Oxygen saturation course and altitude symptomatology during an expedition to broad peak (8047 m)

A Randomized Phase 2 Study to Evaluate Efficacy and Safety of AR36 for Prevention of Acute Mountain Sickness

INTRODUCTION

AR36 is a pharmaceutical-grade plant extract used to support cardiovascular health in traditional Chinese medicine. Studies suggest that AR36 may prevent acute mountain sickness (AMS) during gradual ascent to high altitude. This randomized, placebo-controlled Phase 2 trial aimed to evaluate dosing regimens and assess efficacy and safety of AR36 for AMS prevention during rapid ascent.

METHODS

Participants received placebo, low-dose AR36 (225 mg twice daily for 14 d prior and 5 d at altitude), or high-dose AR36 (12 d placebo, 300 mg twice daily for 2 d prior and 5 d at altitude). The primary efficacy outcome was 1993 Lake Louise Scoring System (LLSS) score on the morning after ascent. Safety was assessed through the proportion of treatment-emergent adverse events (TEAEs).

RESULTS

One hundred thirty-two participants were randomized. Mean±SD age was 31.4±8.6 (range, 19-54) y. Baseline characteristics did not differ across groups. Lake Louise Scoring System scores on Day 16 in the placebo, low-dose, and high-dose groups were 4.03 (2.88), 4.42 (3.17), and 3.5 (2.31), respectively (placebo versus low-dose, P=0.462; placebo versus high-dose, P=0.574; n=110). The incidence of AMS on Day 16 was 66.7% in the placebo, 61.1% in the low-dose, and 55.3% in the high-dose group (P=0.66). The proportion of TEAEs in the placebo, low-dose, and high-dose groups was 38.4% (81), 28.4% (60), and 33.2% (70), respectively (P=0.205; n=127). There was no statistical difference between groups in LLSS, incidence of AMS, or TEAEs.

CONCLUSIONS

AR36 did not improve LLSS or AMS incidence using the current regimens. AR36 was well tolerated.

Effects of Acute Exposure and Acclimatization to High-Altitude on Oxygen Saturation and Related Cardiorespiratory Fitness in Health and Disease

Maximal values of aerobic power (VO₂max) and peripheral oxygen saturation (SpO₂max) decline in parallel with gain in altitude. Whereas this relationship has been well investigated when acutely exposed to high altitude, potential benefits of acclimatization on SpO₂ and related VO₂max in healthy and diseased individuals have been much less considered. Therefore, this narrative review was primarily aimed to identify relevant literature reporting altitude-dependent changes in determinants, in particular SpO₂, of VO₂max and effects of acclimatization in athletes, healthy non-athletes, and patients suffering from cardiovascular, respiratory and/or metabolic diseases. Moreover, focus was set on potential differences with regard to baseline exercise performance, age and sex. Main findings of this review emphasize the close association between individual SpO₂ and VO₂max, and demonstrate similar altitude effects (acute and during acclimatization) in healthy people and those suffering from cardiovascular and metabolic diseases. However, in patients with ventilatory constrains, i.e., chronic obstructive pulmonary disease, steep decline in SpO₂ and V̇O₂max and reduced potential to acclimatize stress the already low exercise performance. Finally, implications for prevention and therapy are briefly discussed.

The Use of Pulse Oximetry in the Assessment of Acclimatization to High Altitude

Background: Finger pulse oximeters are widely used to monitor physiological responses to high-altitude exposure, the progress of acclimatization, and/or the potential development of high-altitude related diseases. Although there is increasing evidence for its invaluable support at high altitude, some controversy remains, largely due to differences in individual preconditions, evaluation purposes, measurement methods, the use of different devices, and the lacking ability to interpret data correctly. Therefore, this review is aimed at providing information on the functioning of pulse oximeters, appropriate measurement methods and published time courses of pulse oximetry data (peripheral oxygen saturation, (SpO₂) and heart rate (HR), recorded at rest and submaximal exercise during exposure to various altitudes. Results: The presented findings from the literature review confirm rather large variations of pulse oximetry measures (SpO₂ and HR) during acute exposure and acclimatization to high altitude, related to the varying conditions between studies mentioned above. It turned out that particularly SpO₂ levels decrease with acute altitude/hypoxia exposure and partly recover during acclimatization, with an opposite trend of HR. Moreover, the development of acute mountain sickness (AMS) was consistently associated with lower SpO₂ values compared to individuals free from AMS. Conclusions: The use of finger pulse oximetry at high altitude is considered as a valuable tool in the evaluation of individual acclimatization to high altitude but also to monitor AMS progression and treatment efficacy.

Rapid ascents of Mt Everest: normobaric hypoxic preacclimatization

BACKGROUND

Acclimatization to high altitude is time consuming. An expedition to Mt Everest (8848 m) requires roughly 8 weeks. Therefore it seems very attractive to reach the summit within 3 weeks from home, which is currently promised by some expedition tour operators. These rapid ascent expeditions are based on two main components, normobaric hypoxic training (NHT) prior to the expedition and the use of high flow supplemental oxygen (HFSO2). We attempted to assess the relative importance of these two elements.

METHODS

We evaluated the effect of NHT on the basis of the available information of these rapid ascent expeditions and our experiences made during an expedition to Manaslu (8163 m) where we used NHT for preacclimatization. To evaluate the effect of an increased O2 flow rate we calculated its effect at various activity levels at altitudes of 8000 m and above.

RESULTS

So far rapid ascents to Mt Everest have been successful. The participants carried out 8 weeks of NHT, reaching sleeping altitudes = 7100 m and spent at least 300 h in NH. At rest a flow rate of 2 l O2/min is sufficient to keep the partial pressure of inspired oxygen (PIO2) close to 50 mm Hg even at the summit. For ativities of ~80% of the maximum rate of oxygen consumption (VO2max) at the summit 6 l O2/min are required to maintain a PIO2 above 50 mm Hg.

DISCUSSION

NHT for preacclimatization seems to be the decisive element of the offered rapid ascent expeditions. An increased O2 flow rate of 8 l/min is not mandatory for climbing Mt Everest.

CONCLUSIONS

Preacclimatization using normobaric hypoxica (NH) is far more important than the use of HFSO2. We think that NHT will be widely used in the future. The most effective regimen of preacclimatization in NH, the duration of each session and the optimal FIO2 are still unclear and require further study.

Wearable physiological sensors and real-time algorithms for detection of acute mountain sickness

This is a minireview of potential wearable physiological sensors and algorithms (process and equations) for detection of acute mountain sickness (AMS). Given the emerging status of this effort, the focus of the review is on the current clinical assessment of AMS, known risk factors (environmental, demographic, and physiological), and current understanding of AMS pathophysiology. Studies that have examined a range of physiological variables to develop AMS prediction and/or detection algorithms are reviewed to provide insight and potential technological roadmaps for future development of real-time physiological sensors and algorithms to detect AMS. Given the lack of signs and nonspecific symptoms associated with AMS, development of wearable physiological sensors and embedded algorithms to predict in the near term or detect established AMS will be challenging. Prior work using [Formula: see text], HR, or HRv has not provided the sensitivity and specificity for useful application to predict or detect AMS. Rather than using spot checks as most prior studies have, wearable systems that continuously measure SpO2 and HR are commercially available. Employing other statistical modeling approaches such as general linear and logistic mixed models or time series analysis to these continuously measured variables is the most promising approach for developing algorithms that are sensitive and specific for physiological prediction or detection of AMS.

Budesonide Versus Acetazolamide for Prevention of Acute Mountain Sickness

BACKGROUND

Inhaled budesonide has been suggested as a novel prevention for acute mountain sickness. However, efficacy has not been compared with the standard acute mountain sickness prevention medication acetazolamide.

METHODS

This double-blind, randomized, placebo-controlled trial compared inhaled budesonide versus oral acetazolamide versus placebo, starting the morning of ascent from 1240 m (4100 ft) to 3810 m (12,570 ft) over 4 hours. The primary outcome was acute mountain sickness incidence (headache and Lake Louise Questionnaire ≥3 and another symptom).

RESULTS

A total of 103 participants were enrolled and completed the study; 33 (32%) received budesonide, 35 (34%) acetazolamide, and 35 (34%) placebo. Demographics were not different between the groups (P > .09). Acute mountain sickness prevalence was 73%, with severe acute mountain sickness of 47%. Fewer participants in the acetazolamide group (n = 15, 43%) developed acute mountain sickness compared with both budesonide (n = 24, 73%) (odds ratio [OR] 3.5, 95% confidence interval [CI] 1.3-10.1) and placebo (n = 22, 63%) (OR 0.5, 95% CI 0.2-1.2). Severe acute mountain sickness was reduced with acetazolamide (n = 11, 31%) compared with both budesonide (n = 18, 55%) (OR 2.6, 95% CI 1-7.2) and placebo (n = 19, 54%) (OR 0.4, 95% CI 0.1-1), with a number needed to treat of 4.

CONCLUSION

Budesonide was ineffective for the prevention of acute mountain sickness, and acetazolamide was preventive of severe acute mountain sickness taken just before rapid ascent.

Oxygen saturation increases over the course of the night in mountaineers at high altitude (3050-6354 m)

BACKGROUND

Blood oxygen saturation (SpO 2 ) is frequently measured to determine acclimatization status in high-altitude travellers. However, little is known about nocturnal time course of SpO 2 (SpO 2N ), but alterations in SpO 2N might be practically relevant as well. To this end, we describe the time-course of SpO 2N in mountaineers at high altitude.

METHODS

SpO 2N was continuously measured in ten male mountaineers during a three-week expedition in Peru (3,050-6,354m). Average SpO 2N of the first (SpO 2N1 ) and second half (SpO 2N2 ) of an individual's sleep duration was calculated from 2h intervals of uninterrupted sleep. Heart rate oscillations and sleep dairies were used to exclude periods of wakefulness. SpO 2 was also measured at rest in the morning.

RESULTS

SpO 2N significantly increased from SpO 2N1 to SpO 2N2 . The magnitude of this increase (ΔSpO 2 ) was reduced with time spent at altitude. On night 1 (3,050m) SpO 2 increased from 83.4% (N1) to 86.3% (N2). At the same location on night 21, SpO 2 increased from 88.3% to 90.1%, which is a relative change of 4.7% and 2.0%, respectively. This pattern of increase in SpO 2N was perturbed when individual acclimatization was poor or altitude was extreme (5630m). SpO 2N was significantly lower than SpO 2 at rest in the morning.

CONCLUSIONS

This study is the first to demonstrate an increase of SpO 2 during the night in mountaineers at high altitude (3,050-6,354m) with high consistency between and within subjects. The magnitude of ΔSpO 2N decreased as acclimatization improved, suggesting that these changes in ΔSpO 2 between nights might be a valuable indicator of individual acclimatization. In addition, the failure of any increase in SpO 2N during the night might indicate insufficient acclimatization. Even though underlying mechanisms for the nocturnal increase remain unclear, the timing of SpO 2N measurement is obviously of utmost importance for its interpretation. Finally our study illustrates the detailed effects of ventilatory acclimatization over several weeks.

Effects of Carbohydrate and Glutamine Supplementation on Oral Mucosa Immunity after Strenuous Exercise at High Altitude: A Double-Blind Randomized Trial

This study analyzed the effects of carbohydrate and glutamine supplementation on salivary immunity after exercise at a simulated altitude of 4500 m. Fifteen volunteers performed exercise of 70% of VO_2peak until exhaustion and were divided into three groups: hypoxia placebo, hypoxia 8% maltodextrin (200 mL/20 min), and hypoxia after six days glutamine (20 g/day) and 8% maltodextrin (200 mL/20 min). All procedures were randomized and double-blind. Saliva was collected at rest (basal), before exercise (pre-exercise), immediately after exercise (post-exercise), and two hours after exercise. Analysis of Variance (ANOVA) for repeated measures and Tukey post hoc test were performed. Statistical significance was set at p < 0.05. SaO₂% reduced when comparing baseline vs. pre-exercise, post-exercise, and after recovery for all three groups. There was also a reduction of SaO₂% in pre-exercise vs. post-exercise for the hypoxia group and an increase was observed in pre-exercise vs. recovery for both supplementation groups, and between post-exercise and for the three groups studied. There was an increase of salivary flow in post-exercise vs. recovery in Hypoxia + Carbohydrate group. Immunoglobulin A (IgA) decreased from baseline vs. post-exercise for Hypoxia + Glutamine group. Interleukin 10 (IL-10) increased from post-exercise vs. after recovery in Hypoxia + Carbohydrate group. Reduction of tumor necrosis factor alpha (TNF-α) was observed from baseline vs. post-exercise and after recovery for the Hypoxia + Carbohydrate group; a lower concentration was observed in pre-exercise vs. post-exercise and recovery. TNF-α had a reduction from baseline vs. post-exercise for both supplementation groups, and a lower secretion between baseline vs. recovery, and pre-exercise vs. post-exercise for Hypoxia + Carbohydrate group. Five hours of hypoxia and exercise did not change IgA. Carbohydrates, with greater efficiency than glutamine, induced anti-inflammatory responses.

[Estimation of arterial oxygen saturation in relation to altitude]

BACKGROUND AND OBJECTIVES

Arterial Oxygen Saturation (AOS) predicts altitude sickness.

OBJECTIVES

To estimate the AOS values with relation to altitude. Furthermore, make a graph to use during activity which assesses the AOS for each altitude and the normal range.

PATIENTS AND METHOD

Values of AOS were assessed during eight high mountain activities in the Alps, Himalaya, Caucasus and Andes; 53 mountaineers participated, 17 of them in more than one activity; 761 measurements of AOS were registered.

RESULTS

A Logistic Regression Model was made to estimate the AOS values dependent on altitude, adjusted to possible related factors. A strong lineal relationship exists between altitude and AOS (R²=.83, P<.001); .7 points more in women. The AOS in a particular altitude is not related to age, weight, height, smoking, heart rate, or even with previous experiences in mountains. The calculation of the AOS responds to the follow equation: Blood Oxygen Saturation=103.3-(altitude × .0047)+(Z), being Z=.7 in men and 1.4 in women. A scatter plot was made to relate the estimated altitude with the AOS, with their normal limits values: percentiles 2.5 and 97.5.

CONCLUSIONS

The simple calculation of the AOS estimated for a particular altitude with the proposed graphic can help in the early decision-making onsite.

Brief Working Memory and Physiological Monitoring During a High-Altitude Expedition

Malle, Carine, Benoît Ginon, and Cyprien Bourrilhon. Brief working memory and physiological monitoring during a high-altitude expedition. High Alt Med Biol. 17:359-364, 2016.-Background: Various studies have shown the deleterious effects of high-altitude hypoxia on cognitive functions, including attention and memory. Since optimal cognitive abilities may be crucial for mountain safety, this study was aimed to assess the relevance of a brief working memory test to quickly assess cognition at high altitude.

METHODS

A set of physiological and cognitive measurements were collected from four professional climbers at various time points during the course of an expedition to Shishapangma (8043 m).

RESULTS

Progressive high-altitude exposure induced a classical physiological response (i.e., decreased SpO₂ and increased heart rate). Except for the final ascent, no participants suffered from acute mountain sickness and perceived exertion remained low. With the exception of an increased number of night awakenings, reported sleep quality was good. No working memory decline was observed in any of the participants, even at the highest altitudes.

CONCLUSION

Altogether, these findings show that the participants were properly acclimatized to altitude. They also highlight the technical feasibility of assessing cognitive functions all along high-altitude expeditions. The direct access of such tools on a smartphone may improve mountain climbing safety.

Benzolamide improves oxygenation and reduces acute mountain sickness during a high-altitude trek and has fewer side effects than acetazolamide at sea level

Acetazolamide is the standard carbonic anhydrase (CA) inhibitor used for acute mountain sickness (AMS), however some of its undesirable effects are related to intracellular penetrance into many tissues, including across the blood-brain barrier. Benzolamide is a much more hydrophilic inhibitor, which nonetheless retains a strong renal action to engender a metabolic acidosis and ventilatory stimulus that improves oxygenation at high altitude and reduces AMS. We tested the effectiveness of benzolamide versus placebo in a first field study of the drug as prophylaxis for AMS during an ascent to the Everest Base Camp (5340 m). In two other studies performed at sea level to test side effect differences between acetazolamide and benzolamide, we assessed physiological actions and psychomotor side effects of two doses of acetazolamide (250 and 1000 mg) in one group of healthy subjects and in another group compared acetazolamide (500 mg), benzolamide (200 mg) and lorazepam (2 mg) as an active comparator for central nervous system (CNS) effects. At high altitude, benzolamide-treated subjects maintained better arterial oxygenation at all altitudes (3-6% higher at all altitudes above 4200 m) than placebo-treated subjects and reduced AMS severity by roughly 50%. We found benzolamide had fewer side effects, some of which are symptoms of AMS, than any of the acetazolamide doses in Studies 1 and 2, but equal physiological effects on renal function. The psychomotor side effects of acetazolamide were dose dependent. We conclude that benzolamide is very effective for AMS prophylaxis. With its lesser CNS effects, benzolamide may be superior to acetazolamide, in part, because some of the side effects of acetazolamide may contribute to and be mistaken for AMS.

The 6-Minute Walk Test as a Predictor of Summit Success on Denali

OBJECTIVE

To test whether the 6-minute walk test (6MWT), including postexercise vital sign measurements and distance walked, predicts summit success on Denali, AK.

METHODS

This was a prospective observational study of healthy volunteers between the ages of 18 and 65 years who had been at 4267 m for less than 24 hours on Denali. Physiologic measurements were made after the 6MWT. Subjects then attempted to summit at their own pace and, at the time of descent, completed a Lake Louise Acute Mountain Sickness Questionnaire and reported maximum elevation reached.

RESULTS

One hundred twenty-one participants enrolled in the study. Data were collected on 111 subjects (92% response rate), of whom 60% summited. On univariate analysis, there was no association between any postexercise vital sign and summit success. Specifically, there was no significant difference in the mean postexercise peripheral oxygen saturation (Spo2) between summiters (75%) and nonsummiters (74%; 95% CI, -3 to 1; P = .37). The distance a subject walked in 6 minutes (6MWTD) was longer in summiters (617 m) compared with nonsummiters (560 m; 95% CI, 7.6 to 106; P = .02). However, this significance was not maintained on a multivariate analysis performed to control for age, sex, and guide status (P = .08), leading to the conclusion that 6MWTD was not a robust predictor of summit success.

CONCLUSIONS

This study did not show a correlation between postexercise oxygen saturation or 6MWTD and summit success on Denali.

Diagnosis and prediction of the occurrence of acute mountain sickness measuring oxygen saturation--independent of absolute altitude?

PURPOSE

Commercialization of trekking tourism enables untrained persons to participate in trekking tours. Because hypoxia is one of the main purported triggers for acute mountain sickness (AMS), pulse oximetry, which measures arterial oxygen saturation (SPO2), is discussed to be a possible and useful tool for the diagnosis of AMS. The purpose of this study was to evaluate possible associations between SPO2 values and the occurrence of AMS.

METHODS

In 204 trekkers, SPO2 values (pulse oximetry) were measured and the Lake Louise Self-assessment Score (LLS) was administered over the first 7 days of their trekking tours.

RESULTS

During treks at altitudes of 2500-5500 m in Nepal, India, Africa, and South America, 100 participants suffered from mild AMS, 3 participants suffered from severe AMS, and 9 participants reported both mild and severe AMS. The lowest mean SPO2 was 85.5 (95 % confidence interval (CI), 83.9-86.1 %) on day 5. SPO2 and LLS exhibited a weak to moderate negative correlation for all days of the study (ρ ranging from -0.142 to -0.370). Calculation of time-shifted associations of 24 and 48 h resulted in the disappearance of most associations. Susceptibility to headaches (odds ratio (OR) 2.9-7.2) and a history of AMS (OR 2.2-3.1) were determined to be potential risk factors for the development of AMS.

CONCLUSION

Since there is no strong altitude-independent association between AMS and SPO2 during the first week of high-altitude adaptation, the implementation of pulse oximetry during trekking in order to detect and predict AMS remains questionable.

Physiology in Medicine: A physiologic approach to prevention and treatment of acute high-altitude illnesses

With the growing interest in adventure travel and the increasing ease and affordability of air, rail, and road-based transportation, increasing numbers of individuals are traveling to high altitude. The decline in barometric pressure and ambient oxygen tensions in this environment trigger a series of physiologic responses across organ systems and over a varying time frame that help the individual acclimatize to the low oxygen conditions but occasionally lead to maladaptive responses and one or several forms of acute altitude illness. The goal of this Physiology in Medicine article is to provide information that providers can use when counseling patients who present to primary care or travel medicine clinics seeking advice about how to prevent these problems. After discussing the primary physiologic responses to acute hypoxia from the organ to the molecular level in normal individuals, the review describes the main forms of acute altitude illness--acute mountain sickness, high-altitude cerebral edema, and high-altitude pulmonary edema--and the basic approaches to their prevention and treatment of these problems, with an emphasis throughout on the physiologic basis for the development of these illnesses and their management.

Carbohydrate and glutamine supplementation modulates the Th1/Th2 balance after exercise performed at a simulated altitude of 4500 m

OBJECTIVE

The aim of this study was to evaluate the effect of carbohydrate or glutamine supplementation, or a combination of the two, on the immune system and inflammatory parameters after exercise in simulated hypoxic conditions at 4500 m.

METHODS

Nine men underwent three sessions of exercise at 70% VO2peak until exhaustion as follows: 1) hypoxia with a placebo; 2) hypoxia with 8% maltodextrin (200 mL/20 min) during exercise and for 2 h after; and 3) hypoxia after 6 d of glutamine supplementation (20 g/d) and supplementation with 8% maltodextrin (200 mL/20 min) during exercise and for 2 h after. All procedures were randomized and double blind. Blood was collected at rest, immediately before exercise, after the completion of exercise, and 2 h after recovery. Glutamine, cortisol, cytokines, glucose, heat shock protein-70, and erythropoietin were measured in serum, and the cytokine production from lymphocytes was measured.

RESULTS

Erythropoietin and interleukin (IL)-6 increased after exercise in the hypoxia group compared with baseline. IL-6 was higher in the hypoxia group than pre-exercise after exercise and after 2 h recovery. Cortisol did not change, whereas glucose was elevated post-exercise in the three groups compared with baseline and pre-exercise. Glutamine increased in the hypoxia + carbohydrate + glutamine group after exercise compared with baseline. Heat shock protein-70 increased post-exercise compared with baseline and pre-exercise and after recovery compared with pre-exercise, in the hypoxia + carbohydrate group. No difference was observed in IL-2 and IL-6 production from lymphocytes. IL-4 was reduced in the supplemented groups.

CONCLUSION

Carbohydrate or glutamine supplementation shifts the T helper (Th)1/Th2 balance toward Th1 responses after exercise at a simulated altitude of 4500 m. The nutritional strategies increased in IL-6, suggesting an important anti-inflammatory effect.

Association of elevation, urbanization and ambient temperature with obesity prevalence in the United States

BACKGROUND

The macrogeographic distribution of obesity in the United States, including the association between elevation and body mass index (BMI), is largely unexplained. This study examines the relationship between obesity and elevation, ambient temperature and urbanization.

METHODS AND FINDINGS

Data from a cross-sectional, nationally representative sample of 422603 US adults containing BMI, behavioral (diet, physical activity, smoking) and demographic (age, sex, race/ethnicity, education, employment, income) variables from the 2011 Behavioral Risk Factor Surveillance System were merged with elevation and temperature data from WorldClim and with urbanization data from the US Department of Agriculture. There was an approximately parabolic relationship between mean annual temperature and obesity, with maximum prevalence in counties with average temperatures near 18 °C. Urbanization and obesity prevalence exhibited an inverse relationship (30.9% in rural or nonmetro counties, 29.2% in metro counties with <250000 people, 28.1% in counties with population from 250000 to 1 million and 26.2% in counties with >1 million). After controlling for urbanization, temperature category and behavioral and demographic factors, male and female Americans living <500 m above sea level had 5.1 (95% confidence interval (CI) 2.7-9.5) and 3.9 (95% CI 1.6-9.3) times the odds of obesity, respectively, as compared with counterparts living ≥ 3000 m above sea level.

CONCLUSIONS

Obesity prevalence in the United States is inversely associated with elevation and urbanization, after adjusting for temperature, diet, physical activity, smoking and demographic factors.

Oximetry fails to predict acute mountain sickness or summit success during a rapid ascent to 5640 meters

OBJECTIVE

The purpose of this study was to determine whether arterial oxygen saturation (Spo(2)) and heart rate (HR), as measured by a finger pulse oximeter on rapid arrival to 4260 m, could be predictive of acute mountain sickness (AMS) or summit success on a climb to 5640 m.

METHODS

Climbers (35.0 ± 10.1 years; 51 men, 5 women) were transported from 2650 m to the Piedra Grande hut at 4260 m on Pico de Orizaba within 2 hours. After a median time of 10 hours at the hut, they climbed toward the summit (5640 m) and returned, with a median trip time of 14 hours. The Lake Louise Self-Assessment Scale (LLSS) for AMS, HR, and Spo(2) were collected on arrival at the hut and repeated immediately before and after the climbers' summit attempts.

RESULTS

Average Spo(2) for all participants at 4260 m before their departure for the summit was 84.4% ± 3.7%. Thirty-seven of the 56 participants reached the summit, and 59% of all climbers met the criteria for AMS during the ascent. The Spo(2) was not significantly different between those who experienced AMS and those who did not (P = .82); neither was there a difference in Spo(2) between summiteers and nonsummiteers (P = .44). Climbers' HR just before the summit attempt was not related to AMS but was significantly lower for summiteers vs nonsummiteers (P = .04).

CONCLUSIONS

The Spo(2) does not appear to be predictive of AMS or summit success during rapid ascents.

Pulse oximetry at high altitude

Pulse oximetry is a valuable, noninvasive, diagnostic tool for the evaluation of ill individuals at high altitude and is also being increasingly used to monitor the well-being of individuals traveling on high altitude expeditions. Although the devices are simple to use, data output may be inaccurate or hard to interpret in certain situations, which could lead to inappropriate clinical decisions. The purpose of this review is to consider such issues in greater detail. After examining the operating principles of pulse oximetry, we describe the available devices and the potential uses of oximetry at high altitude. We then consider the pitfalls of pulse oximetry in this environment and provide recommendations about how to deal with these issues. Device users should recognize that oxygen saturation changes rapidly in response to small changes in oxygen tensions at high altitude and that device accuracy declines with arterial oxygen saturations of less than 80%. The normal oxygen saturation at a given elevation may not be known with certainty and should be viewed as a range of values, rather than a specific number. For these reasons, clinical decisions should not be based on small differences in saturation over time or among individuals. Effort should also be made to minimize factors that cause measurement errors, including cold extremities, excess ambient light, and ill-fitting oximeter probes. Attention to these and other issues will help the users of these devices to apply them in appropriate situations and to minimize erroneous clinical decisions.

[Arterial oxygen saturation during ascent of a mountain higher than 8,000 meters]

BACKGROUND

Arterial oxygen saturation (SaO2) diminishes with altitude.

AIM

To know the values of SaO2 in healthy mountaineers during the ascent of a mountain higher than 8,000 metres.

METHOD

On occasion of an expedition to Gasher brum II (8,035 m), SaO2 at rest was measured by pulse oxymetry during the approach march, in the base camp (on day one and one month later), in camps II and III, during the assault at 7,500 m and on the summit.

RESULTS

During the approach march, the SaO2 in Paiju (3,365 m) was 92.9 +/- 1.4% and in Gore II (4,250 m) 85.0 +/- 4.3%. In the base camp (5,200 m) it was 78.4 +/- 9.5% on the first day and 87.4 +/- 3.0% one month later (p < 0.007). In camp II (6,500 m) it was 72.7 +/- 6.7%. In camp III (7,000 m) it was 68.0 +/- 9.3% (recorded on 21 asymptomatic climbers). At this altitude a SaO2 of 40% was recorded during sleep in an asymptomatic subject, apparently without apnoeic crises. During the assault at 7,500 m, SaO2 was 60.5 +/- 13.5% (measured on 4 climbers). On the summit (8,035 m) the SaO2 of two subjects was 84% and 88%, respectively.

CONCLUSION

During expeditions to mountains higher than 8,000 metres, mountaineers have extremely low values of SaO2, similar to those of patients with severe respiratory failure. SaO2 increases progressively with acclimatization. SaO2 on the summit could have been relatively high, probably because of hyperventilation.

Auto-PEEP in the therapy of AMS in one person at 4,330 m

BACKGROUND

The human organism is exposed to considerable hypoxic stress at high altitudes. Our intention was to investigate if a special breathing pattern with expiration against the resistance of pursed lips leads to an elevation in oxygen saturation (SaO(2)). For the first time ever, oxygen saturation was measured continuously during the initial situation, during self-performed positive end-expiratory pressure breathing (auto-PEEP) itself, and during observation afterwards.

MATERIALS AND METHODS

The investigation was performed on a 33-year-old male suffering from high-altitude illness (Lake Louise Score, 9) after a 4-day rapid ascent from 350 m to 4,330 m during an expedition to Mount McKinley (6,198 m). SaO(2) was measured continuously at 4-s intervals. After a rest of 1.5 h in a dorsal recumbent position with a slightly elevated (about 15 degrees ) upper body, the patient used a wristwatch to breathe according to a special time pattern (inspiration 2 s, expiration 8 s against the resistance of pursed lips). After 30 min, breathing was then allowed without any restrictions, and the inspiration/expiration ratio was approximately 1:1.

RESULTS

There was a relatively sharp rise in SaO(2) from an average of 62% to 85% within only 5 min after auto-PEEP began. This was followed by a comparable rise to values of 95% at the end of the auto-PEEP period. During normal breathing, SaO(2) decreased slowly within half an hour to values of about 70% and remained at this level. The person reported relief in symptoms and no exhaustion. Vertigo-an indication of hypocapnia caused by hyperventilation-was not observed.

DISCUSSION

The 30% rise in SaO(2) and the improved saturation level after auto-PEEP are remarkable. Elevated intra-thoracal pressure may lead to a reopening of collapsed alveoli in addition to an improved gradient of alveolar-capillary pressure. In addition, a pressure-induced displacement of interstitial fluid resulting in a reduced diffusion distance may lead to improved alveolar-capillary diffusion. This would explain the slower rise in SaO(2) after 10 min of auto-PEEP and the elevated level of SaO(2) compared to the initial level before auto-PEEP.

CONCLUSION

As a result of the substantial and lasting improvement in SaO(2) in combination with relief in AMS symptoms and its easy use, auto-PEEP (30 min every 2 h) can be a useful therapy option in the event of high-altitude-induced hypoxia and AMS.

EEG, ECG and oxygen concentration changes from sea level to a simulated altitude of 4000m and back to sea level

In order to describe how high altitude affects the body during a one night stay at 4000m experiments were performed in a hypobaric chamber and compared to a study on Dachstein (mountain in Austria, 2700m). Ten subjects had to perform a reaction time task at different altitudes. The EEG and ECG were recorded simultaneously. Additionally, the oxygen saturation of the blood was measured at different altitudes and the subjects filled out a Lake Louise questionnaire that describes the degree of altitude mountain sickness (AMS). After elevation from 134m to 4000m in the hypobaric chamber heart-rate increased from 68.9bpm to 81.6bpm, RMSSD (root mean square of squared differences of adjacent heart beat intervals) decreased from 54.3ms to 33.3ms, the LF/HF ratio increased from 2.5 to 3.9 and oxygen saturation decreased to 82.7% after 11h at 4000m altitude. The Lake Louise Score (LSS) reached 3.4 after one night at 4000m. EEG beta activity between 14Hz and 18Hz was attenuated at 4000m and also after return to 134m. The results indicate that the subjects were not able to adapt to 4000m within 12h in the hypobaric chamber. Even after 1h after the return to 134m all parameters are still affected from the night at 4000m altitude. ECG and EEG changes are in line with results obtained at 2700m height at Dachstein.

Comparing questionnaires for the assessment of acute mountain sickness

Exposure to high altitude in nonacclimatized subjects may lead to acute mountain sickness (AMS). AMS is a syndrome characterized by headache accompanied by one or more other symptoms, such as light-headedness, dizziness, loss of appetite, nausea, vomiting, fatigue, lassitude, and trouble sleeping. Assessing the presence and degree of AMS can be done using self-administered questionnaires like the Lake Louise Questionnaire (LLQ) and the Environmental Symptoms Questionnaire-III (ESQ-III). We compared LLQ and ESQ-III in 266 trekkers of different nationalities trekking over a 5400-m-high pass to assess if the two questionnaires identify the same population as suffering from AMS and to see whether using English questionnaires poses problems for nonnative English-speaking persons. The use of English questionnaires by nonnative English speakers influenced the outcome for some nationalities. For criterion scores yielding similar prevalence of AMS, ESQ-III labeled 20% of cases differently (AMS or no AMS) when compared to LLQ. Correlations between similar individual questions of ESQ-III and LLQ were variable, and there was considerable scatter between ESQ-III and LLQ scores. In conclusion, English questionnaires may pose problems in some international settings, and ESQ-III and LLQ may identify different populations as suffering from AMS.

[Pathology related to altitude: the experience on K2]

The pathology related with the altitude is a common entity above 3000 m. It includes mild symptoms to severe illness such as cerebral or pulmonary edema. Cold-induced injuries may produce permanent tissue loss and surgical amputation. Recognition is made mainly through symptoms. Adequate treatment of these patients allows for rapid resolution of the symptoms and improves outcome.