Effect of ambient temperatures ranging from cold to heat on thermoregulation in conscious MK801-treated rats.

The glutamate NMDA receptor has been suggested to be involved in thermoregulation. To further analyse its role, the thermoregulatory responses of rats treated with 0.5 mg.

Thermoregulation in the cold after physical training at different ambient air temperatures.

Since human thermoregulation at rest is altered by cold exposure, it was hypothesized that physical training under cold conditions would alter thermoregulation. Three groups (n = 8) of male subjects (mean age 24.3 +/- 0.

Circadian rhythm of rectal temperature during sleep deprivation with modafinil.

Background: Sleep deprivation (SD) induces many adverse psychological and physiological effects, particularly on vigilance and the thermoregulatory system. The drug modafinil appears to suppress or diminish the harmful effects on vigilance. However, the effects of modafinil combined with SD on the circadian rhythm of core temperature are not well established.

Positive end expiratory pressure (PEEP) slightly modifies ventilatory response during incremental exercise.

To clarify the ventilatory effects of a 5-cm H2O positive end expiratory pressure (PEEP) in healthy men during incremental exercise in normoxic conditions, 22 subjects were subjected to a constant workload (0 W, 50 W, 100 W, 150 W and 200 W) on a cycle ergometer for periods of 8 min each, both with and without 5-cm H2O PEEP. Results show that PEEP increases inspiratory (TI) and expiratory (TE) duration and tidal volume (VT) and decreases breathing frequency (fB) at rest (p < 0.05).

Positive expiratory pressure as a method for preventing the impairment of attentional processes by hypoxia.

This study investigated the effects of hypoxia on parallel/preattentional and serial/attentional processes in early vision, and the use of a positive-end-expiratory-pressure (PEEP) to prevent the impairment in performance. Twenty-one subjects were submitted to an 8-h hypoxia exposure in a hypobaric chamber (4500 m, 589 hPa, 22 degrees C), both with and without a 5-cm H2O PEEP. Subjects carried out a visual search task consisting of detecting a target among distractors in normoxia, in acute and in prolonged hypoxia.

Determination of the velocity associated with VO2max.

Purpose: The theoretical velocity associated with VO2max (vVO2max) defined by Daniels (1985) is extrapolated from the submaximal VO2-velocity relationship. VO2 is generally determined by assuming that the aerobic response reacts like a linear first-order system at the beginning of square-wave exercise with a steady-state reached by the 4th minute. However, at supra-ventilatory threshold work rates, the steady state in VO2 is delayed or not attained.

Sympathetic stimulation induced by hand cooling alters cold-induced vasodilatation in humans.

Hand cooling is a cold pressor test, which induces general sympathetic stimulation. This cooling procedure is often performed to investigate cold induced vasodilatation (CIVD) in one finger. To investigate the effects of this sympathetic stimulation on local CIVD, 12 subjects immersed either the right index finger (T1), right hand (T2) or left hand and right index finger (T3) for 30 min in water at 5 degrees C followed by 15-min recovery.

Short hypobaric hypoxia and breathing pattern: effect of positive end expiratory pressure.

The ventilatory effects of a 5-cm H2O positive end expiratory pressure (PEEP) and its influence on the breathing pattern during short hypoxic exposure both at rest and during physical exercise were studied. There were 22 healthy subjects who were submitted to normoxia and to 4-h of hypoxia in a hypobaric chamber (4500 m, PB = 589 hPa) both at rest and during an 8-min cycle ergometer exercise (100 W) without and with a 5 cm H2O PEEP. The results show that hypoxia compared with normoxia induces increases in tidal volume (VT) (+28.

Effects of acute hypobaric hypoxia on the appearance of ingested deuterium from a deuterium oxide-labelled carbohydrate beverage in body fluids of humans during prolonged cycling exercise.

To determine whether or not acute hypobaric hypoxia alters the rate of water absorption from a carbohydrate beverage ingested during exercise, six men cycled for 80 min on three randomly assigned different occasions. In one trial, exercise was performed in hypoxia (barometric pressure, P(B) = 594 hPa, altitude 4,400 m) at an exercise intensity selected to elicit 75% of the individual's maximal oxygen uptake (VO2max) previously determined in such conditions. In the two other experiments, the subjects cycled in normoxia (P(B) = 992 hPa) at the same absolute and the same relative intensities as in hypoxia, which corresponded to 55% and 75%, respectively, of their VO2max determined in normoxia.

Influence of the oxygen uptake slow component on the aerobic energy cost of high-intensity submaximal treadmill running in humans.

During high-intensity running, the oxygen uptake (VO2) kinetics is characterised by a slow component which delays the attainment of the steady-state beyond the 3rd min of exercise. To assess if the aerobic energy cost of running measured at the 3rd min (C3) adequately reflects the variability of the true aerobic energy cost measured during the steady-state (Css), 13 highly-trained runners completed sessions of square-wave running at intensities above 80% maximal oxygen uptake (VO2max) on a level treadmill. To evaluate the time at which the steady-state VO2 was attained (tss), the VO2 responses were described using a general double-exponential equation and tss was defined as the time at which VO2 was less than 1% below the asymptotic value given by the model.

Thermoregulatory changes in the cold induced by physical training in humans.

It has previously been demonstrated that metabolic heat production (M) during cold exposure at rest was related to maximal oxygen uptake (VO2max). Consequently, an increase in VO2max could allow an increase M in the cold. The aim of the present study was therefore to test this hypothesis.

Pre-adaptation, adaptation and de-adaptation to high altitude in humans: hormonal and biochemical changes at sea level.

High altitude residence is known to modify body biochemistry and hormone status. However, the effects of such a sojourn on these status observed at sea level both immediately and later after return are not as well established as are the effects of an intermittent acclimation. The aim of this study was therefore to investigate these changes.

Positive end expiratory pressure as a method for preventing acute mountain sickness.

In order to study the use of positive end expiratory pressure (PEEP) to prevent acute mountain sickness (AMS), 22 subjects were exposed randomly to 8-h hypobaric hypoxia in a hypobaric chamber (4500 m, 589 hPa, 22 degrees C) once being administered 5-cm H2O PEEP and once without. The prevention of AMS by PEEP was evaluated by scoring AMS according to the Lake Louise system (self-report questionnaire and clinical assessment) throughout the experiment with O2 saturation (SO2) and heart rate measurements being made. Arterial blood analyses (partial pressures of arterial O2 and CO2, PaO2, PaCO2, and pH) were made at the end of the exposure.

Cognitive performance during short acclimation to severe hypoxia.

Background: Exposure to high altitudes requires acclimation or acclimatization, to prevent the negative effects of severe hypoxia. Among several methods, short acclimation with intermittent exposure to severe hypoxia in a hypobaric chamber triggers efficient physiological pre-adaptation mechanisms (11-13). However, we have little knowledge about the cognitive repercussions of such an acclimation protocol.

Are the laboratory and field conditions observations of acute mountain sickness related?

In order to study relationships between acute mountain sickness (AMS) observations done both during a short-term hypoxic exposure in a hypobaric chamber, and in field conditions during a high altitude expedition, nine subjects were submitted to a 9-h hypoxic exposure in a hypobaric chamber. Then, they experienced a high altitude expedition in the Himalayas. The Lake Louise AMS scoring system was used to assess AMS in both conditions, especially the self report questionnaire.

[Travelers exposed to extreme temperatures].

Sudden introduction of the unadapted human into extreme environments can result in serious, sometimes fatal, reactions. Most complications are due either to failure of thermoregulatory system or consecutive to the physiological responses to those environmental conditions. In addition to a number of minor diseases, cold can cause two major accidents, i.

Effects of various beverages on the hormones involved in energy metabolism during exercise in the heat in previously dehydrated subjects.

The objective of our study was to examine the effects of beverage content on hormone responses involved in fuel substrate metabolism (catecholamines, insulin and glucagon) in previously dehydrated subjects exercising at a moderate intensity in the heat. Six healthy men walked for 60-min on five occasions at 50% maximal oxygen uptake in a warm environment (dry bulb temperature 35 +/- 0.2 degrees C, relative humidity 20%).

Effects of hydration state on hormonal and renal responses during moderate exercise in the heat.

The effects of hydromineral hormones and catecholamines on renal concentrating ability at different hydration states were examined in five male volunteers while they performed three trials. Each of these trials comprised a 60-min exercise bout on a treadmill (at 50% of maximal oxygen uptake) in a warm environment (dry bulb temperature, 35 degrees C; relative humidity, 20-30%). In one session, subjects were euhydrated before exercise (C).

Effects of different carbohydrate-electrolyte beverages on the appearance of ingested deuterium in body fluids during moderate exercise by humans in the heat.

To determine whether different forms of glucose (free and polymer) associated with sodium chloride influence the rate of water absorption during exercise in the heat, six men took part in five trials. Each trial included a passive heating session which resulted in a 2% loss of body mass, followed by 1h of treadmill exercise (at 50% of maximal oxygen uptake) in warm conditions (dry bulb temperature 35 degrees C, relative humidity 20%-30%). Immediately before exercise, the subjects were given either no fluid or a volume equal to 50% of the fluid previously lost (about 650 ml), chosen from among four D2O-labelled beverages: mineral water, a 6% glucose-electrolyte solution (GS), a 6% maltodextrin solution and a 6% maltodextrin-electrolyte solution.

Cold induced vasodilatation and cardiovascular responses in humans during cold water immersion of various upper limb areas.

To study the physiological responses induced by immersing in cold water various areas of the upper limb, 20 subjects immersed either the index finger (T1), hand (T2) or forearm and hand (T3) for 30 min in 5 degrees C water followed by a 15-min recovery period. Skin temperature of the index finger, skin blood flow (Qsk) measured by laser Doppler flowmetry, as well as heart rate (HR) and mean arterial blood pressure (BPa) were all monitored during the test. Cutaneous vascular conductance (CVC) was calculated as Qak/BPa.

General and local cold responses in humans after 2 weeks at high altitude.

To investigate the effects of a short-term high altitude residence (2 weeks between 4150 m and 6885 m in the Andes) on the general and local cold responses after descent, 11 subjects were submitted both to a whole body standard cold air test (SCAT, dry bulb temperature = 1 degree C, 2 h, nude, at rest) and to a local cold water test of the right upper limb (CWT, 5 degrees C, 5 min) both before and after the expedition. Compared to before the expedition, a lower systolic blood pressure was observed after the high altitude residence [130.00 (SEM 3.

Biometrical characteristics and physiological responses to a local cold exposure of the extremities.

The aim of this study was firstly to describe the physiological responses observed in 19 subjects during immersion of the arm up to the elbow in water at 5 degrees C (5 min) followed by a 10-min recovery and secondly, to correlate the observed physiological responses with biometrical characteristics of the subjects (maximal oxygen uptake, VO2max, percentage fat content of whole body, BF, and arm, forearm and hand skinfold thickness). The results showed that the time courses of changes in forearm and hand skin temperature were different compared to those of finger skin temperatures both during local cooling and during rewarming (P < 0.05).

Pre-adaptation, adaptation and de-adaptation to high altitude in humans: cardio-ventilatory and haematological changes.

The aim of this study was first to investigate cardio-ventilatory and haematological responses induced by intermittent acclimation and second to study de-adaptation from high altitude observed after descent. To achieve these objectives nine subjects were submitted to intermittent acclimation in a low barometric chamber (8 h daily for 5 days, day 1 at 4500 m, day 5 at 8500 m) before an expedition to the Himalayas. Cardio-ventilatory changes were measured during a hypobaric poikilocapnic hypoxic test (4500 m, barometric pressure = 589 hPa) and haematological changes were studied at sea level.

Hypothermic general cold adaptation induced by local cold acclimation.

To study relationships between local cold adaptation of the lower limbs and general cold adaptation, eight subjects were submitted both to a cold foot test (CFT, 5 degrees C water immersion, 5 min) and to a whole-body standard cold air test (SCAT, 1 degree C, 2 h, nude at rest) before and after a local cold acclimation (LCA) of the lower limbs effected by repeated cold water immersions. The LCA induced a local cold adaptation confirmed by higher skin temperatures of the lower limbs during CFT and a hypothermic insulative general cold adaptation (decreased rectal temperature and mean skin temperature P < 0.05) without a change either in metabolic heat production or in lower limb skin temperatures during SCAT after LCA.

Influence of hyperthermia on cochlear micromechanical properties in humans.

We investigated the effect of body temperature on transient evoked otoacoustic emissions (TEOAEs) in humans. Hyperthermic conditions were obtained in adults in a climatic chamber. During hyperthermia up to an average temperature of 38.