Seasonal influence over serum and urine metabolic markers in submariners during prolonged patrols.

Within the framework of earlier publications, we have consistently dedicated our investigations to eliciting the effects of both seasonal vitamin D deficiency and submarine-induced hypercapnia on serum parameters for acid-base balance and bone metabolism in submariners over a 2-month winter (WP) or summer (SP) patrols. The latest findings reported herein, contribute further evidence with regard to overall physiological regulations in the same submariner populations that underwent past scrutiny. Hence, urine and blood samples were collected in WP and SP submariners at control prepatrol time as well as on submarine patrol days 20, 41, and 58. Several urine and serum metabolic markers were quantified, namely, deoxypyridinoline (DPD), lactate, albumin, creatinine, nonesterified fatty acids (NEFA), and ionized sodium (Na(+)) or potassium (K(+)), with a view to assessing bone, muscle, liver, or kidney metabolisms. We evidenced bone metabolism alteration (urine DPD, calcium, and phosphorus) previously recorded in submarine crewmembers under prolonged patrols. We also highlighted transitory modifications in liver metabolism (serum albumin) occurring within the first 20 days of submersion. We further evidenced changes in submariners' renal physiology (serum creatinine) throughout the entire patrol time span. Measurements of ionic homeostasis (serum Na(+) and K(+)) displayed potential seasonal impact over active ionic pumps in submariners. Finally, there is some evidence that submersion provides beneficial conditions prone to fend off seasonal lactic acidosis (serum lactate) detected in WP submariners.

Cold adaptations.

Nowdays, occupational and recreational activities in cold environments are common. Exposure to cold induces thermoregulatory responses like changes of behaviour and physiological adjustments to maintain thermal balance either by increasing metabolic heat production by shivering and/or by decreasing heat losses consecutive to peripheral cutaneous vasoconstriction. Those physiological responses present a great variability among individuals and depend mainly on biometrical characteristics, age, and general cold adaptation. During severe cold exposure, medical disorders may occur such as accidental hypothermia and/or freezing or non-freezing cold injuries. General cold adaptations have been qualitatively classified by Hammel and quantitatively by Savourey. This last classification takes into account the quantitative changes of the main cold reactions: higher or lower metabolic heat production, higher or lesser heat losses and finally the level of the core temperature observed at the end of a standardized exposure to cold. General cold adaptations observed previously in natives could also be developed in laboratory conditions by continuous or intermittent cold exposures. Beside general cold adaptation, local cold adaptation exists and is characterized by a lesser decrease of skin temperature, a more pronounced cold induced vasodilation, less pain and a higher manual dexterity. Adaptations to cold may reduce the occurrence of accidents and improve human performance as surviving in the cold. The present review describes both general and local cold adaptations in humans and how they are of interest for cold workers.

Zaleplon and zolpidem objectively alleviate sleep disturbances in mountaineers at a 3,613 meter altitude.

STUDY OBJECTIVES: To assess the effects of zolpidem and zaleplon on nocturnal sleep and breathing patterns at altitude, as well as on daytime attention, fatigue, and sleepiness. DESIGN: Double-blind, randomized, placebo-controlled, cross-over trial. SETTING: 3 day and night alpine expedition at 3,613 m altitude. PARTICIPANTS: 12 healthy male trekkers. PROCEDURE: One week spent at 1,000 m altitude (baseline control), followed by 3 periods of 3 consecutive treatment nights (N1-3) at altitude, to test 10 mg zolpidem, 10 mg zaleplon, and placebo given at 21:45. MEASURES: Sleep from EEG, actigraphy and sleep logs; overnight arterial saturation in oxygen (SpO2) from infrared oximetry; daytime attention, fatigue and sleepiness from a Digit Symbol Substitution Test, questionnaires, and sleep logs; acute mountain sickness (AMS) from the Lake Louise questionnaire. RESULTS: Compared to baseline control, sleep at altitude was significantly impaired in placebo subjects as shown by an increase in the amount of Wakefulness After Sleep Onset (WASO) from 17 +/- 8 to 36 +/- 13 min (P<0.05) and in arousals from 5 +/- 3 to 20 +/- 8 (P<0.01). Slow wave sleep (SWS) and stage 4 respectively decreased from 26.7% +/- 5.8% to 20.6% +/- 5.8% of total sleep time (TST) and from 18.2% +/- 5.2% to 12.4% +/- 3.1% TST (P<0.05 and P<0.001, respectively). Subjects also complained from a feeling of poor sleep quality combined with numerous 02 desaturation episodes. Subjective fatigue and AMS score were increased. Compared to placebo control, WASO decreased by approximately 6 min (P<0.05) and the sleep efficiency index increased by 2% (P<0.01) under zaleplon and zolpidem, while SWS and stage 4 respectively increased to 22.5% +/- 5.4% TST (P<0.05) and to 15.0% +/- 3.4% TST (P<0.0001) with zolpidem only; both drugs further improved sleep quality. No adverse effect on nighttime SpO2, daytime attention level, alertness, or mood was observed under either hypnotic. AMS was also found to be reduced under both medications. CONCLUSIONS: Both zolpidem and zaleplon have positive effects on sleep at altitude without adversely affecting respiration, attention, alertness, or mood. Hence, they may be safely used by climbers.

Effects of passive hyperthermia versus exercise-induced hyperthermia on immune responses: hormonal implications.

UNLABELLED: Different stress hormones are released during prolonged exercise and passive hyperthermia. We hypothesized that these different hormonal responses could contribute to the different changes in the immune response during these two challenges. METHODS: Eight subjects completed three trials in a randomized order. In the control trial (C), the subjects remained in a sitting posture for three hours in thermoneutral conditions. In the exercise hyperthermia trial (E), they exercised for two hours on a treadmill at 65% max in thermoneutral conditions, followed by 1-h recovery in thermoneutral conditions; in the passive hyperthermia trial (PH), the subjects remained in a semi-recumbent position in a climatic chamber for two hours in hot conditions, followed by 1-h recovery in thermoneutral conditions. During the E and PH trials, wind speed and thermal conditions were modulated to reach a rectal temperature (Tre) of 38.5 degrees C at 60 min and 39 degrees C at 120 min. The subjects did not drink during the experiments. Blood samples (10 mL) were taken at 0, 60, 120 and 180 min of each trial. The total white cell count and its subsets were measured; plasma catecholamines, cortisol and prolactin were assayed. In a whole blood assay, blood leukocytes were stimulated by lipopolysaccharide (LPS) or phytohemagglutinin (PHA) for 24 and 48 hours, respectively. Cytokines, such as TNF-alpha, IL-10 and INF-gamma were measured in the culture supernatant. RESULTS: The plasma levels of catecholamines were increased only during E, prolactin was increased only during PH, and cortisol was increased in both E and PH. Only the exercise caused a mobilization of blood leukocytes and leukocyte subsets. The INF-gamma and TNF-alpha production by PHA- and LPS-stimulated blood, respectively, were inhibited in a substantial way in both E and PH compared to control when Tre reached 39 degrees C. Only LPS-induced IL-10 production was enhanced during the exercise. The effects of the challenges were increased with 39 degrees C compared to 38.5 degrees C. CONCLUSIONS: Catecholamines play a major role in the mobilization of immunocompetent cells and the production of IL-10 during exercise. Prolactin and catecholamines have adverse role on the immune response, whereas cortisol exerts similar effects during both trials. The consequence could be a protection against inflammatory overshooting.

Normo or hypobaric hypoxic tests: propositions for the determination of the individual susceptibility to altitude illnesses.

Assessment of individual susceptibility to altitude illnesses and more particularly to acute mountain sickness (AMS) by means of tests performed in normobaric hypoxia (NH) or in hypobaric hypoxia (HH) is still debated. Eighteen subjects were submitted to HH and NH tests (PIO2=120 hPa, 30 min) before an expedition. Maximal and mean acute mountain sickness scores (AMSmax and mean) were determined using the self-report Lake Louise questionnaire scored daily. Cardio-ventilatory (f, V(T), PetO2 and PetCO2, HR and finger pulse oxymetry SpO2) were measured at times 5 and 30 min of the tests. Arterial (PaO2, PaCO2, pH, SaO2) and capillary haemoglobin (Hb) measurements were performed at times 30 min. Hypoxic ventilatory (HVR) and cardiac (HCR) responses, peripheral O2 blood content (CpO2) were calculated. A significant time effect is found for DeltaSpO2 (P = 0.04). Lower PaCO2 (P = 0.005), SaO2 (P = 0.07) and higher pH (P = 0.02) are observed in HH compared to NH. AMSmax varied from 3 to12 and AMSmean between 0.6 and 3.5. In NH at 30 min, AMSmax is related to PetO2 (R = 0.61, P = 0.03), CpO2 (R = -0.53, P = 0.02) and in HH to CpO2 (R = -0.57, P = 0.01). In NH, AMSmean is related to Deltaf (R = 0.46, P = 0.05), HCR (R = 0.49, P = 0.04), CpO2 (R = -0.51, P = 0.03) and, in HH at 30 min, to V(T) (R = 0.69, P = 0.01) and a tendency for CpO2 (R = -0.43, P = 0.07). We conclude that HH and NH tests are physiologically different and they must last 30 min. CpO2 is an important variable to predict AMS. For practical considerations, NH test is proposed to quantify AMS individual susceptibility using the formulas: AMSmax = 9.47 + 0.104PetO2(hPa)-0.68CpO2 (%), (R = 0.77, P = 0.001); and AMSmean = 3.91 + 0.059Deltaf + 0.438HCR-0.135CpO2 (R = 0.71, P = 0.017).

Acclimation to intermittent hypobaric hypoxia modifies responses to cold at sea level.

INTRODUCTION: Residence at high altitude modifies thremoregulatory responses to cold stress upon return to lower altitude. These changes are difficult to explain since several stresses related to high altitude may interact, including hypoxia, cold, solar radiation, and physical exertion. We hypothesized that adaptation to hypoxia without cold exposure would produce at least part of the observed changes. METHODS: Five men underwent acclimation to intermittent hypoxia (AIH) in a hypobaric chamber (8 h daily for 4 d, and 6 h on the last day, 4500 to 6000 m) at 24 degrees C. Cold stress responses were tested during a whole-body standard cold air test (1 degrees C, 2 h at rest at sea level) both before and after AIH. RESULTS: Increased reticulocyte counts and percentages confirmed acclimation to hypoxia after AIH. Changes in thermoregulation during the cold test included lower mean skin temperature after 60-80 min (18.8 +/- 0.7 degrees C vs. 19.4 +/- 0.7 degrees C); higher mean metabolic heat production (127 +/- 8 W x m(-2) vs. 118 +/- 6 W x m(-2)); and lower heat debt (7.7 +/- 1.3 kJ x kg(-1) vs. 10.3 +/- 1.2 kJ x kg(-1)), without significant change in rectal temperature. Time to onset for continuous shivering decreased after AIH (12 +/- 5 min vs. 21 +/- 6.3 min), and shivering activity occurred at higher mean skin but not rectal temperatures. CONCLUSION: AIH in comfortable ambient temperature leads to a normothermic-insulative-metabolic general cold adaptation. We conclude that AIH modifies the thermoregulatory responses to cold at sea level without cold exposure leading to a cross-adaptation.

PREDICTOL: a computer program to determine the thermophysiological duration limited exposures in various climatic conditions.

PREDICTOL is a PC program used to determine the thermophysiological duration limited exposures (DLE) in humans, nude or clothed, submitted to various climatic conditions (hot and cold climates) at rest or during a physical exercise. DLE are determined following different standards of the International Standardization Organization (ISO), especially ISO 7933 for hot environment and ISO-TR 11079 for cold environment. The original aspect of this program is that it can be used whatever the climatic conditions. The program presents two modes: an educational interactive mode and a scenario mode. The educational interactive mode demonstrates the thermophysiological effects, expressed as DLE, of different parameter changes (temperature, humidity, wind speed, metabolic heat production by physical exercise, clothing insulation and water vapor permeability). The scenario mode determines DLE for given various linked sequences as encountered in occupational, military or even recreational activities, each sequence being characterized by its climatic conditions, physical activities performed and by physical clothing properties. DLE given by PREDICTOL are correlated to those obtained in various controlled climatic laboratory conditions (r = 0.86; P < 0.001). PREDICTOL is written in Visual Basic 6.0. A "help menu" is provided to explain the use of the program and give information concerning the equations used to calculate both the thermal balance and DLE.

Prevention of acute mountain sickness by low positive end-expiratory pressure in field conditions.

OBJECTIVES: This study evaluates the ability of positive end-expiratory pressure (PEEP), a nonpharmacological method, to prevent the occurrence of acute mountain sickness during two ascents of Mount Blanc. METHODS: In a random order (once with PEEP and once without), PEEP was administered or not to eight subjects during two ascents of Mount Blanc. Scores for acute mountain sickness were quantified using the Lake Louise acute mountain sickness scoring system, and oxygen arterial blood saturation by pulse oxymetry (SpO2), heart rate, and systolic and diastolic blood pressures were also measured. RESULTS: The decrease in the prevalence of acute mountain sickness indicated that the PEEP system was effective, one case (12.5%) occurring among the eight participants with PEEP and six cases (75%) occurring among the eight without PEEP (P<0.01). The severity of the cases also decreased (P<0.01). Heart rate and blood pressure did not significantly vary, whereas the SpO2 tended to be higher with PEEP (P=0.07). CONCLUSIONS: This field study shows that PEEP could be an efficient method with which to prevent acute mountain sickness without adverse effects. However, the ergonomics of the PEEP system must be improved to make its use more practical in the future.

Control of erythropoiesis after high altitude acclimatization.

Erythropoiesis was studied in 11 subjects submitted to a 4-h hypoxia (HH) in a hypobaric chamber (4,500 m, barometric pressure 58.9 kPa) both before and after a 3-week sojourn in the Andes. On return to sea level, increased red blood cells (+3.27%), packed cell volume (+4.76%), haemoglobin (+6.55%) ( P<0.05), and increased arterial partial pressure of oxygen (+8.56%), arterial oxygen saturation (+7.40%) and arterial oxygen blood content ( C(a)O(2)) (+12.93%) at the end of HH ( P<0.05) attested high altitude acclimatization. Reticulocytes increased during HH after the sojourn only (+36.8% vs +17.9%, P<0.01) indicating a probable higher reticulocyte release and/or production despite decreased serum erythropoietin (EPO) concentrations (-46%, P<0.01). Hormones (thyroid, catecholamines and cortisol), iron status (serum iron, ferritin, transferrin and haptoglobin) and renal function (creatinine, renal, osmolar and free-water clearances) did not significantly vary (except for lower thyroid stimulating hormone at sea level, P<0.01). Levels of 2,3-diphosphoglycerate (2,3-DPG) increased throughout HH on return (+14.7%, P<0.05) and an inverse linear relationship was found between 2,3-DPG and EPO at the end of HH after the sojourn only ( r=-0.66, P<0.03). Inverse linear relationships were also found between C(a)O(2) and EPO at the end of HH before ( r=-0.63, P<0.05) and after the sojourn ( r=-0.60, P=0.05) with identical slopes but different ordinates at the origin, suggesting that the sensitivity but not the gain of the EPO response to hypoxia was modified by altitude acclimatization. Higher 2,3-DPG levels could partly explain this decreased sensitivity of the EPO response to hypoxia. In conclusion, we show that altitude acclimatization modifies the control of erythropoiesis not only at sea level, but also during a subsequent hypoxia.

Normo- and hypobaric hypoxia: are there any physiological differences?

Since Bert (1878) and Barcroft (1925), studies on hypoxia are realized by lowering ambient O(2) partial pressure (PO(2)) either by barometric pressure reduction (hypobaric hypoxia HH) or by lowering the O(2) fraction (normobaric hypoxia NH). Today, a question is still debated: "are there any physiological differences between HH and NH for the same ambient PO(2)?" Since published studies are scarce and controversial, we submitted 18 subjects in a random order to a 40-min HH test and to a 40-min NH test at an ambient PO(2) equal to 120 hPa (4500 m). Cardioventilatory variables [breathing frequency (f), tidal volume (V(t)), minute ventilation (V(E)), O(2) and CO(2) end-tidal fractions or pressures (FET(O2) and FET(CO2) or PET(O2) and PET(CO2) respectively), heart rate (HR) and O(2) arterial saturation by pulse oxymetry (SpO(2))] were measured throughout the tests. At the end of the tests, arterial blood samples were taken to measure arterial blood gases [O(2) and CO(2) arterial partial pressures ( Pa(O2) and Pa(CO2)), pH and O(2) arterial saturation (SaO(2))]. Results show that during HH compared to NH, f is greater (P

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 +/- 0.9 years) were evaluated: group T (interval training at 21 degrees C), group CT (interval training at 1 degrees C), and group C (no training, equivalent exposure to 1 degrees C). Each group was submitted, before and after 4 weeks of interval training (5 d/week), to a cold air test at rest (SCAT) (dry bulb temperature (Tdb) = 1 degrees C) for a 2-h period for evaluation of the thermoregulatory responses. During SCAT, after the training/acclimation period, group T exhibited a higher rectal temperature (Tre) (P < 0.05) without significant change in mean skin temperature (Tsk) whereas metabolic heat production (M) was higher at the beginning of the SCAT (P < 0.05). For group CT, no thermoregulatory change was observed. Group C showed a lower Tre (P < 0.05) without significant change in either Tsk or in M, suggesting the development of a hypothermic general cold adaptation. This study showed, first, that the cold thermoregulatory responses induced by an interval training differed following the climatic conditions of the training and, second, that this training performed in the cold prevented the development of a general cold adaptation.

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. HYPOTHESIS: We studied the circadian rhythm of rectal temperature (CRTre) during 62 h of SD alone or with three dosage levels of modafinil. METHODS: Six men underwent repeated SD experiments lasting 7 d each, including a 24-h control period, 62 h of SD, and a 24-h recovery period. Experiments were repeated four times in mixed order for placebo and three levels of modafinil (50, 150, or 300 mg x 24 h(-1)). The Tre was recorded each minute throughout the experiment and the CRTre was studied by the single cosinor method. RESULTS: Independent of modafinil, SD increased the mesor (p < 0.05) and reduced the amplitude (p < 0.01) of the CRTre without changing the acrophase. During the recovery period, a rebound increase was seen in the amplitude of the CRTre (p < 0.01). The 50 mg x 24 h(-1) dose of modafinil, but not the higher doses, induced a lower mesor (p < 0.01) independent of SD. CONCLUSIONS: The observed changes may reflect a threshold for the central action of modafinil on core temperature. The hyperthermic effect reported in the literature for SD with modafinil may actually result from the sleep deprivation alone.

Plasma compartment filling after exercise or heat exposure.

PURPOSE: The present study was assessed to study the restoration of the vascular compartment by rehydration after heat exposure or exercise. METHODS: Eight subjects completed four trials in a randomized order: 2.7% dehydration of body mass by passive controlled hyperthermia once with rehydration and once without rehydration during recovery, and 2.7% dehydration of body mass by treadmill exercise once with rehydration and once without rehydration during recovery. An isotonic glucose electrolyte beverage was provided twice during the recovery period for a total volume, which was equivalent to the target value of body mass loss during dehydration procedures. Plasma volume (PV) was measured using Evans Blue dilution technique, and PV changes (deltaPV) were determined using hematocrit and hemoglobin measurements. RESULTS: PV was better maintained during exercise than during heat exposure, and the difference in deltaPV between the two patterns of dehydration was maintained during the first 3 h of recovery. Plasma protein seemed to be accountable for the difference in deltaPV during heat exposure and exercise but not during the 270 min of recovery. Rehydration partly restored body fluid losses, but the plasma compartment was privileged, because 26-30% of the net fluid gain was found in the plasma compartment (about 300 mL). Rehydration restored plasma osmolality and diminished the drive for arginin-vasopressin response. CONCLUSION: The similar selective retention of water in the plasma compartment might essentially be explained by osmotic factors provided by the beverage. As PV was completely restored by rehydration after exercise and only partly restored after heat exposure, the volume of ingested beverage should be higher after heat exposure to completely restore the plasma compartment.

Effects of modafinil on heat thermoregulatory responses in humans at rest.

The effects of modafinil on heat thermoregulatory responses were studied in 10 male subjects submitted to a sweating test after taking 200 mg of modafinil or placebo. Sweating tests were performed in a hot climatic chamber (45 degrees C, relative humidity <15%, wind speed = 0.8 m x s(-1), duration 1.5 h). Body temperatures (rectal (Tre) and 10 skin temperatures (Tsk)), sweat rate, and metabolic heat production (M) were studied as well as heart rate (HR). Results showed that modafinil induced at the end of the sweating test higher body temperatures increases (0.50 +/- 0.04 versus 0.24 +/- 0.05 degrees C (P < 0.01) for deltaTre and 3.64 +/- 0.16 versus 3.32 +/- 0.16 degrees C (P < 0.05) for deltaTsk (mean skin temperature)) and a decrease in sweating rate throughout the heat exposure (P < 0.05) without change in M, leading to a higher body heat storage (P < 0.05). AHR was also increased, especially at the end of the sweating test (17.95 +/- 1.49 versus 12.52 +/- 1.24 beats/min (P < 0.01)). In conclusion, modafinil induced a slight hyperthermic effect during passive dry heat exposure related to a lower sweat rate, probably by its action on the central nervous system, and this could impair heat tolerance.

Anthropological and thermoregulatory changes induced by a survival sojourn in a tropical climate.

OBJECTIVE: A survival sojourn in a tropical climate exposes subjects to 2 main constraints: food restriction and tropical climatic conditions. We hypothesized that such a sojourn could modify anthropological characteristics and thermoregulatory responses to heat and cold on return. METHODS: Eight European male subjects were submitted to a sweating test (ST) for 90 minutes (dry bulb temperature [Tdb] = 47 degrees C, relative humidity (RH) = 10%, and wind speed = 0.8 m x s(-1)) and to a whole-body cold-air test (Tdb = 1 degrees C, RH = 40%, and wind speed = 0.8 m x s(-1)) for 120 minutes in thermoclimatic chambers both before and after a 4-week survival sojourn in French Guyana. RESULTS: The survival sojourn resulted in a decrease in lean body mass (P < .05) without any significant change in body fat content. Heat thermoregulatory changes studied during the ST were characterized both by a lower mean skin temperature (Tsk) (P < .05) and a higher sweat rate measured after the sojourn than before it (m(sw); P < .05). Cold thermoregulatory changes were characterized by a higher T(sk) value (P < .05) and a decreased onset for continuous shivering without any significant change in internal temperature or metabolic heat production (M). CONCLUSIONS: This study showed that this type of sojourn modifies not only biometrical characteristics of the subjects but also the thermoregulatory responses, inducing an adaptation of the thermoregulatory system to heat and an increase in the sensitivity of the thermoregulatory system to cold. This finding could have practical implications on return after such a sojourn.