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PubMed1977

Prediction of heat tolerance from heart rate and rectal temperature in a temperate environment.

To determine if heat tolerance could be predicted from responses to exercise in temperature conditions, 51 young men performed 15 min of bench stepping at an average work load of 80 W at 23 degrees C. On the following day they attempted to perform 3 h of bench stepping at 40 W in heat (39.3 degrees C dry bulb, 30.3 degrees C wet bulb). Of these subjects, 4 were heat intolerant, judged by previous heat stroke episodes during field marches, 12 were heat acclimated, and 35 were unacclimated. The heat-intolerant subjects showed the highest heart rates (HR) and rectal temperatures (Tre) at 23 degrees C and in heat, and the acclimated subjects showed the lowest corresponding values. HR and Tre in each environment were combined into a single score, from 10, indicating the poorest responses, to 100, indicating the best responses. These scores at 23 degrees C when correlated with the corresponding scores in heat resulted in a linear correlation coefficient of r = 0.94 with a standard error of estimate of 8.6%. Scores of the heat-intolerant subjects were below 35, and those of the acclimated subjects were between 70 and 100. Thus heat tolerance can accurately be predicted for HR and Tre responses to exercise at room temperature.

Acclimatization↗
PubMed1980

Correspondence of brain and rectal temperatures of guinea pigs in helium environments.

Brain and rectal temperatures were measured in guinea pigs exposed to helium-oxygen environments at pressures as high as 50 bars. Very high correlations (r = .856, P less than 0.001) between the two values were observed, with an average difference of 0.47 degrees C (computed SD = 0.31). Brain temperature was usually higher than rectal. At a given ambient temperature, heat loss at 50 bars was more rapid than at 20 bars, which supports existing data for lower pressures. At 50 bars, normal equilibrium temperatures (approximately equal to 39 degrees C) could be maintained only if ambient temperature was in the vicinity of 35 degrees C. Lower ambient temperatures resulted in lower equilibrium temperatures. Between 33 and 39 degrees C, brain temperature can be predicted from rectal temperature, with an error of about 0.5 degree C.

Animals↗
PubMed1979

The 24Na-transport increasing effect of veratrine in frog sartorius muscle influenced by the tonicity, composition and temperature of the external environment.

The influence of tonicity, ionic composition and temperature of the incubating medium on the increasing effect of veratrine on 24Na transport in the frog sartorius muscle has been studied. (1) The effect of veratrine applied during 24Na loading on the rate coefficient for sodium loss depended on the tonicity of the medium. The rate of loss of 24Na from muscles loaded in the presence of veratrine was not affected if the muscles had been equilibrated in hypertonic medium. However, when treating the muscles with veratrine in isotonic medium during 24Na loading, we obtained a twofold increase in the rate coefficient for sodium loss. (2) The effect of veratrine applied during the desaturation period on 24Na efflux was also found to depend on the tonicity of the medium. Veratrine applied during the desaturation period increased the 24Na efflux in muscles equilibrated in isotonic Ringer's solution. However, when the muscles were equilibrated in hypertonic medium, veratrine did not influence 24Na efflux, not even after the rate of 24Na loss had been decreased by ouabain. (3) Hypertonic medium inhibited the Li uptake-enhancing effect of veratrine, while in isotonic medium veratrine had a marked enhancing effect. (4) In hypertonic medium lithium inhibited the otherwise characteristic increasing effect of veratrine on 24 Na uptake. (5) The increase of intracellular sodium concentration as a result of incubation in cold, potassium-free Ringer's solution did not influence the 24Na exchange-increasing effect of veratrine in isotonic medium. (6) The increasing effects of 0.1 and 0.5 mM veratrine on 24Na influx had the same degree at room temperature. However, at 5 degrees C 0.5 mM veratrine increased 24Na influx to a greater extent than 0.1 mM. (7) On the basis of our earlier experiments it has been suggested that the site of action of the 24Na uptake-increasing effect of veratrine could be the neural structures in the muscle equilibrated in hypertonic media. The present experiments confirm this suggestion and at the same time demonstrate that there are substantial differences in the mechanism of the sodium transport of veratrine-treated neural and muscle membranes, which become more apparent in hypertonic medium.

Animals↗
PubMed2000

Widespread occurrence of structurally diverse tetraether membrane lipids: evidence for the ubiquitous presence of low-temperature relatives of hyperthermophiles.

Isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs) and branched glycerol dialkyl diethers are main membrane constituents of cultured hyperthermophilic archaea and eubacteria, respectively, and are found in environments with temperatures >60 degrees C. Recently, we developed a new technique for the analysis of intact core tetraether lipids in cell material and sediments. The application of this technique to recent sediments shows that known and newly identified isoprenoid and branched GDGTs are widespread in low-temperature environments (<20 degrees C) and are structurally far more diverse than previously thought. Their distribution indicates the ubiquitous environmental presence of as yet uncultivated, nonthermophilic organisms that may have independently evolved from hyperthermophilic archaea and eubacteria. The structures of some of the new GDGTs point to the hybridization of both typical archaeal and eubacterial biosynthetic pathways in single organisms.

Archaea↗
PubMed2004

Thermal sensation and comfort in transient non-uniform thermal environments.

Most existing thermal comfort models are applicable only to steady-state, uniform thermal environments. This paper presents summary results from 109 human tests that were performed under non-uniform and transient conditions. In these tests, local body areas were independently heated or cooled while the rest of the body was exposed to a warm, neutral or cool environment. Skin temperatures, core temperature, thermal sensation and comfort responses were collected at 1- to 3-min intervals. Based on these tests, we have developed predictive models of local and overall thermal sensation and comfort.

Air Conditioning↗
PubMed1977

Effect of compression rate on HPNS convulsion threshold in the euthermic rat.

The modification of the development of the high pressure nervous syndrome (HPNS) has been demonstrated by varying the external environment (chamber temperature, compression rate) or the internal environment (core temperature, pharmacology, age). This study examined the effects of compression rate on the convulsion-threshold pressure and EEG activity in 68 adult male Wistar rats with chronically implanted electrodes. Restrained animals were individually compressed at a predetermined rate in helium-oxygen to a simulated depth of 4500 fsw (137 ATA), with colonic temperature maintained at normal levels. Six compression rates showed that convulsion-threshold pressure for euthermic rats did not significantly differ between any of the groups.

Animals↗
PubMed1985

Effects of age on body temperature and blood pressure in cold environments.

Mean deep body temperature fell by 0.4 +/- 0.1 (SD) degrees C in five sedentary, clothed 63-70 year old men and by 0.1 +/- 0.1 degrees C in four young adults after 2 h exposure in still air at 6 degrees C (P less than 0.001). The mean increase in systolic and diastolic pressure was significantly greater (P less than 0.002) in the older subjects (24 +/- 4 mmHg systolic, 13 +/- 4 mmHg diastolic) than in the young (14 +/- 6 mmHg systolic, 7 +/- 3 mmHg diastolic) after 2 h at 6 degrees C. A small rise in blood pressure occurred in the older men at 12 degrees C, but there was no increase in either group at 15 degrees C. The association of variables is particularly marked between systolic blood pressure and core temperature changes at 6 degrees C. There were no appreciable cold-adaptive changes in blood pressure or thermoregulatory responses after 7-10 days repeated exposure to 6 degrees C for 4 h each day. Blood pressure elevation in the cold was slower but more marked in the older men. These changes in blood pressure may provide a possible basis for delineating low domestic limiting temperature conditions.

Adolescent↗
PubMed2000

Prediction of the average skin temperature in warm and hot environments.

The prediction of the mean skin temperature used for the Required Sweat Rate index was criticised for not being valid in conditions with high radiation and high humidity. Based on a large database provided by 9 institutes, 1999 data points obtained using steady-state conditions, from 1399 experiments and involving 377 male subjects, were used for the development of a new prediction model. The observed mean skin temperatures ranged from 30.7 degrees C to 38.6 degrees C. Experimental conditions included air temperatures (Ta) between 20 and 55 degrees C, mean radiant temperatures (Tr) up to 145 degrees C, partial vapour pressures (Pa) from 0.2 to 5.3 kPa, air velocities (v(a)) between 0.1 and 2 m/s, and metabolic rates (M) from 102 to 620 W. Rectal temperature (T(re)) was included in the models to increase the accuracy of prediction. Separate models were derived for nude (clothing insulation, I(cl), < or = 0.2 clo, where 1 clo = 0.155 m2 x degrees C x W(-1), which is equivalent to the thermal insulation of clothing necessary to maintain a resting subject in comfort in a normally ventilated room, air movement = 10 cm/s, at a temperature of 21 degrees C and a humidity of less than 50%) and clothed (0.6 < or = I(cl) < or = 1.0 clo) subjects using a multiple linear regression technique with re-sampling (non-parametric bootstrap). The following expressions were obtained for nude and clothed subjects, respectively: T(sk) = 7.19 + 0.064Ta + 0.061Tr + 0.198Pa - 0.348v(a) + 0.616T(re) and T(sk) = 12.17 + 0.020Ta + 0.044Tr + 0.194Pa - 0.253v(a) + 0.0029M + 0.513T(re). For the nude and clothed subjects, 83.3% and 81.8%, respectively, of the predicted skin temperatures were within the range of +/- 1 degree C of the observed skin temperatures. It is concluded that the proposed models for the prediction of the mean skin temperature are valid for a wide range of warm and hot ambient conditions in steady-state conditions, including those of high radiation and high humidity.

Clothing↗
PubMed1983

Stress in farm animals: a need for reevaluation.

In animal husbandry, stress has usually been conceived as a reflex reaction that occurs ineluctably when animals are exposed to adverse environmental conditions, and which is the cause of many unfavorable consequences, ranging from discomfort to death. The inadequacy of this view is apparent from the new concepts that have been developed from research aimed at understanding the relationships between hormonal and behavioral reactions to stressful situations. Psychological aspects of environmental stimuli are powerful activators of endocrine responses. The amount of psychological stress that an animal experiences determines how much the pituitary-adrenal axis responds. Indeed, removing the variable of emotional arousal reduces or eliminates responses to some other stressors such as heat and cold. This means that one of the most important characteristics of the stress response, its nonspecificity, lies in the afferent part of the response, not the efferent. Hormonal and behavioral responses are intimately related in stressful situations. In particular, the perception and ensuing behavior of the subject are critical to the nature and intensity of hormonal response. Evidence from experiments in farm animals is presented to support these concepts. Because adjustment abilities are limited by genetics and previous experience, the respective role of each of these factors needs to be delineated more accurately. In addition, most experimental studies have been concerned with acute stress, while chronic multiple stress, which is more likely to be encountered in intensive husbandry, has received little attention. The approach in this field is hampered by the lack of suitable physiological criteria to assess long-term adaptive changes. Opportunities for further research are delineated and the need for a more integrated view of stress reactions in farm animals is emphasized.

Adaptation, Psychological↗
PubMed1984

Measurement of mean skin temperature of clothed persons in cool environments.

The precision with which mean skin temperature could be estimated from some few points on clothed persons in a cool environment was studied. The skin temperature data were obtained from experiments on 10 clothed persons who were resting and working at an environmental temperature of 10 degrees C. With these data, eleven calculation formulas in current use were compared to a "reference mean skin temperature" based on a weighting formula involving 13 local skin temperatures. It was concluded that no formula including less than seven points gave a reasonably accurate mean skin temperature in this cool environment. In addition, a stepwise correlation analysis involving linear regression was performed on the data. This gave 12 new calculation formulas, which were evaluated for accuracy in estimating mean skin temperature. Among these, a weighting formula involving only four local skin temperatures was selected to be recommended for use in field investigations: Tsk = 9.429 + 0.137 X Tforehead + 0.102 X Thand + 0.290 X Tlower back + 0.173 X Tlower leg.

Adolescent↗