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PubMed1999

Drink composition, voluntary drinking, and fluid balance in exercising, trained, heat-acclimatized boys.

This study examined the effects of beverage composition on the voluntary drinking pattern, body fluid balance, and thermoregulation of heat-acclimatized trained boys exercising intermittently in outdoor conditions (wet bulb globe temperature 30.4 +/- 1.0 degreesC). Twelve boys (age 13.4 +/- 0.4 yr) performed two 3-h sessions, each consisting of four 20-min cycling bouts at 60% maximal aerobic power alternating with 25-min rest. One of two beverages was assigned: unflavored water (W) or flavored water plus 6% carbohydrate and 18 mmol/l Na (CNa). Drinking was ad libitum. Total intake was higher (P < 0.05) during CNa (1,943 +/- 190 g) compared with W (1,470 +/- 143 g). Euhydration was maintained with CNa (+0.18% body wt), but a mild dehydration resulted with W (-0.94% body wt; P < 0.05). Sweat loss, much higher than previously published for children of similar age, was similar between conditions (CNa = 1,644.7 +/- 117.5; W = 1,750.2 +/- 152.7 g). The increase in rectal temperature (CNa = 0.86 +/- 0.3; W = 0.76 +/- 0.1 degreesC), heart rate, and all perceptual variables did not differ between conditions. In conclusion, a flavored carbohydrate-electrolyte drink prevents voluntary dehydration in trained heat-acclimatized boys exercising in a tropical climate despite their large sweat losses. Because hydration changes were minor, the thermoregulatory strain observed was similar between conditions.

Acclimatization↗
PubMed2000

Peripheral chemoreflex function in hyperoxia following ventilatory acclimatization to altitude.

After a period of ventilatory acclimatization to high altitude (VAH), a degree of hyperventilation persists after relief of the hypoxic stimulus. This is likely, in part, to reflect the altered acid-base status, but it may also arise, in part, from the development during VAH of a component of carotid body (CB) activity that cannot be entirely suppressed by hyperoxia. To test this hypothesis, eight volunteers undergoing a simulated ascent of Mount Everest in a hypobaric chamber were acutely exposed to 30 min of hyperoxia at various stages of acclimatization. For the second 10 min of this exposure, the subjects were given an infusion of the CB inhibitor, dopamine (3 microg. kg(-1). min(-1)). Although there was both a significant rise in ventilation (P < 0.001) and a fall in end-tidal PCO(2) (P < 0.001) with VAH, there was no progressive effect of dopamine infusion on these variables with VAH. These results do not support a role for CB in generating the persistent hyperventilation that remains in hyperoxia after VAH.

Acclimatization↗
PubMed1988

Effects of bromocriptine on sweat gland function during heat acclimatization.

This study examined the involvement of the hormones aldosterone and prolactin in sweat gland function during heat acclimatization. Two groups of male subjects (n = 8) were tested - one receiving a placebo (control), the other receiving bromocriptine. Both groups performed cycle ergometer exercise at 50% of maximal oxygen uptake over 10 consecutive days in an environmental chamber maintained at 39 degrees C and 30% relative humidity. Duration of exercise was 90 min on days 2-4 and 6-9, and 45 min on test days 1, 5 and 10. Electrolyte concentrations were determined by total body washdown. Prolactin increased (p less than 0.001) during exercise on day 1 in the control group but not on days 5 and 10. In contrast, prolactin was suppressed by bromocriptine and did not rise in response to exercise or heat exposure. Plasma aldosterone increased during exercise in both groups, showing no differences between groups. The sodium concentration in sweat decreased significantly (p less than 0.05) in the control group from day 1 to 10 but was unchanged in the treatment group. These data suggest that acclimatization-related changes in sweat gland function may be attenuated by increases in central dopaminergic activity and implicate prolactin in control of sweat gland function.

Acclimatization↗
PubMed1971

Pulmonary artery pressure and alveolar gas exchange in man during acclimatization to 12,470 ft.

Pulmonary hemodynamics and gas exchange were studied in four physicians during 72 hr acclimatization to 12,470 ft. Pulmonary catheters were left in three subjects for 72 hr. Resting mean pulmonary arterial pressure (PAP) rose progressively during the first 24 hr from 10.3 +/-1.0 to 21.1 +/-4.0 torr and remained at this level. During this same 24 hr period cardiac output increased from 7.1 +/-1.4 to 8.4 +/-2.0 liters/min and total pulmonary resistance rose from 122 +/-16 to 209 +/-40 dynes.sec/cm(-5). Excercise at 60 w after 24 hr of hypoxia increased PAP to 28.8 +/-5.1 torr and decreased total pulmonary resistance to 155 +/-25. Shunt fractions were 11 +/-3.8% after 24 hr at altitude and fell to 7 +/-0% after 72 hr. Alveolar to arterial O(2) difference (P(A-a)(O2)) breathing oxygen fell from 116 +/-10.8 to 92 +/-33.3 torr during the same period of acclimatization, whereas dead space to tidal volume ratio (V(D)/V(T)) rose from 33 +/-4.0% to 40 +/-5.3% and P(A-a)(O2) breathing ambient air rose from 8 +/-2.6 to 11 +/-3.0 torr. Inspiratory static lung compliance decreased significantly from a control of 176 +/-8 to 141 +/-8 ml/cm H(2)O after 72 hr of hypoxia. After 4-7 days at altitude, further deterioration in gas exchange was observed after a 5 mile, 1800 ft climb to the summit (14,255 ft) and return. P(A-a)(O2) on air rose from 2.5 +/-2.1 just before starting, to 16.3 +/-2.8 at the summit (rested), and was still 9.0 +/-2.2 several hours after returning. The O(2)-breathing values paralleled these, whereas dead space appeared to fall. We speculate that the hypoxic pulmonary hypertension which develops over 24 hr in some way may be responsible for a reduction of compliance and deterioration in oxygen exchange efficiency, possibly representing a sub-clinical form of pulmonary edema of high altitude. The increased alveolar to arterial O(2) difference induced by hypoxic exercise persists for several hours of hypoxic rest.

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PubMed2002

Extended acclimatization is required to eliminate stress effects of periodic blood-sampling procedures on vasoactive hormones and blood volume in beagle dogs.

Important in all experimental animal studies is the need to control stress stimuli associated with environmental change and experimental procedures. As the stress response involves alterations in levels of vasoactive hormones, ensuing changes in cardiovascular parameters may confound experimental outcomes. Accordingly, we evaluated the duration required for dogs (n = 4) to acclimatized to frequent blood sampling that involved different procedures. On each sampling occasion during a 6-week period, dogs were removed from their pen to a laboratory area and blood was collected either by venepuncture (days 2, 15, 34, 41) for plasma renin activity (PRA), epinephrine (EPI), norepinephrine, aldosterone, insulin, and atrial natriuretic peptide, or by cannulation (dogs restrained in slings; days 1, 8, 14, 22, 30, 33, 37, 40) for determination of haematocrit (HCT) alone (days 1 to 22) or HCT with plasma volume (PV; days 30 to 40). PRA was higher on days 2 and 15 compared with days 34 and 41 and had decreased by up to 48% by the end of the study (day 41 vs day 15; mean/SEM: 1.18/0.27 vs 2.88/0.79 ng ANG I/ml/h, respectively). EPI showed a time-related decrease from days 2 to 34, during which mean values had decreased by 51% (mean/SEM: 279/29 vs 134/20.9 pg/ml for days 2 and 34, respectively), but appeared stable from then on. None of the other hormones showed any significant variability throughout the course of the study. HCT was relatively variable between days 1 to 22 but stabilized from day 30, after which all mean values were approximately 6% lower than those between days 1 and 8. We conclude that an acclimatization period of at least 4 weeks is required to eliminate stress-related effects in dogs associated with periodic blood sampling.

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PubMed1993

Acclimatization and tolerance to extreme altitude.

During the last ten years, two major experiments have elucidated the factors determining acclimatization and tolerance to extreme altitude (over 7000 m). These were the American Medical Research Expedition to Everest, and the low pressure chamber simulation, Operation Everest II. Extreme hyperventilation is one of the most important responses to extreme altitude. Its chief value is that it allows the climber to maintain an alveolar PO2 which keeps the arterial PO2 above dangerously low levels. Even so, there is evidence of residual impairment of central nervous system function after ascents to extreme altitude, and maximal oxygen consumption falls precipitously above 7000 m. The term 'acclimatization' is probably not appropriate for altitudes above 8000 m, because the body steadily deteriorates at these altitudes. Tolerance to extreme altitude is critically dependent on barometric pressure, and even seasonal changes in pressure probably affect climbing performance near the summit of Mt Everest. Supplementary oxygen always improves exercise tolerance at extreme altitudes, and rescue oxygen should be available on climbing expeditions to 8000 m peaks.

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PubMed2000

Work performance after dehydration: effects of physical conditioning and heat acclimatization. 1958.

Three groups of five men each were dehydrated overnight in the heat (115 degrees F) on two occasions (D1 and D2) to approximately 5.5% of their starting body weight. During the 3-week period between D1 and D2, one group (AC) was acclimatized to heat and physically conditioned, the second group (C) was physically conditioned and the third group (S) remained sedentary. The response to work after dehydration was assessed by the following criteria: pulse rate (P), rectal temperature (Tr) and maximal oxygen intake (Max. VO2). Pulse rates during and after walking and after running were elevated with dehydration. This elevation was reduced in groups AC and C at D2 as compared to D1, but not in group S. An elevation in T1 with walking also occurred with dehydration, but this elevation was not significantly different at D2 as compared with D1 in any group. Physical conditioning elicited an elevation in Max. VO2 (group AC and C), but the elevation was no greater in group AC than in group C. Dehydration was associated with an equal decrement in Max. VO2 at D1 and D2 in all groups, but the conditioned men (AC and C) maintained a relatively higher Max. VO2 than group S. Thus, physical conditioning was associated with enhanced work performance during dehydration (assessed by the above criteria), whereas acclimatization to heat did not appreciably supplement this effect.

Acclimatization↗
PubMed2004

Vitamin status of high altitude (3660 m) acclimatized human subjects during consumption of tinned rations.

OBJECTIVE: To find out the nutritional status of sea-level residents acclimated to an altitude of 3660 m with respect to vitamin and nutrient requirements while consuming fresh and tinned rations. METHODS: Initially, high altitude acclimatized human subjects (n = 40) were evaluated for their general nutritional status along with energy intake and expenditure and physical fitness score while they were on fresh rations. Thereafter, subjects were fed tinned rations in two groups of 20 each. Of the two groups, one group had vitamin supplementation and the other was without any vitamin supplementation for 30 days. Thereafter, all the variables were studied once again. RESULTS: Daily total energy intake when subjects consumed fresh and tinned rations was 19.087 +/- 0.347 MJ and 19.417 +/- 0.342 MJ, respectively, whereas the total energy expenditure was 15.705 +/- 1.054 MJ per day for both the groups. After consuming tinned rations for 30 days, the placebo group showed a significant (P < .01) decrease in levels of plasma vitamin A and erythrocyte trans-ketolase activity (a marker of thiamin status) in comparison to the status when subjects were on fresh rations. However, levels of these variables were well within acceptable range. Subjects maintained their body weights and physical fitness scores. No clinical deficiency was seen after consuming tinned rations for 30 days. CONCLUSION: The study indicates that no additional vitamin supplementation is required at high altitude after acclimatization when consuming fresh rations and at least for 30 days when consuming tinned rations.

Acclimatization↗
PubMedDate not supplied

On the mechanism of protective action of cold acclimatization against carbon tetrachloride- and ethionine-induced fatty liver.

In this study the hepatic lipoprotein lipase (LPL) activity was evaluated in adult female mice acclimatized at 5 degrees C and submitted to carbon tetrachloride (CCl4) or ethionine, in order to determine the possible role of this enzyme in the fatty liver. The results were compared with those obtained in mice kept at room temperature (27 degrees C) that received the same hepatoesteatosis inducing agent. In contrast to animals kept at room temperature, in cold acclimatized mice neither the enhancement of the LPL-liver activity by the action of CCl4 or ethionine occurred nor the development of fatty infiltration in the liver was observed. We conclude that the low temperature induced a protective effect against CCl4- or ethionine-induced fatty liver that was correlated with the no-increase of the hepatic LPL activity.

Acclimatization↗
PubMed1981

Seasonal changes in heat balance of dogs acclimatized to outdoor climate.

Heat production (M), dry heat loss (R+C), evaporative heat loss (E) and rectal temperature (Tre) were measured in a direct calorimeter in female mongrel dogs acclimatized to outdoor climate at Kanazawa (latitude; 36 degrees 35" N), Japan. M and total dry and evaporative heat losses (HL) were minimum at calorimeter wall temperatures (TW) of 26-29 degrees C in summer and 22-26 degrees C in winter (thermoneutral temperature; TNT). The seasonal shift of the lower critical temperature was confirmed. At TW below TNT, the values of M and HL were significantly higher in summer. At TW above TNT, these values increased. A TNT and above, M and HL were significantly higher in winter. (R+C) decreased linearly with increasing TW in both seasons. AT TW below 26 degrees C, (R+C) were significantly higher in summer. At TW above 26 degrees C, E increased greatly. The values of E were significantly higher in winter at TW 29-32 degrees C. Tre remained nearly constant at TNT and below, and increased at TW above TNT in both seasons. Mean body surface temperature (Tsf) decreased with decreasing TW. Body thermal conductance (K) was minimum at TW below 26 degrees C in summer and at TW below 22 degrees C in winter. At TW above these temperatures, K increased significantly. Whole body insulation (I) was significantly higher in winter, particularly at TW 18 degrees C. These results suggest that the dogs reared outdoors in winter acclimatized to cold in two ways; by increasing the insulating effect of the fur coat and by elevating resting heat production.

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PubMed2007

Mitochondrial contribution to the molecular mechanism of heart acclimatization to chronic hypoxia: role of nitric oxide.

A remarkable number of adaptive responses; including changes in the cardiovascular, respiratory and hematologic systems; takes place during acclimatization to natural or simulated high altitude. This adaptation to chronic hypoxia confers the heart an improved tolerance to all major deleterious consequences of acute O2 deprivation, not only reducing infarct size but also alleviating post-ischemic contractile dysfunction and ventricular arrhythmias. There is growing evidence about the involvement of mitochondria and NO in the establishment of cardioprotection. This review focuses on evidence about the putative role of different effectors of heart acclimatization to chronic hypoxia. Along with classical parameters, we consider NO, specially that generated by mtNOS, mitochondrial respiratory chain, mitoK(ATP) channels, reactive oxygen species and control of gene expression by HIF-1.

Acclimatization↗
PubMed2003

Evidence of acclimatization in persons with severe-to-profound hearing loss.

The present study examined the phenomenon of acclimatization in persons with a severe-to-profound hearing loss. A secondary purpose was to examine the efficacy of a digital nonlinear power hearing aid that has a low compression threshold with expansion for this population. Twenty experienced hearing aid users wore the study hearing aids for three months and their performance with the study hearing aids was evaluated at the initial fitting, one month, and three months after the initial fitting. Performance of their current hearing aids was also evaluated at the initial fitting. Speech recognition testing was conducted at input levels of 50 dB SPL and 65 dB SPL in quiet, and 75 dB SPL in noise at a +10 SNR. Questionnaires were used to measure subjective performance at each evaluation interval. The results showed improvement in speech recognition score at the one-month evaluation over the initial evaluation. No significant improvement was seen at the three-month evaluation from the one-month visit. In addition, subjective and objective performance of the study hearing aids was significantly better than the participants' own hearing aids at all evaluation intervals. These results provided evidence of acclimatization in persons with a severe-to-profound hearing loss and reinforced the precaution that any trial of amplification, especially from linear to nonlinear mode, should consider this phenomenon.

Acclimatization↗
PubMed2000

Intraocular pressure and acclimatization to 4300 M altitude.

BACKGROUND: Studies were conducted to determine the effect of altitude exposure on intraocular pressure (IOP) and any relationship with the severity of acute mountain sickness (AMS). HYPOTHESES: a) IOP is decreased during exposure to 4300 m altitude; b) there is a positive correlation between IOP and AMS; and c) there is a correlation between changes in urinary catecholamines and IOP. METHODS: IOP (noncontact tonometry) was measured in 11 resting males during acute simulated altitude (446 mmHg, < 2 h, hypobaric chamber), during altitude acclimatization (15 d at 4300 m), and in 6 of the 11 volunteers during re-exposure in the chamber after 8 d at sea level (Study A). In a second study (Study B) of 12 females, IOP (contact tonometry) and 24-h urinary catecholamines were measured during a 50-h chamber exposure (446 mmHg). AMS severity was assessed using the Environmental Symptoms Questionnaire (ESQ-C). RESULTS: IOP decreased 25% after 2 d at altitude and returned toward sea level values by 15 d (Study A). IOP was reduced 13% after 5 h of exposure followed by return toward sea level values (Study B). Significant correlation was found between the sea level IOP and ESQ-C (Study A); significant correlation was found between the reduction in IOP and the ESQ-C and urinary epinephrine concentrations (Study B). CONCLUSIONS: Altitude exposure resulted in a reduction in IOP that occurred within hours and recovered during acclimatization. This reduction may be related to increases in epinephrine concentration. Measurement of IOP before and during altitude exposure may provide an objective method of assessing an individual's response to hypoxic stress.

Acclimatization↗
PubMed2002

In vitro propagation of Opuntia ellisiana Griff. and acclimatization to field conditions.

The genus Opuntia is a valuable forage resource in arid and semiarid lands during periods of drought and shortage of herbaceous plants. However, absolute minimum temperatures in the plains of Mendoza represent a limiting factor to cultivate several species. Opuntia ellisiana is a cold hardy species, so the goals of this study were to massively propagate is using in vitro culture techniques, and then to acclimatize plantlets obtained to field conditions. Different sterilization protocols were tested. Areoles were isolated in laminar airflow cabinet, and cultured on Murashige-Skoog medium, supplemented with sucrose and different BAP and IBA combinations. Explants were grown at 27 +/- 2 degrees C, under a 16-h photoperiod. The shoots produced were used in the rooting assay using different auxin combinations. In the most efficient growth treatment, plantlets reached 100% shooting after 35 days of culture, and a mean length of 10.2 mm after 49 days of culture. A 100% rooted plantlets was obtained on a medium containing 5 mg L-1 IBA, after 12 days of culture. Acclimatization was achieved under greenhouse conditions, showing 100% plantlet survival. This study suggests that O. ellisiana can be successfully micropropagated by areoles, and easily acclimatizated to field conditions.

Acclimatization↗
PubMed1992

[The characteristics and changes in high altitude ventilatory response during acclimatization at 5000 meters altitude].

To assess the characteristics and changes of high altitude ventilation response during acclimatization at 5000m altitude. The poikilocapnic hypoxic ventilatory responses (PHVR) were tested on nineteen healthy men who sojourned 5000m altitude for 12 weeks. The results were that there was a linear correlation between predicated ventilations which were calculated for 5000m altitude depended on PHVR values before ascent and actual ventilations tested when arrived at altitude. The PHVR was increased at second week after ascent, but at twelth week it was dropped near the level before ascent. The authors thought that peripheral chemoreceptor function might be enhanced within a period after ascent. With the acclimatization becomes perfected, the role of compensatory hyperventilation drops gradually to secondary position. So the activity of the chemoreceptor was restored gradually. The PHVR values in Xining group were lower than that in sea level group before ascent, but opposite change appeared at second week at 5000m altitude. There were no significant difference in PHVR between with and without acute mountain sickness groups.

Acclimatization↗
PubMed1991

[Prerequisites and guidelines for acclimatization to great and extreme altitude in prevention of altitude sickness].

Acute mountain sickness is a possible danger of life but it appears in fact absolutely not as fateful or unavoidable because it's evidence occurs as the consequence of missed observation of the specific conditions as much as of individual misbehaviour to altitude. Before someone plans to travel or climb at high altitudes by sharing a trekking-tour or an expedition-team medical advices for prevention of severe incidences caused by the reduced oxygen at altitudes are of utmost importance. Thereby it is not the question of the individual suitability to altitude which appears in the foreground but the need to find out typical health restrictions and, first of all, to develop an individual concept of optimal acclimatization to altitude. In this synopsis therefore all relevant aspects of preparation, precautions and detailed methods of acclimatization to altitude are laid down corresponding to the actual knowledge of altitude medicine and will be presented as crucial guiding principles for trekking and climbing to high altitudes.

Acclimatization↗
PubMed1989

Reticuloendothelial phagocytic activity in high-altitude acclimatized rats.

Experiments were undertaken with rats to determine the effects of chronic exposure to a simulated high altitude of 5,000 m on phagocytic activity of the reticuloendothelial system (RES). Phagocytic index (K) was determined by measuring the rate of blood clearance of colloidal carbon given intravenously. K value of the chronically altitude exposed rats was found to be greater than that of the sea level control animals (p less than 0.02), indicating that acclimatization to high altitude stimulated the RES phagocytosis. On analysis of the weights of the liver and spleen, the corrected phagocytic index (alpha) of the high altitude-acclimatized rats was also found to be higher than that of the sea level control animals (p less than 0.05) while the weights of the liver and spleen expressed in percent body weight were not affected by high altitude exposure. The increased number of carbon-containing Kupffer cells in the liver and the increased phagocytic indices (both K and alpha values) suggested that most of the increase in RES phagocytic activity was due to increased RES tissue activity per unit mass of tissue rather than tissue hypertrophy.

Acclimatization↗
PubMed1987

Increase and regression of the protective effect of high altitude acclimatization on the isoprenaline-induced necrotic lesions in the rat myocardium.

Cardiac resistance to the cardiotoxic effect of isoprenaline--ISO (single dose of 0.1 mg X kg-1) was studied in rats acclimatized to intermittent high altitude--IHA (barochamber, 8 h a day, 5 days a week, stepwise up to 7000 m). The extent of lesions was evaluated quantitatively by means of the increased accumulation of 203HgCl2. Five weeks' acclimatization was followed by a marked increase in the resistance of the myocardium to the necrogenic effect of ISO; this effect was more expressed in the left ventricle, so that the right to left difference generally observed under normoxic conditions disappeared. The increased resistance of the myocardium to ISO-induced damage persisted long after the animals had been returned to normoxic conditions; even six weeks after the last hypoxic exposure the sensitivity of the myocardium to damage had still not returned to the values of unacclimatized animals.

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