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  • 1
    ISSN: 1432-1254
    Keywords: Polyol pathway ; Diabetes mellitus ; Water immersion ; Heat stress
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Abstract Activities of erythrocyte aldose reductase were compared in 34 normal subjects, 45 diabetic patients, and nine young men following immersion in water at 25, 39, and 42° C. Mean basal enzyme activity was 1.11 (SEM 0.12) U/g Hb and 2.07 (SEM 0.14) U/g Hb in normal controls and diabetic patients, respectively (P〈0.0001). Activities of the enzyme showed a good correlation with hemaglobin A1 (HbA1) concentrations (P〈0.01) but not with fasting plasma glucose concentrations. After immersion at 42° C for 10 min, enzyme activity was increased by 37.6% (P〈0.01); however, the activity decreased by 52.2% (P〈0.005) after immersion for 10 min at 39° C and by 47.0% (P〈0.05) at 25° C. These changes suggest that heat stress might aggravate diabetic complications, and body exposure to hot environmental conditions is not recommended for diabetic patients.
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  • 2
    ISSN: 1432-1254
    Keywords: Keywords Heat-related mortality ; Apparent temperature ; Heat stress ; Southern Ontario ; Canada
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Abstract  The Toronto–Windsor corridor of Southern Ontario, Canada, experiences hot and humid weather conditions in summer, thus exposing the population to heat stress and a greater risk of mortality. In the event of a climate change, heat-stress conditions may become more frequent and severe in Southern Ontario. To assess the impact of summer weather on health, we analyzed heat-related mortality in the elderly (older than 64 years) in the metropolitan areas of Windsor, London, Kitchener-Waterloo-Cambridge, Hamilton, and Toronto for a 17-year period. Demographic, socioeconomic, and housing factors were also evaluated to assess their effect on the potential of the population to adapt and their vulnerability to heat stress. Heat-stress days were defined as those with an apparent temperature (heat index) above 32°C. Mortality among the elderly was significantly higher on heat-stress days than on non-heat-stress days in all cities except Windsor. The strongest relationships occurred in Toronto and London, followed by Hamilton. Cities with the greatest heat-related mortality have relatively high levels of urbanization and high costs of living. Even without the warming induced by a climate change, (1) vulnerability is likely to increase as the population ages, and (2) ongoing urban development and sprawl are expected to intensify heat-stress conditions in Southern Ontario. Actions should be taken to reduce vulnerability to heat stress conditions, and to develop a comprehensive hot weather watch/warning system for the region.
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  • 3
    ISSN: 1432-1254
    Keywords: Environmental profile ; Heat stress ; Critical temperatures ; Milk production
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Abstract The environmental profile of central Arizona is quantitatively described using meteorological data between 1971 and 1986. Utilizing ambient temperature criteria of hours per day less than 21° C, between 21 and 27° C, and more than 27° C, the environmental profile of central Arizona consists of varying levels of thermoneutral and heat stress periods. Milk production data from two commercial dairy farms from March 1990 to February 1991 were used to evaluate the seasonal effects identified in the environmental profile. Overall, milk production is lower during heat stress compared to thermoneutral periods. During heat stress, the cool period of hours per day with temperature less than 21° C provides a margin of safety to reduce the effects of heat stress on decreased milk production. Using minimum, mean and maximum ambient temperatures, the upper critical temperatures for milk production are 21, 27 and 32° C, respectively. Using the temperature-humidity index as the thermal environment indicator, the critical values for minimum, mean and maximum THI are 64, 72 and 76, respectively.
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  • 4
    ISSN: 1432-1254
    Keywords: Fertility ; Microclimates ; Heat stress
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Abstract Records were obtained over a 3 year period from six Holstein dairy farms of 300 to 500 cows each in the Phoenix, Ariz. area. Dairies were selected on the basis of similar management practices, herd size, milk production and facilities (with the exception of cooling systems). Microclimatic modifications (two dairies each) were shade only (approximately 3.7 m2/cow), evaporative-cooled shades and low-pressure water foggers under the shades. Data were categorized by season of calving (spring, Feb.–May; summer, June–Sept.; and fall, Oct.–Jan.). Traits evaluated were calving interval, days open and services/conception. Calving interval was shortest for cows calving in the spring (378 days), intermediate in fall (382 days) and longest in summer (396 days). Similar seasonal trends were observed for days open (103, 103 and 119 days, respectively) and services/conception (1.54, 1.81 and 1.93, respectively). All differences between spring and summer were significant (P 〈 0.05). Calving interval and days open were less for evaporative-cooled groups (374 and 98 days, respectively), with no difference between shade only and foggers (391 and 392 days, 112 and 116 days, respectively). Services/conception were similar for all groups (1.72 to 1.79). A significant interaction between microclimate and season for services/conception could be interpreted as (i) smaller season differences for evaporative-cooled groups than for shade or foggers, or (ii) a change in the ranking of control and fogger groups during summer versus fall. Evaporative cooling was more effective than fogging for reducing the detrimental effects of seasonal high temperatures on fertility.
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  • 5
    ISSN: 1432-1254
    Keywords: Aldosterone ; Electrolytes ; Broiler ; Heat stress
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Abstract An experiment was conducted to evaluate the effects of supplementing drinking water with isomolar (0.067 mol/l) KCl or NaCl on mass gain, food and water consumption, rectal temperature, and plasma concentrations of aldosterone, Na+, and K+ in broiler chickens reared in thermoneutral and cycling heat stressing environments. Heat stress decreased (P≤0.05) mass gain, food consumption, and plasma concentrations of Na+ and K+, while increases (P≤0.05) in plasma concentrations of aldosterone, rectal temperature, and water consumption were observed. Drinking water supplemented with either KCl or NaCl increased (P≤0.05) broiler mass gain and water consumption, but had no effect (P〉0.1) on the other variables evaluated. The results of this study indicate that broiler chickens in a heat stress environment are under osmotic stress and supplementing drinking water with 0.067 mol/1 KCl or NaCl does not lessen this stress.
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  • 6
    ISSN: 1432-1254
    Keywords: Key words Carotid sinus baroreceptors ; R-R intervals ; Reference point ; Power spectra ; Heat stress
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Abstract  The purpose of this study was to examine the effect of hyperthermia on the carotid baroreceptor-cardiac reflexes in humans. Nine healthy males underwent acute hyperthermia (esophageal temperature ∼38.0° C) produced by hot water-perfused suits. Beat-to-beat heart rate (HR) responses were determined during positive and negative R-wave-triggered neck pressure steps from +40 to −65 mm Hg during normothermia and hyperthermia. The carotid baroreceptor-cardiac reflex sensitivity was evaluated from the maximum slope of the HR response to changes in carotid distending pressure. Buffering capacity of the HR response to carotid distending pressure was evaluated in % from a reference point calculated as (HR at 0 mm Hg neck pressure−minimum HR)/HR range ×100. An upward shift of the curve was evident in hyperthermia because HR increased from 57.7±2.4 beats/min in normothermia to 88.7±4.1 beats/min in hyperthermia (P〈0.05) without changes in mean arterial pressure. The maximum slope of the curve in hyperthermia was similar to that in normothermia. The reference point was increased (P〈0.05) during hyperthermia. These results suggest that the sensitivity of the carotid baroreflex of HR remains unchanged in hyperthermia. However, the capacity for tachycardia response to rapid onset of hypotension is reduced and the capacity for bradycardia response to sudden hypertension is increased during acute hyperthermia.
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  • 7
    ISSN: 1432-1254
    Keywords: Key words Circadian rhythm ; Locomotor activity ; Exercise ; Heat stress
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Abstract  Several timed daily environmental cues alter the pattern of nycthemeral variations in body core temperature in rodents. The present study investigated the effect of timed exercise on variations of daily body core temperature. Male rats were housed in cages with a running wheel at an ambient temperature of 24° C with a 12:12 h light/dark cycle. Timed daily exercise rats (TEX) were allowed access to the wheel for 6 h in the last half of the dark phase, freely exercising rats (FEX) could run at any time, and sedentary rats (NEX) were not allowed to run. After a 3-week exercise period, all animals were denied access to the wheel. The intraabdominal temperatures (T ab) and spontaneous activities of rats were measured for 6 days after the exercise period. The T ab values of the TEX rats were significantly higher than those of the other two groups only in the last half of the dark phase, while T ab in the FEX and NEX rats showed no significant difference. The specific T ab changes in the TEX rats lasted for 2 days after the exercise period. Spontaneous activity levels were higher in the TEX rats than the FEX and NEX rats in the last half of the dark phase for 1 day after the exercise period. The results suggest that daily exercise limited to a fixed time per day modifies nycthemeral variations of body core temperature in rats so that the temperature increases during the period when the animals had previously exercised. Such a rise in body core temperature is partly attributed to an increase in the spontaneous activity level.
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  • 8
    ISSN: 1432-1254
    Keywords: Key words Indomethacin ; Hyperthermia ; Heat stress ; Broilers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Abstract  An investigation was carried out to verify whether the heat stress hyperthermia response of broilers is prostaglandin-dependent. Male broiler chickens of the Hubbard-Petterson strain, aged 35–49 days, were used. Chickens were injected with indomethacin (1 mg/kg intraperitoneally ) 15 min before or 2 h after heat exposure (at 35°C for 4 h), and rectal temperature was measured before injection and up to 4 h thereafter. Birds were separated into two groups with and without access to water during heat stress. The increase in rectal temperature was lower (P〈0.05) in birds with access to drinking water during heat exposure. All birds injected with indomethacin exhibited an increase in rectal temperature, irrespective of whether indomethacin was administered before or in the course of the rise in temperature. The results revealed that the increase in rectal temperature during heat exposure is not prostaglandin-dependent, and that the use of cyclooxigenase inhibitors is not recommended to attenuate heat stress hyperthermia in broiler chickens.
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  • 9
    ISSN: 1432-1254
    Keywords: Heat stress ; Growth performance ; Physiological response ; Broiler chickens
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Abstract An experiment was conducted to elucidate the influence of four constant ambient temperatures (20°, 25°, 30° and 35°C) on the performance and physiological reactions of male commercial broiler chicks from 3 to 7 weeks of age. A 12 h light-dark cycle was operated, while relative humidity and air circulation were not controlled. Exposure of broiler chickens to the 20°, 25°, 30° and 35°C treatments showed highly significant (P〈0.0001) depression in growth rate, food intake and efficiency of food utilization, and a significant increase in water consumption for the 30° and 35°C groups. Mortality was, however, not affected by the temperature treatments. Changes in physiological status, such as increased rectal temperatures, decreased concentration of red blood cells, haemoglobin, haematocrit, and total plasma protein were observed in birds housed in the higher temperature (30° and 35°C) environments. Moreover, in these broiler chickens, there was an increased blood glucose concentration and a decreased thyroid gland weight. These results indicate that continuous exposure of broiler chickens to high ambient temperatures markedly affects their performance and physiological response.
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  • 10
    ISSN: 1432-1254
    Keywords: Key words Haemodilution ; Hyperthermia ; Heat stress ; Anaemia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Abstract  Cats anaesthetized with a mixture of chloralose and urethane were exposed to heat stress in two groups. In the first group (n=10) of control animals, the effect of heat stress on haemodynamic variables was recorded at control haematocrit (HCT) of 42.0±1.0%. In a second group, the effect of heat stress was studied after induction of acute normovolaemic haemodilution (HCT of 13.0±1.0%). Haemodilution was induced to a maximum of 60% replacement of blood with dextran (mol.wt. 150000). Heat stress was induced by surface heating and core body temperature was raised from 37° C to 42° C. The effect of heat stress and haemodilution on various haemodynamic variables, viz. left ventricular pressure (LVP), left ventricular contractility (LVdP/dt max), heart rate (HR), cardiac output (CO), arterial blood pressure (ABP), right atrial pressure (RAP), and arterial blood PO2, PCO2 and pH was examined. Haemodilution produced significant (P〈0.05) increases in HR and CO but there were no significant (P〉0.05) changes in ABP, RAP, LVdP/dt max and total peripherial resistance (TPR). Hyperthermia caused a significant fall (P〈0.05) in TPR. However, the percentage fall in TPR was higher in the control group. On exposure to heat stress, there were significant (P〈0.05I increases in HR and CO in both the groups; however, HR and CO values were significantly (P〈0.05) higher in the haemodiluted group compared to the control. The latter findings could be due either to the higher basal values of these variables with the fall in HCT or to inefficient cardiovascular regulatory mechanisms. The lack of efficient regulatory control under such severe stress conditions makes the cardiovascular system of anaemic animals more vulnerable to heat stress. In conclusion, the results of the present study showed deleterious effects of heat stress in both the groups. The higher values of HR and CO in the haemodiluted group may be responsible for circulatory failure at low HCT values, indicating a higher risk in the haemodiluted group as compared to the control group.
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