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PubMed1981

Body composition of high altitude natives on descent to the plains: a densitometric, hydrometric, and anthropometric evaluation.

Body density was experimentally determined at a field location at 3,920 m on 32 medically fit and active high altitude native males using a water displacement technique. Stature, body weight and the bony widths at the elbow, wrist, knee, and ankles; and thickness of skin folds at eight sites were measured. Based on body density and bony widths, body fat, total body water (TBW), mineral mass and total cell solids (TCS) were calculated. Similar measurements were made on another group of 16 high altitude natives after one months stay in Dehli (200 m). TBW of 11 of these subjects was experimentally determined by the oral administration of 200 muCi of tritiated water. This group of subjects was physically less active in Delhi. At high altitude the natives consumed a balanced diet which provided 20.21 MJ, but in the plains the diet provided only 15.69 MJ though it was nutritionally balanced. In spite of the reduced calorie intake this group showed greater fat content in Delhi than the group located at high altitude. These men were also hyperhydrated. Hyperhydration of the lean body could be an adaptive response of the high altitude natives to the new environment. Due to the disturbed state of hydration of the lean body of these men in the plains, use of Siri's formula for the computation of total body fat is questioned.

Adaptation, Physiological↗

PubMed1983

Chemoreceptor sensitivity and maladaptation to high altitude in man.

Studies were carried out to find out the role of chemoreceptor sensitivity in the causation of maladaptation syndromes on acute exposure to altitude. The experiments were done in two phases. In phase I, the responses in chemoreceptor sensitivity were studied in altitude acclimatized subjects and compared with those who suffered from either High Altitude Pulmonary Oedema (HAPO) or Acute Mountain Sickness (AMS). In Phase II, a similar comparison was done in two groups of subjects, one representing normal sojourners at 3,500 m and the other being subjects who had just recovered from HAPO. The first phase was done at Delhi; and the second at an altitude of 3,500 m. Parameters of assessment were hypoxic sensitivity, carbon dioxide sensitivity, ventilation (VE), respiratory frequency (Rf), forced vital capacity (FVC), forced expiratory volume at the first second (FEV1), heart rate (HR), blood pressure (BP), and oral temperature (Tor). The results showed significantly lower sensitivity to both hypoxia and carbon dioxide in maladapted subjects, as compared to those who were acclimatized in both the categories suggesting thereby that reduced chemoreceptor sensitivity might be an initiating factor in the causation of maladaptation syndromes at altitude.

Adult↗

PubMed1988

Changes in plasma lipids and lipoprotein cholesterol during a high altitude mountaineering expedition (4800 m).

Effects of high altitude exposure on plasma lipids and lipoprotein cholesterol were studied in 8 mountaineers who spent 3 weeks at the Annapurna IV base camp (4800 m) after a 12 day trek. In spite of the moderate physical exertion at the camp, the loss of body weight was more pronounced during the stay at high altitude than during the trekking period. Compared with baseline values observed at sea level, marked reductions in plasma cholesterol (-27%) and phospholipids (-19%) were found 3 days after arrival at the camp and persisted during the next 17 days. A less marked fall in plasma triglycerides occurred, weakly significant at the end of the stay. Because there were no relevant changes in very low density lipoproteins or in high density lipoprotein (HDL)-cholesterol, the low plasma cholesterol levels at the high altitude resulted mainly from the reduction in low density lipoprotein (LDL)-cholesterol: the mean HDL/LDL cholesterol ratio changed from 0.39 at sea level to 0.63 at the end of the stay at 4800 m. Fluctuations in LDL-cholesterol were not concomitant with those in body weight and were independent of the exercise training during the expedition. This study shows moreover that the early drop in LDL-cholesterol was associated with an opposite change in plasma levels of catecholamines and thyroid hormones. Taking into account that such hormonal responses are classically observed at high altitude, the concomitant decrease in LDL-cholesterol might be interpreted as being a relevant adaptative response to hypoxic conditions at high altitude.

Adult↗

PubMed1996

Comparison of muscle force, muscle endurance, and electromyogram activity during an expedition at high altitude.

Handgrip force (HF), maximal pinch force (MF), muscle endurance (ME), and the median power frequency (MdPF) of the activity shown in the electromyogram (EMG) were studied at various altitudes in eight normal healthy subjects. MF and ME were measured between the index finger and thumb, and all measurements were obtained at altitudes ranging from 610 to 4860 m during an expedition in the Qinghai Plateau in China. With the change in altitude HF, ME, and MF showed no significant change. Compared to the MdPF at 2260 m on ascent, the MdPF at other altitudes showed a significant decrease (P < 0.01). Thus, we conclude that muscle performance (HF, MF, and ME) was not affected by the environment at high altitude. However, MdPF was affected and the mean MdPF at 610 m after the expedition did not recover to initial values of MdPF. We suggest these results may have been affected by fatigue and chronic exposure to the hypobaric hypoxic environment, since the members of the expedition party expressed feelings of sluggishness and fatigue after the expedition.

Acclimatization↗

PubMed1993

The effects of acute altitude exposure in Swiss highlanders and lowlanders.

The functional characteristics at rest in responding to stepwise acute exposure to simulated altitude (6000 m) were compared in 10 acclimatized mountaineers (highlanders), residents of Zermatt (1616 m) working at an altitude up to about 4000 m, and in 11 nonacclimatized control subjects (lowlanders) living and working in Zurich (450 m). In comparison with the lowlanders, the highlanders showed at altitude significantly greater hyperventilation, lower heart rate and systolic blood pressure, smaller haemoconcentration, lower urodilatin secretion and natriuresis, and a preserved neuropsychological ability (attentiveness) and vasomotor tone (diastolic blood pressure); the critical altitude at which hypoxic short-term adaptation became insufficient was 6000 m. The lowlanders, however, manifested reduced tolerance of hypoxia, i.e. insufficient short-term adjustment with subjective and objective distress coinciding with the first signs of hypoxia of the central nervous system, already apparent at and above 4000 m. It was concluded that the functional differences between highlanders and lowlanders in responding to acute gradual hypoxia indicated factors contributing to altitude acclimatization.

Acclimatization↗

PubMed1988

Effect of exposure to the altitude of 300 meters below sea-level on testosterone, luteinizing hormone, follicle-stimulating hormone and prolactin in man.

Serum testosterone, luteinizing hormone (LH), follicle-stimulating hormone (FSH) and prolactin (PRL) responses to exposure to sea-level altitude (LA) were examined in 13 eugonadal males, age 21-22 yr, 3 and 5 days after residing at LA and on the second day of return to basal altitude 90 days later. After 3 days at their respective residence altitude, there was elevation in LH (p less than 0.05) and depression in testosterone levels (p less than 0.05), with similar results on day 5. These effects were all of transient nature, LH and testosterone concentrations returned to their basal levels on second day of the return to basal altitude. The FSH and PRL levels did not show any significant change during the stay at LA or after return to basal altitude. The observations suggest that exposure to LA is associated with increase in plasma levels of LH and decrease in testosterone. The decreased levels of testosterone could be due to a reduction in the sensitivity of the testis to LH, or due to inhibition of steroidogenesis in the testis.

Adult↗

PubMed2000

Simulated moderate altitude elevates serum erythropoietin but does not increase reticulocyte production in well-trained runners.

The purpose of this study was to investigate whether the modest increases in serum erythropoietin (sEpo) experienced after brief sojourns at simulated altitude are sufficient to stimulate reticulocyte production. Six well-trained middle-distance runners (HIGH, mean maximum oxygen uptake, VO2max = 70.2 ml x kg(-1) x min(-1) spent 8-11 h per night for 5 nights in a nitrogen house that simulated an altitude of 2650 m. Five squad members (CONTROL, mean VO2max= 68.9 ml x kg(-1) x min(-1) undertook the same training, which was conducted under near-sea-level conditions (600 m altitude), and slept in dormitory-style accommodation also at 600 m altitude. For both groups, this 5-night protocol was undertaken on three occasions, with a 3-night interim between successive exposures. Venous blood samples were measured for sEpo after 1 and 5 nights of hypoxia on each occasion. The percentage of reticulocytes was measured, along with a range of reticulocyte parameters that are sensitive to changes in erythropoiesis. Mean serum erythropoietin levels increased significantly (P < 0.01) above baseline values [mean (SD) 7.9 (2.4) mU x ml(-1)] in the HIGH group after the 1st night [11.8 (1.9) mU x ml(-1), 57%], and were also higher on the 5th night [10.7 (2.2) mU x ml(-1), 42%] compared with the CONTROL group, whose erythropoietin levels did not change. After athletes spent 3 nights at near sea level, the change in sEpo during subsequent hypoxic exposures was markedly attenuated (13% and -4% change during the second exposure; 26% and 14% change during the third exposure; 1st and 5th nights of each block, respectively). The increase in sEpo was insufficient to stimulate reticulocyte production at any time point. We conclude that when daily training loads are controlled, the modest increases in sEpo known to occur following brief exposure to a simulated altitude of 2650 m are insufficient to stimulate reticulocyte production.

Adult↗

PubMed2005

Seed weight increases with altitude in the Swiss Alps between related species but not among populations of individual species.

Seed weight is a crucial plant life history trait, determining establishment success and dispersal ability. Especially in stressful environments, larger seeds may be selected at the expense of seed number, because larger seeds have a better chance of giving rise to an established offspring. We tested the hypotheses that between related species-pairs and among populations of single species a similar trend for increasing seed weight with increasing altitude should be present. Firstly, we measured seed weights from 29 species-pairs, with one species occurring in lowland areas and a congeneric species from high altitudes. Seeds of the alpine species were 28+/-8% larger than seeds from lowland species (P < 0.01). Compared to the related lowland species, 55% of the alpine species had heavier seeds, 3% (one species) had lighter, and 41% had seeds of approximately equal weight. Secondly, we compared seed weights among populations of four species from different habitats and with different life histories. Seeds from between 11 and 34 populations per species were sampled along altitudinal gradients of 800-1,500 m (ca. 800 m in Scabiosa lucida, ca. 1,000 m in Saxifraga oppositifolia, ca. 1,000 m in Epilobium fleischeri, and ca. 1,500 m in Carex flacca). In all the four species, we found no indication for heavier seeds at higher altitudes. Our results indicate a selection pressure for species with heavier seeds at higher altitude, but the trend does not seem to operate across all cases. Phylogenetic constraints may limit the correlation among altitude and seed weight, operating particularly against selection for larger seed size, the closer populations and species are related to each other.

Altitude↗

PubMed2006

Growth and leaf physiology of monkeyflowers with different altitude ranges.

Every species is limited both geographically and ecologically to a subset of available habitats, yet for many species the causes of distribution limits are unknown. Temperature is thought to be one of the primary determinants of species distributions along latitudinal and altitudinal gradients. This study examined leaf physiology and plant performance under contrasting temperature regimes of sister species of monkeyflower, Mimulus cardinalis and Mimulus lewisii (Phrymaceae), that differ in altitude distribution to test the hypothesis that temperature is the primary determinant of differences in fitness versus altitude. Each species attained greatest aboveground biomass, net photosynthetic rate, and effective quantum yield of photosystem II when grown under temperatures characteristic of the altitudinal range center. Although both species exhibited greater stem length, stomatal conductance, and intercellular CO2 concentration in hot than in cold temperatures, these traits showed much greater reductions under cold temperature for M. cardinalis than for M. lewisii. Survival of M. lewisii was also sensitive to temperature, showing a striking decrease in hot temperatures. Within each temperature regime, the species native to that temperature displayed greatest growth and leaf physiological capacity. Populations from the altitude range center and range margin of each species were used to examine population differentiation, but central and marginal populations did not differ in most growth or leaf physiological responses to temperature. This study provides evidence that M. cardinalis and M. lewisii differ in survival, growth, and leaf physiology under temperature regimes characterizing their contrasting low and high altitude range centers, and suggests that the species' altitude range limits may arise, in part, due to metabolic limitations on growth that ultimately decrease survival and limit reproduction.

Altitude↗

PubMed1993

Low serum prolactin levels in native women at high altitude.

OBJECTIVES: To determine the serum prolactin levels in women at sea level and at high altitude, and the prevalence of hyperprolactinemia in both places. METHODS: The study included 303 normal women and 112 women with any reproductive dysfunction (menstrual abnormalities, galactorrhea or dysmenorrhea). From these, 228 were living in Lima at 150 m above sea level and 187 were living in Cerro de Pasco at 4340 m. Normal women included nonpregnant and pregnant women. Menstrual abnormalities included amenorrhea, oligomenorrhea and polymenorrhea. RESULTS: Serum prolactin levels were significantly lower in nonpregnant and pregnant women living at high altitude than at sea level. Prevalence of hyperprolactinemia, galactorrhea and menstrual abnormalities were significantly lower at high altitude than at sea level. CONCLUSIONS: It is concluded that menstrual abnormalities associated with hyperprolactinemia is a rare condition at high altitude. The low serum prolactin level observed at high altitude could be due to a high dopaminergic activity.

Adolescent↗

PubMed1994

Altitude and socio-biological determinants of pregnancy-associated hypertension.

OBJECTIVES: To study the prevalence of gestation-associated hypertension and to determine the effect of altitude and related socio-biological factors. METHODS: A stratified random sample of 3988 pregnant women living at high altitude and 2744 at sea level in the Asir region, Saudi Arabia was interviewed for socio-biological conditions and examined for blood pressure, proteinuria and body mass. RESULTS: An overall prevalence of 2.4% was found. Certain groups of pregnant women are at high risk of developing hypertension. They include women who are over 40 years, high multipara, having short inter-pregnancy spacing, are overweight, are illiterate and those living at high altitude. Multivariate analysis showed that high altitude is a strong risk factor (adjusted odds ratio (OR), 1.879; 95% confidence interval (CI), 1.123-2.819) and cannot be masked when other variables are controlled. CONCLUSIONS: Special health education and more frequent screening programs at primary health care level should be given to pregnant women living at high altitude.

Adult↗

PubMed1984

Aortic enzymes and lactate in high altitude-raised and cholesterol-fed rabbits.

Fourteen male rabbits born at elevation 4000 ft (first experimental series) were transferred at age of 2 months to elevation 12470 ft and raised there for 18 weeks. Half of the animals remained on a commercial rabbit chow (group H) while the other half was on the same diet supplemented with cholesterol (group C). Eight male rabbits raised at sea level served as controls (group S). Intima-media homogenates from the thoracic aortas were assayed for lactate dehydrogenase (LDH), malate dehydrogenase (MDH), lipoamide dehydrogenase, pyruvate kinase (PK), phosphofructokinase (PFK) and the lysosomal hydrolases beta-glucuronidase and N-acetyl-beta-glucosaminidase (NAGA). Aortic lactate and glucose were also measured. Thirty-two male rabbits (second experimental series) were subdivided into 4 groups. Rabbits were fed a cholesterol-supplemented diet not only at high altitude (8 rabbits matching group C) but also 8 animals raised at sea level. The degree of atherosclerosis in the aortas of these 4 groups was assessed by measuring the aortic cholesterol contents. Plasma cholesterol was also determined. In the aortas of the rabbits of group H the activity of PK was significantly elevated, and the activity of the lysosomal hydrolases significantly decreased compared with aortas of group S rabbits. There was no difference in the other enzyme activities or in the aortic glucose and lactate content of these groups. Cholesterol feeding of the animals of group C resulted in a significantly increased activity of the lysosomal hydrolases as well as of LDH and PK. The lipid analyses (second experimental series) revealed a trend to a lower concentration of aortic cholesterol in the high altitude than in the sea level animals, both fed a cholesterol diet, in spite of the higher plasma cholesterol concentrations in the high altitude animals. The low aortic lysosomal hydrolase activities in the high altitude rabbits are in accord with their comparatively lower susceptibility to experimental atherosclerosis. This metabolic feature may be due to a lower degree of exposure of these aortas to injurious factors, such as infections or lower blood pressure. The elevated activity of PK without increased lactate content in group H animals seems to parallel the well-known general adaptation of the organism to high altitude hypoxia, and does not indicate a metabolic switch toward anaerobic glycolysis.

Acetylglucosaminidase↗

PubMed1989

Human adrenoceptor system response to the development of high altitude pulmonary arterial hypertension.

High-altitude pulmonary arterial hypertension affects people with a long-term residence at altitudes over 2500 m above the sea level and is characterized by elevated pulmonary artery pressure (over 35/15 mmHg). In order to assess the role of beta-adrenoreceptors in the development of high-altitude pulmonary arterial hypertension, we studied the beta-adrenoreceptor density on mononuclear leukocytes in Kirghiz male natives of Eastern Pamir (3600-4200 m above sea level) with the diagnosis of high-altitude pulmonary arterial hypertension, and in healthy men. It was shown that patients with signs of right ventricular hypertrophy (RVH) of the second and third grade have beta-adrenoreceptor density 4.5 times lower than control (2.27 +/- 0.22 vs. 9.85 +/- 1.28 fmol/10(6) cells). Values of Kd also proved to be lower, by 2.5 times (0.57 +/- 0.14 vs. 1.44 +/- 0.18 nM). Stimulation of adenylate cyclase by isoproterenol and other beta-agonists was lower in patients than in controls (+33% and +120%, respectively). These results demonstrate that the desensitization of beta-adrenoreceptors is present in patients with high-altitude pulmonary arterial hypertension associated with severe right ventricular hypertrophy. Patients with pulmonary arterial hypertension due to mitral stenosis do not have any signs of beta-adrenoreceptor desensitization associated with high plasma levels of catecholamines.

Adenylyl Cyclases↗

PubMed1981

Acute mountain sickness and the edemas of high altitude: a common pathogenesis?

Within days of ascent to high altitude when symptoms of acute mountain sickness (AMS) are common, pulmonary and cerebral edema may also develop. Although peripheral edema of the hands, face or feet may also appear, its association with AMS is unclear. In addition, persons with high altitude pulmonary edema often report an antidiuresis. Hence, altitude sickness appears to result from abnormalities in the handling of body water. To test this hypothesis, we studied 102 men and women who were trekking in the Mount Everest region of Nepal. Most were seen both at low (1377 m) and at high (4243 m) altitude. Severity of AMS was measured by an established Symptom Score derived from a questionnaire and physical examination. Change in body water was inferred from change in body weight in less than 10 days. Peripheral edema was assessed separately by physical examination. AMS Symptom Score correlated directly with weight change; those who remained well lost weight, whereas increasing signs and symptoms of AMS occurred in those with increasing weight gain. The symptomatic subjects also developed peripheral edema and reported decreased urinary output. These findings support the hypothesis that with rapid ascent to high altitude, abnormalities in the handling of body water, with antidiuresis, result in fluid retention (weight gain) manifest as peripheral, pulmonary, and/or cerebral edema.

Adolescent↗

PubMed1984

Increased metabolism contributes to increased resting ventilation at high altitude.

Ventilatory acclimation to high altitude results in an increase in total or minute ventilation, and is associated with a fall in alveolar PCO2, i.e. alveolar hyperventilation. However, the extent to which the increase in total ventilation is matched by a greater metabolic rate (VO2, VCO2) vs alveolar hyperventilation is unclear. We sought to determine the contribution of changes in metabolic rate to the increase in minute ventilation observed during exposure to high altitude. In 12 healthy male subjects taken from Denver, Colorado (1600 m) to Pikes Peak, Colorado (4300 m) for 5 days, resting minute ventilation increased from low to high altitude (+ 26% for the 5 days) and arterialized PCO2 fell. Resting metabolic rate increased 16% for the 5 days and could account for more than half of the increase in minute ventilation. Among subjects the increases in ventilation on days 1, 2 and 4 were positively correlated with increased CO2 production; they were not correlated with arterial oxygen saturation on any day. During exercise at high altitude, PCO2 values were not different from those at rest and minute ventilation rose above low altitude values (+ 58% by day 5), but the increase could not be accounted for by an increased CO2 production. Thus at rest but not during exercise a substantial portion of the rise in minute ventilation could be attributed to increased metabolic rate.

Acclimatization↗

PubMed1991

Acclimatization to hypoxia modulates the tryptophan 2,3-dioxygenase activity in rats exposed to simulated high altitude.

1. Exposure of rats to an 8000 m altitude increased the hepatic tryptophan 2,3-dioxygenase (EC 1.13.1.12) activity. 2. Acclimatization to hypoxia by a repeated exposure to an altitude of 5000 m induced a marked decrease in liver tryptophan dioxygenase activity after the rats were subjected to an 8000 m altitude, but a pre-exposure to 4000 m altitude showed no effect on the enzyme activity. 3. Plasma tryptophan was rapidly decreased by exposure to 8000 m altitude to the same extent in the acclimatized and non-acclimatized rats. 4. Plasma tryptophan may be utilized as the substrate for tryptophan dioxygenase in liver of the non-acclimatized rats under highly hypoxic conditions; however, acclimatized rats can reserve tryptophan as the substrate for the alternative metabolism other than the degradation pathway in liver.

Acclimatization↗

PubMed1995

Ice-based altitude distribution of natural radiation annual exposure rate in the Antarctica zone over the latitude range 69 degrees S-77 degrees S using a pair-filter thermoluminescence method.

Both ice-based altitude distributions of natural ionizing radiation exposure and the quasi-effective energy of natural radiation over Antartica over the latitude range 69 degrees S - 77 degrees S during approx. 500 days were measured using thermoluminescent dosimeters. The results shows that dependence on altitude above sea level of the exposure rate increases by almost three-fold with each increase of 2000 m of altitude, thus deviating from the general rule stating that the exposure rate should double with each 2000 m. Although the exposure rate shows a dependence on altitude, altitude dependence of the quasi-effective energy of natural radiation over Antartica is not observed. In the present study it is observed that natural radiation occurring over the ice base of Antartica consists mainly of cosmic rays.

Altitude↗

PubMed2004

High altitude training of dogs results in elevated erythropoietin and endothelin-1 serum levels.

Living at 2300-m altitude combined with intermittent training at 3500 m leads to cardiovascular alterations in dogs, including increase in systemic and pulmonary artery pressure. Despite moderate to marked hypoxemia at these altitudes, erythrocytosis does not develop. To study humoral mechanisms of acclimatisation to high altitude, erythropoietin (EPO), endothelin-1 (ET-1), big endothelin (Big-ET) and vascular endothelial growth factor (VEGF) were measured in dogs living at 2300 m and intermittently ascending to 3500 m, and compared to the values obtained in control dogs living at 700-900 m. While the median EPO and ET-1 level in dogs at 2300 m did not differ from the one measured at 700-900 m, exposure from 2300 to 3500 m resulted in significantly elevated EPO and ET-1 levels. Big-ET levels were significantly higher at 2300 and 3500 m compared to dogs at low altitude, but did not differ between 2300 and 3500 m. VEGF was significantly elevated in dogs at 2300 m compared to dogs at low altitude. The increases in EPO, VEGF, ET-1 and Big-ET are thought to reflect the effect of hypoxia on a cellular level in these dogs. Obviously, the mild elevation of EPO levels observed at 3500 m was not sufficient to cause erythrocytosis. Elevations of the vasoconstrictors Big-ET and ET-1 may play some, but not a central role in hypoxic vasoconstriction in these dogs. Finally, serum VEGF measurement may be a sensitive and useful test to assess hypoxic stress in dogs.

Acclimatization↗