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Biomedical subjects

G Thomas

Publications and source records attributed to G Thomas.

At least 955 records · Page 53Linked to original sources
PubMedDate not supplied

Forces exerted by a conventional dental explorer during clinical examination.

PURPOSE: To measure the range of forces exerted clinically in order to determine whether research in this area uses forces that are similar to those generally seen in a clinical setting. METHODS: A transducer was manufactured consisting of a force measurement sleeve positioned over the handle of a conventional explorer. The sleeve housed 4 strain gauges oriented to detect forces in a vertical and lateral direction. Five experienced dentists performed a full-mouth caries exam on three fully dentate caries-free subjects with the force-detecting probe. RESULTS: The overall average force was 340 +/- 6 (SEM) g with a standard deviation of 218 g and a range of 14-1,006 g. The average number of contacts per tooth was 6.2 +/- 0.2 (SEM) with a standard deviation of 2.7. CONCLUSIONS: The data from this study show that the forces used in previous studies were sometimes greater than the average force, but were still within the observed range of forces.

Analysis of Variance↗
PubMedDate not supplied

Factors involved in the antihypertensive action of calcium antagonists.

The main mechanism underlying the antihypertensive action of calcium antagonists is believed to be the vasodilation of peripheral vessels. To compare the effects of calcium antagonists with those of other vasodilators, nifedipine or its antihypertensive analog nitrendipine were tested in different normotensive and hypertensive rat strains and situations. The acute blood-pressure-lowering effect of nifedipine in the Dahl salt-sensitive rat was characterized by a rapid onset of action, the minimal effective oral dosage (0.1 mg/kg) being effective for up to 6 hours. Nifedipine was approximately 3 times more potent than hydralazine and equipotent to, but of shorter duration of action than, minoxidil. Natriuretic activity in normotensive Wistar and hypertensive Dahl salt-sensitive rats was observed with nitrendipine after an acute saline load (30 ml/kg by mouth), whereas vasodilators such as minoxidil and hydralazine decreased renal function under these conditions. Treatment of spontaneously hypertensive rats (SHR) with nifedipine in food (315 parts per million) for 60 weeks prevented the development of hypertension and resulted in decreased plasma renin activity and plasma aldosterone concentration in comparison to untreated SHR controls. Moreover, absolute and relative heart weights were reduced in the treated rats. Results suggest that the antihypertensive action of calcium antagonists, at least those of the dihydropyridine type, is not only due to peripheral vasodilation, since in contrast to other vasodilators a hyperdynamic circulation is not induced, the renin-angiotensin-aldosterone system is not activated, and sodium/volume retention cannot be expected because of a primary natriuretic effect. Therefore, a reduced volume load in addition to the decrease in afterload contributes to the antihypertensive effect of calcium antagonists and their prevention of heart hypertrophy.

Aldosterone↗
PubMedDate not supplied

Free radicals, arachidonic acid metabolites, and nutrition.

Oxygen reactive species are normally formed in cells and play an essential part of the bactericidal activity of phagocytic cells. The damaging effect of these oxygen reactive species is prevented by the endogenous scavengers SOD, glutathione peroxidase, catalase, circulating transferrin, ascorbic acid, and membrane-bound alpha-tocopherol. However, when excess amounts of oxygen radicals and hydrogen peroxide are formed, as in reperfusion injury or trauma, the endogenous scavengers are insufficient to react with these active molecules. Lipid peroxidation is an important part of the formation of oxygen reactive species. Lipid peroxidation, especially peroxidation of LDL, may have a significant role in atherosclerosis. Thus dietary manipulation of PG and TX formation through either feeding cold water fish oils or plant oils containing high amounts of polyunsaturated fatty acids may be a two-edged sword. Also, the dietary manipulation of arachidonic acid through increasing its precursor linoleate may cause a decrease in the immune response as seen in animal experiments. The marine oils may be regarded as a natural aspirin in that formation of PGs of the bisenoic series will be replaced by the PGs of the trienoic series. This results in the formation of TXA3, which is biologically inactive, and PGI3, which is biologically active like PGI2. This may have no physiologic consequences but it is used to illustrate a possible mechanism for the postulated beneficial cardiovascular effects of these oils. The issues and the mechanisms are controversial and frequently highly speculative. The subject is a boon for the lipid biochemist and nutritionist.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Oral cancer among patients under the age of 35 years.

BACKGROUND: Cancer of the oral cavity is one of the commonest cancers among males. AIMS: To assess the aetiological factors, patient characteristics, treatment and the outcome in young patients with oral cancer. SETTINGS AND DESIGN: A retrospective descriptive study of patients under the age of 35 years with cancer of the oral cavity treated between 1982-1996, with the last follow-up till 2001, using the tumour registry data of Regional Cancer Centre (RCC), Trivandrum, Kerala, India. SUBJECT AND METHOD: The detailed clinical, treatment and follow-up data were obtained from the computerised records of RCC and recorded on a preset proforma. This was analysed with emphasis on age, sex, risk factors, site, histology, clinical extent and treatment methods and survival in the study group. STATISTICAL ANALYSIS: The survival analysis was carried by Kaplan-Meier method and the difference in survival was analysed using log-rank test. RESULTS: Out of 264 patients analysed, tongue was the commonest site identified in 136 (52%) patients followed by buccal mucosa in 69 (26%) patients. A male female ratio of 2.3:1 was observed with a significantly higher male preponderance in buccal mucosa (4.3:1). Prior exposure to tobacco or alcohol was noted in 59.4% patients, with more habitués in buccal mucosa cancer. Histological confirmation was present only in 83.7% patients and among them most were squamous cell carcinoma (85.9%). Radiotherapy, surgery or combined modalities of treatment were employed for majority of patients. The 5-year survival was 57.3%. T stage of the tumour was found to be significant in predicting disease free survival (P=0.03). CONCLUSIONS: The importance of early detection for clinical down staging is stressed. There is a need to investigate the aetiology of intra oral cancers in younger patients since a significant proportion (almost 40%) of these patients do not have associated risk factors for cancer.

Adult↗
PubMedDate not supplied

[Homografts allogeneic of the knee and hip joints].

The technique and instruments of PAP, Krompecher and Jaros allow a precise preparation of the femoral head, acetabulum, femoral condyles and tibial plateau in the donor and recipient for the application of homograft transplants of joint articular surfaces of 5 millimetre thickness. In the present series, specimens were preserved by freezing at 30 degrees below zero to prevent immunologic reactions in the recipient. Immunogenic control tests in 12 patients have shown that freezing at 30 degrees below zero does not eliminate antigens in the transplant. In future, therefore, it is intended to transplant only cartilage with living cells in relation to the HLA system. The problem of prevention of infection has been solved by a special antibiotic preparation of the specimen. Radiographic examination 4 years after operation shows that only two of 12 patients had an unsatisfactory result. Function in these two hip joints is, however, better than before operation although the transplant has been partly resorbed. The technique of homograft transplantation of the hip and knee joints is suitable for young or middle-aged individuals in whom the only alternative would be an arthrodesis. For older persons a joint prosthesis is preferable.

Adult↗
PubMedDate not supplied

[Neurocomportmental disorders in an urban population exposed to lead].

A study was performed in 278 people living in a Mexican town with a high lead environmental pollution. Lead blood level was found very high (m:59.7 micrograms/l) and some abnormalities were also found for free erythrocyte Protoporphyrin and ALA dehydratase. A significant dose-response relationship was also found with somatic complaints like loss of appetite, insomnia and headache.

Environmental Exposure↗
PubMedDate not supplied

Granulocytic differentiation induced by retinoic acid in HL-60 cells is associated with changes in adenylate cyclase activity.

The effect of all-trans Retinoic Acid (RA) on the activity of membrane bound adenylate cyclase (AC) of human malignant cell lines (HL-60 and U-937) was studied. Granulocytic terminal differentiation of the HL-60 cells was correlated to an increase of AC activity and to a potentiation of guanosine 5' triphosphate (GTP) inhibitory effects on the enzyme activity. No direct in vitro effect of RA on HL-60 membranes was found. Monocytic terminal differentiation obtained on 1 B-D arabinofuranosyl cytosine (Ara-C) treated HL-60 cells, or on RA treated U-937 cells, did not modify AC activity. The results here reported suggest relations between the modification of GTP binding protein activity and RA induced granulocytic differentiation of malignant cells.

Adenylyl Cyclases↗
PubMedDate not supplied

An unwelcome companion.

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Adaptation, Psychological↗