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Biomedical subjects

K J Collins

Publications and source records attributed to K J Collins.

52 records · Page 3Linked to original sources
PubMed1976

Physiological performance and work capacity of Sudanese cane cutters with Schistosoma mansoni infection.

Physiological tests of work performance and measurement of field productivity were made in 194 Sudanese cane cutters in order to study the effect of Schistosoma mansoni infection. The cane cutters were selected from two age ranges (16-24 and 25-45 years) and subdivided into three clinical groups: not infected, infected with, and infected without clinical signs of hepatosplenomegaly. Men infected with Schistosoma haemotobium, malaria (blood film), or with hemoglobin levels less than 10 g/100 ml were excluded. There was a statistically significant (P less than 0.002) higher mean hemoglobin concentration in those not infected but the mean difference was less than 1 g/100 ml. Submaximal responses to exercise on a stationary bicycle ergometer, oxygen intake, ventilation, tidal volume, cardiac frequency and estimated maximal aerobic power output calculated both in absolute terms and relative to lean body mass and leg volume were similar in the six groups of cane cutters. No significant differences were found in physique, body composition or in thermoregulatory function tests. The cane cutters were found to have little natural acclimatization to heat in terms of sweating capacity when compared with a group of fully acclimatized Sudanese soldiers. The mean productivity (mean daily weight of cane cut per man) was significantly correlated with the individual's estimated maximum aerobic capacity determined in the laboratory, but not with the degree of S. mansoni infection. The noninfected group was less "efficient" (mean productivity:oxygen intake) during cutting than the infected groups but a larger proportion of the noninfected were in their first season of cutting. There was a positive correlation between the number of seasons' cutting experience and the individual's age, degree of infection and mean productivity. Cane cutters studied in this investigation were a relatively fit, active population from whom the more seriously ill were excluded. These results do not, therefore necessarily reflect the effects of S. mansoni on physiological work capacity and productivity of more static populations in areas of high endemicity.

Adolescent↗
PubMed1969

Stimulation of adrenal glucocorticoid secretion in man by raising the body temperature.

1. Plasma cortisol and corticosterone concentrations increased significantly in eleven resting, unacclimatized subjects after 2 hr exposure to an ambient temperature of 46 degrees C dry bulb, 36 degrees C wet bulb and in two subjects investigated by controlled elevation of body temperature in a hyperthermia test-bed.2. In the same experiments the urinary excretion of 17-hydroxycorticosteroids (17-OHCS) estimated as the 11-oxy and 11-deoxy fractions did not differ significantly in hot and in control conditions.3. Following an initial fall in plasma cortisol concentration during the first hour of heat exposure, cortisol levels increased in the second hour when body temperatures exceeded a ;critical' level of 38.3 degrees C. Two acclimatized subjects did not attain this body temperature even after 2 hr heating and showed no increase in plasma glucocorticoid levels.4. Sweat collected in arm bags, or by suction, in controlled hyperthermia experiments contained negligible amounts of cortisol (0.34-1.70 mug/100 ml. sweat).5. Changes in plasma cortisol specific activity after intravenous injection of 1,2[(3)H]cortisol indicated that the raised plasma concentration was brought about by increased adrenal secretion, though this was accompanied by more rapid removal of cortisol from the circulation in hot conditions. Excretion of tritium by the kidney was not significantly altered. It was not possible to determine whether changes in liver function contributed to the elevation of the plasma cortisol level but it was found that a larger proportion of cortisol was oxidized to cortisone, or to a metabolite closely resembling cortisone, in the heat.

17-Hydroxycorticosteroids↗
PubMed1966

The local training effect of secretory activity on the response of eccrine sweat glands.

1. The influence of repeatedly raising the body temperature by radiant heat to a level at which acclimatization to heat is normally acquired was investigated in two series of experiments, the first without the subjects sweating, the second with sweating.2. In a second investigation local sweat-gland activity was induced by drug injections on successive days without raising the body temperature.3. These experiments show that the increased sweating capacity characteristic of acclimatization to heat is a result of sweat-gland activity and does not appear to be induced by or to depend on an elevated body temperature.4. Secretory activity results in a loss of glycogen from sweat-gland cells on the first day of heat exposure but not after the glands have been ;trained' by acclimatization to heat.5. The state of acclimatization has no influence on the threshold concentration of acetylcholine required to elicit sweating when injected intradermally.

Acclimatization↗
PubMedDate not supplied

Physiological variation and adaptability in human populations.

This review traces some of the developments in population physiology based on contributions to the Annals over the last 25 years. Two broad themes are evident, physiological systems variation and adaptation, and by way of introduction an historical perspective of their relationship within human ecology is explored. Studies of physical fitness and work capacity, and the efforts to create standardized field procedures make up a number of the early papers. Longitudinal studies have provided reliable reference standards for Westernized populations, but are virtually non-existent for primitive groups. The relative importance of phenotypic and genotypic variations in working capacity have yet to be clearly defined. The level of habitual activity during childhood contributes to the development of ventilatory capacity though constitutional influences are of major importance. Variability in strength and motor performance of skeletal muscles are shown to have a direct bearing on aspects of growth, development and biological maturation. Physical and psychological stress in communities have been investigated. These and other studies contribute valuable data on the issue of stress, hypertension and cardiovascular morbidity and mortality. On the theme of human adaptability, high altitude populations, variations in thermal tolerance and adaptations in ageing populations have all received recent investigation. Highland people of all ages have considerably larger lung volumes than coastal dwellers. Haematological, biochemical and pulmonary function show adaptive phenomena that vary in different highland groups. In the tropical biome, more recent work includes the functional consequences of malnutrition, ethnic and cultural differences in work capacity, and the effects of endemic disease on physical performance. Annals of Human Biology papers have more recently contributed to investigations on morphological and physiological changes with human ageing. Though there is a decline in the ability to adapt to environmental stresses with age this may be met by changes in adaptational strategy in physiological systems.

Adaptation, Physiological↗