Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Altitude”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 199 records · Page 11Linked to original sources
PubMed2026

High-altitude hypoxia alters the visual control of standing balance in lowlanders and Tibetan highlanders.

High-altitude hypoxia affects both visual function and postural control, yet the influence of optic-flow perturbations on standing balance under hypoxic stress remains unclear. Tibetan highlanders (TH) exhibit adaptations to chronic hypoxia, but whether their visually driven postural responses differ from those of lowlanders (LL) has not been investigated. We examined how high-altitude exposure and acclimatization influence static and dynamic visual contributions to balance by delivering sinusoidal optic-flow perturbations in virtual reality at low altitude (1,400 m) and after incremental ascent to high altitude (4,300 m) in acclimatizing LL (n = 15) and TH (n = 14). Anteroposterior center of pressure (AP CoP) velocity and mean power frequency (MPF) were measured during three visual-field conditions (full-, central-, and peripheral-vision) and two optic-flow velocities (peak 1 m/s and 8 m/s at 0.25 Hz). At high altitude, both groups showed attenuated responses to optic flow compared with 1,400 m, reflected by reduced AP CoP velocity and lower MPF across visual-field conditions, consistent with reduced responsiveness to dynamic visual-motion cues under high altitude hypoxia. In contrast, during eyes-open quiet stance [no virtual reality (VR)], TH but not LL exhibited increased AP CoP velocity and MPF at 4,300 m, and no altitude effect was observed with eyes-closed in either group. This finding indicates that TH adopt a visually dependent postural strategy at altitude, whereas LL show minimal changes in static visual balance control but reduced responsiveness to fast dynamic motion. Together, these findings demonstrate that high-altitude hypoxia disrupts dynamic visual processing for balance control in both groups, while revealing group differences in the use of static visual cues during quiet stance.NEW & NOTEWORTHY This is the first study to investigate how high-altitude hypoxia alters visually driven postural control using virtual reality (VR) optic-flow perturbations. We show that hypoxia attenuates sway responses to optic-flow in both lowlanders and Tibetan highlanders, and that visual weighting differs between these groups. These findings reveal altitude- and population-related changes in sensory weighting during standing balance, advancing sensorimotor understanding of postural control in hypoxia.

Humans↗
PubMed1997

Pulmonary ventilatory function decreases in proportion to increasing altitude.

The objective of this study was to examine how pulmonary ventilatory function, including response to bronchodilation, is related to altitude during high-altitude trekking. This cohort experiment consisted of multiple spirometric tests before and after bronchodilation in participants at baseline (1624 m) and at different altitudes (3404-4896 m) during a 2-week trek. The setting was in the Himalayas. Eleven men (ages 22-68 years) and eight women (ages 19-42 years) participated. Interventions were at altitudes of 1624 m to 5265 m; albuterol was administered via Rotahaler. Forced vital capacity (FVC) decreased by an average of 3.8% [95% confidence interval (CI) 1.6 to 6.0] per 1000-m altitude increment. Forced expiratory volume in 1 second (FEV1.0) decreased 3.7% (95% CI 1.9 to 5.5) per each 1000-m altitude increment. Maximal midexpiratory flow rate (FEF25-75%) decreased by 3.6% (95% CI 0.9 to 6.3) per each 1000-m altitude increment. Small, postalbuterol flow increases were present at baseline and at altitude. Ventilatory function returned quickly toward baseline upon descent. One trekker developed cough, dyspnea at rest, extreme weakness, rales, tachycardia, and oxygen desaturation to 71%. His ventilatory measurements did not differ significantly (p > 0.32) from the group means. We concluded that changes in some pulmonary ventilatory parameters (FVC, FEV1.0, and FEF25-75%) were proportional to the magnitude of altitude during a high-altitude trek. These were tolerated well and do not seem to relate to acute mountain sickness. A bronchodilator effect was not increased at altitude.

Adult↗
PubMed2004

To air is human: altitude illness during an expedition length adventure race.

OBJECTIVE: To calculate the incidence and prevalence of altitude illness (acute mountain sickness [AMS], high altitude pulmonary edema, and high altitude cerebral edema) during an expedition length adventure race and to determine factors contributing to its development as well as identify cases requiring medical treatment, withdrawal from the event, or both. METHODS: The Primal Quest Expedition Length Adventure Race was held in Colorado in July 2002. Sixty-two coed teams of four participated in the event. It began at an altitude of over 9500 feet, ascended to an altitude over 13,500 feet with a cumulative elevation gain of 69,400 feet, of which 40,000 feet occurred in the first 12 hours of the event. There was 138,800 total feet of altitude change during the event. All racers underwent a prerace medical assessment 24 hours before the start of the race and completed an Environmental Systems Questionnaire version 3-R (ESQ 3-R). Onsite medical staff provided treatment during the event. A standard medical encounter form was used to record all patient encounters including a presumed diagnosis and disposition. RESULTS: At the start of the race, the prevalence of altitude illness was 4.5%. The incidence of altitude illness requiring medical treatment during the race was 14.1% (AMS, 33 [13.3%]; high altitude pulmonary edema, 2 [.81%]) resulting in 4 (14.3%) of the 28 medical withdrawals from the race. There was no correlation between home altitude, prerace ESQ scores, and successful completion of the race. CONCLUSIONS: Altitude illness occurs among participants in expedition length adventure races and contributes significantly to withdrawal from the event.

Adult↗
PubMed2000

Correlation between raised body temperature and acute mountain sickness score at moderate altitude.

UNLABELLED: In high altitude mountaineering, a rise in body temperature has long been associated with acute mountain sickness. No data exist on the situation at moderate altitudes in the Austrian Alps. The objective of this study was to investigate a potential relationship between an increase in body temperature and acute mountain sickness (AMS) and hypoxemia at moderate altitude. Body temperature and arterial oxygen saturation (SaO2) were measured in 40 alpinists at 1000 m altitude and after ascent to 3100 m altitude, and the AMS score was measured at 3100 m altitude. At 3100 m altitude, 3 alpinists with AMS (score 3) experienced a 0.87 +/- 0.12 degree C rise in body temperature and a 10.67 +/- 1.15% reduction in SaO2. In 8 moderately affected alpinists, temperature increased by 0.49 +/- 0.16 degree C and SaO2 was reduced by 6.75 +/- 1.75%. In 29 alpinists without signs of AMS, temperature did not change (difference 0.02 +/- 0.14 degree C) and SaO2 decreased by 4.59 +/- 0.82%. The difference between temperatures at the two altitudes correlated significantly with the SaO2 difference between the two altitudes (rs = 0.408, p < 0.01) and with the AMS scores (rs = 0.814, p < 0.01). CONCLUSION: Comparable with maximal forms of AMS at high altitude, our data provide reason to speculate that systemic inflammatory disease could also be causal in less severe forms of acute mountain sickness. Therefore, in cases of fever at moderate altitude, the differential diagnosis must include acute mountain sickness.

Acute Disease↗
PubMed1982

The effect of high altitude on the growth of children of high socioeconomic status in Bolivia.

The physical growth of middle to upper class children of primarily European ancestry attending the private French School in L Paz, Bolivia is described and analyzed to determine how high altitude affects growth in this group of children. The sample consists of 323 children, most between the ages of 8 and 14, who reside at altitudes between 3200 and 3600 meters, but who have spent different amounts of time at high altitude. Comparisons between children who differ in their exposure to high altitude, and comparisons between French School children and other samples of high and low altitude children were used to assess the effect of high altitude on growth. Children who had lived all their lives at high altitude were found to be smaller in terms of general body size than those who had spent the shortest amount of time at high altitude, confirming the results of previous investigations of child growth in the Andes. Most studies of indigenous Andean populations have found that chest dimensions relative to stature increase with altitude, but it is not clear that this same trend exists in Bolivian French School children. Although exposure to high altitude does affect the growth of French School children, their height is essentially the same as that of Guatemalan children of high socioeconomic status. Within the age range studied, the effect of high altitude is small relative to that of other environmental factors and genetic factors, even in these children of high socioeconomic status.

Adolescent↗
PubMed1993

Protection from intrauterine growth retardation in Tibetans at high altitude.

Intrauterine growth retardation has long been recognized at high altitude. Since growth-retarded babies have a decreased chance of survival, intrauterine growth retardation would be expected to have been selected against in populations long resident at high altitude. We have previously reported that Tibetan babies born at 3,658 m weighed more than their North or South American altitude counterparts. This study sought to determine whether Tibetans were protected from altitude-associated intrauterine growth retardation. We compared birth weights in Tibetans living at low altitude in Kathmandu, Nepal (elevation 1,200 m), or at high altitude in Lhasa, Tibet Autonomous Region, China (elevation 3,658 m). Birth weights were similar in 45 low-altitude and 34 high-altitude Tibetan births regardless of whether all infants or only full-term births were considered, or whether birth weight was adjusted for variation in maternal parity, gestational age, and infant sex. In comparison with literature observations, the altitude-associated difference in birth weight was smallest in Tibetans, intermediate in South America, and greatest in North America. These data support the hypothesis that Tibetans are protected from altitude-associated intrauterine growth retardation and suggest that selection for optimization of birth weight at high altitude has occurred in Tibetans.

Adult↗
PubMed2001

The effects of altitude training are mediated primarily by acclimatization, rather than by hypoxic exercise.

For training at altitude to be effective, it must provide some advantage above and beyond similar training at sea level. This advantage could be provided by: 1) acclimatization to altitude which improves oxygen transport and/or utilization; 2) hypoxic exercise which "intensifies" the training stimulus; or 3) some combination of both. Controlled studies of "typical" altitude training, involving both altitude acclimatization and hypoxic exercise have never been shown to improve sea level performance. This failure has been attributed to reduced training loads at altitude. One approach developed by Levine and Stray-Gundersen, called "living high-training low" has been shown to improve sea level performance over events lasting 8-20 minutes. This strategy combines altitude acclimatization (2,500 m) with low altitude training to get the optimal effect. The opposite strategy, "living low-training high" is proposed by Dr. Hoppeler in this debate. In defense of the primacy of the altitude acclimatization effect, data will be presented to support the following: 1). Living high-training low clearly improves performance in athletes of all abilities; 2). The mechanism of this improvement is primarily an increase in erythropoietin leading to increased red cell mass, VO2max, and running performance; 3). Rather than intensifying the training stimulus, training at altitude leads to the opposite effect--reduced speeds, reduced power output, reduced oxygen flux--and, following the principal of symmorphosis, is not likely to provide any advantage for a well trained athlete; 4). At the moderate altitudes used by most athletes, resting oxygen delivery to skeletal muscle is well preserved, arguing against any detrimental effect on "protein synthesis"; 5). It is possible however, that at significantly higher altitudes, acclimatization leads to appetite suppression, inhibition of protein synthesis, muscle wasting, excessive ventilatory work, and metabolic compensation that is NOT advantageous for a competitive athlete.

Acclimatization↗
PubMed2001

Cardiopulmonary and metabolic responses in healthy elderly humans during a 1-week hiking programme at high altitude.

Worldwide there are approximately 100 million visitors to high altitude annually and about 15% of those are elderly. Nevertheless, basic information on the cardiopulmonary and metabolic responses to physical activity at high altitude in the elderly is scarce. Therefore, we studied 20 voluntary healthy elderly subjects (55-77 years) who were randomly assigned to a low- (600 m) or a high altitude (2,000 m) group. Both groups increased the duration of their daily hiking from 2.5 to 5 h during a period of 1 week. Pre- and post-hiking cardiopulmonary variables at rest were measured daily. Exercise tests (3 min step test) were performed on days 1, 4 and 7. Of the morning values at rest, only arterial oxygen saturation (SaO2) had decreased after the 1st night at high altitude. After hiking however, SaO2 was diminished on all days at high altitude. Post-hiking heart rates increased from baseline on days 1 and 2 in the low- and on days 1-5 in the high-altitude group. Exercising SaO2 (%) in the three tests was decreased [84.9 (SD 2.8), 88.1 (SD 2.1), 87.2 (SD 2.3)] compared to baseline [93.2 (SD 2.0); P < 0.05] and blood lactate concentrations were increased [3.1 (SD 0.7), 3.4 (SD 0.3), 3.3 (SD 0.2)] compared to baseline [2.7 (SD 0.6); P < 0.05] in all tests at high altitude. The 1-week hiking programme was well tolerated by the healthy elderly at both low and high altitudes. Ventilatory adaptation to high altitude in the elderly seemed to have been completed within the first 2 days during the measurements at rest. However, cardiopulmonary and metabolic responses to exercise were increased and recovery from exercise was delayed during the 1-week hiking programme at high altitude. Heart rate and SaO2 measurements are considered to be highly sensitive in estimating the state of acclimatisation and for monitoring exercise intensity and duration at high altitude.

Aged↗
PubMed1982

Blood oxygen affinity in high- and low-altitude populations of the deer mouse.

There is little solid evidence for specific genetic adaptations in animal populations native to high altitude. There is also continuing debate over what oxygen transport characteristics are truly adaptive at high altitude. We have attempted to elucidate both problems through population genetic and physiological studies of the deer mouse, Peromyscus maniculatus. That species is noteworthy because it inhabits the widest range of altitudes of any North American mammal, and it shows a high degree of genetic variation in hemoglobins. Deer mice were collected from 35 populations representing ten nominal subspecies covering a broad geographical range of the United States. The mice were acclimated to low altitude (340 m); then a mixing method was used to determine P50 and other blood gas parameters on samples pooled from individuals of representative hemoglobin genotypes. When the data from all subspecies wee combined, there was a highly significant negative correlation between P50 and the native altitude of the population. Tests on progeny reared at low altitude indicated that the differences in P50 were primarily genetic. Part of the clinal variation in P50 could be attributed to 2,3-DPG effects; high-altitude populations showed lower baseline DPG/Hb ratios. Surprisingly, within those subspecies which inhabit a wide range of altitudes, there was no correlation between P50 and native altitude. Our tentative conclusion from these data and data presented elsewhere is that deer mouse populations do show genetic adaptations to high altitude. However, because of gene exchange between populations, the genetic characteristics of a population reflect the average altitude over a relatively broad geographic area.

2,3-Diphosphoglycerate↗
PubMed2004

Maternal adaptation to high-altitude pregnancy: an experiment of nature--a review.

A long and productive history of studies at high altitude has demonstrated that chronic hypoxia plays a key role in the aetiology of intrauterine growth restriction (IUGR) and pre-eclampsia. Susceptibility to altitude-associated IUGR varies among high-altitude populations in relation to their duration of altitude exposure, with multigenerational residents demonstrating one-third the birth weight fall present in shorter-resident groups. Higher uteroplacental blood flow during pregnancy in multigenerational high-altitude residents suggests that such population differences are due, at least in part, to differences in maternal vascular responses to pregnancy. We hypothesize that natural selection acting on hypoxia-inducible factor (HIF)-targeted or -regulatory genes has enabled maternal vascular adaptation to pregnancy in long-resident high-altitude groups. Preliminary evidence in support of this hypothesis demonstrates that the potent HIF-targeted vasoconstrictor, endothelin-1 (ET-1), is differentially regulated by pregnancy and chronic hypoxia in Andean vs European residents of high altitude. Andeans show the normal, pregnancy-associated fall in ET-1 levels previously reported at low altitude, whereas Europeans have higher ET-1 levels and little pregnancy-associated change, like pre-eclamptic women. Single nucleotide polymorphisms (SNPs) in the ET-1 gene also differ in Andeans compared with low-altitude populations. We conclude that high altitude serves as an experiment of nature for elucidating genetic factors underlying susceptibility to complications of pregnancy and fetal life. Such studies may be important for identifying persons at risk for these complications at any altitude.

Acclimatization↗
PubMed1987

Altitude and birth weight.

The effect of altitude on birth weight was measured with data in U.S. natality records from 1978 to 1981 after correlation with the mean altitude of the mother's resident county. For comparison of the low birth weight (LBW) rate at different altitudes, certain socioeconomic risk factors known to affect birth weight were controlled by the selection of an idealized subpopulation of singleton births. With 500 m gradations for altitude, a curvilinear dose-response relationship of birth weight reduction with increasing altitude was demonstrated (P less than 0.001). In comparison with neonates born at sea level, neonates born at higher altitudes (greater than 2000 m) had a twofold to threefold increase in LBW rate, mainly related to a higher incidence of intrauterine growth retardation. Comparison of the LBW rate on the basis of small geographic divisions in the mountain states showed a positive correlation between the LBW rate and the high altitude. The birth weight frequency distribution curves of the idealized subpopulation at each altitude approximate normal distributions and parallel one another, indicating that altitude has a general effect on all births. Such nearly normal birth weight distributions allowed the determination of altitude-specific LBW cutoff limits that can be used to detect areas of greater risk for LBW but independent of the altitude effect.

Altitude↗
PubMed2001

Are very low birth weight infants born at high altitude at greater risk for adverse outcomes?

OBJECTIVE: To determine if neonatal intensive care at higher altitudes was associated with any variation in mortality or morbidity. METHODS: We reviewed demographic and outcome data on 5450 neonates with birth weights between 500 and 1500 g cared for in 76 different level II and III neonatal intensive care units (NICUs). The altitude break point of 4300 feet was prospectively chosen. Care was provided at 63 NICUs located below 4300 feet, "low-altitude," (n = 4534 neonates) and at 13 NICUs at or above 4300 feet, "high-altitude" (n = 916 neonates). RESULTS: Compared with neonates cared for at low altitude, neonates cared for at high altitude were more often non-Hispanic white and exposed to prenatal steroids. Neonates born at high altitude were more often treated with surfactant (60% vs 53%, P <.01). At 28 days of age, neonates cared for at high altitude were less often in room air (33% vs 50%, P <.01) compared with neonates cared for at low altitude. However, when corrected for barometric pressure, the calculated partial pressure of inspired oxygen at 28 days of age was lower for neonates cared for at high altitude compared with low altitude (165 +/- 80 vs 183 +/- 57, P <.01). There were no differences in the rates of mortality, severe intraventricular hemorrhage (grades 3 and 4), severe retinopathy of prematurity (stages 3 and 4), or necrotizing enterocolitis requiring surgical treatment. CONCLUSIONS: Being cared for at NICUs located above 4300 feet above sea level was not associated with any increase in adverse events compared with NICUs located below 4300 feet.

Altitude↗
PubMed2002

Effects of high altitude and season on fasting heat production in the yak Bos grunniens or Poephagus grunniens.

Thirty growing yaks Bos grunniens or Poephagus grunniens, 1.0-3.5 years and 50-230 kg, from their native altitudes (3000-4000 m), were used to study the basal metabolism in this species and to evaluate the effects of high altitude and season on the energy metabolism. Fasting heat production (FHP) was measured at altitudes of 2260, 3250 and 4270 m on the Tibetan plateau in both the summer and the winter, after a 90 d adaptation period at each experimental site. Gas exchanges of the whole animals were determined continuously for 3 d (4-5 times per d, 10-12 min each time) after a 96 h starvation period, using closed-circuit respiratory masks. Increasing altitude at similar ambient temperature (Ta) did not affect (P>0.10) FHP in the summer, but decreased (P<0.05) it at different Ta in the winter. However, the decrease of FHP in the winter was mainly due to the decrease of Ta instead of the increase of altitude. In the summer, the respiratory rate, heart rate and body temperature were unaffected by altitude, except for a decrease (P<0.05) in body temperature at 4270 m; in the winter, they were decreased (P<0.05) by increasing altitude. In both seasons, the RER was decreased (P<0.05) by increasing altitude. At all altitudes for all groups, the daily FHP was higher (P<0.05) in the summer (Ta 6-24 degrees C) than in the winter (Ta 0 to -30 degrees C), and the Ta-corrected FHP averaged on 920 kJ/kg body weight(0.52) at Ta 8-14 degrees C and on 704 kJ/kg body weight(0.52) at Ta -15 degrees C respectively. We conclude that in the yak high altitude has no effect on the energy metabolism, whereas the cold ambient temperature has a significant depressing effect. The results confirm that the yak has an excellent adaptation to both high altitude and extremely cold environments.

Adaptation, Physiological↗
PubMed2003

Improving oxygenation at high altitude: acclimatization and O2 enrichment.

When lowlanders go to high altitude, the resulting oxygen deprivation impairs mental and physical performance, quality of sleep, and general well-being. This paper compares the effects of ventilatory acclimatization and oxygen enrichment of room air on the improvement of oxygenation as judged by the increase in the alveolar P(O2) and the reduction in equivalent altitude. The results show that, on the average, complete ventilatory acclimatization at an altitude of 5000 m increases the alveolar P(O2) by nearly 8 torr, which corresponds to a reduction in equivalent altitude of about 1000 m, although there is considerable individual variability. By comparison, oxygen enrichment to 27% at 5000 m can easily reduce the equivalent altitude to 3200 m, which is generally well tolerated. Because full ventilatory acclimatization at altitudes up to about 3600 m reduces the equivalent altitude to about 3000 m, oxygen enrichment is not justified for well-acclimatized persons. At an altitude of 4200 m, where several telescopes are located on the summit of Mauna Kea, full acclimatization reduces the equivalent altitude to about 3400 m, but the pattern of commuting probably would not allow this. Therefore, at this altitude, oxygen enrichment would be beneficial but is not essential. At higher altitudes such as 5050 m, where other telescopes are located or planned, the gain in oxygenation from acclimatization is insufficient to produce an adequate mental or physical performance for most work, and oxygen enrichment is highly desirable. Full ventilatory acclimatization requires at least a week of continuous exposure, although much of the improvement is seen in the first 2 days.

Acclimatization↗
PubMed2002

Flow-mediated dilatation of the brachial artery in pregnancy at high altitude.

OBJECTIVE: Pregnancy at high altitude has been associated with increased prevalence of pre-eclampsia and reduced maternal oestrogen levels, factors that have been associated with endothelial dysfunction. The aim of this study was to examine the effect of high altitude (4370 m above sea level) on endothelial function during pregnancy as assessed by a non-invasive method. DESIGN: Cross-sectional study. SETTING: Two maternity units providing routine antenatal care: one at high altitude (District General Hospital--IPSS in Cerro de Pasco, Peru) and one at sea level (Instituto Materno-Perinatal in Lima, Peru). POPULATION: Sixty pregnant women at 6-42 weeks of gestation resident at high altitude (Cerro de Pasco, Peru, 4370 m above sea level) and 54 at sea level (Lima, Peru). Comparisons were performed also in 11 and 14 non-pregnant women at each altitude, respectively. METHODS: Endothelial function was assessed by flow-mediated dilatation of the brachial artery using high-resolution ultrasound. MAIN OUTCOME MEASURES: Differences in flow mediated dilatation of the brachial artery in two groups of pregnant women, one at high altitude and one at sea level. RESULTS: Both at high altitude and sea level flow-mediated dilatation of the brachial artery increased in the first two trimesters to levels 32% higher than non-pregnant controls. However, in the third trimester, flow-mediated dilatation of the brachial artery was lower than non-pregnant levels. Resting vessel size increased during pregnancy by 15% compared with non-pregnant controls at term, with no difference between the two populations at high and low altitude. Pregnancy at high altitude, compared with sea level, was associated with 59% lower baseline blood flow and 76% higher reactive hyperaemia. Similarly, non-pregnant controls at high altitude compared with sea level demonstrated similar flow-mediated dilatation of the brachial artery and 40% lower resting blood flow of the brachial artery. However, the difference in reactive hyperaemia did not reach statistical significance. CONCLUSION: These data suggest that, during pregnancy at high altitude, endothelial function, as assessed by flow-mediated dilatation of the brachial artery, is not impaired.

Adult↗
PubMed2006

Cerebral blood flow and oxygenation in ovine fetus: responses to superimposed hypoxia at both low and high altitude.

For the fetus, although the roles of arterial blood gases are recognized to be critical in the regulation of cerebral blood flow (CBF) and cerebral oxygenation, the relation of CBF, cortical tissue P(O2) (tP(O2)), sagittal sinus P(O2), and related indices of cerebral oxygenation to arterial blood gases are not well defined. This is particularly true for that fetus subjected to long-term hypoxia (LTH). In an effort to elucidate these interrelations, we tested the hypothesis that in the fetus acclimatized to high altitude, cerebral oxygenation is not compromised relative to that at low altitude. By use of a laser Doppler flowmeter with a fluorescent O2 probe, in near-term fetal sheep at low altitude (n = 8) and those acclimatized to high altitude hypoxia (3801 m for 90 +/- 5 days; n = 6), we measured laser Doppler CBF (LD-CBF), tP(O2), and related variables in response to 40 min superimposed hypoxia. At both altitudes, fetal LD-CBF, cerebral O2 delivery, tP(O2), and several other variables including sagittal sinus P(O2), correlated highly with arterial P(O2) (P(a,O2)). In response to superimposed hypoxia (P(a,O2) = 11 +/- 1 Torr), LD-CBF was significantly blunted at high altitude, as compared with that at low altitude. In the two altitude groups fetal cerebral oxygenation was similar under both control conditions and with superimposed hypoxia, cortical tP(O2) decreasing from 8 +/- 1 and 6 +/- 1 Torr, respectively, to 2 +/- 1 Torr. Also, for these conditions sagittal sinus P(O2) and [HbO2] values were similar. In response to superimposed hypoxia, cerebral metabolic rate for O(2) decreased approximately 50% in each group (P < 0.05). For both the fetus at low altitude and that acclimatized to high altitude LTH, we present the first dose-response data on the relation of LD-CBF, cortical tP(O2), and sagittal sinus blood gas values to P(a,O2). In addition, despite differences in several variables, the fetus at high altitude showed evidence of successful acclimatization, supporting the hypothesis that such fetuses demonstrate no compromise in cerebral oxygenation.

Altitude↗
PubMed1976

Effect of altitude exposure on thermoregulatory response of man to cold.

The thermoregulatory responses to 10 degrees C (for 3 h) were investigated in 1) 12 natives from sea level (lowlanders) at 150 m, and on arrival at 3,350 and 4,340 m; 2) 6 of these during a 6-wk sojourn at 4,360 m, and on return to sea level; and 3) 5 natives from each of the two altitudes (highlanders) in their respective habitat, and after descent to 150 m. The cold-induced increase in the rate of O2 consumption (Vo2) of the lowlanders was significantly smaller at both altitudes than at sea level. It did not recover substantially during the 6 wk at altitude, but was restored to its initial rate on return to sea level. By contrast, visible shivering activity was augmented on arrival at altitude. It persisted throughout the 6 wk there, but was greatly depressed on return to sea level, despite the increased Vo2. Mean skin temperatures (Tsk) stabilized in the cold at significantly higher values at altitude. Rectal temperature (Tre) decreased similarly at all altitudes. Vo2 of the highlanders in the cold was significantly greater at sea level than at their resident altitudes, although shivering activity was less intense; Tsk stabilized at significantly lower levels at 150 m than at either altitude. These results indicate that altitude exposure reduces the calorigenic response of man to cold, and that this effect is not moderated by acclimatization to altitude, yet is reversible immediately on descent to sea level. The component of cold thermogenesis which appeared to be reduced by altitude exposure was nonshivering thermogenesis rather than visible shivering.

Acclimatization↗
PubMed1985

Increased lung vasoreactivity in children from Leadville, Colorado, after recovery from high-altitude pulmonary edema.

Cardiac catheterization was performed on seven children after recovery from high-altitude pulmonary edema. All were life-long residents at elevations above 10,000 feet. Three of the seven had developed pulmonary edema without antecedent travel to low altitude but had an upper respiratory infection. Response of pulmonary arterial pressure to 16% inspired oxygen in all seven was compared with that in six well children who resided at a similar altitude and had no history of high-altitude pulmonary edema. With hypoxia the susceptible patients had a greater mean pulmonary arterial pressure (56.3 +/- 23.8) than the nonsusceptible children (18.8 +/- 3.9, p less than .05). Comparison with historical hemodynamic responses in children at high altitudes showed a similar greater mean pulmonary arterial pressure in the susceptible children. Thus, in children from high altitudes, increased pulmonary vasoreactivity to hypoxia may play a role in the pathogenesis of high-altitude pulmonary edema. The development of pulmonary edema in high-altitude residents with upper respiratory infections and no antecedent low-altitude journey is consistent with the presence of other factors such as inflammation, which may play a role in the pathogenesis of the edema. The finding of right ventricular hypertrophy on an electrocardiogram in children from high altitudes may be predictive of their susceptibility to high-altitude pulmonary edema.

Altitude↗