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Biomedical subjects

D J Thomas

Publications and source records attributed to D J Thomas.

At least 199 records · Page 11Linked to original sources
PubMed1985

W value measurements for protons in tissue-equivalent gas and its constituent gases.

Values of W (the mean energy required to create an ion pair when a charged particle is stopped in a gas) are needed in radiation dosimetry to convert ionisation chamber current readings to absorbed dose. For neutron dosimetry the most important W values are those for protons, and this paper describes absolute measurements for protons with energies between 1.2 and 3.5 MeV for methane-based tissue-equivalent gas and its constituent gases, i.e. methane, carbon dioxide and nitrogen. An ionisation chamber with a parallel-plate arrangement was used to determine the integrated charge created by a measured number of protons, and W values were determined with an estimated uncertainty of about +/- 0.5%. The results are presented and compared with previous measurements. In general the present data tend to be somewhat lower than previously reported values. Finally the accuracy of a formula for predicting W values for gas mixtures from the values for the individual constituents is investigated.

Animals↗
PubMed1985

W value measurements for 241Am alpha particles in various gases.

Measurements of W, the mean energy expended per ion pair formed, have been performed for 241Am alpha particles stopping in a number of the gases commonly used in ionisation chambers. Both absolute and relative measurements were made with nitrogen used as the reference gas for the relative measurements. The absolute method entailed a simultaneous measurement of a quantity of charge and the number of alpha particles which produced that charge, whilst the relative approach simply required a determination of the ratio of ion currents. Results were obtained for methane-based tissue-equivalent gas, for its constituents, i.e. methane, carbon dioxide and nitrogen, for argon, and also for a gas mixture with a composition approximately equivalent to A-150 plastic.

Americium↗
PubMed1985

Regional cerebral oxygen utilization, blood flow, and blood volume in benign intracranial hypertension studied by positron emission tomography.

Using PET, we measured regional cerebral oxygen utilization, oxygen extraction, blood flow, and blood volume in five patients with benign intracranial hypertension. No significant differences in regional cerebral function were found between the patients and 15 age-matched normal controls. Cerebral decompression with a lumboperitoneal shunt produced little change in regional cerebral function in one patient studied serially. The raised CSF pressure of benign intracranial hypertension is therefore not associated with any significant deterioration in cerebral oxygen metabolism or hemodynamics.

Adult↗
PubMed1985

Erythrocyte porphobilinogen synthase activity as an indicator of lead exposure in children.

The European standardized method for measuring porphobilinogen synthase (PBGS, EC 4.2.1.24) activity in peripheral erythrocytes is widely used in epidemiological studies of low-level Pb absorption. We have modified it to include activation with dithiothreitol (DTT). In children with concentrations of Pb in whole blood ranging from 0.29 to 1.93 mumol/L, we found the following statistically significant correlations (r): blood Pb vs nonactivated PBGS activity = -0.773 (p less than 0.005); blood Pb vs DTT-activated PBGS activity = -0.265 (p less than 0.005); blood Pb vs the ratio of DTT-activated/nonactivated PBGS activity = +0.818 (p less than 0.005). At a DTT-activated/nonactivated PBGS activity ratio of 1, which indicates no Pb-dependent inhibition of PBGS, a corresponding blood Pb concentration of 0.24 mumol/L (50 micrograms/L) would be predicted. In individuals with hematological disorders, the DTT-activated/nonactivated ratio better predicted blood concentration of Pb than did the nonactivated PBGS activity, and largely compensated for the high variability in PBGS activity. We also describe techniques to minimize contamination by Zn and Pb and to stabilize enzyme activity during collection, transport, storage, and analysis of samples.

Adolescent↗
PubMed1985

Use of 2,3-dimercaptopropane-1-sulfonate in treatment of lead poisoning in children.

2,3-Dimercaptopropane-1-sulfonate (DMPS) is a water-soluble metal complexing agent. Administration to lead-poisoned children of 5-day courses of 200 or 400 mg of DMPS per m2 surface area per day given p.o. in divided doses resulted in a significant decline in the concentration of lead in blood. DMPS treatment did not significantly alter the concentrations of zinc or copper in plasma. Urinary excretion of lead, zinc and copper was increased by DMPS administration and these increases were sustained throughout the 5-day course of treatment. No significant changes in hepatic, renal or hematological function were found in DMPS-treated children and no side effects attributable to DMPS were noted. It is concluded that a 5-day course of DMPS given p.o. may be safe and effective in the treatment of asymptomatic lead poisoning in children.

Aspartate Aminotransferases↗
PubMed1984

Intravenous chelated gadolinium as a contrast agent in NMR imaging of cerebral tumours.

NMR imaging was performed on 12 patients with cerebral tumour before and after administration of intravenous gadolinium diethylene triamine penta-acetic acid (DTPA) (0.1 mmol/kg). Contrast enhancement was seen in all cases. Ring enhancement was most frequent (7 cases) but central, linear, patchy, and diffuse enhancement were also seen with both inversion-recovery and spin-echo sequences. The degree of enhancement was greater than that seen with X-ray computed tomography (CT) in 8 cases, equal to it in 3 cases, and less in 1 case. NMR distinguished between tumour and peritumoral oedema to the same extent as did CT. No side-effects were encountered and there was no significant change in urea, creatinine and electrolytes, liver function tests, blood coagulation, or urine testing after administration of gadolinium-DTPA. Gadolinium-DTPA is likely to be of considerable value in NMR imaging of the brain.

Adult↗
PubMed1984

Effects of coadministered sodium selenite on short-term distribution of methyl mercury in the rat.

Adult male Sprague-Dawley rats received iv injections of 1 mumole of methyl mercury/kg alone or coadministered with 5 mumole of sodium selenite/kg. Tissue concentrations of methyl mercury were determined at 5, 20, and 60 min after treatment. Selenite treatment produced a significant increase in cerebral methyl mercury concentrations and a significant decrease in kidney methyl mercury concentrations at all time points. The concentration of methyl mercury in liver was significantly increased by selenite coadministration at 5 and 20 min but at 60 min after injection the concentration was not significantly different from that found in rats receiving methyl mercury alone. Selenite treatment also significantly lowered blood methyl mercury concentrations at all time points. This decrease was associated with a significant decrease in the concentration of methyl mercury in erythrocytes at 5, 20, and 60 min. Plasma methyl mercury levels at 5 min postinjection were slightly higher in selenite-treated rats but were significantly lower in treated animals at 20 and 60 min. Treatment of rats with selenite did not specifically alter the extent of methyl mercury binding to glutathione in the 108,000g supernatant of cerebrum or in erythrocyte hemolysates. In rats receiving either methyl mercury alone or with selenite, low-molecular-weight methyl mercury complexes could not be detected in plasma 5 min after iv injection. These results suggested that selenite exerted immediate effects on the distribution of methyl mercury in the rat but did not alter the binding of methyl mercury to glutathione in the soluble components of erythrocytes and cerebrum or lead to formation of a persistent low-molecular-weight methyl mercury complex in plasma.

Animals↗
PubMed1984

Insulin-dependent diabetes during the peri-operative period. An assessment of continuous glucose-insulin-potassium infusion, and traditional treatment.

Twenty seven insulin-dependent diabetics, and six non-diabetic subjects undergoing elective surgery have been studied. Twelve diabetics received continuous glucose-insulin-potassium (GIK) infusion for at least 4 hours after surgery terminated. Six diabetic patients having morning surgery received a proportion of their morning insulin dose with intravenous glucose (25 g) before surgery and the remaining five operated on in the afternoon received their morning insulin with breakfast. Non-GIK groups were combined and compared with GIK. Postoperative diabetic treatment was the same in both groups. Plasma glucose changes were studied in all patients and other metabolites whenever possible. Mean pre-operative glucose, non-esterfied fatty acid, and 3-hydroxybutyrate concentrations were similar in GIK and non-GIK groups. Four hours postoperatively plasma glucose, and 3-hydroxybutyrate values were lower in the GIK group than in the non GIK group (p less than 0.05) as were mean plasma non-esterfied fatty acid levels. Plasma glucose concentration was also lower in GIK subjects at 72 hours postoperatively (p less than 0.01). At other times measured metabolic variables were similar in both GIK and non GIK groups.

Blood Glucose↗
PubMed1984

Release of aspartate and glutamate caused by chloride reduction in synaptosomal incubation media.

Release of the amino acid neurotransmitter candidates aspartate and glutamate from synaptosomes can be stimulated by reduction of [Cl-] in the incubation medium by replacement with the impermeant anions propionate and isethionate. Replacement by the permeant anion Br- is without effect on amino acid release. This release offers a biochemical method of studying the Cl-ion channel in CNS membrane.

Animals↗
PubMed1984

Supplemental zinc restores antibody formation in cultures of aged spleen cells.

The in vitro production of antibody to T-dependent antigens is depressed as a function of age. The addition of supplemental zinc to cultures of cells from young adult, middle-aged, and immunodepressed-aged mice enhances antibody production. The responses of young mice are enhanced 30 to 40%, but the responses in cultures from aged mice are increased 5- to 12-fold and the maximum response achieved is often equivalent to that of young, fully competent mice. The addition of zinc at varying times during the culture period suggests that zinc affects early events in the activation of antibody-forming cells.

Aging↗
PubMed1984

Precursors of hypertension in black medical students: the Meharry cohort study.

Data were collected on a cohort of 435 black medical students whose attendance at Meharry Medical College fell within the period 1958 to 1965, providing baseline measurements on multiple possible hypertension precursors. Relevant family history, sociodemographic, and clinical characteristics were obtained. Fifty percent of the students had at least one of the following possible precursors of hypertension: systolic blood pressure >120 mmHg; diastolic blood pressure >80 mmHg; pulse >80 beats/min; and relative body weight >120 percent of ideal body weight. Contrary to expectations, students from professional families were more likely to have higher systolic blood pressures. Students whose parents had a positive history of hypertension or stroke were likely to have higher diastolic blood pressures. Of the 24 students found to be hypertensive on survey (1981), 73 percent had a positive parental history of hypertension or stroke compared with only 40 percent of a control group matched by age and sex. A 17-year follow-up is currently underway to develop a risk profile for hypertension among black professionals.

Adult↗
PubMed1983

Nuclear magnetic resonance imaging of the posterior fossa: 50 cases.

Fifty patients with clinical diagnoses of disease within the posterior fossa were examined with a nuclear magnetic resonance (NMR) scanner and the results were compared with X-ray computed tomography (CT). A variety of NMR pulse sequences reflecting proton density, T1, T2 and blood flow were used and imaging was performed in transverse coronal and sagittal planes. In many cases NMR provided diagnostic information unavailable from CT scans. This included recognition of lesions not seen with CT in infarction and multiple sclerosis, as well as more precise definition of mass effects, oedema and anatomical relationships in other diseases. Extrinsic and intrinsic tumours were readily distinguished, as were brain-stem and cerebellar tumours. Arnold-Chiari malformations were demonstrated with sagittal scans and cerebellar atrophy was identified. A patient treated with radiotherapy displayed more extensive changes in the surrounding brain with NMR than with CT. Evidence of occlusion or reduced flow was found in two cases with vertebro-basilar disease. Occlusion of the internal carotid artery was also demonstrated. Computed tomography was superior to NMR in demonstrating calcification and bone erosion. In four of 14 tumours studied, contrast-enhanced CT demonstrated the margin between tumour and surrounding oedema or brain better than NMR. Nuclear magnetic resonance imaging is a versatile, non-invasive technique capable of demonstrating a wide spectrum of disease within the posterior fossa.

Adolescent↗
PubMed1983

The management of insulin dependent diabetes during cardiopulmonary bypass and general surgery.

Two groups of insulin dependent diabetic subjects have been studied: six undergoing general surgical procedures and six undergoing hypothermic cardiopulmonary bypass surgery for coronary artery vein grafting. Intravenous glucose insulin mixtures were infused from the onset of surgery in both groups of patients, supplying 0.4 units of insulin per gram of glucose per hour, and 0.6 units of insulin per gram of glucose per hour in general and cardiac surgical patients respectively. Postoperatively diabetes was controlled carefully with an insulin syringe pump regulated by venous blood glucose monitoring. In cardiac surgical patients far more insulin was required to control diabetes postoperatively than in the general surgery patients (at 1 hour 1.6 units, SEM 0.4 compared to 0.7 SEM 0.1, p less than 0.05; and at 4 hours 2.0 units SEM 0.3 compared to 0.8 units SEM 0.1, p less than 0.02). Five non-diabetic subjects who underwent surgery for coronary artery venous bypass grafting were also studied. They developed significant postoperative hyperglycaemia (5.0, SEM 0.2, mmol/litre pre-operatively, compared with 8.8, SEM 0.7, mmol/litre p less than 0.03 at 1 hour and 10.2, SEM 1.7, mmol/litre, p less than 0.02 at 4 hours after bypass terminated).

Adult↗
PubMed1983

Presynaptic cholinergic dysfunction in patients with dementia.

Indices of presynaptic cholinergic nerve endings were assayed in neocortical biopsy samples from patients with presenile dementia. For those patients in whom Alzheimer's disease was histologically confirmed, [14C]acetylcholine synthesis, choline acetyltransferase activity and choline uptake were all found to be markedly reduced (at least 40%) below mean control values. The changes occurred in samples from both the frontal and temporal lobes and for [14C]acetylcholine synthesis the decrease was similar under conditions of high and low neuronal activity (as assessed by incubations in 31 mM and 5 mM K+ respectively). Samples from other demented patients, in whom the histological features of Alzheimer's disease were not detected, produced values for all three biochemical parameters which were similar to controls. For the total group of patients with presenile dementia there were correlations between values for the three markers of presynaptic cholinergic nerve endings suggestive of a loss of functional activity at these sites in Alzheimer's disease.

Acetylcholine↗
PubMed1983

Evidence for an association between rheumatoid arthritis and autoimmune endocrine disease.

Evidence is presented for the first time of a significantly increased prevalence of type 1 (insulin-dependent) diabetes in the close relatives of patients with rheumatoid arthritis. Thirty-nine (13%) of 295 patients with classical or definite rheumatoid arthritis had a first or second degree relative with type 1 diabetes and 38 (13%) had a close relative with autoimmune thyroid disease. These findings could be compatible with a possible common genetically determined mechanism of susceptibility to both diseases.

Adult↗