Does pulse oximetry reliably detect aspiration in dysphagic stroke patients?

BACKGROUND AND PURPOSE: The aim of the present study was to examine the value of pulse oximetry in the diagnosis of aspiration by comparing it with the gold standard, videofluoroscopy, by use of a prospective, controlled, single-blind study design. METHODS: Pulse oximetry was performed simultaneously with videofluoroscopy in 54 consecutive dysphagic stroke patients. Oxygen saturation measurements were taken before the video-fluoroscopic examination (baseline), on swallowing and continuously for 2 minutes after swallowing, and 10 minutes later. RESULTS: Pulse oximetry reliably predicted aspiration or lack of it in 81.5% of cases. The predictive value of the test was low in patients aged > or = 65 years and possibly those with chronic lung disease. One smoker also had a false-negative pulse oximetry result, ie, normal oxygen saturation despite radiological evidence of aspiration. CONCLUSIONS: Pulse oximetry is a reliable method of diagnosis of aspiration in most dysphagic patients. However, careful interpretation of pulse oximetry data is necessary in older subjects, possibly those with chronic pulmonary disease, and smokers. The method is noninvasive, simple, and quick, and can be used routinely in the clinical assessment of dysphagic patients.

Adult↗
PubMed1997

Measurement of ultraviolet radiation at the surface of the eye.

PURPOSE: A new method for the measurement of ultraviolet radiation that reaches the surface of the eye is described. METHODS: The technique uses contact lenses produced from the ultraviolet-sensitive plastic polysulfone. Two types of polysulfone contact lenses (9 mm and 12 mm in diameter) were manufactured from a polysulfone rod. The 9-mm polysulfone contact lens could be calibrated and used to determine the ocular-to-ambient exposure ratio in a fashion similar to polysulfone film badges. The 12-mm polysulfone contact lens was designed as a "piggy-back" lens and required a larger diameter polymethlylmethacrylate carrier lens to fit the eye adequately. A method of in vivo stabilization was developed to minimize lens rotation. RESULTS: During four wearing trials, the ratio of ocular-to-ambient ultraviolet exposure ranged from 4% to 23%. CONCLUSIONS: Contact lenses manufactured from polysulfone offer the potential to study the exposure of the eye to ultraviolet radiation. The smaller diameter lens can measure an average ocular exposure, whereas the larger, stabilized, piggy-back design may allow regional dose assessment across the entire lens surface.

Biocompatible Materials↗
PubMed1996

The relation between corneal and total astigmatism.

Using computer-assisted videokeratoscopy we measured corneal astigmatism and compared these results over a range of corneal zone diameters with total ocular astigmatism derived by subjective refraction. Videokeratoscopes permit a more detailed analysis of the power distribution within a given corneal surface area, enabling comparison to the total astigmatism for equivalent aperture sizes. Although there were significant individual variations, the group average data supports the traditional view of a linear relation between corneal and total astigmatism. This was true across the range of apertures tested from 2 to 7 mm, with the coordinates of the relation being consistent with that of the modified Javal's rule; namely a slope of 1 and an intercept of approximately 0.50 D against-the-rule residual astigmatism.

Adult↗
PubMed1995

Measurement of monochromatic ocular aberrations of human eyes as a function of accommodation by the Howland aberroscope technique.

Further development of the objective version of the Howland and Howland [(1976) Science, 193, 580-582; (1977) Journal of the Optical Society of America, 67, 1508-1518] aberroscope technique for measuring ocular aberrations is described. Compensation for refractive corrections and calibration is discussed. The technique was used to investigate the effect of accommodation upon the monochromatic aberrations of the right eyes of 15 subjects. Coma and coma-like aberrations were the dominant aberrations for most people at different accommodation levels, thus confirming previous findings. Variations in aberrations were considerable between subjects. About half the subjects showed the classical trend towards negative spherical aberration with accommodation. Changes in spherical aberration with accommodation in this study were less than found in previous studies where all monochromatic aberration was considered to be spherical aberration.

Accommodation, Ocular↗
PubMed1995

Monochromatic aberrations and myopia.

The monochromatic aberrations present in the eyes of a group of 21 young myopic subjects and 16 young emmetropic subjects were measured along the visual axis at three levels of accommodation. The aberrations were measured using a modified aberroscope technique which makes use of a retinal camera to photograph the shadow image of the aberroscope grid on the retina, while accommodation levels of 0, 1.5 and 3.0 D were induced consensually. Fourth-order aberrations were significantly different between the emmetropic and myopic groups, with the myopes showing lower fourth-order terms. A high proportion of the aberroscope grids photographed in the myopic eyes were too highly aberrated to permit analysis.

Accommodation, Ocular↗
PubMed1995

Development of a chitin assay for the quantification of fungus.

Chitin, a unique structural polysaccharide found in fungi and arthropods, is not produced by vertebrates. Thus, the potential applications of a specific and sensitive assay for chitin are numerous, including the evaluation of the extent of fungal keratitis. Chitin is a homopolymer of beta (1, 4) linked D-N-acetylglucosamine. We have developed a simple and reproducible assay for chitin and applied it to Candida albicans cultures. The assay involves homogenization of the culture and treatment with 21.1 M KOH to remove soluble materials, including proteins. This base treatment also deacetylates the chitin to the glucosamine polymer, chitosan. Chitosan is hydrolyzed by 0.5 M H2SO4 to glucosamine monomers which are then deaminated by the addition of NaNO2 to the acid solution. The resulting 2,5-anhydromannose is reduced by NaB[3H]4 to 1-[3H] 2,5-anhydromannitol. This radiolabelled sugar is isolated by paper chromatography and quantified via liquid scintillation. The sensitivity of this assay is assessed by comparison of colony forming units (CFU's) with a glucosamine standard. A typical run of the assay detects 53.1 CFU/c.p.m., and 356,000 c.p.m. per nanomole of N-acetylglucosamine. The specificity of the assay is very high because of the unique nature of chitin. This method of chitin determination may be a useful alternative method for future investigations involving the study of fungal infections in mammalian tissues.

Candida albicans↗
PubMed1994

Chronic active hepatitis and associated liver tumors in mice caused by a persistent bacterial infection with a novel Helicobacter species.

BACKGROUND: In the autumn of 1992, a novel form of chronic, active hepatitis of unknown etiology was discovered in mice at the National Cancer Institute-Frederick Cancer Research and Development Center (NCI-FCRDC), Frederick, Md. A high incidence of hepatocellular tumors occurred in affected animals. The disease entity was originally identified in A/JCr mice that were untreated controls in a long-term toxicologic study. PURPOSE: Our original purpose was to determine the origin and etiology of the chronic hepatitis and to quantify its association with hepatocellular tumors in mice of low liver tumor incidence strains. After a helical microorganism was discovered in hepatic parenchyma of diseased mice, we undertook characterization of the organism and investigation of its relationship to the disease process. METHODS: Hepatic histopathology of many strains of mice and rats, as well as guinea pigs and Syrian hamsters, in our research and animal production facilities was reviewed. Steiner's modification of the Warthin-Starry stain and transmission electron microscopy were used to identify bacteria in the liver. We transmitted the hepatitis with liver suspensions from affected mice and by inoculation with bacterial cultures. Bacteria were cultivated on blood agar plates maintained under anaerobic or microaerophilic conditions and characterized morphologically, biochemically, and by 16S rRNA sequence. RESULTS: We report here the isolation of a new species of Helicobacter (provisionally designated Helicobacter hepaticus sp. nov.) that selectively and persistently colonizes the hepatic bile canaliculi of mice (and possibly the intrahepatic biliary system and large bowel), causing a morphologically distinctive pattern of chronic, active hepatitis and associated with a high incidence of hepatocellular neoplasms in infected animals. CONCLUSIONS: The novel Helicobacter is a likely candidate for the etiology of hepatocellular tumors in our mice. The Helicobacter-associated chronic active hepatitis represents a new model to study mechanisms of carcinogenesis by this genus of bacteria. IMPLICATIONS: Adenocarcinoma of the stomach, the second most prevalent of all human malignancies world-wide, is associated with infection at an early age with Helicobacter pylori. Infection leads to several distinctive forms of gastritis, including chronic atrophic gastritis, which is a precursor of adenocarcinoma. H. hepaticus infection in mice constitutes the only other parallel association between a persistent bacterial infection and tumor development known to exist naturally. Study of the H. hepaticus syndrome of chronic active hepatitis and liver tumors in mice may yield insights into the role of H. pylori in human stomach cancer and gastric lymphoma.

Adenoma, Liver Cell↗
PubMed1994

Interocular blur suppression and monovision.

The ability of the binocular system to suppress blur from the defocused eye is an important mechanism underlying the success of monovision correction. With a group of 60 new monovision wearers, we found that blur suppression ability varied substantially between subjects and that crossed dominance influenced blur suppression ability. Symptoms of ghosting amongst the monovision wearers appeared to be influenced by the strength of rivalry dominance. An understanding of the suppression processes underlying monovision may assist in patient selection and management.

Anisometropia↗
PubMed1994

Helicobacter hepaticus sp. nov., a microaerophilic bacterium isolated from livers and intestinal mucosal scrapings from mice.

A bacterium with a spiral shape and bipolar, single, sheathed flagella was isolated from the livers of mice with active, chronic hepatitis. The bacteria also colonized the cecal and colonic mucosae of mice. The bacterium grew at 37 degrees C under microaerophilic and anaerobic conditions, rapidly hydrolyzed urea, was catalase and oxidase positive, reduced nitrate to nitrite, and was resistant to cephalothin metronidazole. On the basis of 16S rRNA gene sequence analysis, the organism was classified as a novel helicobacter, Helicobacter hepaticus. This new helicobacter, like two other murine Helicobacter species, H. muridarum and "H. rappini," is an efficient colonizer of the gastrointestinal tract, but in addition, it has the pathogenic potential to elicit persistent hepatitis in mice.

Animals↗
PubMed1993

Optical spectropotentiometric resolution of the hemes of hydroxylamine oxidoreductase. Heme quantitation and pH dependence of Em.

The hemes of hydroxylamine oxidoreductase (HAO) have been analyzed optically by potentiometric titrations using a low volume optically transparent thin layer electrochemical cell. The electrochemical behavior of the HAO monomeric unit has been interpreted by modeling the spectroelectrochemical data at several wavelengths to eight one-electron Nernst sites: seven c-type hemes and one P460 heme. Of the seven c-hemes, six show alpha-bands with absorption maxima at or near 553 nm. One c-heme has an alpha-band absorption maximum at 559 nm. The six c-553 hemes have midpoint potentials at pH 7.0 of +288, -10, -162, -192, -265 and -412 mV versus the normal hydrogen electrode (NHE). The c-559 heme has a midpoint potential (Em') at pH 7.0 of +11 mV versus NHE. The midpoint potential of the P460 heme is at -260 mV versus NHE at pH 7.0. In contrast, the midpoint potential for the P460 heme in another protein, cytochrome P460, from the same organism is -402 mV versus NHE at pH 7.0. Midpoint potentials of the c-hemes show little, if any, pH dependence over the range of pH 6-8. In contrast, Em' for the P460 heme changes with a slope of -60 mV/pH unit over the same range. Electrochemical isolation of the P460 heme at pH 8.0 led to the discovery of a broad spectroscopic feature centered near 740 nm that was assigned to the oxidized P460 heme. Changes in the spectroelectrochemical behavior of HAO after inactivation by H2O2 was almost exclusively restricted to the P460 heme of HAO. Both the 464-nm absorption band of the reduced P460 heme and the 740-nm band of the oxidized heme were no longer present. For the c-hemes, the only effect seems to be a slight shift in Em' for a single c-553 heme from -162 to -135 mV.

Cytochromes↗