Search PubMed⌕ Search

Biomedical subjects

R L Thomas

Publications and source records attributed to R L Thomas.

At least 73 records · Page 4Linked to original sources
PubMed1981

The fallacy of the postpill amenorrhea syndrome.

In conclusion, although there are changes in the hypothalamic pituitary axis in terms of release of FSH and LH resulting in anovulation in women on oral contraceptives, the evidence to date does not support a cause and effect phenomenon. On the basis of both epidemiologic as well as biochemical studies, the etiology of secondary amenorrhea is diverse. This serves only to indicate that amenorrhea is a symptom, not a diagnosis. It appears at the present time that amenorrhea following the use of oral contraceptives should indicate only the preceding temporal use of exogenous steroids without implication as to a cause of the amenorrhea. Investigation should be aimed at determining the underlying cause of the amenorrhea.

Amenorrhea↗
PubMed1980

Preparation of a homogeneous tomato fruit peroxidase.

Tomato fruit (Lycopersicon esculentum Mill cv. Walters) peroxidase was purified to apparent homogeneity by a three step procedure: hydrophobic chromatography, DEAE Sephacel chromatography and semi-preparative electrophoresis. A purification of 71 fold and a yield of 52% relative to crude extract were obtained. The pure enzyme was brown in color and showed a molecular weight of 45,000 as estimated from SDS disc gel electrophoresis and gel filtration on Ultrogel AcA 34. The pH optimum of tomato peroxidase varied with substrate dyes used and the enzyme may have some hydrophobic properties near its active site. The optimum temperature was 35 degrees C for this enzyme, and IAA oxidase activity was evident in the presence of 2,4-dichlorophenol and manganese. The apparent KM for IAA was measured to be 0.24 mM.

Ammonium Sulfate↗
PubMed1980

Tympanic neurectomy and chorda tympani section.

Tympanic neurectomy with or without chorda tympani section is a surgical procedure which can play a role in the treatment of diseases for which more extensive procedures have in the past been performed. The surgical approach is familiar to most ear, nose and throat surgeons, and the operation, which can be satisfactorily performed under local anaesthesia, is associated with very little, if any, discomfort to the patient.

Adult↗
PubMed1980

Computed tomography in the assessment of patients with juvenile post-nasal angiofibroma.

Surgery for juvenile angiofibroma demands a knowledge of tumor size and site, the degree of lateral extension being of particular importance. This study compares information obtained from computed tomography with findings at time of surgery. Computed tomography is found to be a reliable and accurate means of tumor assessment. It is recommended that this should be an essential pre-operative investigation for patients with juvenile angiofibroma.

Adolescent↗
PubMed1980

Facial paralysis with absence of internal and external carotid arteries.

A case is reported of congenital facial nerve palsy associated with ipsilateral absence of internal and external carotid ateries. Exploration of the facial nerve in the temporal bone was thwarted because of excessive soft tissue bleeding in the mastoid tip area. Angiography subsequently demonstrated the vascular anomaly with a rich collateral vasculature arising from the external carotid artery on the normal side.

Carotid Artery, External↗
PubMed1980

Secondary airway support in the management of croup.

Over a four year period of 2,567 croup admissions, 65 required secondary airway support, 45 were intubated, and 30 underwent tracheotomy. The median duration of nasotracheal intubation was six days and of tracheotomy 11 days. The overall morbidity was less for nasotracheal intubation but tubal obstruction resulted in the death of one patient in this group.

Croup↗
PubMed1979

Organochlorine insecticides and PCB in the sediments of Lake Huron (1969) and Georgian Bay and North Channel (1973).

Surficial and core sediments were collected from the main body of Lake Huron in 1969 and Georgian Bay and North Channel in 1973. These were analysed for organochlorine insecticides and PCB. Residues of organochlorines were higher in the twelve depositional basins in Lake Huron and Georgian Bay than in sediment in the non-depositional zones. PCB was present at similar concentrations to sigma DDT; with mean levels of 13 and 10 ng/g for PCB and sigma DDT in the main body of Lake Huron and 11 and 5 ng/g for PCB and sibma DDT in Georgian Bay. Residues of PCB varied from 9--33 ng/g in the 12 basins. With respect to sigma DDT, both parent DDT and its two metabolites were present in sediment at a mean residue of 7.8 ng/g for the whole lake. The main lake had residues of 10.2 ng/g while Georgian Bay had 5.8 ng/g and North Channel 4.1 ng/g in keeping with use pattenrs since 1943. HEOD was present in only 5.7% of sediment samples from main Lake Huron, 30% from Georgian Bay and 15% from North Channel. The highest residues 1.7 ng/g occurred in the North Channel. No chlordane was detected, however, heptachlor epoxide was identified in 8.5% of sediments collected in Lake Huron, 23% from Georgian Bay and 14% in North Channel. Endosulfan appeared in 4% of samples from both Georgian Bay and North Channel.

Canada↗
PubMed1978

Regional deposition of inhaled 137 Cs-labeled monodisperse and polydisperse aluminosilicate aerosols in Syrian hamsters.

Two groups of eighty Syrian hamsters were exposed to aerosols of 137Cs-labeled fused aluminosilicate particles. One group was exposed to a monodisperse aerosol with AMAD (activity median aerodynamic diameter) of 1.53 micron and sigma g (geometric standard deviation) of 1.15. The other group was exposed to a polydisperse aerosol with AMAD of 1.87 micron and sigma g of 1.46. After exposure, the hamsters were killed and carefully dissected and tissues were assayed for 137Cs to determine regional deposition of the inhaled aerosols. The relative lung deposition was similar for the two groups and was estimated as 9.5% of the inhaled aerosols. The right apical lobe consistently contained more activity and the right cardiac and right diaphragmatic lobes less activity on a per gram lung weight basis than the total lung.

Aerosols↗
PubMed1975

Phytochrome-mediated Carotenoids Biosynthesis in Ripening Tomatoes.

Red light induced and far red light inhibited carotenoid biosynthesis in ripening tomatoes (Lycopersicon esculentum Mill.) when compared to controls kept in the dark. Red illumination following far red illumination reversed the inhibitory action of far red light on carotenoid biosynthesis, suggesting a phytochrome-mediated process. Quantitation of individual carotenoids favored the hypothesis of two separate carotenoid biosynthetic pathways in tomatoes.

Journal Article↗
PubMed1975

A widely applicable method for computing dose distributions from external megavoltage beams.

A method of computing megavoltage dose distributions using an empirical mathematical model is described. The dose at a point in a medium is calculated as the product of a central axis percentage depth dose, a crossplot factor and a wedge factor. For a given set of conditions (i.e. type of machine, source-skin distance and wedge) 16 parameters are required to calculate the values of the three factors and hence the dose at any point. These parameters can be obtained from a relatively small number of experimental measurements. Dose distributions from a variety of different treatment machines have been computed by the method, and some comparisons of the calculated and measured doses have been made using "Goodness of Fit" score values. These show that the use of the method as a basis for computer treatment planning should be clinically acceptable.

Computers↗