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Biomedical subjects

G Mitchell

Publications and source records attributed to G Mitchell.

At least 127 records · Page 7Linked to original sources
PubMed1991

Prenatal diagnosis of fetal anomalies during the second trimester of pregnancy: their characterization and delineation of defects in pregnancies at risk.

During a follow-up study of 19,790 pregnancies at risk for a genetic disease, from 1968 to 1989, 1083 fetuses were found to have an anomaly during the second trimester, leading to 977 terminations of pregnancy. Neural tube defects (31.4 per cent), chromosomal disorders (27.1 per cent), and Mendelian or multifactorial diseases (10.6 per cent) were the main causes of fetal anomaly. More than half (52.9 per cent) of the fetal anomalies were detected by routine ultrasound examination. Forty-two per cent of cystic hygromas were secondary to a chromosomal defect. We stress the importance of a comprehensive fetal and newborn examination to ensure an accurate diagnosis so that subsequently accurate counselling can be provided.

Abdominal Muscles↗
PubMed1991

Kinase activity and protein phosphorylation in control and malignant hyperthermic skeletal muscle.

1. Native 6% Laemmli gels were used to resolve 7 protein kinase activity bands in control and malignant hyperthermia (MH)-susceptible porcine and human skeletal muscle extracts. 2. MH-susceptible samples were consistently more active than the controls. 3. Following halothane treatment, a 43 kDa component displayed increased phosphorylation by a calcium-calmodulin dependent kinase in MH-susceptible vs control human samples. 4. Increased phosphorylation of additional endogenous protein components of molecular mass 116 and 60 kDa was observed.

Animals↗
PubMed1991

Water homeostasis in desert-dwelling horses.

This study set out to investigate tolerance of the body water pool to short-term water deprivation in horses and, in particular, to assess whether feral horses from the Namib Desert showed tolerance to dehydration superior to Transvaal. Hydration status was compared in six feral horses from the Namib Desert and in six Boerperd farm horses under conditions of normal hydration and after 72 h of dehydration. Under normal hydration, the two groups did not differ significantly in water intake, plasma sodium and potassium concentrations, plasma osmolality, hematocrit, total plasma protein, body water content, or water turnover (ml.kg-0.82.day-1). The Namib horses were significantly smaller (P less than 0.0001) and turned over 5 liters less water per day than the Boerperd during normal hydration and 4 liters less during dehydration. Increases in plasma sodium concentration after 72 h of dehydration were greater (P less than 0.05) in the Namib horses. It was concluded that horses can easily tolerate water deprivation that results in a 12% reductions in body mass. The feral horses of the Namib desert were not significantly different per unit mass from domestic horses with regard to indexes of total body water content under conditions of normal hydration and after 72 h of dehydration. Their smaller size and, hence, lower water turnover might be mechanisms they use for survival in the Namib Desert.

Adaptation, Physiological↗
PubMed1990

Selection of medical students--a follow-up study.

The attributes of 1,026 medical students admitted to university on academic criteria and by interview between 1980 and 1983, and the characteristics of 822 of them who graduated between 1985 and 1988, were analysed. There were 133 students (13%) who failed and were excluded, 99 (10%) repeated 1 or more years of study, 67 (7%) voluntarily withdrew, 42 (4%) completed a B.Sc. degree during their medical training, and 675 graduated in the minimum time. The admitted and graduated students were mainly white (85%), male (67%) and had no academic experience other than matriculation (69%). During the review period the proportion of 'non-whites', women and applicants with university experience increased. Students who voluntarily withdrew had significantly low interview scores; applicants with university experience and applicants who subsequently failed had significantly high interview scores. It is concluded that the interview is useful, that the demographic characteristics of the classes are changing, and that traditional academic standards have been maintained.

Educational Measurement↗
PubMed1990

Neurologic crises in hereditary tyrosinemia.

Hereditary tyrosinemia results from an inborn error in the final step of tyrosine metabolism. The disease is known to cause acute and chronic liver failure, renal Fanconi's syndrome, and hepatocellular carcinoma. Neurologic manifestations have been reported but not emphasized as a common problem. In this paper, we describe neurologic crises that occurred among children identified as having tyrosinemia on neonatal screening since 1970. Of the 48 children with tyrosinemia, 20 (42 percent) had neurologic crises that began at a mean age of one year and led to 104 hospital admissions. These abrupt episodes of peripheral neuropathy were characterized by severe pain with extensor hypertonia (in 75 percent), vomiting or paralytic ileus (69 percent), muscle weakness (29 percent), and self-mutilation (8 percent). Eight children required mechanical ventilation because of paralysis, and 14 of the 20 children have died. Between crises, most survivors regained normal function. We found no reliable biochemical marker for the crises (those we evaluated included blood levels of tyrosine, succinylacetone, and hepatic aminotransferases). Urinary excretion of delta-aminolevulinic acid, a neurotoxic intermediate of porphyrin biosynthesis, was elevated during crises but also during the asymptomatic periods. Electrophysiologic studies in seven patients and neuromuscular biopsies in three patients showed axonal degeneration and secondary demyelination. We conclude that episodes of acute, severe peripheral neuropathy are common in hereditary tyrosinemia and resemble the crises of the neuropathic porphyrias.

Acute Disease↗
PubMed1990

Selective brain cooling after bilateral superior cervical sympathectomy in sheep (Ovis aries).

We have investigated the role of the sympathetic innervation of the vasculature of the head in the control of selective brain cooling of sheep, during exposure to high and low ambient temperatures and during endotoxin-induced fever. Bilateral removal of the superior cervical ganglia resulted in a significant reduction of hypothalamic temperature during all procedures. Respiratory rate was also depressed by the sympathectomy, apparently mainly as a result of a decrease in nasal airway patency. Rectal temperature changes after sympathectomy were dependent on the experimental conditions, and the rectal - hypothalamic temperature difference was enhanced during heat exposure and fever. Our results support the contention that sympathetically mediated changes in nasal blood flow and in venous return from the nasal cavity, via the angularis oculi and facial veins, may be involved in the control of selective brain cooling in sheep.

Animals↗
PubMed1989

Stress resistant and stress susceptible landrace pigs: comparison of blood variables after exposure to halothane or exercise on a treadmill.

Stress susceptible pigs develop pale, soft, exudative pork as a consequence of exposure to natural stress or exposure to halothane. Hyperstimulation of glycolysis is a major component of the stress reaction. Whether natural and artificial stress have other similarities was investigated by exposing pigs to halothane or to physical exercise, and measuring their blood composition. There were many similarities between the two groups but the significant differences suggest that although both halothane and exercise induce glycolysis, the mechanisms involved are different.

Animals↗
PubMed1989

Slaying the dinosaur. The need for locally organised evaluation of mental health services.

The need for mental health services to be community rather than institutionally based is generally agreed, but not all districts are finding the change easy. A blueprint will not do because a service must be shaped to the particular community. Gordon Mitchell and Graham Rodwell argue that a locally based research and evaluation help in the evolution of a unit responsive to local needs.

Community Mental Health Services↗
PubMed1988

Stress in cattle assessed after handling, after transport and after slaughter.

Blood samples were collected from unstressed cattle and from cattle undergoing handling stress, transport stress and slaughter. The blood was analysed for ACTH, cortisol, thyroxine stimulating hormone, tri-iodothyronine (T3) and catecholamine concentrations, and for haematocrit, total plasma protein, plasma lipid, lactate and glucose concentrations. Compared to control values handling significantly increased T3, cortisol, lipid and lactate concentrations. Compared to handling, transport stress was associated with increased catecholamines and lactate concentrations, a decreased cortisol concentration and similar concentrations of T3, lipid and glucose. Compared to transport, slaughter resulted in high catecholamines, lactate and glucose, and low T3, cortisol and lipid levels. It is concluded that the response to stress has two phases, a hypothalamic-adrenal cortex phase which is associated with perceived environmental stress such as noise, and a sympathetic-adrenal-medulla phase which is associated with neurogenic stress such as transport or specifically the massive sympathetic discharge caused by stunning. Combinations of stresses produce a mixed response.

Animals↗
PubMed1988

Selection of medical students--effect on class composition of using non-academic criteria.

The attributes of 2,304 applicants for admission to the University of the Witwatersrand Medical School were analysed. Those measured by previous academic performance, biographical history and assessment at interview were significantly different. Inclusion of non-academic criteria in admission decisions broadens the personal attributes of the class, and alters the ethnic and gender composition, without affecting subsequent failure rate.

Educational Measurement↗
PubMed1988

Effects of tracheostomy breathing on brain and body temperatures in hyperthermic sheep.

1. We measured rectal and hypothalamic temperature in sheep breathing nasally and via a tracheostomy, during hyperthermia resulting from exposure to a hot environment, exercise and fever. 2. In normothermic and hyperthermic sheep hypothalamic temperature was up to 1.0 degree C lower than rectal temperature when the sheep breathed nasally. Tracheostomy breathing abolished the rectal-hypothalamic temperature difference. 3. In sheep breathing via the tracheostomy and exposed to a dry-bulb temperature of 45-50 degrees C for 2 h, hypothalamic temperature exceeded rectal temperature by about 0.4 degrees C, and was significantly higher than that in sheep breathing nasally in the same environment. 4. During exercise on a treadmill and in the post-exercise period, the difference between hypothalamic and rectal temperature was abolished in the sheep while breathing through the tracheostomy, and rectal temperature rose to higher levels compared to those evident in the same activity while breathing nasally. 5. After an I.V. injection of 0.4 micrograms/kg lipopolysaccharide (LPS), the difference between hypothalamic and rectal temperature again was abolished in the sheep when breathing through the tracheostomy, but rectal temperature rose significantly less compared to when breathing nasally. 6. Our results indicate that selective brain cooling depends on upper respiratory tract cooling in normo- and hyperthermic states in sheep.

Animals↗
PubMed1988

Effect of intragastric pH on mucosal protective action of sucralfate.

Acid intragastric pH is believed to be mandatory for mucosal protective action of sucralfate, but evidence for its efficacy at neutral pH is lacking. The effect of sucralfate on gastric mucosal erosions induced by oral administration of aspirin and bile acids at acidic pH of 1.5 and 3.9, and near neutral pH of 6.5 was investigated in 320 rats. The effect of sucralfate on the intragastric pH four hours after the ingestion of test solutions was also examined. The incidence and severity of mucosal erosions induced by aspirin and bile acids were lower in animals treated with sucralfate at acidic (p less than 0.001) and near neutral (p less than 0.01) intragastric pH. Mucosal protection was greater with ingestion of sucralfate 300 mg/kg and 200 mg/kg, than with 100 mg/kg. The intragastric pH was higher (p less than 0.001) in sucralfate treated groups at pH 3.9 and 6.5. This study provides evidence that sucralfate protects against mucosal injury at near neutral, as well as at acidic pH.

Animals↗