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Biomedical subjects

D W Thompson

Publications and source records attributed to D W Thompson.

At least 19 recordsLinked to original sources
PubMed2005

Infrared optical properties and AFM of spin-cast chitosan films chemically modified with 1,2 Epoxy-3-phenoxy-propane.

Chemical modification of spin-cast chitosan films has been performed. This modification involves the attachment of 1,2 Epoxy-3-phenoxy-propane, commonly known as glycidyl phenyl ether (GPE), to the amine group of the chitosan molecule. Optical properties of modified films have been determined in the infrared region of the spectrum using spectroscopic ellipsometry, and are reported in this paper. Special attention is paid to the infrared region where the index of refraction and extinction coefficients from 750 to 4000 cm(-1) were determined. Difference plots of IR optical data before and after chemical modification were generated to confirm that modification had occurred. Optical modeling of infrared spectroscopic ellipsometry (IRSE) data with respect to chemical bond vibrations has also been performed. This modeling involved curve fitting of resonant chemical bond absorptions using Lorentz oscillators. These oscillator models allow for comparison of modified chitosan to unmodified chitosan. The purpose of this research was to determine infrared optical constants of chemically modified chitosan films This work shows that surface chemistry of biomaterials can be studied quite sensitively with spectroscopy ellipsometry, detecting as little as 100 ng/cm(2) of GPE.

Adsorption↗
PubMed2005

UV-vis-infrared optical and AFM study of spin-cast chitosan films.

Optical properties of spin-cast chitosan films have been determined in the infrared, visible, and ultraviolet region of the spectrum using spectroscopic ellipsometry. Optical constants for the UV-vis-near IR spectra from 130 to 1700 nm were determined using Cauchy dispersion forms combined with Lorentzian oscillator models in the absorptive shorter wavelength regions. Infrared index of refraction and extinction coefficients from 750 to 4000 cm(-1) were determined using ellipsometric data fits to dispersion models based on harmonic oscillators. This modeling determined that optical anisotropy was present and measurable over all wavelength regions of ellipsometric data. To obtain information on the micro- and nano-scale surface structure, tapping mode atomic force microscopy (AFM) imaging was employed to determine morphology and roughness information of dry spin-cast chitosan films.

Algorithms↗
PubMed2001

Regional climate impacts of the Northern Hemisphere annular mode.

The Northern Hemisphere annular mode (NAM) (also known as the North Atlantic Oscillation) is shown to exert a strong influence on wintertime climate, not only over the Euro-Atlantic half of the hemisphere as documented in previous studies, but over the Pacific half as well. It affects not only the mean conditions, but also the day-to-day variability, modulating the intensity of mid-latitude storms and the frequency of occurrence of high-latitude blocking and cold air outbreaks throughout the hemisphere. The recent trend in the NAM toward its high-index polarity with stronger subpolar westerlies has tended to reduce the severity of winter weather over most middle- and high-latitude Northern Hemisphere continental regions.

Journal Article↗
PubMed2001

Massive cerebral edema after recanalization post-thrombolysis.

BACKGROUND: Intravenous thrombolysis with tissue plasminogen activator is an approved and effective therapy for acute ischemic stroke within the first 3 hours from onset. In addition to the risk of hemorrhage, there is a risk of postrecanalization cerebral edema. The authors present the case of a patient with an ischemic stroke treated successfully with intra-arterial thrombolysis who subsequently developed massive brain edema in the face of clinical improvement. CASE: An 81-year-old man presented within 1 hour of developing a full right middle cerebral artery (MCA) syndrome. Computed tomography (CT) was normal. A cerebral angiogram demonstrated an occlusion of the M1 segment of the right MCA. The patient was treated with intra-arterial urokinase 750,000 units. He recovered during the procedure. Serial CT scans demonstrated progressive edema with mass effect in the right MCA distribution. The patient remained asymptomatic except for a mild sensory deficit. DISCUSSION: Postrecanalization cerebral edema is an uncommon but potentially lethal complication of thrombolysis. It is postulated that the edema is due to ischemic injury aggravated by reperfusion with vasogenic edema. The presence of this massive edema is usually associated with clinical worsening. The present case illustrates that this disorder can be associated with good outcome.

Aged↗
PubMed2000

Can ozone depletion and global warming interact to produce rapid climate change?

The atmosphere displays modes of variability whose structures exhibit a strong longitudinally symmetric (annular) component that extends from the surface to the stratosphere in middle and high latitudes of both hemispheres. In the past 30 years, these modes have exhibited trends that seem larger than their natural background variability, and may be related to human influences on stratospheric ozone and/or atmospheric greenhouse gas concentrations. The pattern of climate trends during the past few decades is marked by rapid cooling and ozone depletion in the polar lower stratosphere of both hemispheres, coupled with an increasing strength of the wintertime westerly polar vortex and a poleward shift of the westerly wind belt at the earth's surface. Annular modes of variability are fundamentally a result of internal dynamical feedbacks within the climate system, and as such can show a large response to rather modest external forcing. The dynamics and thermodynamics of these modes are such that strong synergistic interactions between stratospheric ozone depletion and greenhouse warming are possible. These interactions may be responsible for the pronounced changes in tropospheric and stratospheric climate observed during the past few decades. If these trends continue, they could have important implications for the climate of the 21st century.

Journal Article↗
PubMed1997

Clinical epidemiology of stroke.

The effect of stroke as a major health issue in the United States is well established. Well-designed epidemiologic studies have contributed important information about the natural history of stroke and its associated risk factors. These cerebrovascular profiles have provided the foundation for many of the current ischemic stroke trials, but the cause and prevention of the hemorrhagic subtypes remain elusive.

Cerebral Hemorrhage↗
PubMed1996

Clinical epidemiology of stroke.

The effect of stroke as a major health issue in the United States is well established. Well-designed epidemiologic studies have contributed important information about the natural history of stroke and its associated risk factors. These cerebrovascular profiles have provided the foundation for many of the current ischemic stroke trials, but the cause and prevention of the hemorrhagic subtypes remain elusive.

Adult↗
PubMed1991

Dysplasia and the natural history of cervical cancer: early results of the Toronto Cohort Study.

A sample of 176,808 Pap smears, taken from 70,236 women, was constructed from the records of a large cytopathology laboratory between 1962 and 1981. The prevalence of cervical dysplasia, based on the distribution of initial smear results, rose from 42.7 to 94.9 per 1000 during the study period. The relative risks (RR) for the manifestation of a malignancy (carcinoma in situ or worse) in a subsequent cervical smear were 1.48, 3.42, 20.9 and 71.5 for women with minimal, mild, moderate and severe dysplasia, respectively, compared with the entire cohort. The initial degree of dysplasia for women developing a malignancy was much more likely to be interpreted as moderate (RR = 5.0) or severe (RR = 42.3) than were those for controls. These results are strongly supportive of the hypothesis that the degree of dysplasia is related to the risk of development of cancer of the cervix.

Adult↗
PubMed1988

Maternal sex chromosome mosaicism diagnosed by amniocentesis and percutaneous umbilical cord sampling.

We present a remarkable chain of events in which percutaneous umbilical cord sampling was performed in an attempt to clarify a situation of possible fetal sex chromosome mosaicism in an amniotic fluid culture and led to the discovery that the mother herself had a 45,X/46,XX/47,XXX chromosome constitution. This may have simply represented the chance concurrence of pseudo-mosaicism in the amniotic fluid culture of a woman with an abnormal sex chromosome constitution, but it is also possible that the 45,X colony was maternal in origin. Although clearly a most unusual circumstance, the possibility should be kept in mind when termination of a pregnancy is being considered because of apparent mosaicism in a prenatal diagnostic study.

Adult↗
PubMed1985

Surface properties of Streptococcus sanguis FW213 mutants nonadherent to saliva-coated hydroxyapatite.

Seventeen mutants of Streptococcus sanguis FW213 nonadherent to saliva-coated spheroidal hydroxyapatite were isolated after mutagenesis with ethyl methanesulfonate, nitrosoguanidine, nitrous acid, hydroxylamine, or 2-aminopurine. Enrichment for nonadherent mutants was accomplished by successive adsorptions of the adherent strains to saliva-coated hydroxyapatite. After enrichment, variant colonial morphology on tryptic agar was used as a screening technique for selection of nonadherent mutants, with loss of colonial opacity frequently associated with loss of adherence ability. These mutants were further characterized for additional surface properties, including twitching motility, saliva-induced aggregation, coaggregation with Actinomyces species, surface hydrophobicity, and presence of fimbriae. Results from these assays indicated that the nonadherent mutants fell into six phenotypic groups. A correlation between the loss of adherence ability, a decrease in cell fimbriation, and a decrease in surface hydrophobicity is apparent.

Adhesiveness↗
PubMed1983

An analytical ultrastructural study of the iron-rich surface layer in rat-incisor enamel.

Electron-dense particles, approximately 4 nm (40 A) in diameter were present. Evidence is offered that these particles represent iron probably in the form of amorphous hydrous ferric hydroxide. From X-ray probe analytical data, it is suggested that this iron component is accommodated through the process of adsorption rather than by direct substitution of calcium and phosphorus. The iron-rich surface layer was more resistant to acid etching than subsurface enamel. Reported areas of reduced mineral density of enamel at the enamel-dentine junction appear to be preparation artifacts.

Animals↗
PubMed1982

GLC method for iminodibenzyl and desipramine impurities in imipramine hydrochloride and its formulated products.

A GLC method is described for the determination of iminodibenzyl and desipramine impurities in imipramine hydrochloride and its formulated products. These impurities were extracted from an alkaline solution with a mixture of 30% methylene chloride in hexane for chromatography on a 3% OV-17 GLC column. Iminodibenzyl was determined using anthracene as an internal standard and desipramine was determined (after derivatization) using nortriptyline as an internal standard. Based on spiked excipient mixtures typically used to compound imipramine tablets, recoveries were 93-109% for iminodibenzyl and 93-107% for desipramine at 0.2-0.4% of the labeled claim of imipramine. Minimum detection levels were approximately 0.02% for each impurity, and procedural standards gave coefficients of variation of less than 1% for each impurity. The method was linear in the 0.05-0.5 microgram range and typically gave correlation coefficients greater than or equal to 0.999.

Amines↗
PubMed1981

High pressure liquid chromatographic determination of antihistamine-adrenergic combination products: collaborative study.

A reverse phase high pressure liquid chromatographic method in which ion-pairing is used for the determination of combinations of pseudoephedrine hydrochloride with triprolidine hydrochloride or chlorpheniramine maleate in syrups and tablets was collaboratively studied by 8 laboratories. Collaborators were supplied with 12 samples including synthetic and commercial syrup formulations and commercial tablet composites. Mean recoveries of pseudoephedrine hydrochloride and triprolidine hydrochloride from synthetic syrup formulations were 100.5 and 99.6%, respectively. Mean recoveries of pseudoephedrine hydrochloride and chlorpheniramine maleate from synthetic syrups were 98.8 and 100.5%, respectively. Mean coefficients of variation for syrups and tablets ranged from 1.68 to 3.07% for pseudoephedrine hydrochloride, from 2.92 to 3.85% for triprolidine hydrochloride, and from 1.34 to 2.15% for chlorpheniramine maleate. The method has been adopted official first action.

Chlorpheniramine↗