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PubMed2006

Urine acid-base compensation at simulated moderate altitude.

Acute exposure to high altitude elicits respiratory alkalosis, and this is partially corrected by renal compensation. To determine the time course and magnitude of renal compensation during short-term moderate altitude exposure, we measured urine gas tensions and acid-base status in 48 healthy men and women at four levels of simulated altitude exposures. Each subject was exposed in pseudorandom order to simulated altitudes of 1780, 2085, 2455, and 2800 m in a decompression chamber for 24 h, separated by 1 week at sea level. Fresh urine was collected anaerobically at sea level and after 6 and 24 h of each altitude exposure. Urine pH increased significantly (p < 0.01) after 6 h at all altitudes and returned to baseline values by 24 h at the lowest altitudes. In contrast, urine pH remained elevated at the highest altitudes. The mean value of urine HCO at sea level was 1.67 +/- 0.25 mmol/L, increased significantly after 6 h at all altitudes, and then returned to near baseline after 24 h at three lower altitudes (1780, 2085, and 2455 m). However, it remained elevated at 2800 m. PCO2 in urine was significantly increased after 6 h and returned to baseline after 24 h at all altitudes. These results suggest that (1) short-term low to moderate altitude exposure results in a marked HCO diuresis, which may be caused by inhibition of the secretion of renal tubular H+, and (2) renal HCO compensation was completed by 24 h at low to moderate altitude, but still incomplete at higher altitude.

Acid-Base Equilibrium↗
PubMedDate not supplied

Lung function of Han Chinese born and raised near sea level and at high altitude in Western China.

Forced vital capacity (FVC), forced expiratory volume at 1 second (FEV(1)), and FEV(1)/FVC ratios were determined for 531 individuals of Han Chinese descent living at low altitude (250 m) near Beijing and for 592 individuals of Han descent who were born and raised at three high altitudes (3,200 m, 3,800 m, 4,300 m) in Qinghai Province, P.R.C. The study included males and females, ages 6-51 years. Thorax widths, depths, and circumferences of Han females and males born and raised at high altitude are similar to those of low-altitude Han. On the other hand, high-altitude children and adolescents have larger relative sitting heights, indicating greater thorax lengths. After adjusting for this variation in morphology, mean FVC values among 6-21 year-old Han at high altitude are only between 136 mL (for females) and 173 ml (for males) greater than those determined at low altitude but the differences are statistically significant and are maintained consistently throughout the growth period. These data indicate that growth at high altitude produces small-to-moderate increases in lung volumes (about 6%) relative to genetically similar groups growing up at low altitude. In addition, there is no evidence that lung volume growth is accelerated relative to morphological growth among Han children born and raised at high altitude. Adults, 22-51 years, also show greater FVC values at high altitude but the size of the increase relative to Han at low altitude is variable (3% in males and 11% in females). Greater lung function at high altitude is unlikely to result from increased activity or lower pollution, and thus appears to be primarily a result of development in a hypoxic environment. Differences in FVC and FEV(1) at 3,200 m, 3,800 m, and 4,300 m are generally not significant, so that living at altitudes between 3,200 m and 4,300 m appears to have little additional effect on volumetric growth.

Adolescent↗
PubMed1992

High-altitude training. Aspects of haematological adaptation.

Physical training at high altitude improves performance at high altitude. However, studies assessing performance improvements at sea level after training at higher altitudes have produced ambiguous and inconclusive results. Hypoxia-induced secondary polycythemia is a major contributor to increased work capacity at altitude. The common finding upon exposure to hypoxia is a transient increase in haemoglobin concentration and haematocrit because of a rapid decrease in plasma volume followed by an increase in erythropoiesis per se. Both nonathletes and elite endurance athletes have maximal reticulocytosis after about 8 to 10 days at moderate altitude. Training periods of 3 weeks at moderate altitudes result in individual increase of haemoglobin concentration of about 1 to 4%. A more accentuated increase in haemoglobin can be obtained with longer sojourns at moderate altitude. The normal erythropoietin reaction upon exposure to hypoxia comprises initially increased levels followed by a decrease after about 1 week. Thus, the maintenance of a high erythropoietin concentration is not a prerequisite for a sustained increase in erythrocyte formation at high altitude. The main pharmacological modulator of erythropoietin production seems to be adenosine. But modulators such as growth hormone and catecholamines may also potentiate the effect of hypoxia per se on erythropoietin production. On the other hand, there is a risk that the stress hormones may induce a relative depression of the bone marrow particularly in the early phase of altitude training when the adaptation is minimal and the stress reaction is most accentuated. The most important 'erythropoiesis-specific' nutrition factor is iron availability which can modulate erythropoiesis over a wide range in humans. Adequate iron stores are a necessity for haematological adaptation to hypoxia. However, at moderate altitude, there is a need for rapid mobilisation of iron and even if the stores are normal there is a risk that they cannot be mobilised fast enough for an optimal synthesis of haemoglobin. Data from healthy athletes training at moderate altitudes suggest a true increase in haemoglobin concentration of about 1% per week. Complete haematological adaptation occurred when sea level residents have similar haemoglobin concentrations at moderate altitude compared with residents. The normal difference in haemoglobin concentrations can be estimated to be about 12% between permanent residents at sea level and at 2500m above sea level. This difference indicates a necessary adaptation time of about 12 weeks. If the training period at moderate altitude must be shorter, several sojourns at short intervals are recommended. The important factor in haematological adaptation in athletes at moderate altitude is hypoxia.(ABSTRACT TRUNCATED AT 400 WORDS)

Acclimatization↗
PubMed2000

Interaction of chemical defense clothing and high terrestrial altitudes on lift/carry and marksmanship performance.

BACKGROUND: The increased metabolic energy requirement imposed by a chemical defense uniform (CDU) and the lower maximal aerobic capacity associated with increased altitude should produce greater demands on the cardiopulmonary system during the performance of a given work task at increasing altitudes. We hypothesized that: a) relative to sea level, the decrements in physical work performance caused by ascending to high terrestrial altitudes would be greater in a CDU compared with a standard fatigue uniform (U.S. Army, BDU); b) the aversive subjective reactions to the CDU would be accentuated with increasing altitude; and c) that staging at moderate altitude, to induce acclimatization, would restore work performance at higher altitudes to sea level norms. METHODS: The physiological and subjective responses of 8 male soldiers to work (10-min lift-and-carry task and rifle marksmanship) were measured. Subjects wore the BDU and a CDU ensemble (U.S. Army, BDO) at sea level, intermediate (2743 m) and high (4,300 m) altitudes following rapid and staged (3 d at 1,830 m) ascents to the higher altitudes. RESULTS: Lift/carry task performance tended to be lower (p = 0.076) in the CDU vs. the BDU at altitude. The cardiopulmonary responses to the lift/carry task increased at altitude and were greater in the CDU. The subjects' perception of their ability to perform the lift/carry task at altitude was adversely impacted more in the CDU than the BDU. Rapid ascent to intermediate altitude degraded marksmanship in both uniforms. Following staged ascent, lift/carry task and marksmanship performance was restored to sea level norms. CONCLUSIONS: Personnel wearing CDU or equivalent protective clothing at intermediate to high terrestrial elevations should anticipate proportionally larger CDU-induced decrements of work performance and lower tolerance to working in a CDU than experienced near sea level. Staging at moderate altitude is an effective strategy for restoring work performance to sea level norms at higher altitudes.

Activities of Daily Living↗
PubMed1987

Altitude-aggravated illness: examples from pregnancy and prenatal life.

Nearly 40 million persons worldwide live permanently at elevation above 8,000 ft (2,439 m) and perhaps as great a number visit high-altitude regions annually. Health effects include the well-recognized altitude-specific syndromes of acute mountain sickness and high-altitude pulmonary edema. Emphasis is placed in this article on altitude-aggravated illness or those preexisting conditions that may be adversely affected by reduced O2 availability at high altitude. Examples from studies of pregnant women and their infants at high altitude are reviewed to demonstrate the effect of high altitude on maternal and fetal well-being. Increased maternal ventilation and ventilatory response to hypoxia during pregnancy at 10,200 ft (3,110 m) and 14,200 ft (4,329 m) raised arterial O2 saturation, helped to preserve arterial O2 content at levels present when nonpregnant, and correlated positively with the offspring's birth weight. Fetal growth retardation and an increased incidence of the complications of pre-eclampsia and neonatal hyperbilirubinemia at high altitude suggested that altitude may aggravate complications of pregnancy and prenatal life. Other conditions that may be aggravated at high altitude are reviewed. Virtually all studies on altitude-aggravated illness have been conducted on permanent residents. Future studies should seek to determine whether high altitude aggravates pre-existing conditions among the large and growing number of high-altitude visitors.

Adaptation, Physiological↗
PubMed2001

[Mountaineering and altitude sickness].

Almost every second trekker or climber develops two to three symptoms of the high altitude illness after a rapid ascent (> 300 m/day) to an altitude above 4000 m. We distinguish two forms of high altitude illness, a cerebral form called acute mountain sickness and a pulmonary form called high altitude pulmonary edema. Essentially, acute mountain sickness is self-limiting and benign. Its symptoms are mild to moderate headache, loss of appetite, nausea, dizziness and insomnia. Nausea rarely progresses to vomiting, but if it does, this may anticipate a progression of the disease into the severe form of acute mountain sickness, called high altitude cerebral edema. Symptoms and signs of high altitude cerebral edema are severe headache, which is not relieved by acetaminophen, loss of movement coordination, ataxia and mental deterioration ending in coma. The mechanisms leading to acute mountain sickness are not very well understood; the loss of cerebral autoregulation and a vasogenic type of cerebral edema are being discussed. High altitude pulmonary edema presents in roughly twenty percent of the cases with mild symptoms of acute mountain sickness or even without any symptoms at all. Symptoms associated with high altitude pulmonary edema are incapacitating fatigue, chest tightness, dyspnoe at the minimal effort that advances to dyspnoe at rest and orthopnoe, and a dry non-productive cough that progresses to cough with pink frothy sputum due to hemoptysis. The hallmark of high altitude pulmonary edema is an exaggerated hypoxic pulmonary vasoconstriction. Successful prophylaxis and treatment of high altitude pulmonary edema using nifedipine, a pulmonary vasodilator, indicates that pulmonary hypertension is crucial for the development of high altitude pulmonary edema. The primary treatment of high altitude illness consists in improving hypoxemia and acclimatization. For prophylaxis a slow ascent at a rate of 300 m/day is recommended, if symptoms persist, acetazolamide at a dose of 500 mg/day is effective. Mild acute mountain sickness may also be treated with the same dose acetazolamide. Glucocorticoids are the first line treatment of the malignant form of acute mountain sickness. Nifedipine is effective only for the prophylaxis and treatment of high altitude pulmonary edema.

Acetazolamide↗
PubMed1998

Cardiovascular autonomic modulation and activity of carotid baroreceptors at altitude.

1. To assess the effects of acute exposure to high altitude on baroreceptor function in man we evaluated the effects of baroreceptor activation on R-R interval and blood pressure control at high altitude. We measured the low-frequency (LF) and high-frequency (HF) components in R-R, non-invasive blood pressure and skin blood flow, and the effect of baroreceptor modulation by 0. 1-Hz sinusoidal neck suction. Ten healthy sea-level natives and three high-altitude native, long-term sea-level residents were evaluated at sea level, upon arrival at 4970 m and 1 week later.2. Compared with sea level, acute high altitude decreased R-R and increased blood pressure in all subjects [sea-level natives: R-R from 1002+/-45 to 775+/-57 ms, systolic blood pressure from 130+/-3 to 150+/-8 mmHg; high-altitude natives: R-R from 809+/-116 to 749+/-47 ms, systolic blood pressure from 110+/-12 to 125+/-11 mmHg (P<0.05 for all)]. One week later systolic blood pressure was similar to values at sea level in all subjects, whereas R-R remained elevated in sea-level natives. The low-frequency power in R-R and systolic blood pressure increased in sea-level natives [R-R-LF from 47+/-8 to 65+/-10% (P<0.05), systolic blood pressure-LF from 1.7+/-0. 3 to 2.6+/-0.4 ln-mmHg2 (P<0.05)], but not in high-altitude natives (R-R-LF from 32+/-13 to 38+/-19%, systolic blood pressure-LF from 1. 9+/-0.5 to 1.7+/-0.8 ln-mmHg2). The R-R-HF decreased in sea-level natives but not in high-altitude natives, and no changes occurred in systolic blood pressure-HF. These changes remained evident 1 week later. Skin blood flow variability and its spectral components decreased markedly at high altitude in sea-level natives but showed no changes in high-altitude natives. Neck suction significantly increased the R-R- and systolic blood pressure-LF in all subjects at both sea level and high altitude.3. High altitude induces sympathetic activation in sea-level natives which is partially counteracted by active baroreflex. Despite long-term acclimatization at sea level, high-altitude natives also maintain active baroreflex at high altitude but with lower sympathetic activation, indicating a persisting high-altitude adaptation which may be genetic or due to baroreflex activity not completely lost by at least 1 year's sea-level residence.

Adult↗
PubMed1997

Pituitary, gonadal and adrenal hormones after prolonged residence at extreme altitude in man.

High altitude-induced alterations in pituitary, gonadal and adrenal hormones were studied in (i) eugonadal men from the armed forces who were resident at sea level (SL), (ii) SL residents staying at an altitude of 3542 m for periods ranging from 3 to 12 months (acclimatized lowlanders, ALL), (iii) ALL who stayed at 6300 m for 6 months, (iv) ALL who trekked from 3542 to 5080 m and stayed at an altitude of more than 6300 m in the glacier region for 6 months, and (v) high-altitude natives (HAN) resident at an altitude of 3300-3700 m. Circulating levels of LH, FSH, prolactin, cortisol, testosterone, dihydrotestosterone (DHT) and progesterone in ALL at 3542 m and in HAN were not significantly different (p > 0.05) from the SL control values. When the ALL living at 3542 m trekked to an extreme altitude of 5080 m, their testosterone levels showed a significant decrease (p < 0.01) compared to the preceding altitude values but had returned to SL values when measured after 6 months' continuous stay at 6300 m. As with testosterone, the levels of DHT and oestradiol-17 beta (E2) after prolonged stay at extreme altitude were also not significantly different (p > 0.05) from the SL values. The LH levels after trekking to 5080 m were significantly higher (p < 0.01) than at an altitude of 3542 m, but decreased to levels found at 3542 m or SL after prolonged residence at extreme altitude. Plasma levels of ACTH, prolactin, FSH and cortisol on arrival at 5080 m, and after a 6-month stay at extreme altitude, were not significantly different (p > 0.05) from the SL values. Plasma progesterone levels tended to increase on arrival at 5080 m but a significant increase (p < 0.001) was evident only after a 6-month stay at extreme altitude. These observations suggest that prolonged residence at lower as well as at extreme altitude does not appreciably alter blood levels of pituitary, gonadal or adrenal hormones except for plasma levels of progesterone. The exact mechanism and significance of this increase remains unknown, but may be important in increasing the sensitivity of the hypoxic ventilatory response and activation of haemoglobin synthesis.

Acclimatization↗
PubMed1998

Individual variation in response to altitude training.

Moderate-altitude living (2,500 m), combined with low-altitude training (1,250 m) (i.e., live high-train low), results in a significantly greater improvement in maximal O2 uptake (V(02)max) and performance over equivalent sea-level training. Although the mean improvement in group response with this "high-low" training model is clear, the individual response displays a wide variability. To determine the factors that contribute to this variability, 39 collegiate runners (27 men, 12 women) were retrospectively divided into responders (n = 17) and nonresponders (n = 15) to altitude training on the basis of the change in sea-level 5,000-m run time determined before and after 28 days of living at moderate altitude and training at either low or moderate altitude. In addition, 22 elite runners were examined prospectively to confirm the significance of these factors in a separate population. In the retrospective analysis, responders displayed a significantly larger increase in erythropoietin (Epo) concentration after 30 h at altitude compared with nonresponders. After 14 days at altitude, Epo was still elevated in responders but was not significantly different from sea-level values in nonresponders. The Epo response led to a significant increase in total red cell volume and V(O2) max in responders; in contrast, nonresponders did not show a difference in total red cell volume or V(O2)max after altitude training. Nonresponders demonstrated a significant slowing of interval-training velocity at altitude and thus achieved a smaller O2 consumption during those intervals, compared with responders. The acute increases in Epo and V(O2)max were significantly higher in the prospective cohort of responders, compared with nonresponders, to altitude training. In conclusion, after a 28-day altitude training camp, a significant improvement in 5,000-m run performance is, in part, dependent on 1) living at a high enough altitude to achieve a large acute increase in Epo, sufficient to increase the total red cell volume and V(O2)max, and 2) training at a low enough altitude to maintain interval training velocity and O2 flux near sea-level values.

Acclimatization↗
PubMedDate not supplied

[Hormonal variation during physical exertion at high altitude].

The influence of the physical exercise at high altitude on the endocrine function was studied in 8 normal native men of sea level and in 8 natives men of high altitude. The sea level dwellers were studied both, at sea level, during an acute exposure to low barometric pressure and after 3 months of acclimatization to altitudes over 3,500 meters above the sea level. The experiments at high altitude were conducted at an altitude of 4,500 meters above the sea level. Two types of exercise were carried out, sub-maximal and maximal, at fasting state, between 8 and 10 a.m. During an acute exposure to altitude the physical exercise produced a marked rise of glucose, cortisol and growth hormone and a fall in the insulin content of plasma. In the sea level dwellers, acclimatized to altitude during 3 months, an elevation of growth hormone was observed only during maximal physical effort. Marked variation in glucose and cortisol were observed during both types of exercise. This shows that in these subjects some adaptative changes have ocurred but of lesser extent as those observed in altitude natives. In the high altitude native higher basal concentrations of growth hormone and glucagón as well as a lower glucose concentration in blood, were found. During exercise the high altitude dweller showed no significant changes in somatotropin, meanwhile an important elevation of cortisol occurred. These findings indicate that the high altitude native has metabolic and endocrine responses to exercise similar to those found in well fitted atletes of sea level. The exposure to altitude provoked a rise in glucagon concentration directly proportional to the time of exposition ot altitude. The physical exercise did not elucidate any change in the glucagon content of blood.

Adult↗
PubMed1996

Pharmacokinetics of meperidine in healthy volunteers after short- and long-term exposure to high altitude.

Increased numbers of erythrocytes have been shown ex vivo to increase meperidine uptake, and one of the major physiologic changes that occurs at high altitude is an increase in hematocrit and erythrocytes. A study was therefore conducted to evaluate the effects of high altitude on the pharmacokinetics of meperidine. Intramuscular doses (0.75 mg/kg) of meperidine were given to three groups of healthy volunteers (age range, 18-20 years): participants living at sea level (group L), those same participants the day after arrival at high altitude (4,360 m; group HA), and participants who had lived at high altitude for > or = 10 months (group HC). Blood samples were collected for 12 hours after drug administration. Meperidine was measured in whole blood, plasma, and plasma water. Elimination rate constant (lambda z) and clearance uncorrected for bioavailability (Cl/F) were significantly lower at high altitudes than at sea level in plasma (HA and HC) and in whole blood (HA only). Mean residence time (MRT) was significantly higher at high altitudes than at sea level in plasma (HA and HC) and in whole blood (HA only). Hematocrit was significantly increased at both time points at high altitude in comparison to values at sea level, and was also higher after a long-term stay at high altitude than after arrival at high altitude. Erythrocyte binding increased significantly from 41.3% at sea level to 43.8% at arrival at high altitude to 50.9% after a long-term stay at high altitude. The extent of protein binding tended to decrease with high altitude, but this decrease was not significant. Free concentrations of meperidine in plasma water measured 1, 2, and 4 hours after administration were significantly increased after 2 and 4 hours.

Adolescent↗
PubMed2006

Adventures in high-altitude physiology.

I have probably had more fun doing high-altitude physiology than most people. Some 45 years ago I applied to be a member of Sir Edmund Hillary's Silver Hut expedition and was accepted in spite of having no previous climbing experience. On this project a group of physiologists wintered at an altitude of 5800 m just south of Everest and carried out an extensive research program. Subsequently measurements were extended up to an altitude of 7440 m on Makalu. In fact the altitude of these field measurements of VO(2max) has never been exceeded. This led to a long interest in high-altitude medicine and physiology which culminated in the 1981 American Medical Research Expedition to Everest during which 5 people reached the summit and the first physiological measurements on the summit were made. Among the extraordinary findings were an extremely low alveolar PCO2 of 7-8 mmHg, an arterial pH (from the measured PCO2 and blood base excess) of over 7.7, and a VO(2max) of just over one liter/min. More recently a major interest has been the pathogenesis of high altitude pulmonary edema which we believe is caused by damage to pulmonary capillaries when the pressure inside some of them increases as a result of uneven hypoxic pulmonary vasoconstriction ("stress failure"). Another interest is improving the conditions of people who need to work at high altitude by oxygen enrichment of room air. This enhances well-being and productivity, and is now being used or planned for several high-altitude telescopes up to altitudes of 5600 m. Other recent high-altitude projects include establishing an international archive on high-altitude medicine and physiology at UCSD, several books in the area including the historical study High Life, and editing the journal High Altitude Medicine & Biology.

Altitude↗
PubMed2002

Work at high altitude and oxidative stress: antioxidant nutrients.

A significant portion of the world's geography lies above 10,000 feet elevation, an arbitrary designation that separates moderate and high altitude. Although the number of indigenous people living at these elevations is relatively small, many people travel to high altitude for work or recreation, exposing themselves to chronic or intermittent hypoxia and the associated risk of acute mountain sickness (AMS) and less frequently, high altitude pulmonary edema (HAPE) and high altitude cerebral edema (HACE). The symptoms of AMS (headache, nausea, anorexia, fatigue, lassitude) occur in those who travel too high, too fast. Some investigators have linked the development of these symptoms with the condition of altered blood-brain barrier permeability, possibly related to hypoxia induced free radical formation. The burden of oxidative stress increases during the time spent at altitude and may even persist for some time upon return to sea level. The physiological and medical consequences of increased oxidative stress engendered by altitude is unclear; indeed, hypoxia is believed to be the trigger for the cascade of signaling events that ultimately leads to adaptation to altitude. These signaling events include the generation of reactive oxygen species (ROS) that may elicit important adaptive responses. If produced in excess, however, these ROS may contribute to impaired muscle function and reduced capillary perfusion at altitude or may even play a role in precipitating more serious neurological and pulmonary crisis. Oxidative stress can be observed at altitude without strenuous physical exertion; however, environmental factors other than hypoxia, such as exercise, UV light exposure and cold exposure, can also contribute to the burden. Providing antioxidant nutrients via the diet or supplements to the diet can reduce oxidative stress secondary to altitude exposure. In summary, the significant unanswered question concerning altitude exposure and antioxidant supplementation is when does oxidative stress become potentially damaging enough to merit antioxidant therapy and conversely, what degree of oxidative stress is necessary to foster the adaptive response of altitude exposure?

Adaptation, Physiological↗
PubMed2005

Awareness of altitude sickness among a sample of trekkers in Nepal.

OBJECTIVE: To quantify awareness of altitude sickness in a sample of trekkers in Nepal and identify strategies for increasing knowledge in that population. METHODS: Sixty-five high-altitude trekkers were surveyed. Demographic data were gathered. Respondents were asked about their experience in high-altitude environments, and they answered clinical-vignette questions designed to test their abilities to recognize and identify treatments for common symptoms of altitude sickness. An altitude-awareness score was generated by tabulating correct answers to questions. Scores were correlated with demographic data. RESULTS: Respondents who scored highest (n = 8) had significantly more experience in high-altitude environments, averaging 5 to 10 years (P < .05), and achieved higher average altitudes on their treks of 5171 m (P < .05) than did low scorers. Respondents with low scores (n = 17) trekked to an average altitude of 4138 m. Seventy-three percent wanted to learn more about altitude sickness, 30% said they would prefer to learn from the Internet, and 27% said they would ask a doctor. CONCLUSION: This study suggests that a large population of at-risk high-altitude travelers may be relatively naive to the dangers of altitude sickness. Overall, respondents were interested in learning more about altitude sickness. Physicians and the Internet are the most attractive sources of information for this population.

Adult↗
PubMedDate not supplied

Birth weight among Tibetans at different altitudes in India: are Tibetans better protected from IUGR?

We report the variation in birth weight among the Tibetans at different altitudes in India to test the hypothesis of greater protection from intrauterine growth retardation (IUGR) among Tibetan compared with other high-altitude native populations. We found that the birth weight of Tibetans at Leh (3521 m, high altitude) is quite similar to what has been reported previously for Tibetans at similar altitudes and is significantly higher than the low-altitude native populations living at similar altitudes. Tibetan birth weights are greater than those of other ethnic groups, both at high and low altitudes. Compared with Tibetans at high altitude (Leh, India; 3521 m), Tibetans at low altitudes (Bylakuppe, India; 800 m and Chandragiri, India; 970 m) have heavier birth weights. This finding is similar to what has been observed previously for other high-altitude native populations. Greater protection from IUGR is not observed for Tibetans compared with other high-altitude native populations as was reported previously. Genetic potential for birth weight is seemingly manifested only at low altitude.

Adaptation, Physiological↗
PubMed1985

Effects of ambient temperature and altitude on ventilation and gas exchange in deer mice (Peromyscus maniculatus).

The effects of different ambient temperatures (Ta) on gas exchange and ventilation in deer mice (Peromyscus maniculatus) were determined after acclimation to low and high altitude (340 and 3,800 m). At both low and high altitude, oxygen consumption (VO2) decreased with increasing Ta at Ta from -10 to 30 degrees C. The VO2 was 15-20% smaller at high altitude than at low altitude at Ta below 30 degrees C. Increased VO2 at Ta below thermoneutrality was supported by increased minute volume (VI) at both low and high altitude. At most Ta, the change in VI was primarily a function of changing respiration frequency (f); relatively little change occurred in tidal volume (VT) or oxygen extraction efficiency (O2EE). At Ta = 0 degree C and below at high altitude, VI was constant due to declining VT and O2EE increased in order to maintain high VO2. At high altitude, VI (BTP) was 30-40% higher at a given Ta than at low altitude, except at Ta below 10 degrees C. The increased VI at high altitude was due primarily to a proportional increase in f, which attained mean values of 450-500 breaths/min at Ta below 0 degree C. The VI (STP) was equivalent at high and low altitude at Ta of 10 degrees C and above. At lower Ta, VI (STPD) was larger at low altitude. At both altitudes, respiratory heat loss was a small fraction (less than 10%) of metabolic heat production, except at high Ta (20-30 degrees C).

Acclimatization↗
PubMed1996

Effects of altitude above sea level on the cooking time and nutritional value of common beans.

The present study was conducted with the objective to determine the effects of altitude above sea level, on the cooking time and nutritional value of common black beans (Phaseolus vulgaris). Three 100 g samples of the Ostua variety were cooked at 8 individual locations, ranging in altitude from 0 to 2256 meters, in Guatemala, to establish water uptake and cooking time. The cooked samples were separated into cooked beans and cooking broth for chemical analysis. This included moisture, protein, lysine, tannins, total and enzyme susceptible starch, and fiber fractionation. The cooking liquor was analyzed for total solids, moisture, protein, ash and K. A 1200 g sample was cooked for the cooking time established previously, for biological testing of nutritional value, which included Net Protein Ratio (NPR), Protein Efficiency Ratio (PER), and protein digestibility. Altitude influenced cooking time which increased from 78 min at 0 m, to 264 min at 2256 m. Final moisture content in the cooked bean was similar at all altitudes and there was a tendency to yield smaller amounts of solids in the cooking broth at higher altitudes. The increase in cooking time was significant. Bean water uptake at all times was significantly slower and smaller at ambient as compared to water uptake at boiling T, at all altitudes. Protein and lysine content were not affected by altitude, however, tannin and catechin were lower in cooked samples, as compared to the raw material. Altitude did not affect the content of these substances. Total starch and total sugars were higher in the raw sample, as compared to the cooked samples, but there was no effect of altitude. Enzyme susceptible starch (ESS) was lower in the raw sample as compared to the cooked samples, which contained similar amounts with respect to altitude. No change was observed in fiber fractions of the cooked beans. Likewise, the composition of the cooking broth was very similar between cooking locations. There was a small tendency to a lower protein quality, with respect to altitude, the effect of which was more obvious in the apparent protein digestibility values. Undercooking or overcooking at one location influenced protein quality values. The extended cooking time of beans at high altitudes, has important economic and environmental implications, since significant amounts of wood have to be used.

Altitude↗
PubMed1995

A comparison of cardiopulmonary adaptations to exercise in pregnancy at sea level and altitude.

OBJECTIVE: The purpose of this study was to compare maternal cardiopulmonary and fetal responses of lowlander pregnant women in the third trimester to exercise at sea level and at an altitude of 6000 feet. STUDY DESIGN: Seven women at 33.86 +/- 1 weeks' gestation performed a symptom-limited maximal exercise test and a submaximal cardiac output exercise test at sea level at an altitude of 6000 feet. Cardiopulmonary and metabolic variables were measured and compared at sea level and altitude. RESULTS: Maximal oxygen consumption and work levels were limited by short-term altitude exposure. Ventilatory variables were not significantly influenced by altitude exposure. During submaximal exercise no alteration in exercise efficiency or response was seen for most of the variables when altitude and sea level data were compared. Both cardiac output and stroke volume were elevated at altitude at rest but not during exercise, suggesting a lower reserve for both variables at altitude. Level of plasma glucose, lactate, norepinephrine, and epinephrine were not significantly influenced by altitude exposure. Fetal heart rate responses did not differ between the sea level and altitude conditions. CONDITIONS: Lowlander pregnant women in the third trimester have some limitations to maximal aerobic capacity but not submaximal exercise on short-term altitude exposure. No ominous fetal responses have been observed during this study. The results suggest that pregnant women may engage in at least brief moderate exercise bouts at moderate altitude without adverse consequences.

Adaptation, Physiological↗