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The Science of Altitude Training

Revision as of 05:57, 24 July 2018 by User:Fellrnr (User talk:Fellrnr | contribs)

Revision as of 05:57, 24 July 2018 by User:Fellrnr (User talk:Fellrnr | contribs)

If you're travelling to higher altitude or using Altitude Training to improve performance, it's worth understanding the science of how altitude effects athletes. The key takeaways are that acclimation takes about two weeks and most people will benefit from iron supplements, ideally starting weeks or months before altitude exposure.

Contents

1 The Effects of Altitude

  • At altitude there is lower air pressure. This lower pressure means that each lung full of air has less oxygen (lower partial pressure of O2). This results in lower oxygen saturation in the blood (Hypoxia).
  • Altitude is generally considered High altitude as 1500 to 3500m (5,000' to 11,500'), Very high altitude as 3500 to 5500m (11,500' to 18,000'), and Extreme altitude as above 5500m (18,000')[1].
  • Rapid ascent from near sea level to above 2500m/8,000' can result in problems ranging from mild sickness to life-threatening Acute Mountain Sickness (AMS), but with gradual acclimation extreme altitudes can be tolerated[1].
  • One "rule of thumb" is that above 3000m/10,000', you shouldn't sleep more than 300m/1,000' higher than the previous night[1].
  • A key feature of acclimation to altitudes up to 5,000m/16,000' is an increase in breathing[2]. Other changes include an increase in heart rate, increase in blood pressure, increase in red blood cells, reduction in blood volume (increased urine output), increase in capillary density, and an increase in mitochondria and oxidative enzymes[3]. However, the increase in capillary density might be at least partly due to a reduction in muscle fiber size[4].
  • The human body adjusts to lower blood oxygen saturation in many ways, and one key adaptation that is of interest to athletes is an increase in red blood cells, but the performance improvements from Altitude Training may come from additional sources[5][6].
  • The effects of altitude are non-linear. From sea level to Leadville (10,170 ft), your blood oxygen levels may drop 6% from 96% to 90%. Going up another 4,000 ft to Pike's Peak (14,110), blood oxygen levels may drop a further 8% to 82%. Running is harder at altitude as seen by the VO2max drop. At Leadville your VO2max may drop by ~15% (range 4-30%)
  • SpO2 at altitude may be slightly misleading as the oxygen deliver to the muscles may be modified by O2 dissociation curve shifts caused by changes in pH, PCO2, and blood temperature[7]. However, SpO2 is cheap and easy to monitor and should not be ignored.
  • There is great individual variability in the response to altitude[8]. Some studies have classified subjects as 'responders' and 'non-responders' due to the significance of this variability. This variability can change over time within an individual. I met someone in Tanzania who had been a porter on Kilimanjaro (19,334 ft) until he lost his ability to cope with the altitude.
  • Some variability may be due to differences in iron intake/availability. Low blood iron (serum ferritin < 20 ng/ml female, < 30 ng/ml male) may limit the body's ability to generate new red blood cells, which is part of the altitude adaptation. Studies in the USSR and CIS have shown genetic factors as well. See below for more details.
  • Generally, 'live high, train low' seems to work better than 'live high, train high'. Intermittent Hypoxic Exposure may have additional benefits over other Altitude Training Approaches.
  • Altitude acclimatization takes time, with 2 weeks being a point of diminishing returns. This is based on a study of athletes traveling to 2340m/7,766' that showed a performance decrease of 26% on arrival, they recovered by 6.0% after 7 days, another 5.7% after 14 days, but only another 1.4% after 21 days[9]. These findings seem broadly similar for those sleeping in an altitude tent (normobaric hypoxia) [10].
  • Training needs to be reduced at altitude, and this reduction can lead to detraining. 'Live high, train low' and Intermittent Hypoxic Exposure help mitigate this problem.
  • It is a myth that if you can't arrive at altitude with time to acclimate, it's best to arrive near within a day of your event. This is based on the idea that performance at altitude declines for a period before improving. However, research shows that the reduction in performance occurs immediately and improves gradually over time[11]. At moderate altitudes (1700m/5,600') performance was better after just 18 hours compared with 6 hours[12].

2 Nutrition and Altitude

There's good evidence that nutrition is important for altitude acclimation, at least as far as iron goes. For other nutrients, the evidence is a little less clear.

2.1 Iron

For adaptation to altitude, probably the most critical nutrient is Iron. Low iron stores can result in reduced adaptation to altitude[13] and altitude training will reduce the body's stores of iron[14]. It's been suggested that iron supplementation may need to be started some months prior to the needed altitude acclimation due to the time taken for iron store to accumulate[15], and six weeks may be insufficient time[8]. One study found that in a group of 178 athletes, iron stores (serum ferritin) reduced by 33% without supplementation, reduced by 14% with 105mg/day of iron and increased by 37% with 210 mg/day of iron[16]. Further, the non-supplemented athletes only increased hemoglobin mass by 1.1%, those on 105mg/day by 3.3% and those on 210 mg/day by 4.0%. The supplements were started one week before, and during, altitude exposure. The supplements were not given randomly but based on serum ferritin status. Those with levels above 100 ug/L were not supplemented, those with 30-100 ug/L were given 105 mg/day and those below 30 ug/L were given 210 mg/day. This suggests that even those with good iron status may need supplementation. However, that's a lot of iron, considering the RDA for men is only 8 mg/day and women 18 mg/day, and the tolerable upper intake is only 45 mg/day. Taking more than four times the tolerable upper intake is a little worrying, and the study made no mention of reported side effects. The study used a prolonged release supplement that included 105 mg iron with 1,000 mg Vitamin C (which can increase absorption of Iron) in a product called "Ferro Grad C."

2.2 Antioxidants

There's some indications that "live high, train low" may increase the need for antioxidants[17]. However, while some studies suggest that antioxidant supplementation might be beneficial[18][19], it seems the preponderance of evidence is that antioxidant supplements may hinder recovery and adaptation to training stress[20][21][22].

2.3 Carbohydrate

It's unclear if the macronutrient mix of carbohydrate/protein/fat should be different at altitude, as most claims of the need for a high carbohydrate diet at altitude are based on sea level studies rather than any change due to altitude[23].

2.4 Vitamin D

There's no evidence for Vitamin D supplementation at altitude specifically, though there is the suggestion[23] that Vitamin D benefits might be particularly valuable as it may act as a vasodilator[24][25]. There's also the possibility that longer term (months) exposure to extreme altitude could result in bone loss[26].

3 Hydration and Altitude

Within 90 minutes of exposure to higher altitudes, urine output increases[27][28], resulting in the loss of water and sodium[29]. The diuretic effects of low pressure at altitude may be exacerbated by the temperature, as cold conditions can result in "cold diuresis"[30][31]. One study suggests that hydration could exacerbate performance problems at altitude, but the study was short term (1 hour) and used dehydration that was not related to the altitude[32]. While there is a net loss of water as a response to altitude, it's unclear if increased fluid intake would help or hinder performance. There is an argument that this loss of fluid is an important adaptation to altitude that concentrates the blood and reduces the demand on the heart[33]. There is some evidence that increased hydration does not increase the blood volume and may exacerbate fluid retention[34]. (Fluid retention is the build up of fluid between or inside the cells rather than in the blood.) There is further risk of Hyponatremia with excessive drinking, so caution is needed, and the advice to "drink to thirst" would seem to remain valid. (Note that while people with kidney problems may be able to tolerate short durations at modest altitudes, the risks are unclear[35].)

4 Assessing Altitude Impact

The Lake Louise Scoring System (LLSS) is used to assess the severity of AMS (Acute Mountain Sickness, or altitude sickness). The 2018 version of the LLSS scores headache, Gastrointestinal symptoms, fatigue, dizziness, and functional disruption to provide an overall assessment of AMS severity[36]. (Sleep disruption was removed as it does not appear to be well corelated with AMS[37].) However, analysis has shown that a single question is just as effective as the LLSS[38]. This is the Clinical Functional Score, which asks "overall if you had any symptoms, how did they affect your activity?", with possible answers of

  1. "Not at all."
  2. "Symptoms present but did not force any change in activity or itinerary."
  3. "My symptoms forced me to stop the ascent or to go down on my own power."
  4. "I had to be evacuated to a lower altitude."

5 Effects of hypoxia

Low levels of SpO2 effect brain functioning as shown in the following table[39].

SpO2 Description Effect Notes
100-80% Mild Hypoxia Normal brain functioning This mild level of hypoxia does not affect the functioning of the brain, but some people can be sensitive enough to detect changes.
80-60% Moderate Hypoxia Decreasing brain function Vision can be altered, including tunnel vision. Coordination is impaired in things like handwriting will deteriorate. Below 80% the skin may become blue (cyanosis). Mental functioning is impaired, sometimes creating euphoria or tranquility, including indifference to everything including pain. At this level some people become fixated on whatever they were doing when the hypoxia began, which can be dangerous. Memory and speech can also be impaired. There may be older treat visual hallucinations, feelings of depersonalization and even out of body experiences.
60-40% Severe hypoxia Muscle paralysis Apparent unconsciousness.
<40% Extreme hypoxia Unconsciousness and eventually death

6 Hypoxia and Altitude

The following table[40] gives an idea of different SpO2 levels at different altitudes. Intermittent Hypoxic Exposure can increase SpO2 levels at a given altitude[41], which are specified in the table below for some altitudes. However, the actual SpO2 value at a given altitude will vary on many factors, so use this as a rough guide only.

Altitude(feet) Altitude(meters) Air Pressure(mmHg) Oxygen Pressure(mmHg)  % of sea level Oxygen Equivalent O2 partial

pressure at sea level

SpO2

Unconditioned

SpO2

Conditioned

0 0 760 159 100 20.9 98%
5,000 1,524 639 134 84 17.6 95%
7,500 2,286 584 122 77 16.1 93%
9,000 2,740 554 116 73 15.3 90.3% (+/-3.4%) 93.8% (+/-2%)
10,000 3,048 534 112 70 14.6 89%
11,000 3,360 514 107 68 14.2 86.4 % (+/- 4.8%) 90.2% (+/-2.7%)
12,500 3,810 487 102 64 13.4 87%
14,000 4,267 460 96 61 12.7 83%
15,000 4,570 443 93 58 12.1 81.7% (+/-6%) 89.1% (+/-3%)
16,500 5,029 418 87 55 11.5 77%
18,000 5,490 395 83 52 10.9 84.9% (+/-4%)
20,000 6,096 365 76 48 10.0 65%
21,000 6,400 351 73 46 9.6 79.2% (+/-6%)
25,000 7,620 299 62 39 8.2 <60%

7 See Also

8 References

  1. ↑ 1.0 1.1 1.2 SwapnilJ Paralikar, JagdishH Paralikar, High-altitude medicine, Indian Journal of Occupational and Environmental Medicine, volume 14, issue 1, 2010, pages 6, ISSN 0019-5278, doi 10.4103/0019-5278.64608
  2. ↑ J. B. West, Human responses to extreme altitudes, Integrative and Comparative Biology, volume 46, issue 1, 2006, pages 25–34, ISSN 1540-7063, doi 10.1093/icb/icj005
  3. ↑ A. S. Goldfarb-Rumyantzev, S. L. Alper, Short-term responses of the kidney to high altitude in mountain climbers, Nephrology Dialysis Transplantation, volume 29, issue 3, 2013, pages 497–506, ISSN 0931-0509, doi 10.1093/ndt/gft051
  4. ↑ Masao Mizuno, Gabrielle K Savard, Nils-Holger Areskog, Carsten Lundby, Bengt Saltin, Skeletal Muscle Adaptations to Prolonged Exposure to Extreme Altitude: A Role of Physical Activity?, High Altitude Medicine & Biology, volume 9, issue 4, 2008, pages 311–317, ISSN 1527-0297, doi 10.1089/ham.2008.1009
  5. ↑ CJ. Gore, SA. Clark, PU. Saunders, Nonhematological mechanisms of improved sea-level performance after hypoxic exposure., Med Sci Sports Exerc, volume 39, issue 9, pages 1600-9, Sep 2007, doi 10.1249/mss.0b013e3180de49d3, PMID 17805094
  6. ↑ Christopher J Gore, Will G Hopkins, Counterpoint: Positive effects of intermittent hypoxia (live high:train low) on exercise performance are not mediated primarily by augmented red cell volume, Journal of Applied Physiology, volume 99, issue 5, 2005, pages 2055–2057, ISSN 8750-7587, doi 10.1152/japplphysiol.00820.2005
  7. ↑ Jerome A. Dempsey, Peter D. Wagner, Exercise-induced arterial hypoxemia, Journal of Applied Physiology, volume 87, issue 6, 1999, pages 1997–2006, ISSN 8750-7587, doi 10.1152/jappl.1999.87.6.1997
  8. ↑ 8.0 8.1 Robert F. Chapman, James Stray-Gundersen, Benjamin D. Levine, Individual variation in response to altitude training, Journal of Applied Physiology, volume 85, issue 4, 1998, pages 1448–1456, ISSN 8750-7587, doi 10.1152/jappl.1998.85.4.1448
  9. ↑ B. Schuler, JJ. Thomsen, M. Gassmann, C. Lundby, Timing the arrival at 2340 m altitude for aerobic performance., Scand J Med Sci Sports, volume 17, issue 5, pages 588-94, Oct 2007, doi 10.1111/j.1600-0838.2006.00611.x, PMID 17316377
  10. ↑ NE. Townsend, CJ. Gore, AG. Hahn, MJ. McKenna, RJ. Aughey, SA. Clark, T. Kinsman, JA. Hawley, CM. Chow, Living high-training low increases hypoxic ventilatory response of well-trained endurance athletes., J Appl Physiol (1985), volume 93, issue 4, pages 1498-505, Oct 2002, doi 10.1152/japplphysiol.00381.2002, PMID 12235052
  11. ↑ B. Schuler, J. J. Thomsen, M. Gassmann, C. Lundby, Timing the arrival at 2340 m altitude for aerobic performance, Scandinavian Journal of Medicine & Science in Sports, volume 17, issue 5, 2007, pages 588–594, ISSN 09057188, doi 10.1111/j.1600-0838.2006.00611.x
  12. ↑ AR. Weston, G. Mackenzie, MA. Tufts, M. Mars, Optimal time of arrival for performance at moderate altitude (1700 m)., Med Sci Sports Exerc, volume 33, issue 2, pages 298-302, Feb 2001, PMID 11224821
  13. ↑ J. Stray-Gundersen, C. Alexander, A. Hochstein, D. deLemos, B D Levine, FAILURE OF RED CELL VOLUME TO INCREASE TO ALTITUDE EXPOSURE IN IRON DEFICIENT RUNNERS, Medicine & Science in Sports & Exercise, volume 24, issue Supplement, 1992, pages S90, ISSN 0195-9131, doi 10.1249/00005768-199205001-00541
  14. ↑ D. Roberts, DJ. Smith, Training at moderate altitude: iron status of elite male swimmers., J Lab Clin Med, volume 120, issue 3, pages 387-91, Sep 1992, PMID 1517685
  15. ↑ E W Askew, Environmental and physical stress and nutrient requirements, The American Journal of Clinical Nutrition, volume 61, issue 3, 1995, pages 631S–637S, ISSN 0002-9165, doi 10.1093/ajcn/61.3.631S
  16. ↑ James R. Connor, Andrew D. Govus, Laura A. Garvican-Lewis, Chris R. Abbiss, Peter Peeling, Christopher J. Gore, Pre-Altitude Serum Ferritin Levels and Daily Oral Iron Supplement Dose Mediate Iron Parameter and Hemoglobin Mass Responses to Altitude Exposure, PLOS ONE, volume 10, issue 8, 2015, pages e0135120, ISSN 1932-6203, doi 10.1371/journal.pone.0135120
  17. ↑ V Pialoux, R Mounier, E Rock, A Mazur, L Schmitt, J-P Richalet, P Robach, J Brugniaux, J Coudert, N Fellmann, Effects of the 'live high–train low' method on prooxidant/antioxidant balance on elite athletes, European Journal of Clinical Nutrition, volume 63, issue 6, 2008, pages 756–762, ISSN 0954-3007, doi 10.1038/ejcn.2008.30
  18. ↑ P. Tauler, A. Aguiló, I. Gimeno, E. Fuentespina, JA. Tur, A. Pons, Response of blood cell antioxidant enzyme defences to antioxidant diet supplementation and to intense exercise., Eur J Nutr, volume 45, issue 4, pages 187-95, Jun 2006, doi 10.1007/s00394-005-0582-7, PMID 16365696
  19. ↑ AH. Goldfarb, MJ. McKenzie, RJ. Bloomer, Gender comparisons of exercise-induced oxidative stress: influence of antioxidant supplementation., Appl Physiol Nutr Metab, volume 32, issue 6, pages 1124-31, Dec 2007, doi 10.1139/H07-078, PMID 18059586
  20. ↑ MC. Gomez-Cabrera, E. Domenech, M. Romagnoli, A. Arduini, C. Borras, FV. Pallardo, J. Sastre, J. Viña, Oral administration of vitamin C decreases muscle mitochondrial biogenesis and hampers training-induced adaptations in endurance performance., Am J Clin Nutr, volume 87, issue 1, pages 142-9, Jan 2008, doi 10.1093/ajcn/87.1.142, PMID 18175748
  21. ↑ TT. Peternelj, JS. Coombes, Antioxidant supplementation during exercise training: beneficial or detrimental?, Sports Med, volume 41, issue 12, pages 1043-69, Dec 2011, doi 10.2165/11594400-000000000-00000, PMID 22060178
  22. ↑ VH. Teixeira, HF. Valente, SI. Casal, AF. Marques, PA. Moreira, Antioxidants do not prevent postexercise peroxidation and may delay muscle recovery., Med Sci Sports Exerc, volume 41, issue 9, pages 1752-60, Sep 2009, doi 10.1249/MSS.0b013e31819fe8e3, PMID 19657294
  23. ↑ 23.0 23.1 Małgorzata Michalczyk, Miłosz Czuba, Grzegorz Zydek, Adam Zając, Józef Langfort, Dietary Recommendations for Cyclists during Altitude Training, Nutrients, volume 8, issue 6, 2016, pages 377, ISSN 2072-6643, doi 10.3390/nu8060377
  24. ↑ YC. Li, G. Qiao, M. Uskokovic, W. Xiang, W. Zheng, J. Kong, Vitamin D: a negative endocrine regulator of the renin-angiotensin system and blood pressure., J Steroid Biochem Mol Biol, volume 89-90, issue 1-5, pages 387-92, May 2004, doi 10.1016/j.jsbmb.2004.03.004, PMID 15225806
  25. ↑ M. Wacker, MF. Holick, Vitamin D - effects on skeletal and extraskeletal health and the need for supplementation., Nutrients, volume 5, issue 1, pages 111-48, Jan 2013, doi 10.3390/nu5010111, PMID 23306192
  26. ↑ Hiroyuki Tanaka, Keiji Minowa, Tetsuya Satoh, Tatsuya Koike, Bone atrophy at high altitude, Journal of Bone and Mineral Metabolism, volume 10, issue 1, 1992, pages 31–36, ISSN 0914-8779, doi 10.1007/BF02383459
  27. ↑ Wulf Hildebrandt, Andy Ottenbacher, Markus Schuster, Erik R. Swenson, Peter Bärtsch, Diuretic effect of hypoxia, hypocapnia, and hyperpnea in humans: relation to hormones and O2 chemosensitivity, Journal of Applied Physiology, volume 88, issue 2, 2000, pages 599–610, ISSN 8750-7587, doi 10.1152/jappl.2000.88.2.599
  28. ↑ ER. Swenson, TB. Duncan, SV. Goldberg, G. Ramirez, S. Ahmad, RB. Schoene, Diuretic effect of acute hypoxia in humans: relationship to hypoxic ventilatory responsiveness and renal hormones., J Appl Physiol (1985), volume 78, issue 2, pages 377-83, Feb 1995, doi 10.1152/jappl.1995.78.2.377, PMID 7759405
  29. ↑ E. R. Swenson, T. B. Duncan, S. V. Goldberg, G. Ramirez, S. Ahmad, R. B. Schoene, Diuretic effect of acute hypoxia in humans: relationship to hypoxic ventilatory responsiveness and renal hormones, Journal of Applied Physiology, volume 78, issue 2, 1995, pages 377–383, ISSN 8750-7587, doi 10.1152/jappl.1995.78.2.377
  30. ↑ D. Scott, JA. Rycroft, J. Aspen, C. Chapman, B. Brown, The effect of drinking tea at high altitude on hydration status and mood., Eur J Appl Physiol, volume 91, issue 4, pages 493-8, Apr 2004, doi 10.1007/s00421-003-1015-z, PMID 14872247
  31. ↑ M. Hynynen, R. Ilmarinen, I. Tikkanen, F. Fyhrquist, Plasma atrial natriuretic factor during cold-induced diuresis, European Journal of Applied Physiology and Occupational Physiology, volume 67, issue 3, 1993, pages 286–289, ISSN 0301-5548, doi 10.1007/BF00864230
  32. ↑ John W. Castellani, Stephen R. Muza, Samuel N. Cheuvront, Ingrid V. Sils, Charles S. Fulco, Robert W. Kenefick, Beth A. Beidleman, Michael N. Sawka, Effect of hypohydration and altitude exposure on aerobic exercise performance and acute mountain sickness, Journal of Applied Physiology, volume 109, issue 6, 2010, pages 1792–1800, ISSN 8750-7587, doi 10.1152/japplphysiol.00517.2010
  33. ↑ RF. Grover, JV. Weil, JT. Reeves, Cardiovascular adaptation to exercise at high altitude., Exerc Sport Sci Rev, volume 14, pages 269-302, 1986, PMID 3525187
  34. ↑ P. Bärtsch, N. Pfluger, M. Audétat, S. Shaw, P. Weidmann, P. Vock, W. Vetter, D. Rennie, O. Oelz, Effects of slow ascent to 4559 M on fluid homeostasis., Aviat Space Environ Med, volume 62, issue 2, pages 105-10, Feb 1991, PMID 1825779
  35. ↑ A. M. Luks, R. J. Johnson, E. R. Swenson, Chronic Kidney Disease at High Altitude, Journal of the American Society of Nephrology, volume 19, issue 12, 2008, pages 2262–2271, ISSN 1046-6673, doi 10.1681/ASN.2007111199
  36. ↑ Robert C. Roach, Peter H. Hackett, Oswald Oelz, Peter Bärtsch, Andrew M. Luks, Martin J. MacInnis, J. Kenneth Baillie, Eric Achatz, Edi Albert, Jon S. Andrews, James D. Anholm, Mohammad Zahid Ashraf, Paul Auerbach, Buddha Basnyat, Beth A. Beidleman, R.R. Berendsen, Marc Moritz Berger, Konrad E. Bloch, Hermann Brugger, Annalisa Cogo, Ricardo Gonzalez Costa, Andrew Cumpstey, Allen Cymerman, Tadej Debevec, Catriona Duncan, David Dubowitz, Angela Fago, Michael Furian, Matt Gaidica, Prosenjit Ganguli, Michael P.W. Grocott, Debra Hammer, David Hall, David Hillebrandt, Matthias Peter Hilty, Gigugu Himashree, Benjamin Honigman, Ned Gilbert-Kawai, Bengt Kayser, Linda Keyes, Michael Koehle, Samantha Kohli, Arlena Kuenzel, Benjamin D. Levine, Mona Lichtblau, Jamie Macdonald, Monika Brodmann Maeder, Marco Maggiorini, Daniel Martin, Shigeru Masuyama, John McCall, Scott McIntosh, Gregoire Millet, Fernando Moraga, Craig Mounsey, Stephen R. Muza, Samuel Oliver, Qadar Pasha, Ryan Paterson, Lara Phillips, Aurélien Pichon, Philipp A. Pickerodt, Matiram Pun, Manjari Rain, Drummond Rennie, Ge Ri-Li, Steven Roy, Samuel Verges, Tatiana Batalha Cunha dos Santos, Robert B. Schoene, Otto D. Schoch, Surinderpal Singh, Talant Sooronbaev, Craig D. Steinback, Mike Stembridge, Glenn Stewart, Tsering Stobdan, Giacomo Strapazzon, Andrew W. Subudhi, Erik Swenson, A. A. Roger Thompson, Martha Tissot van Patot, Rosie Twomey, Silvia Ulrich, Nicolas Voituron, Dale R. Wagner, Shih-hao Wang, John B. West, Matt Wilkes, Gabriel Willmann, Michael Yaron, Ken Zafren, The 2018 Lake Louise Acute Mountain Sickness Score, High Altitude Medicine & Biology, volume 19, issue 1, 2018, pages 4–6, ISSN 1557-8682, doi 10.1089/ham.2017.0164
  37. ↑ Christian Schulz, David P. Hall, Ian J. C. MacCormick, Alex T. Phythian-Adams, Nina M. Rzechorzek, David Hope-Jones, Sorrel Cosens, Stewart Jackson, Matthew G. D. Bates, David J. Collier, David A. Hume, Thomas Freeman, A. A. Roger Thompson, John Kenneth Baillie, Network Analysis Reveals Distinct Clinical Syndromes Underlying Acute Mountain Sickness, PLoS ONE, volume 9, issue 1, 2014, pages e81229, ISSN 1932-6203, doi 10.1371/journal.pone.0081229
  38. ↑ David Meier, Tinh-Hai Collet, Isabella Locatelli, Jacques Cornuz, Bengt Kayser, David L. Simel, Claudio Sartori, Does This Patient Have Acute Mountain Sickness?, JAMA, volume 318, issue 18, 2017, pages 1810, ISSN 0098-7484, doi 10.1001/jama.2017.16192
  39. ↑ anesthesia and hypoxia, Anesthesia !!website!!, http://www.anesthesiaweb.org/hypoxia.php, 2018-05-31 !!access-date!!
  40. ↑ "The Pilot: An Air Breathing Mammal," Mehler, Stanley R. MD, Human Factors Bulletin, Flight Safety Foundation, 1981
  41. ↑ Ronald K. Hetzler, Christopher D. Stickley, Iris F. Kimura, Michelle LaBotz, Andrew W. Nichols, Kenneth T. Nakasone, Ryan W. Sargent, Lawrence P.A. Burgess, The Effect of Dynamic Intermittent Hypoxic Conditioning on Arterial Oxygen Saturation, Wilderness & Environmental Medicine, volume 20, issue 1, 2009, pages 26–32, ISSN 10806032, doi 10.1580/08-WEME-OR-218.1
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