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Biomedical subjects

D J Thomas

Publications and source records attributed to D J Thomas.

At least 181 records · Page 10Linked to original sources
PubMed1988

The effect of altitude on tests of reaction time and alertness.

Psychomotor performance was assessed in 20 subjects on each of 2 mountaineering expeditions. During the first, which reached 5,008 m, simple reaction time and alertness were measured, on the second to 4,790 m these were replaced by a three-choice reaction time test. In both, mean reaction times increased significantly at altitude in subjects with marked symptoms of Acute Mountain Sickness (AMS), whereas the alertness tests showed no effects. Reaction times were not affected by other environmental factors but adverse conditions increased the number of errors. The increase in reaction time may be ascribed either to the lethargy associated with AMS or alternatively may have been a direct effect of hypoxia. The latter explanation is favoured because of reports by other workers of an increase in reaction time with altitude in the absence of AMS.

Acetazolamide↗
PubMed1988

Type A behavior and black physicians: the Meharry Cohort Study.

A group of 261 black, male physicians was examined for the prevalence of Type A behavior and other sociomedical correlates.Type A behavior, as measured by the Jenkins Activity Survey (JAS), was collected together with type of practice specialty, blood pressure, weight, and height. Type A behavior tended to vary by physician practice specialty. The job involvement subscale correlated significantly with blood pressure but total JAS and other JAS subscale measurements did not. The job-involvement relationship with blood pressure parallels James's finding in lower socioeconomic status blacks. Type A behavior was not found to be related to hypertension but did tend to favor leanness.

Black or African American↗
PubMed1987

Ontogenic variation in acute lethality of cadmium in C57BL/6J mice.

Susceptibility of C57BL/6J mice to the lethal effects of parenterally administered Cd declined as a function of age at exposure. The 7-day LD50 increased from 1.65 mg Cd/kg body wt in 7-day-old mice to 4.08 mg/kg in adult mice. Survival time following treatment with Cd also increased as a function of age. High constitutive concentrations of metallothionein, a transition metal-binding protein, in livers of young mice did not protect against the lethality of Cd. These results suggest that, in the mouse, the interaction between Cd and this metal-binding protein may be affected by age at exposure to this toxic metal.

Aging↗
PubMed1987

Deoxyribonucleic acid polymorphism of the apoprotein AI-CIII-AIV gene cluster and coronary heart disease in non-insulin-dependent diabetes.

The prevalence of an uncommon allelic variant (S2) of the apoprotein AI-CIII-AIV gene cluster was determined in non-insulin-dependent diabetics with or without evidence of coronary heart disease and in controls. Frequencies of the S2 allele were 14% for diabetics with coronary heart disease compared with 2% for non-diabetics with no clinical evidence of occlusive vascular disease. No subject with the S2 allele was detected among a further group of matched diabetics without clinical features of macrovascular disease. The results suggest that a genetic component contributes to the susceptibility to coronary heart disease in non-insulin-dependent diabetics. Whether the observed deoxyribonucleic acid variant is aetiological for atherosclerosis or in linkage disequilibrium with other atherogenic loci on chromosome 11 remains to be clarified.

Alleles↗
PubMed1987

Precursors of hypertension in black compared to white medical students.

Data were collected on 433 black medical students at Meharry Medical College (MMC) and 573 white medical students at The Johns Hopkins University School of Medicine (JHMS) during the period of 1958 through 1965 consisting of baseline measurement of some possible precursors of hypertension. Similar methods were employed in both cohorts. Comparison as to prevalence and significance of hypertension precursors revealed the following: Black males had significantly higher casual and resting blood pressures than whites (p less than 0.01); and higher mean changes in blood pressure following the cold pressor test. White males had a significantly higher mean change in heart rate following cold pressor test (p less than 0.01). Upon exercise black males had significantly higher mean change in blood pressure and heart rate (p less than 0.01). There appears to be more blood pressure lability in blacks as indicated by higher mean SBP + DBP changes following the cold pressor test, and by mean pulse pressure level at peak exercise. The difference in blood pressure lability observed between blacks and whites in young adulthood may be one of the earliest identifiers of later differences in the incidence of hypertension. However, of even more importance is the difference in blood pressure levels between the two groups, though both are normotensive.

Adult↗
PubMed1987

Sexual differences in the excretion of organic and inorganic mercury by methyl mercury-treated rats.

Adult male and female Long Evans rats received 1 mumole of methyl (203Hg) mercuric chloride per kilogram sc. Whole-body retention of mercury and excretion of organic and inorganic mercury in urine and feces were monitored for 98 days after dosing. Females cleared mercury from the body more rapidly than did males. The major route of mercury excretion was feces. By 98 days after dosing, cumulative mercury excretion in feces accounted for about 51% of the dose in males and about 54% of the dose in females. For both sexes, about 33% of the dose was excreted in feces as inorganic mercury. Cumulative excretion of organic mercury in feces accounted for about 18 and 21% of the dose in males and females, respectively. Urinary excretion of mercury was quantitatively a smaller route for mercury clearance but important sexual differences in loss by this route were found. Over the 98-day experimental period, males excreted in urine about 3.2% of the dose and females excreted 7.5%. Cumulative organic Hg excretion in urine accounted for 1.8% of the dose in males and 5.3% of the dose in females. These sexual differences in urinary and fecal excretion of organic and inorganic mercury following methyl mercury treatment were consistent with previous reports of sexual differences in mercury distribution and retention in methyl mercury-treated rats, particularly sexual differences in organic mercury uptake and retention in the kidney. Relationships between body burdens of organic or inorganic Hg and output of these forms of Hg in urine and feces were also found to be influenced by the interval after MeHg treatment and by sex. Relationship between concentration of Hg in liver and feces and in kidney and urine differed for organic and inorganic Hg and depended upon sexual status and interval after MeHg treatment. These findings emphasize that sexual differences in distribution, retention, and metabolism of methyl mercury are factors to be considered in estimations of hazards associated with exposure to this agent.

Animals↗
PubMed1987

Hyperprolactinaemia and microadenomas in primary hypothyroidism.

The presence at presentation of hyperprolactinaemia and abnormalities on high resolution computed tomographic (CT) scanning of the pituitary gland have been documented in 19 patients with primary hypothyroidism. The changes on thyroid hormone replacement were followed for up to 28 months after presentation. At presentation serum PRL was elevated in 12 subjects (454 to 2612 mU/l); after stabilization of thyroid replacement PRL remained raised in 9 patients (525 to 1888 mU/l) despite 10-18 months of treatment. Pretreatment CT scans showed enlarged pituitaries in 11 patients with suprasellar extension in five. In 11 patients there was initially an area of low attenuation suggesting a microadenoma and on rescanning this appearance remained in five patients. Hyperprolactinaemia in hypothyroid patients does not always return to normal with thyroid hormone replacement.

Adenoma↗
PubMed1987

Cerebral haemodynamic changes after extracranial-intracranial bypass surgery.

Regional cerebral blood flow, oxygen utilisation, fractional oxygen extraction, and cerebral blood volume were measured by positron emission tomography in twelve patients with carotid artery occlusion. Follow-up studies were carried out at a mean interval of eleven weeks after extracranial-intracranial bypass surgery. Clinical improvement was observed in three patients who had presented with frequent transient ischaemic attacks. One patient with multiple vascular occlusions suffered a stroke at the time of surgery. Follow-up studies showed an increase of regional cerebral blood flow in only two of the twelve patients. In the group as a whole, there was no significant change of cerebral blood flow, oxygen consumption or fractional oxygen extraction after bypass surgery. The most consistent post-operative change, observed in eleven of the twelve patients, was a fall of cerebral blood volume in the cortical territory of the bypassed carotid artery (p less than 0.01). This effect was most marked in patients with bilateral carotid occlusion, in whom there was often an accompanying fall of blood volume in the contralateral hemisphere. The post-operative findings were consistent with an increase of regional cerebral perfusion pressure as a result of the bypass procedure. Although this effect is potentially of value, those patients with most to gain from bypass surgery may also run the highest risk of peri-operative cerebral ischaemia.

Aged↗
PubMed1986

Visceral and skin granuloma annulare, diabetes, and polyendocrine disease.

A middle aged man suffered with insulin dependent diabetes, autoimmune Addison's disease, myxoedema, and severe ulcerative colitis, for which he had undergone subtotal colectomy with formation of an ileostomy. Granuloma annulare confined to the anterior abdominal wall was diagnosed in 1981. In 1983 an episode of severe colicky pain and excessive working of the ileostomy occurred associated with severe hyperglycaemia and increased irritation of the granuloma annulare. Laparotomy disclosed adhesions and numerous white nodules over bowel, mesentery, and peritoneum histologically identical with the skin lesions. Two further episodes of subacute small bowel obstruction occurred, and a repeat laparotomy showed widespread intra-abdominal granuloma annulare. Visceral granuloma annulare appears not to have been reported before, and in this patient exacerbation of the skin lesion was associated with poor diabetic control.

Diabetes Complications↗
PubMed1986

Insulin infusion (GIK) in the treatment of type 2 (non-insulin dependent) diabetes during the perioperative period.

The effect of surgery on intermediary metabolism has been studied in six non-diabetic subjects, eleven type 2 diabetic subjects untreated during surgery, and nine type 2 diabetic subjects treated by glucose-insulin-potassium (GIK) infusion during surgery. Plasma glucose results were studied in all subjects and other metabolites whenever possible. Initial glucose concentrations were similar in both groups of diabetic subjects. Four hours postoperatively the plasma glucose was lower in the GIK group (10.1 +/- 1.0 mmol/l) than in untreated subjects (14.2 +/- 1.3 mmol/l, P less than 0.05) but still far above levels found in non-diabetic subjects. Lactate concentration was higher in the GIK treated diabetic subjects than in both non-GIK treated diabetic and non-diabetic patients 15 min after induction (1.32 +/- 0.07 compared with 0.93 +/- 0.09 and 0.89 +/- 0.08 mmol/l, P less than 0.02). Non-esterified fatty acid (NEFA) was lower one hour postoperatively in the GIK treated diabetic group than in the non-GIK diabetic patients (0.47 +/- 0.09 mmol/l compared with 1.09 +/- 0.22 mmol/l, P less than 0.05). All NEFA concentrations were lower in GIK treated diabetic subjects than in non-diabetic subjects for the time of insulin infusion. Blood 3-hydroxybutyrate was also lower in GIK treated (0.04 +/- 0.02) than in untreated diabetic subjects 4 h postoperatively (0.25 +/- 0.07 mmol/l, P less than 0.05). The levels of non-esterified fatty acid and 3-hydroxybutyrate found in the untreated diabetic did not differ from those found in non-diabetic controls. Plasma cortisol levels had risen in all groups 4 h postoperatively (P less than 0.01).

3-Hydroxybutyric Acid↗
PubMed1986

Effects of cadmium exposure on zinc and copper distribution in neonatal rats.

Tissue zinc and copper concentrations undergo marked changes in the neonatal rat during the first several weeks of life and it was of considerable interest to study the effect of cadmium exposure on these ontogenic changes. Long evans rats received either 2 or 10 mumol cadmium chloride per kg SC at 9 days of age and were sacrificed at 20 or 36 days of age. Tissue copper and zinc concentrations in cadmium-treated rats were compared to those of age-matched controls for statistically significant changes. The tissue affected, the element altered and the direction of change in concentration, increased (+) or decreased (-), are summarized for the two dosing groups (age at dosing, age at sacrifice in days): 2 mumol/kg (9, 20): kidney Zn (+), blood Zn (-), cerebral Cu (-), cerebellar Cu (+); 2 mumol/kg (9, 36): blood Zn (-); 10 mumol/kg (9, 20); liver, kidney, cerebral and cerebellar and blood Zn (-), cerebellar Cu (+); 10 mumol/kg (9, 36): liver and heart Zn (+), blood Zn (-); liver and heart Zn (+), blood Zn (-); kidney, cerebral, cerebellar and heart Cu (+). Changes in tissue zinc or copper concentrations produced by cadmium treatment could not be accounted for by the direct replacement of these elements by cadmium and may be due to alterations in transport of these elements. These results indicate that early life exposure to low levels of cadmium can have large and persistent effects on the distribution of the essential metals, copper and zinc.

Age Factors↗
PubMed1986

Obesity and hypertension in a longitudinal study of black physicians: the Meharry Cohort Study.

Obesity has been considered a risk factor among the precursors of essential hypertension for many years. Most related studies were general population surveys or predominantly white, male cohorts. This paper reports results of a longitudinal study of former black medical students, now practicing physicians for an average of 22.5 years. A remarkably high 43.8% were found to have developed hypertension. Fifty nine per cent of those who became obese during the study were hypertensive compared with 40% of the non-obese, 36% of those initially obese only, and 45% of those obese on both examinations. The risk ratio was 1.7 for the most obese (greater than or equal to 130% relative body weight) compared with 1.0 for the leanest group Dynamic weight change together with baseline diastolic blood pressure, were more prominent precursors than the other variables studied. Weight control would appear to be a potentially important nonpharmacologic hypertension risk reduction measure.

Adult↗
PubMed1986

Sexual differences in the distribution and retention of organic and inorganic mercury in methyl mercury-treated rats.

At 56 days of age, male and female Long-Evans rats received 1 mumole of 203Hg-labeled methyl mercuric chloride per kilogram sc and total, organic, and inorganic mercury contents and concentrations in tissues were determined for up to 98 days postdosing. Whole body clearance of mercury was faster in females than in males, and females attained higher peak percentages of the methyl mercury dose in kidney and brain than did males. Females had significantly higher mean percentages of the mercury dose present in the kidney and brain as organic or total mercury and in brain as inorganic mercury than did males. Males had significantly higher mean percentages of the dose present as organic or total mercury in pelt and whole body than did females. When expressed on a concentration basis, the only significant sexual difference was in the higher average concentration of organic mercury in the kidneys of females. When expressed on a tissue content basis, significant male-female differences in the kinetics (sex X time interactions) of organic mercury retention were found in kidney, brain, skeletal muscle, pelt, and whole body. Significant sex X time interactions in the concentrations of organic mercury were found in kidney, skeletal muscle, and whole body. Kinetics of retention and concentration of inorganic Hg in the pelt differed significantly for males and females. Discordance in degree of statistical significance of differences in mercury contents and concentrations reflected in part differences in relative body composition of males and females. Integrated exposures of tissues of males and females to organic or inorganic mercury were determined by fitting multiexponential retention functions to retention data. Differences in integrated exposure were estimated by the female-to-male ratio of areas under retention curves. Reconstruction of whole body organic and inorganic mercury burdens from constituent tissues indicated that integrated exposures of males and females to inorganic mercury were equal but females had a lower integrated exposure to organic mercury. Integrated exposure of liver to either form of mercury was about equal in males and females. However, the integrated exposure of the brain of females to inorganic mercury was 2.19 times that of males suggesting a sexual difference in accumulation or retention of inorganic mercury in the nervous system. These sexual differences in distribution and retention of organic and inorganic mercury after methyl mercury exposure may underlie reported sexual differences in sensitivity to the toxic effects of methyl mercury.

Animals↗
PubMed1986

A study of the haematological and haemorheological consequences of venesection.

A study has been made of a number of haematological and haemorheological factors following venesection therapy. Haematocrit was very effectively reduced by the venesection regimen and led to a fall in whole blood viscosity in spite of the microcytosis that was eventually induced in all the subjects. No clinically significant coagulation changes were observed. It is concluded that a simple venesection regimen without volume replacement is a safe procedure for improving blood rheology.

Aged↗
PubMed1986

Lead, zinc and copper decorporation during calcium disodium ethylenediamine tetraacetate treatment of lead-poisoned children.

Asymptomatic Pb poisoning of children remains a serious public health problem in the United States. Ca disodium EDTA is often used therapeutically to reduce the body burden of Pb. Although this chelating agent promotes increased urinary excretion of Pb and lowers blood Pb concentration, it is a nonspecific metal chelator and it promotes a substantial increase in the urinary loss of the essential metal, Zn. In the work described here, the pattern and extent of changes in blood Pb and plasma Zn and Cu concentrations and of the urinary loss of these metals have been characterized in Pb-poisoned children receiving 5-day courses of 1000 mg of Ca disodium EDTA per m2 of surface area per day, given i.m. Both blood Pb and plasma Zn concentrations were reduced rapidly during treatment; plasma Cu concentration was unaffected. At 60 hr after the cessation of Ca disodium EDTA treatment, plasma Zn concentration rebounded rapidly to its pretreatment value but blood Pb concentration remained at about 60% of its pretreatment value. Treatment with Ca disodium EDTA produced an approximate 21-fold increase in the daily rate of urinary loss of Pb and about a 17-fold increase in the daily rate of Zn loss in urine. There was no increase in urinary loss of Cu above the endogenous level. The chelatable body burden of Pb was estimated by two related methods. Statistically significant correlations were found between chelatable Pb burdens estimated by either method and blood Pb concentrations before Ca disodium EDTA treatment. In contrast, no correlation was found between plasma Zn concentration and the urinary loss of Zn during chelation therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Body Composition↗
PubMed1985

Nuclear magnetic resonance imaging (NMR), (MRI), of brain stem tumours.

The NMR scans of twenty-six patients who were referred with the clinically suspected or histologically verified diagnoses of brain stem tumour were reviewed. Twenty-one patients (eleven children and ten adults) had scans that were positive for tumour. Nine of these had histological confirmation. Eleven were irradiated without histology on the basis of the clinical diagnosis. The remaining patient was treated expectantly. The other five patients (two children and three adults) had CT and NMR scans that were negative for tumours. Clinical follow-up of these five cases for 9 to 29 months disclosed no further evidence of tumour. All but one tumour had evidence of an increased T1 and T2. Mass effects were seen in all but one case (not the same as the first exception). Multiplanar imaging was useful in determining intra- or extra-axial location as well as tumour extent. Intravenous Gadolinium-DTPA (a paramagnetic contrast agent) showed tumour enhancement in the two patients in whom it was used. NMR showed more extensive abnormality than CT in nineteen patients and similar abnormality to CT in two patients. CT demonstrated calcification better than NMR in the three cases in which it was observed.

Adolescent↗
PubMed1985

Risk factors and the incidence of hypertension in black physicians: the Meharry Cohort Study.

A prospective longitudinal study of black medical students was conducted to determine the predictive value of hypertension precursors. Follow-up examinations, averaging 22.5 years later, were performed on 341 subjects (78.8%); 25 (5.8%) additional subjects were identified as dead out of 433 original participants. Results are reported on 313 reexamined men. A remarkable 43.8% of the physicians had elevated blood pressure higher than 140/90 mm Hg or gave a history of hypertension and treatment. Correlation coefficients, quintile distributions, and regressions all confirmed the ability of baseline SBP and DBP to predict their respective pressures on follow-up examination. Discriminant function tests yielded baseline SBP, DBP, smoking, and parental history of stroke or hypertension to be the most significant precursors distinguishing hypertensive from normotensive groups, and the model correctly classified 69.7% of the subjects. Baseline cholesterol and Quetelet index levels did not reach statistical significance. The cold pressor test was not predictive but interim weight gain was highly significant. Results are discussed in relation to comparable studies on white populations.

Adult↗