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Biomedical subjects

G Alexander

Publications and source records attributed to G Alexander.

At least 127 records · Page 7Linked to original sources
PubMed1979

Hyaline membrane disease. Comparison of continuous negative pressure and nasal positive airway pressure in its treatment.

The effectiveness of continuous negative pressure (CNP) and nasal continuous positive airway pressure (CPAP) in the treatment of hyaline membrane disease and the incidence of complications were compared in 36 preterm infants randomly treated with CNP or nasal CPAP. Both methods of treatment were effective in increasing PaO2 and allowing a decrease in inspired O2 concentration. The time required with mechanical assistance and with an O2 concentration of more than 40% was equal in both groups. In the CNP group, four infants required mechanical ventilation because of clinical deterioration whereas in the nasal CPAP group, seven needed this type of therapy. Three infants in each group had extraalveolar air, and two patients in each group died. The results suggest that both methods of applying continuous distending airway pressure are effective. Nasal CPAP has the advantages of easier application and better access to the infant.

Blood Pressure↗
PubMed1979

Cold thermogenesis.

Explore the source record for details and available documents.

Adipose Tissue, Brown↗
PubMed1978

Ultrastructural development of adipose tissue in foetal sheep.

The development of subcutaneous and perirenal adipose tissue in foetal sheep of 40--150 days conceptual age was examined using electromicroscopy. Adipose tissue from both sites developed from pre-adipose cells of similar appearance, with few mitochondria, and commenced accumulating lipid on about day 70 of gestation. In the perirenal fat there was marked proliferation of mitochondria between days 80 and 90 and the tissue developed into brown fat, cell profiles being characterized by many mitochondria with numerous distinct cristae, whereas in the subcutaneous cells which developed into white adipose tissue few mitochondria with fewer cristae were observed. Multilocular and unilocular cells occurred in both tissues near term. Nerves were first seen between brown adipose cells in a 130-day-old foetus and were frequently seen in older foetuses, but very few nerves were seen in the white adipose tissue. In hypophysectomized foetuses, either full- or post-term, the subcutaneous fat and internal fat were shown to be white and brown adipose tissue respectively, as in normal foetuses, although in one 164-day-old foetus the perirenal tissue appeared to be a mixture of brown and white fat.

Adipose Tissue↗
PubMed1976

Analysis of the acidic fraction of marijuana smoke condensate by capillary gas chromatography-mass spectrometry.

A method for the analysis of organic acids and phenols isolated from marijuana smoke condensate has been developed. Comparative analyses of standard tobacoo, Mexican, and Turkish marijuana smoke condensates carried out by means of capillary gas chromatography indicated both qualitative and quantitative changes in the constituents of chromatographic profiles. Samples were converted to volatile derivatives by methylation and trimethylsilylation; whereupon, 49 aliphatic acids, aromatic acids, and phenolic compounds were identified by means of capillary gas chromatography-mass spectrometry.

Acids↗
PubMed1975

Brown adipose tissue in the new-born calf (Bos taurus).

1. Electron microscopic examinations revealed that most of the adipose tissue of new-born calves had the cellular morphology of brown adipose tissue; only subcutaneous tissue had the cellular morphology of white adipose tissue. 2. The cellular morphology of the brown adipose tissue changed progressively to that of white adipose tissue as the age of the calves increased. 3. Infusion of noradrenaline (I.V.) at rates of 1 and 5 mug/kg.min into new-born calves exposed to a thermoneutral environment increased metabolic rate two- to threefold, and also increased rectal temperature and respiration rate. The responses declined as age of calf increased. 4. Approximately 2% of the body weight of new-born calves appears to be brown adipose tissue.

Adipose Tissue↗
PubMed1975

Maximum thermogenic response to cold in relation to the proportion of brown adipose tissue and skeletal muscle in the body and to other parameters in young lambs.

No relationship was apparent between the maximum thermogenic response of lambs to cold (summit metabolism) and the dissectable brown adipose tissue content, or the chemically extractable lipid content of the whole animal or the weight of various skeletal muscles. Correlations of summit metabolism with other parameters also suggested that the level of glucose, FFA and glycerol in the circulation, and the glycogen stores in liver and muscle, did not limit summit metabolism. However, significant correlations of summit metabolism with cardiac output and arteriovenous differences in oxygen content of blood focused attention on the possible role of the cardiovascular system and on the metabolic capability of the thermogenic tissues in determining summit metabolism.

Adipose Tissue, Brown↗
PubMed1975

Quantity and calculated oxygen consumption during summit metabolism of brown adipose tissue in new-born lambs.

Macroscopic dissection of new-born lambs of several breeds revealed that brown adipose tissue comprised approximately 1.5% of the body weight. The perirenal-abdominal and prescapular-cervical depots were by far the largest, and the overall distribution was largely consistent with that reported for other species, although there was no significant interscapular depot. The oxygen consumption of the brown adipose tissue in lambs was calculated to reach 70 ml/(g-h), which is consistent with published data for rabbit brown adipose tissue, in vivo, but 35 times higher than that for the same tissue in vitro. It was also calculated that a substantial portion, perhaps two thirds, of the lipid available for metabolism was stored outside the adipose tissue. The study also made it possible to examine the validity of methods of estimating blood flow through brown adipose tissue. Untenable venous blood oxygen saturations were calculated from results obtained using 86-Rb, but saturation calculated from results with the radio-active microsphere method were entirely plausible.

Adipose Tissue, Brown↗
PubMed1973

Effects of cold exposure on tissue blood flow in the new-born lamb.

1. Conscious lambs less than 2 days old were exposed to thermoneutral and to cold environments, and the radioactive microsphere technique was used to obtain measurements of blood flow to most tissues of the body.2. Cold stress was such as to evoke a summit metabolic response. Deep body temperature was within the normal range for thermoneutral conditions, while metabolic rate increased by about 300%, cardiac output by about 30%, and blood pressure by about 25%.3. Blood flow to the thermogenic tissues increased: perirenal, inguinal, pericardial, prescapular and cervical brown fat depots showed a five- to sixfold increase, while the longissimus dorsi, trapezius, gastrocnemius and biceps femoris muscles showed a five- to ninefold increase.4. There was an increase in blood flow in the diaphragm, intercostal, panniculus and cardiac muscles, but a decrease in flow in the skin of the leg, ear and midside, the maxillo turbinals, thyroids, spleen, kidneys, liver and gut. There were no significant changes in total or regional blood flow in the brain or spinal cord, or in the adrenals, nasal mucosa or tongue.5. Results support other evidence that thermogenesis in both brown fat and skeletal muscle is very important in the new-born lamb exposed to cold. Changes in flow in other tissues correlated with known functions in the cold animal. The redistribution of cardiac output during cold stress is a further example of circulatory adjustments which enable animals to cope with stress states.6. Many differences between blood flow values obtained by the radio-active microsphere and other techniques for measuring blood flow are noted and discussed.

Adipose Tissue, Brown↗
PubMed1972

Regional distribution of cardiac output in young lambs: effect of cold exposure and treatment with catecholamines.

1. Lambs less than 3 days old, exposed to thermoneutral or intensely cold conditions in a respiration chamber, were infused with adrenaline or noradrenaline, 1 or 10 mug/kg.min; and the effects on oxygen consumption, cardiac output and its distribution to skin, skeletal and cardiac muscle, liver, spleen, kidney, gut, brown adipose tissue and brain were determined. Cardiac output was estimated by the Fick and dye dilution methods and the distribution of cardiac output by Sapirstein's method of fractional distribution of indicators.2. Under thermoneutral conditions, metabolic rate was stimulated by both doses of noradrenaline and by the low, but not the high dose of adrenaline. Under cold conditions, the low dose of catecholamines had little effect on the already elevated metabolic rate, but the high doses depressed the metabolic response to cold.3. The low dose of adrenaline increased cardiac output under thermoneutral conditions whereas the high dose decreased cardiac output; the effects of noradrenaline were less marked, in contrast to reported effects in new-born rabbits. The low doses of catecholamine given under cold conditions had little effect on the already elevated cardiac output, but the high doses, particularly of adrenaline, decreased cardiac output.4. Blood flow through the skin of the extremities was markedly reduced by cold exposure, while flow through the peri-renal fat was doubled, flow through the skeletal muscle was quadrupled and flow through the cardiac muscle was trebled. These increases, particularly in skeletal muscle, were due to increased cardiac output and to vasodilation, as indicated by the reduced ratio of blood pressure to blood flow. Results are contrasted with published reports that blood flow through brown fat in new-born rabbits was greatly increased by cold, but muscle flow was scarcely altered.5. In almost all organs examined the high doses of adrenaline infused in either environment markedly reduced blood flow, presumably by generalized vasoconstriction. Changes due to noradrenaline were small under thermoneutral conditions and flow through brown fat was increased by only 60% during infusion of 10 mug/kg.min. Much greater increases have been reported in new-born rabbits. Under cold conditions the high doses of noradrenaline tended to decrease flow in most organs including brown fat and muscle.6. The results provide likely explanations for published reports that adrenaline failed to stimulate non-shivering thermogenesis or suppressed the mobilization of metabolites and the metabolic response to cold.

Adipose Tissue, Brown↗