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At least 649 records · Page 36Linked to original sources
PubMed2000

Acclimatization near home? Early respiratory changes after short-term intermittent exposure to simulated altitude.

OBJECTIVE: With the ultimate goal of finding a straightforward protocol for acclimatization at simulated altitude, we evaluated the early effects of repeated short-term exposure to hypobaric hypoxia on the respiratory response to exercise in hypoxia. METHODS: Nine subjects were exposed to a simulated altitude of 5000 m for 2 hours a day for 14 days. Arterial oxygen saturation (SaO2), expired volume per minute (VE), respiratory rate, tidal volume (VT), and heart rate were measured during rest and during exercise (cycloergometer, at 30% of maximum oxygen consumption at sea level), both in normoxia and at 5000 m of simulated altitude on the first and 15th days. On the same days, blood samples were obtained for hematological tests. RESULTS: During exercise in hypoxia, SaO2 rose from 65 to 71% (P = .02), and VE rose from 55.5 to 67.6 L.min-1 (P = .02) due to an increase in VT from 2 to 2.6 L (P = .003). No significant differences were found in any of the variables studied at rest either in normoxia or in hypoxia or in exercise in normoxia after the exposure program. In the second week, changes in packed cell volume and blood hemoglobin concentration were nonsignificant. CONCLUSIONS: After short-term intermittent exposure to hypobaric hypoxia, subjects increased their ventilatory response and SaO2 during exercise at simulated altitude. These changes may be interpreted as acclimatization to altitude. The monitoring of ventilatory response and SaO2 during moderate exercise in hypobaric hypoxia may be used to detect the first stages of acclimatization to altitude.

Acclimatization↗
PubMed2004

Ventilation after supplemental oxygen administration at high altitude.

OBJECTIVE: The present study assessed the effects of acute hyperoxia on resting-minute ventilation (VE) during altitude acclimatization to 4300 m. METHODS: Resting-minute ventilation, end-tidal partial pressure carbon dioxide (PETCO2) and oxygen (P(ET)O2), and arterial oxygen saturation (SpO2) were measured during chronic poikilocapnic hypobaric hypoxia, supplemental oxygen breathing, and the subsequent return to hypobaric poikilocapnic hypoxia at altitude. Fifteen adult male lowlanders were studied at sea level and on the 3rd and 12th days at 4300 m. At sea level, subjects first breathed room air that was followed by 25-minute steady-state poikilocapnic hypoxia (FIO2 = 0.125). Ventilatory responses to acute poikilocapnic hypoxia (APH) were collected over the first 1-10 minutes, and responses to chronic poikilocapnic hypoxia (CPH) were collected over the last 3 minutes of the hypoxia exposure. At altitude, CPH was provided by ambient-air breathing (PIO2 = 86 mm Hg) that was interrupted by 10 minutes of oxygen breathing (FIO2 = 1.0, PIO2 = 460 mm Hg) and then a subsequent return to ambient air to measure APH ventilatory responses. RESULTS: Between day 1 and day 12, during CPH, VE and SpO2 increased (P < .05) by 46% and 6%, respectively, whereas P(ET)CO2 decreased. On day 3 and day 12, breathing oxygen did not lower VE compared with CPH. However, the VE during APH immediately after oxygen breathing at high altitude was always greater (P < .05) than during CPH and did not change with duration of residence at altitude. CONCLUSIONS: These results show that short-duration oxygen breathing increases the subsequent ventilatory response to poikilocapnic hypoxia in altitude-acclimatized lowlanders, resulting in a transient elevation of SpO2.

Acclimatization↗
PubMed2006

Changes in metabolic and hematologic laboratory values with ascent to altitude and the development of acute mountain sickness in Nepalese pilgrims.

OBJECTIVE: During August of each year, thousands of Nepalese religious pilgrims ascend from 2050 m to 4500 m in 1 to 3 days. Our objectives were to evaluate the incidence of acute mountain sickness (AMS) among this large group of native people, to explore changes in serum electrolytes as subjects ascend to high altitude, and to attempt to determine whether decreased effective circulating volume is associated with the development of AMS. METHODS: This was a prospective study with 2 parts. In the first part, demographic, physiologic, and laboratory data were collected from a cohort of 34 pilgrims at both moderate (2050 m) and high altitude (4500 m). Changes that occurred with ascent were compared in subjects who did and did not develop AMS. The second part was a cross sectional study of a different group of 57 pilgrims at the high-altitude site to further determine variables associated with AMS. RESULTS: In the cohort of 34 subjects, Lake Louise score, heart rate, respiratory rate, blood urea nitrogen (BUN), BUN:creatinine ratio, and pH increased at high altitude, whereas oxygen saturation, bicarbonate, creatinine, and PCO2 decreased. Sixteen of these 34 subjects (42%) were diagnosed with AMS; these patients had a statistically significantly lower hematocrit, oxygen saturation, and self-reported water consumption than those without AMS. Of the 57 subjects enrolled in the cross sectional study, 31 (54%) were diagnosed with AMS. These pilgrims had higher heart rates and BUNs than did their non-AMS counterparts. CONCLUSIONS: Fifty-two percent of the subjects developed AMS. With ascent to altitude, subjects showed some evidence of decreased effective circulating volume, though there were no clinically significant changes. The data did not show whether decreased circulating volume is a significant risk factor in the development of AMS at high altitude.

Acute Disease↗
PubMed1999

Hemoglobin correction factors for estimating the prevalence of iron deficiency anemia in pregnant women residing at high altitudes in Bolivia.

This study had two primary objectives: 1) to derive a method to determine hemoglobin cutoffs that could be used to better estimate the prevalence of iron deficiency anemia in pregnancy at high altitudes and 2) to estimate the prevalence of anemia in a sample of pregnant women residing in two cities in Bolivia, La Paz (3,600 meters) and El Alto (4,000 meters). We derived a hemoglobin-altitude curve from previously published data on the mean hemoglobin concentrations of nonanemic women of childbearing age at various altitudes. In addition, we abstracted data on hemoglobin concentration during pregnancy from medical records of women from La Paz and El Alto who had given birth at a maternity hospital in La Paz between January and June of 1996. Using our approach and two other previously published, currently used methods, we calculated and compared prevalences of iron deficiency anemia in this population using hemoglobin cutoffs determined from a hemoglobin-altitude curve corrected for pregnancy. The hemoglobin-altitude curve derived in this study provided a better fit to data for women of childbearing age than the two other models. Those models used cutoffs based on non-iron-replete populations of children or men, both of which were residing below 4,000 m, and then extrapolated to women and higher altitudes. The estimated prevalences of iron deficiency anemia in pregnancy using the hemoglobin cutoffs determined in this study were higher than those estimated by the two other approaches.

Adult↗
PubMed1993

Effects of altitude on mood, behaviour and cognitive functioning. A review.

Alterations in psychological mood, personality, behaviour and cognitive functioning associated with altitude have been recognised for many years. Psychological and behavioural changes resulting from the effects of hypoxia often include increases in euphoria, irritability, hostility and impairment of neuropsychological functions such as vision and memory. There is limited research to indicate that some decrements may persist for up to a year, or longer, after return to lower elevation. However, generalisations of the effects of altitude on mood, behaviour and cognitive function are complicated by differences between studies including the specific tasks or dimensions measured, methods of measurement, degree of altitude, duration of exposure and types of participants. There also appear to be wide individual differences in the response to altitude sojourns. Investigations designed to measure symptoms and mood changes during actual mountain climbs are needed, since most of the systematic research has been conducted in altitude chambers. The extent to which these simulations can be generalised to actual altitude settings remains to be documented.

Affect↗
PubMed1996

Altitude training for improvements in sea level performance. Is the scientific evidence of benefit?

Altitude training invokes physiological changes that are very similar to those caused by endurance training, As a result, it has been incorporated in the training regimes of elite athletes in an effort to improve sea level performance. Several training strategies, such as constant altitude exposure, intermittent altitude exposure or 'live high train low', have been used in an effort to incur an advantage in sea level performance over just sea level training alone. In spite of the accumulating scientific evidence that altitude training affords no advantage over sea level training, many coaches and athletes believe that it can enhance sea level performance for any athlete, whether endurance or power is the focus in their particular sport. However, altitude training may not be suitable for some athletes depending on their age, fitness level, health, iron status and the energy and technical requirements of their sport. The issue of whether altitude training enhances sea level performance remains a controversial topic.

Acclimatization↗
PubMedDate not supplied

Vacation at moderate and low altitude improves perceived health in individuals with metabolic syndrome.

BACKGROUND: Recent data suggest that vacation may improve cardiovascular health, an effect possibly moderated by altitude. The aim of the present study was to study the effect of a 3-week vacation at moderate and low altitude on perceived health in individuals with increased cardiovascular risk. METHODS: Seventy-two overweight males, both occupationally active and retired (mean age=56.6 +/- 7.2 years), with signs of metabolic syndrome were randomly assigned to identical sojourns at either moderate (1,700 m) or low (300 m) altitude and engaged in four 3- to 4-h heart-rate-controlled hiking tours per week. Perceived health was measured 2 weeks before vacation, at the beginning and end of vacation, and 7 weeks after vacation. RESULTS: Fitness, recreational ability, positive and negative mood and social activities improved during vacation, independent of altitude and occupational status, although the day-to-day improvement in quality of sleep was delayed at moderate altitude. During the follow-up examinations, improvements in all reported aspects of health except for social activities were maintained. In comparison to retired individuals, active individuals showed a greater long-term improvement in social activities. CONCLUSION: Vacation positively affects perceived health independent of altitude or occupational status in generally inactive overweight males.

Adult↗
PubMed1998

Altitude-related illnesses.

Altitude-related illnesses are a frequent cause of morbidity and occasional mortality in travelers to high altitudes in the United States and throughout the world. The primary altitude illnesses are acute mountain sickness, high-altitude pulmonary edema, and high-altitude cerebral edema. The pathogenesis of these syndromes remains unclear despite considerable research. Altitude also has potential deleterious effects on common medical conditions including coronary artery disease, pulmonary disease, hemoglobinopathies, and pregnancy. Most of these problems are primarily preventable with appropriate information before travel. Education should include information about rate of ascent, diet, alcohol intake, physical activity, and preventive medications, including acetazolamide, nifedipine, and dexamethasone in selected circumstances.

Altitude Sickness↗
PubMed1988

Elevated plasma atrial natriuretic factor and vasopressin in high-altitude pulmonary edema.

A diagnosis of acute high-altitude pulmonary edema was made in five male skiers (age, 35.0 +/- 1.8 years) by history and physical examination and was confirmed by a characteristic chest radiogram showing alveolar infiltrates associated with a normal cardiac silhouette. Five healthy age- and sex-matched subjects with similar physical activity at the same altitude served as controls. Plasma sodium was 135.0 +/- 1.5 mmol/L in the acutely ill patients compared with 144.0 +/- 3.3 mmol/L in the controls (P less than 0.025). Mean plasma atrial natriuretic factor immunoreactivity averaged 17.6 +/- 5.6 pmol/L in patients with high-altitude pulmonary edema compared with 6.8 +/- 0.7 pmol/L in the controls at the same altitude (P less than 0.05). Elevated atrial natriuretic factor levels normalized to 7.5 +/- 1.9 pmol/L (P less than 0.05) during recovery in Denver (altitude, 1600 meters) 24 hours later. Plasma arginine vasopressin levels were 1.8 +/- 0.37 pmol/L in patients with high-altitude pulmonary edema at diagnosis compared with 0.92 +/- 0.28 pmol/L in controls (P = 0.07). The inappropriately elevated arginine vasopressin levels decreased to 1.29 +/- 0.37 pmol/L during recovery (P less than 0.025), but the lowered plasma sodium concentration had not normalized by discharge within 24-hours of transfer to Denver and averaged 135.8 +/- 1.2 mmol/L. The pathophysiologic implications of these findings are discussed.

Acute Disease↗
PubMed2004

Sildenafil increased exercise capacity during hypoxia at low altitudes and at Mount Everest base camp: a randomized, double-blind, placebo-controlled crossover trial.

BACKGROUND: Alveolar hypoxia causes pulmonary hypertension and enhanced right ventricular afterload, which may impair exercise tolerance. The phosphodiesterase-5 inhibitor sildenafil has been reported to cause pulmonary vasodilatation. OBJECTIVE: To investigate the effects of sildenafil on exercise capacity under conditions of hypoxic pulmonary hypertension. DESIGN: Randomized, double-blind, placebo-controlled crossover study. SETTING: University Hospital Giessen, Giessen, Germany, and the base camp on Mount Everest. PARTICIPANTS: 14 healthy mountaineers and trekkers. MEASUREMENTS: Systolic pulmonary artery pressure, cardiac output, and peripheral arterial oxygen saturation at rest and during assessment of maximum exercise capacity on cycle ergometry 1) while breathing a hypoxic gas mixture with 10% fraction of inspired oxygen at low altitude (Giessen) and 2) at high altitude (the Mount Everest base camp). INTERVENTION: Oral sildenafil, 50 mg, or placebo. RESULTS: At low altitude, acute hypoxia reduced arterial oxygen saturation to 72.0% (95% CI, 66.5% to 77.5%) at rest and 60.8% (CI, 56.0% to 64.5%) at maximum exercise capacity. Systolic pulmonary artery pressure increased from 30.5 mm Hg (CI, 26.0 to 35.0 mm Hg) at rest to 42.9 mm Hg (CI, 35.6 to 53.5 mm Hg) during exercise in participants taking placebo. Sildenafil, 50 mg, significantly increased arterial oxygen saturation during exercise (P = 0.005) and reduced systolic pulmonary artery pressure at rest (P < 0.001) and during exercise (P = 0.031). Of note, sildenafil increased maximum workload (172.5 W [CI, 147.5 to 200.0 W]) vs. 130.6 W [CI, 108.8 to 150.0 W]); P < 0.001) and maximum cardiac output (P < 0.001) compared with placebo. At high altitude, sildenafil had no effect on arterial oxygen saturation at rest and during exercise compared with placebo. However, sildenafil reduced systolic pulmonary artery pressure at rest (P = 0.003) and during exercise (P = 0.021) and increased maximum workload (P = 0.002) and cardiac output (P = 0.015). At high altitude, sildenafil exacerbated existing headache in 2 participants. LIMITATIONS: The study did not examine the effects of sildenafil on normoxic exercise tolerance. CONCLUSIONS: Sildenafil reduces hypoxic pulmonary hypertension at rest and during exercise while maintaining gas exchange and systemic blood pressure. To the authors' knowledge, sildenafil is the first drug shown to increase exercise capacity during severe hypoxia both at sea level and at high altitude.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed1999

Hallucinatory experiences in extreme-altitude climbers.

OBJECTIVE: This study attempted a systematic investigation of incidence, type, and circumstances of anomalous perceptual experiences in a highly specialized group of healthy subjects, extreme-altitude climbers. BACKGROUND: There is anecdotal evidence for a high incidence of anomalous perceptual experiences during mountain climbing at high altitudes. METHOD: In a structured interview, we asked eight world-class climbers, each of whom has reached altitudes above 8500 m without supplementary oxygen, about hallucinatory experiences during mountain climbing at various altitudes. A comprehensive neuropsychological, electroencephalographic, and magnetic resonance imaging evaluation was performed within a week of the interview (8). RESULTS: All but one subject reported somesthetic illusions (distortions of body scheme) as well as visual and auditory pseudohallucinations (in this order of frequency of occurrence). A disproportionately large number of experiences above 6000 m as compared to below 6000 m were reported (relative to the total time spent at these different altitudes). Solo climbing and (in the case of somesthetic illusions) life-threatening danger were identified as probable triggers for anomalous perceptual experiences. No relationship between the number of reported experiences and neuropsychological impairment was found. Abnormalities in electroencephalographic (3 climbers) and magnetic resonance imaging (2 climbers) findings were likewise unrelated to the frequency of reported hallucinatory experiences. CONCLUSIONS: The results confirm earlier anecdotal evidence for a considerable incidence of hallucinatory experiences during climbing at high altitudes. Apart from hypoxia, social deprivation and acute stress seem to play a role in the genesis of these experiences.

Adult↗
PubMed1999

Altitude: a determinant for tuberculosis in Kenya?

OBJECTIVE: To determine to what extent tuberculosis incidence is associated with altitude. METHODS: Notification rates were obtained from all 41 districts in Kenya in the period 1988-1990; the mean altitude of each district was estimated. Data on indicators of socio-economic status such as literacy rate and infant mortality rate were obtained from the 1989 census, as well as data on other potential confounders such as urbanisation and median household size. RESULTS: The notification rate of new smear-positive tuberculosis was 32/100000 overall, varying between districts from 5 to 222/100000. Notification rates steeply reduced with increasing altitude (r = -0.71; 95% confidence interval [CI] -0.51 to -0.83). At altitudes of 1000 m or more the notification rates were less than 30% of those in districts at altitudes below 500 m, also after adjustment for confounding. CONCLUSION: Tuberculosis incidence in Kenya decreases strongly with increasing altitude. If the association is not due to unknown confounding factors, a range of potential biological explanations needs to be explored.

Altitude↗
PubMed1999

Improvement in hypoxemia at 4600 meters of simulated altitude with carbohydrate ingestion.

BACKGROUND: Carbohydrate ingestion increases the relative production of carbon dioxide which results in an increase in ventilation in normal individuals. An increase in ventilation at altitude can result in improvement of altitude-induced hypoxemia. HYPOTHESIS: Carbohydrate ingestion will increase the arterial blood oxygen tension and oxyhemoglobin saturation during acute high altitude simulation. METHODS: There were 15 healthy volunteers, aged 18-33 yr, who were given a 4 kcal x kg(-1) oral carbohydrate beverage administered 2.5 h into an exposure to 15,000 ft (4600 m) of simulated altitude (5.5 h after the last meal). Altitude was simulated by having subjects breath a 12% oxygen/balance nitrogen mixture while remaining at sea level. Arterial blood gas samples were drawn at baseline and at regular intervals up to 210 min after carbohydrate ingestion. Subjects were evaluated for AMS by use of the Environmental Symptoms Questionnaire (ESQ) and a weighted average of cerebral symptom score (AMS-C). RESULTS: Baseline PaO2 increased significantly (p < 0.01) from 43.0 +/- 3.0 mmHg at 4600 m before carbohydrate ingestion to 46.8 +/- 6.2 mmHg at 60 min after carbohydrate ingestion. Arterial oxygen saturation rose significantly (p < 0.01) from a baseline of 79.5% +/- 5.1 to 83.8% +/- 6.42 at 60 min. CONCLUSIONS: Carbohydrate consumption significantly increased oxygen tension and oxyhemoglobin saturation in arterial blood of normal subjects during simulated altitude. Effects reached statistical significance across all subjects at 60 min. There was no significant difference in arterial oxygen levels or arterial oxygen saturation in subjects who developed AMS vs. those who did not develop AMS.

Adolescent↗
PubMed2000

The effectiveness of ground level oxygen treatment for altitude decompression sickness in human research subjects.

BACKGROUND: Current therapy for altitude decompression sickness (DCS) includes hyperbaric oxygen therapy and ground-level oxygen (GLO). The purpose of this paper is to describe the Air Force Research Laboratory experience in the extensive use of GLO for the treatment of altitude DCS in research subjects. METHODS: Data were collected from 2001 altitude chamber subject-exposures. These data, describing DCS symptoms, circulating intracardiac venous gas emboli, and treatment procedures used were collected for each subject exposure and stored in an altitude DCS database. RESULTS: In the database of 2001 subject exposures, 801 subjects (40.0%) were diagnosed with altitude DCS. Subjects reporting DCS symptoms were immediately recompressed to ground level. Of the 749 subjects who received 2 h GLO, 739 (98.7%) resolved completely and required no further treatment. CONCLUSIONS: Although not an operational study, these data provide indirect support for the current USAF guidelines for the treatment of altitude DCS with GLO.

Aerospace Medicine↗
PubMed1999

[Quality of sleep and periodic breathing in healthy individuals working at an altitude of 3700 meters].

We performed full polysomnography (PSG) in 7 healthy miners of Kyrghyz origin (mean age 25 +/- 6 years) working in 2 weeks shifts at Kumtor gold mines at the elevation of 4200 m. They slept in comfortable dormitories situated at 3700 m. To avoid acute mountain sickness all subjects received acetazolamide 3 x 0.25 daily during 2 days preceding ascent and during 2 days at altitude: PSG was performed three times: at 760 m (1) and on the 1st (2) and 7th night (3) after rapid ascent (aircraft) to high altitude using SomnoTrac 4250 sleep laboratory. We found that sleep efficiency was good at lowland and in the mountains averaging 81.79% and 84% respectively. Although there were no significant differences in percentage of sleep stages and of total sleep time between lowland and both nights at high altitude, arousals and awakenings were more frequent in the mountains. Episodes of periodic breathing (PB) appeared at high altitude. There was a large individual variability in PB on both nights at altitude. The time spent in PB ranged from 4 to 30 minutes during the first night at altitude and from 3 to 17 minutes during the second one. PB appeared mainly during non-REM sleep and aggravated arterial blood desaturation.

Adult↗
PubMed2000

Attention to detail: injuries at altitude among U.S. Army Military static line parachutists.

Altitude injuries, defined as injuries sustained by military static line parachutists before ground impact, have not been reviewed for 50 years. There are indications that these injuries are increasing at Fort Bragg, North Carolina. Between May 1, 1994, and April 30, 1996, surveillance was conducted for parachute-related injuries and altitude injuries at Fort Bragg. The incidence of all jump-related injuries was 8.1/1,000 aircraft exits. Significant risk factors for injury included being 30 years of age or older (p < 0.001) and being female (p = 0.003). The overall incidence of altitude injuries was noted to be 0.46/1,000 aircraft exits. Risk factors for altitude injury included being 40 years of age or older (p = 0.005) and in the rank of E-1 to E-3 (p = 0.0001). Fifty-four percent of injuries occurred during exiting before complete parachute deployment, and 46% occurred during the opening shock of the parachute. Mechanisms of injury included static line entanglement (33%), riser/suspension-line entanglement (46%), aircraft strikes (21%), unsecured equipment strikes (1%), and opening shock deceleration (1%). The majority of severe altitude injuries are caused by riser/suspension-line entanglement (63%) and involve the knee joint (37%). Although the incidence of altitude injury is quite small, the potential risk for career-threatening and/or life-threatening injury is great. This risk can be reduced by appropriate training and attention to detail.

Adolescent↗
PubMed2000

[Diagnosis and therapy of acute altitude sickness].

Today we distinguish cerebral (acute mountain sickness AMS, high altitude cerebral edema HACE) and pulmonal (high altitude pulmonary edema HAPE) altitude disorders. Incidence, predisposition and risk factors of all kinds of altitude sickness vary both individually and geographically. For practical reasons the leading symptoms are essential: altitude headache, ataxia and sudden loss of strength. Depending on the severity of symptoms the main emergency measures are: rest, descent or evacuation, warmth. Additional therapeutical measures can be helpful if a sudden evacuation to lower altitudes is delayed: oxygen, portable hyperbaric chamber, ibuprofen/naproxen, nifedipine, dexamethasone. Acetazolamide should not be used as an emergency therapy any more.

Acute Disease↗
PubMed2000

[Performance enhancement through training at medium altitude-- from the perspective of sports medicine].

In the last 20 years, maximal oxygen uptake (VO2max) of athletes in different sport disciplines has increased, and the world records in endurance sports have improved markedly. One of the factors that has influenced the increase in endurance performance has been perceived to be altitude training. In this paper we describe the advantages and disadvantages of a "regular" altitude training (live high/train high) aiming to improve sea level performance and compare it with a new method, the so called "live high/train low" method. This method uses the advantages and avoids the side effects of altitude exposure. Several papers have shown that altitude training is able to improve VO2max but the individual response may be substantially different. In most cases it is not possible to prove statistical significance and therefore we have no data about differences between both altitude training methods. However, it is suspected that the risk of overtraining is reduced in the high/low method. Although not statistically significant it is suggested that the "high/low" method can more efficiently improve endurance performance at sea level. A monitoring of submaximal variables of exercise performance is recommended to avoid overtraining and to control the development of performance. From the current knowledge the "live high/train low" method is suggested to be the more effective altitude training method for athletes.

Acclimatization↗