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At least 883 records · Page 49Linked to original sources
PubMed2003

Cognitive effects of dexamethasone at high altitude.

OBJECTIVE: The major therapeutic effect of dexamethasone on persons affected by high-altitude illness may be upon vascular leakiness with a consequent decrease in cerebral edema. We set out to determine if dexamethasone ameliorates the cognitive/psychomotor effects of acute exposure to high altitude on asymptomatic subjects. METHODS: Six adult subjects were tested at baseline (2500 m) with standard, computerized cognitive and psychomotor tests. Over the next 4 days, subjects were acclimatized to an altitude of 3700 m. On the fifth day, subjects ascended to 4800 m where predexamethasone testing was administered. No subject had symptoms of frank altitude illness at 4800 m. To limit acclimatization, subjects descended to 3700 m within 4 hours. The first 4-mg dose of oral dexamethasone was given in the evening of day 5. A second 4-mg dose of dexamethasone was given the following morning, and subjects reascended to 4800 m where postdexamethasone testing was performed. RESULTS: All cognitive and psychomotor tests showed improved reaction times in subjects who were given dexamethasone. Mean reaction time (+/- SD) for shape recognition went from 1.20 +/- 0.36 seconds at 2500 m to 1.40 +/- 0.37 seconds at 4800 m. After dexamethasone administration, mean shape recognition time declined to 1.26 +/- 0.32 seconds (P = .052). CONCLUSION: These data show a trend toward decreased cognitive deficits in subjects pretreated with dexamethasone. One possibility for this trend is that cognitive deficits in otherwise asymptomatic subjects exposed to high altitude are caused by subclinical cerebral edema.

Administration, Oral↗
PubMed2006

Entomological evaluation of malaria vectors at different altitudes in Hai district, northeastern Tanzania.

Entomological monitoring in four villages situated along an altitude transect in the Hai District of Northeastern Tanzania identified Anopheles arabiensis Patton as the principal vector of malaria and detected seasonal changes in vector behavior. Over a 13-mo sampling period, 10,557 mosquitoes were collected with CDC light traps, pyrethrum spray catches, and pit traps of which 5,969 (56.5%) wereAn. arabiensis, 762 (7.2%) wereAnopheles funestus Giles s.l., 3,578 (33.9%) were culicines, and 248 (2.3%) were nonvector anophelines. Vector densities declined rapidly with increasing altitude, demonstrating a 50% decrease in annual human biting rate for every 86-m rise in altitude. Light traps were found to be more efficient than spray catches for the collection of An. arabiensis. This observation was attributed to increased exophily of this species, most notably in the wet season, and is supported by seasonal changes in the human blood index and fed/gravid ratio. These results indicate that spray catches may underestimate the abundance of exophilic vectors such as An. arabiensis and that entomological monitoring may require more than one collection method, especially at low vector densities. The annual entomological inoculation rate (EIR) decreased sharply with increasing altitude, with large variation around the estimate at low vector densities. Increased transmission because of unpredictable short rains at low altitudes and spatial clustering of infective mosquitoes may contribute to elevated EIR estimates.

Altitude↗
PubMed1979

Alterations in adrenal growth and corticosteroid content in foetal and neonatal rats developing at high altitude.

To study the effects of chronic maternal hypoxia on the growth and functional development of foetal and neonatal adrenal glands, Long-Evans rats were acclimatized to high altitude (3800 m) before mating and were maintained at this height throughout gestation. The body growth of the progeny at high altitude was essentially normal during the perinatal period, but adrenal weight and adrenocortical function showed marked differences from those of control rats maintained at sea level. The adrenal glands were larger in foetuses but smaller in neonates, compared with the adrenal glands of control animals maintained at sea level. Differences in the protein content of the adrenal glands between the two groups paralleled differences in adrenal weight. The concentration and content of corticosterone in the adrenal glands of both foetuses and neonates kept at high altitude were markedly lower than values in animals kept at sea level. The lower adrenal corticosterone content was not reflected in the concentration of the hormone in the peripheral plasma, since this was essentially the same at high altitude and at sea level in both mothers and perinatal animals. The reduction in the adrenal corticosterone content was accompanied by and may have resulted from, a reduction in the concentration of cytochrome P-450 in the adrenal tissue of foetuses maintained at high altitude. Possible explanations for the dichotomous results are discussed.

Adrenal Cortex Function Tests↗
PubMed2006

Evidence for life history changes in high-altitude populations of three perennial forbs.

Relatively little is known about how the life histories of perennial forb species, and especially their lifetime patterns of growth, vary across environmental gradients. We used a post hoc approach (herb-chronology) to determine plant age and previous growth (width of successive annual rings in roots) in three species of perennial forb (two long-lived species [Penstemon venustus, Lupinus laxiflorus] and one short-lived [Rudbeckia occidentalis]) along a 1000-m altitudinal gradient in the Wallowa Mountains (northeast Oregon, USA). Plants from the highest altitude tended to be considerably older and produced up to five times as many flowering shoots as lowland plants. In addition, mean ring widths of high-altitude plants were about half those of lowland plants. In plants from low and intermediate altitudes, ring width either decreased linearly or varied inconsistently during the life of the plant. In contrast, ring widths of high-altitude plants increased at first and later decreased, resulting in curvilinear growth trajectories that were highly consistent among species. Together, these data for three ecologically distinct forb species provide evidence of a consistent shift toward more conservative and strongly constrained life histories at higher altitudes. More generally, the results indicate the possible importance of changes in selection pressures across strong environmental gradients on life history strategies within a single species.

Altitude↗
PubMed1997

The effect of high altitude and other risk factors on birthweight: independent or interactive effects?

OBJECTIVES: This study examined whether the decline in birth-weight with increasing altitude is due to an independent effect of altitude or an exacerbation of other risk factors. METHODS: Maternal, paternal, and infant characteristics were obtained from 3836 Colorado birth certificates from 1989 through 1991. Average altitude of residence for each county was determined. RESULTS: None of the characteristics related to birthweight (gestational age, maternal weight gain, parity, smoking, prenatal care visits, hypertension, previous small-for-gestational-age infant, female newborn) interacted with the effect of altitude. Birthweight declined an average of 102 g per 3300 ft (1000 m) elevation when the other characteristics were taken into account, increasing the percentage of low birthweight by 54% from the lowest to the highest elevations in Colorado. CONCLUSIONS: High altitude acts independently from other factors to reduce birthweight and accounts for Colorado's high rate of low birthweight.

Adult↗
PubMed1996

Influence of simulated altitude on the performance of five blood glucose meters.

OBJECTIVE: To determine the reliability of five blood glucose meters (BGMs) at various simulated altitudes using a hypobaric chamber. RESEARCH DESIGN AND METHODS: Blood glucose levels (ranged from 1.5 to 26.3 mmol/l, according to the reference method) were measured in 18 venous blood samples by each BGM at 200, 1,000, and every 500 m up to 4,000 m in a hypobaric chamber, where temperature and humidity were held constant. RESULTS: Four BGMs underestimated and one overestimated blood glucose concentration while barometric pressure decreased. The average percent error varied in relation to simulated altitude from 0.26 +/- 4.8% (SD) at 200 m to -28.9 +/- 4.5% at 4,000 m (Glucometer 3; P < 0.05), from 28.4 +/- 5.7 to 49.3 +/- 5.9% (Accu-Chek Easy; P < 0.05), from -10.5 +/- 2.6 to 19.8 +/- 4.3% (Tracer, P < 0.05), from -5.5 +/- 2.6 to -11.2 +/- 3.0% (Reflolux; NS), and from 17.8 +/- 4.3 to 14.8 +/- 3.6% (One Touch; NS). The most accurate seemed to be the Reflolux, except for high blood glucose levels at simulated high altitudes. The One Touch II showed a good agreement, whatever the barometric pressure and the range of blood glucose concentrations. The highest underestimation was seen with the Glucometer 3. CONCLUSIONS: Except for the Accu-Chek Easy, low barometric pressure underestimated the BGM results in comparison with measurements taken at simulated low altitudes. The lack of accuracy and consistency of performance > 2,000 m should be known by diabetic patients practicing sports activities, such as trekking or skiing at high altitudes.

Altitude↗
PubMed1975

Influence of altitude and age on pulmonary arterial pressure in cattle.

Pulmonary arterial pressures in native cattle ranging in age from 3 months to 10 yr were found to be increased with increasing altitudes of residence from sea level to 3048 m. At altitudes of 2590 and 3048 m, but not at sea level or 1524 m, the pressures were higher in older than in younger cattle. The magnitude of the pulmonary arterial pressure, and probably the rate of progression of pulmonary hypertension at high altitude, were much less in native cattle than in cattle that were newcomers from low altitude. Natural and artificial selection are believed to have minimized the level of pulmonary hypertension in native high altitude cattle, thus protecting them from high mountain or brisket disease.

Age Factors↗
PubMed2003

Creating an altitude-adjusted hematocrit reference standard for adults 18-40 years of age in China.

This study was conducted to provide a scientific basis for development of a unified hematocrit reference standard for young adults (i.e., 18-40 yr of age) in China. Hematocrit values for healthy young adults (n = 34,383 men and 24,040 women) were collected in accordance with the Wintrobe method. The author used correlation and regression analyses to investigate the relationship between hematocrit values and altitude. Hematocrit values increased gradually with altitude, and the relationship was statistically significant (p < 0.01). It was determined that regression equations could be used to calculate hematocrit reference standards for healthy male and female adults in the aforementioned age group, provided that the mean altitude of a region was used in the analysis. The author offers examples that represent 3 regions of China characterized by different mean altitudes: (1) Qingzang District (4,000-m altitude), Central District (2,000-1,000 m), and Eastern District (< 500 m).

Adolescent↗
PubMed2003

High altitude pulmonary oedema.

Altitude, speed and mode of ascent and, above all, individual susceptibility are the most important determinants for the occurrence of high altitude pulmonary oedema (HAPE). This illness usually develops only within the first 2-5 days after acute exposure to altitudes above 2500-3000 m. An excessive rise in pulmonary artery pressure preceding oedema formation is the crucial pathophysiological factor. Recent investigations using right heart catheterisation and bronchoalveolar lavage (BAL) in incipient pulmonary oedema have shown that HAPE is a hydrostatic oedema in the presence of normal left atrial pressure with non-inflammatory high permeability leakage of the alveolocapillary barrier and mild alveolar haemorrhage. An inflammatory response may develop later in more advanced cases, as has been documented by BAL. Furthermore, decreased fluid clearance from the alveoli may contribute to such non-cardiogenic pulmonary oedema. Supplemental oxygen is the primary treatment in areas with medical facilities, while the treatment of choice in remote mountain areas is immediate descent. When this is impossible and supplemental oxygen is not available, treatment with nifedipine is recommended until descent is possible. Even susceptible individuals can avoid HAPE if they ascend slowly with an average gain of altitude not exceeding 300-350 m/day above an altitude of 2500 m.

Altitude Sickness↗
PubMedDate not supplied

Body temperature and basal metabolic changes during acclimatization to altitude (3,500 m) in man.

Oral temperature (Tor), mean weighted skin temperature (Ts), mean body temperature (Tb) and basal oxygen consumption were studied on twelve young men at sea level. Then they were flown to an altitude of 3,500 m and the readings were continued after 24 hours of their arrival and thereafter at four day intervals for a period of 25 days. Thereafter the subjects were flown back and retested at sea level. Oxygen consumption was recorded at weekly intervals only. The changes in body temperature were compared with those of their basal oxygen consumption. The results indicate that there is a slight rise in the Tor on arrival at altitude and thereafter a gradual fall. A steady and continuous fall was recorded in Ts and Tb throughout the stay at altitude. The basal oxygen consumption showed an initial rise which has come back to normal by the third week of their stay at altitude. On retest, the valves of body temperature and oxygen consumption reached their own initial sea-level pattern. The observation suggests that central mechanisms are involved in bringing about a fall in body temperature during altitude acclimatization.

Acclimatization↗
PubMed1999

Effect of time exposure to high altitude on zinc and copper concentrations in human plasma.

BACKGROUND: Research has focused mainly on the relationship of zinc and copper contents and physical stresses like running, cycling, etc. It has also been reported that other forms of stresses change the concentration of these trace elements in humans. However,there are no reports on the effects of high altitude induced hypoxic stress on the plasma levels of these metals. Since hypoxia is one of the important stresses, we considered it appropriate to observe the changes in the levels of zinc and copper concentrations and in certain related zinc and copper enzymes and hormones in the plasma of human volunteers on acute induction to high altitude. From these findings, we intended to ascertain whether supplementation of these trace elements would be required for optimal health under such conditions. HYPOTHESIS: On acute induction to hypoxia, contents of these trace elements may change as the requirements of stressed organs and tissue may increase. Hence, further supplementation may be beneficial under hypoxic stress for better adaptability. METHOD: Volunteers were divided into two groups: with and without zinc and copper salt supplementation. Blood samples were collected at sea level and on induction to acute hypoxia on days 3 and 10. Trace mineral contents and their related enzyme (alkaline phosphatase) and hormone (ceruloplasmin) levels were determined in plasma samples. RESULTS: Plasma zinc contents were significantly reduced upon induction to high altitude in the non-supplemented group, but not in the zinc-supplemented group. Alkaline phosphatase activity increased significantly upon induction to the high altitude stress. The enzyme activity remained elevated up to day 10 of the stress. Plasma copper contents and ceruloplasmin activity did not change upon induction to high altitude. CONCLUSION: Under hypoxic stress, circulating levels of zinc and alkaline phosphatase in plasma changed appreciably as plasma zinc was transported into the organs and tissues. However, circulating levels of copper and ceruloplasmin in plasma did not change, indicating no extra supplementation of copper is required under hypoxic stress.

Acute Disease↗
PubMed2000

Exaggerated pulmonary hypertension is not sufficient to trigger high-altitude pulmonary oedema in humans.

High altitude pulmonary oedema (HAPE) is a paradigm of pulmonary oedema that occurs in otherwise healthy subjects and thereby allows us to study underlying mechanisms in the absence of damning factors. Exaggerated pulmonary hypertension, which is related at least in part to endothelial dysfunction, is a hallmark of high-altitude pulmonary oedema. It is thought to play an important part in the pathogenesis of HAPE, but the predisposing factors are not clear. In rats, transient exposure to hypoxia during the first few days of life predisposes to exaggerated hypoxic pulmonary vasoconstriction in adulthood. We hypothesised that a similar mechanism may operate in humans, and if so may predispose to high-altitude pulmonary oedema. To test this hypothesis we studied the effects of high-altitude exposure (4559 m) on pulmonary-artery pressure and incidence of pulmonary oedema in 10 healthy young adults who had suffered from transient hypoxic pulmonary hypertension during perinatal period, and compared these effects with those observed in 10 controls of similar age and sex distribution, and in 14 HAPE-prone mountaineers. We found that at high altitude, the subjects who had suffered from transient perinatal hypoxic pulmonary hypertension had exaggerated pulmonary hypertension compared to controls (62 +/- 7 vs 50 +/- 11 mm Hg, p < 0.01). Despite exaggerated pulmonary vasoconstriction of similar magnitude to that observed in HAPE-prone subjects (59 +/- 10 mm Hg), none of the young adults developed HAPE. In contrast, 8 of the 14 HAPE-prone subjects had radiographic evidence of lung oedema (p < 0.001 for the comparison with the other 2 groups). These data challenge previous concepts and indicate that exaggerated hypoxic pulmonary vasoconstriction, while consistently associated with HAPE, is not sufficient to trigger pulmonary oedema. This suggests that additional mechanisms play a role.

Adult↗
PubMed2000

Effects of mountaineering training at high altitude (4,350 m) on physical work performance of women.

BACKGROUND: Little is known about work performance of women in hypobaric hypoxia. Moreover, whether native women of moderate altitude (2,000-2,100 m) differ from their lowland counterparts in their ability to adjust to hypobaric hypoxia is also not known. Hence, physiological alterations on work performance due to mountaineering training with altitude adaptation was evaluated in two groups of women and compared to the differences in the responses of the native women of moderate altitudes (Highlanders-HL) with those of the plains (Lowlanders-LL). METHODS: Pre-training tests were conducted at 2,100 m, then during sojourn to 4,350 m and re-tested again after return to 2,100 m. Physical work performance was assessed following standard step-test-exercise on a 30 cm stool with 24 cycles x min(-1) for 5 min. Heart rate, BP, ventilation, oxygen consumption and oxygen saturation were monitored at rest and during exercise followed by 5 min recovery in all three situations. RESULTS: During initial assessment, HL showed higher cardiovascular efficiency with faster recovery of exercise heart rate. Both groups showed significant improvement in physical performance due to mountaineering training at high altitude (HA). The difference in performance between two groups narrowed down at 4,350 m and further reduced during re-test with maintenance of initial superiority of the HL. CONCLUSIONS: a) Native women of moderate altitude (HL) are more fit compared with their plains counterparts (LL); b) All women achieved marked improvement in cardiovascular and respiratory efficiency as well as the step-test score due to intense mountaineering training at HA, and the rate of improvement in physical performance was higher in LL; c) Further, induction by trekking under progressive hypoxia coupled with rigorous mountaineering activity at HA merits in understanding better acclimatization and improved physical performance.

Acclimatization↗
PubMed2000

[Altitude hypoxia: effects on selected endocrinological parameters].

During the past few years, the investigation of altitude hypoxia and its effect on metabolic functions in humans has increasingly attracted the attention of endocrinologists. Most of the studies have been performed as field studies at moderate or high altitude, but with conflicting results. One of the possible reasons certainly is the fact that standardisation of field studies is almost impossible. Furthermore, many factors such as wind, temperature, radiation and others, may affect certain endocrine parameters, but they cannot be individually quantified. Hence, their inclusion into statistical analyses of the obtained data is not useful. Nevertheless, several endocrine parameters were shown to be affected by altitude hypoxia. Among them, there is erythropoietin, a hormone which is well known to stimulate erythropoiesis. This hormone shows a rapid increase after ascent to moderate or high altitude. There is also evidence that urinary and serum noradrenalin levels increase significantly, whereas adrenalin seems to be less affected. Another "stress-hormone", cortisol, also shows a significant increase. Furthermore, the biologically active fraction of the thyroidal hormones thyroxine and triiodothyronine increases significantly. And last but not least, one of the most important proinflammatory cytokines, interleukin-6, shows a manyfold increase compared to the basal level. However, the clinical significance of most of these studies is not yet clear. Hence, from an endocrinological point of view, no specific recommendations may be given to people staying at moderate or high altitude.

Adaptation, Physiological↗
PubMed2000

[Excitatory amino acid enhance prepro-somatostatin mRNA expression induced by altitude hypoxia in the rat hypothalamus].

AIM AND METHODS: Contents of glutamate (Glu), asparate (Asp) and expression of prepro-somatostatin mRNA (PPS-mRNA) in rat hypothalamus were measured by using imitated altitude hypoxia rat model, amino acid analyzer and in situ hybridization technique. RESULTS: After rats were subjected to altitude hypoxia, contents of Glu and Asp in hypothalamus and PPS-mRNA expression in periventricular nucleus (PeVN), paraventricular nucleus (PaVN) and arcuate nucleus (ArcN) were increased significantly. Ketamine, a NMDA receptor antagonist, could decrease the number of PPS-mRNA neurons in rat hypothalamus evoked by altitude hypoxia, but had no effect on Glu and Asp contents evoled by altitude hypoxia. CONCLUSION: It is suggested that somatostatin maybe paticipate in altitude hypoxia reaction, Glu can enhance PPS-mRNA expression through NMDA receptor.

Altitude Sickness↗
PubMed1996

[Altitude training--what is true?].

Because of the importance of oxygen transport and consumption in the body for endurance performance altitude training as preparation for competitions at sea level has come into use. In hypoxia maximal O2 uptake decreases. Thus for equal work load training at altitude is harder and stimulates adaptation processes more than sea level training. A specific altitude training effect, however, can only be proven if a relative equal load (in % of VO2max) is more effective than during sea level training. In only 3 of 10 investigations with this design a significant improvement of either maximal performance, VO2max or endurance was found, in 2 there was a nonsignificant tendency. When training in hypoxia combined with living in normoxia was investigated two of four groups improved. Presumably there exists a small specific altitude effect on performance capacity, which may be counteracted by negative influences like reduced muscular metabolic intensity. A series of single physiological changes at altitude might have positive or negative influences on training success: training of ventilatory muscles, increase of hypoxic ventilatory stimulation, reduced heart training by vegetative 'braking', increase of red cell and plasma volume (the latter after descent), right shift of the oxygen dissociation curve, increase of oxidative muscle enzymes (only after hypoxia training), shift from carbohydrate to fat combustion, reduced lactic acid and ammonia production, improvement of buffering.

Acclimatization↗
PubMed1975

Changes in exercise heart rate in lowlanders after prolonged stay at high altitude (4000 m).

Studies were conducted on cardiac frequency during submaximal and maximal work on 26 sea-level residents prior to transfer to and during stay at high altitude for 1, 10, and 20 months. Maximal O2 uptake and performance in a 1.6 km run were observed. Results indicated a significant drop in Vo2 after arrival at altitude followed by recovery with further stay. The mean maximum heart rate decreased to 182.8 beats/min after 1 month at high altitude from a seal-level mean value of 188.4 beats/min. It increased to 199.2 beats/min and decreased to 185.6 beats/min after 10 and 20 months, respectively. Heart rate, during submaximal work requiring 1.0 and 1.5 102/min, indicated the highest rate after 1 month at altitude and decreased with prolonged stay, but remained higher than the sea-level value. These changes were compared with the high-altitude native residents.

Acclimatization↗
PubMed2001

Altitude decompression sickness. Case presentation.

The in-flight altitude-related decompression sickness (DCS) is not as common as DCS occurring after working or recreational diving, or, at least, it is not commonly described in the medical literature. Though modern aircraft are safer and more reliable, occupants are still subject to the stress of high altitude flight, and altitude DCS still represents a risk to the occupants, mostly if they are exposed to altitudes of 25,000 ft or higher. The authors report their experience about two different accidents involving a US Air Force pilot and a navigator, treated at the Service of Hyperbaric Medicine at Landspitallin Fossvogur, the University of Reykjavik City Hospital, Iceland, because of occurrence of type II altitude-related DCS. A US Navy Oxygen Treatment Table 6 was successfully applied in both cases. Also considered are some aspects related to physiopathology, clinical presentation and therapy of DCS, with particular regard to the occurrence of DCS during flight.

Adult↗