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Acclimation, Altitude Science, Athletic Training, Health, High Altitude, High Altitude Training & Fitness

PORTRAIT OF A HIGH-ALTITUDE ATHLETE: THE ULTRA MOUNTAIN ATHLETE, 2.0

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Six years ago, I sat down with ultra mountain athlete Yuki Ikeda for the first time for an interview about his experience training, competing and recovering in the extreme altitudes of Colorado’s central Rocky Mountains. At the time, Yuki had only recently started competing in running races at over 10,000′ (3048m) since beginning his career as a cyclist in 2003, going pro in 2007.

In 2019, he managed to compete in his first Leadville Race Series, which included 50- and 100-mile MTB and trail run courses starting at above 10,000′ and rising to over 12,000′.

This summer, I had the pleasure of catching up with this extraordinary athlete and his wife Sayako, a dietitian and high-altitude runner herself who inspired Yuki to compete as a runner as well as a cyclist. The pair have been spending summers in the Colorado high country every year to train and compete before returning to their home in Japan to continue competing year-round, and between their experience training and racing and nutritional expertise, they make a formidable team.

Six years ago, we were all three of us in our thirties, and when I asked about what has changed about training and acclimating to the altitude since then, there was certainly a consensus about how it hasn’t gotten easier now that we are all in our forties. A significant part of their strategy for success has always been nutrition, and at this elevation, maximizing the delivery of oxygen throughout the body makes a huge difference. In our last interview, Yuki talked about incorporating foods rich in nitrates, which facilitate your body’s production of nitric oxide, like red bell peppers, arugula and beets, and these are still a big part of their diet.

Something they’ve been paying closer attention to lately is iron, also a critical component of blood. It’s dangerous for iron levels to be too high, but it can be a critical supplement for healthy circulation. In the case of long distance runners, blood vessels can take a considerable beating as feet hit ground over and over again for long periods of time. One food in particular that contains a high level of iron is clams. In Japan and the Pacific, asari, also known as Manila clam or Japanese cockle, is a regular part of cuisine and easy to find. Here in the middle of the Rockies, however, Yuki and Sayako have been buying canned clams to supplement their iron.

Every summer, the couple have come to the Colorado Rockies to train and compete. They’re full-time residence is in Tokyo, Japan, so each time they are traveling from sea-level, a dramatic and quick ascent to a high elevation. The decrease in available oxygen in the air at high altitude prompts a response in the body to create more red blood cells in order to carry more oxygen throughout the body. This requires more iron, which is vital for this process.

Additionally, the two athletes are paying special attention to nutrient absorption. Most of their diet is plant-based, and until recently, Yuki has been eating a completely vegan diet. Organic compounds found in plants called tannins and polyphenols — while beneficial — can inhibit your body’s absorption of nutrients you eat by up to 90%. So consuming something with these compounds along with your meal may dramatically decrease the benefits of nutrition in the food you’re eating. Coffee contains these compounds, so Sayako recommends waiting at least an hour after a meal to have a cup of coffee in order to maximize nutrient uptake. Even better, vitamin C can enable greater absorption, so consuming it (even in other foods such as a citrus) with a meal can be very helpful.

“… iron is also necessary for the hypoxia-inducible-factor (HIF) pathway, cellular energy production, myoglobin function (the muscle oxygen acceptor), and thyroid hormone function,” write DeLoughery and DeLoughery in a recent article for the Wilderness Medical Society. “The HIF pathway is the key regulator of the body’s response to hypoxia. Typically, the HIF-1 and HIF-2 proteins are rapidly degraded, but they are stabilized by hypoxic conditions when prolyl hydroxylase, which tags the HIFp roteins for degradation, is inhibited. When stabilized, the HIF proteins function as transcription factors that coordinate the synthesis of various proteins essential for the body’s response to hypoxia. Prolyl hydroxylase requires iron to function, and with a low iron level, this is less effective, leading to an exaggerated response to hypoxia.”

It is also important to note that, as Yuki and Sayako point out, it can take three to four weeks for anyone to experience noticeable results from any change in diet and nutrition. Keeping this in mind, it is advisable to increase iron intake weeks ahead of a trip to a high altitude environment, although further research may be needed to recommend just how much.

References

DeLoughery, MD, Emma P. Emma P. DeLoughery, MD and Thomas G. DeLoughery, MD, “Women, Iron, and Altitude — Path to the Peak”, Wilderness Medical Society 2025.

Acclimation, Altitude Science, Diabetes, Exposure, Genetics, Health, High Altitude

Living High and Testing Higher: Can Living at High Altitudes Skew Diagnostic Diabetes Tests? 

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by Hailey Garin PA-S

Diabetes is very prevalent in our society, with around 11% of the population in the United States diagnosed with this disease2. A key diagnostic test used in healthcare is the hemoglobin A1c (HbA1c) blood test. This blood test measures an individual’s average blood sugar over a 3-month period. A value of less than 5.7% is normal, 5.7%-6.4% is pre-diabetic range, and 6.5% and greater is a diagnosis of diabetes1. There are other blood tests that are used in the diagnoses of diabetes including fasting plasma glucose (FPG) and 2-hour postprandial glucose (2-h PG) testing. FPG testing measures blood sugar levels after 8 or more hours of fasting. A FPG value of 126 mg/dl or greater is diagnostic of diabetes. The 2-h PG test is a blood sugar reading 2 hours after eating a meal. A 2-h PG value of 200 mg/dl or higher is diagnostic of diabetes3. Currently the HbA1c blood test is the most used to diagnose diabetes, and many individuals around the world are diagnosed and placed on medications based off HbA1c results alone.

But is this appropriate for individuals living at altitude? 

A groundbreaking study completed in mainland China has begun to answer this question for us. Altitudes and Hemoglobin A1c Values: An Analysis Based on Two Nationwide Cross-sectional Studies by Zheng et al was published in 2024. In this study, 95,000 adults were examined by comparing HbA1c, fasting blood glucose, and 2-hour postprandial (after a meal) glucose levels between individuals living above and below 2,500 meters (8,200 feet)4. 

A key finding of this study was that individuals living above 2,500 meters had higher HbA1c levels but the same FPG and 2-h PG results as individuals below 2,500 meters4. The individuals at altitude may have HbA1c levels that are falsely elevated. This inaccuracy can lead to an inappropriate diagnosis of diabetes in individuals living at altitude. The researchers explained that oxygen levels at higher elevations are lower, and the body reacts to these low levels by increasing levels of red blood cells and the lifespan of red blood cells. When lifespan is increased, the hemoglobin is exposed to glucose in our blood stream for longer, eliciting a higher HbA1c result despite normal blood sugar levels4. 

Another study by Bazo-Alvarez et. al in 2017 sought to evaluate the relationship between HbA1c and FPG among individuals at sea level compared to those at high altitude.

The study analyzed data from 3613 Peruvian adults without diagnosed diabetes from both sea level and high altitude (>3000m). The mean values for hemoglobin, HbA1c, and FPG differed significantly between these populations. The correlation between HbA1c and FPG was quadratic at sea level but linear at high altitude, suggesting different glucose metabolism patterns. Additionally, for an HbA1c value of 48 mmol/mol (6.5%), corresponding mean FPG values were significantly different: 6.6 mmol/l at sea level versus 14.8 mmol/l at high altitude.

These studies show that one-size-fits all screening for diabetes may not work for everyone, especially those living at altitude. Ebert Family Clinic, at 2743m (9000 ft) in the Colorado Rocky Mountains, has been researching the effects of altitude on many aspects of health including examining HbA1c levels in our residents and thus far we have seen elevated HbA1c levels in our otherwise healthy, “thin”, and active patients despite implementing appropriate lifestyle interventions to lower blood sugar. This can lead to unnecessary health anxiety that we hope to avoid by determining if HbA1c will continue to be an appropriate diagnostic tool with our residents living well above 2,500 meters.

References

1. Centers for Disease Control and Prevention. (n.d.-a). A1C test for diabetes and Prediabetes. Centers for Disease Control and Prevention. https://www.cdc.gov/diabetes/diabetes-testing/prediabetes-a1c-test.html 

2. Centers for Disease Control and Prevention. (n.d.-b). National Diabetes Statistics Report. Centers for Disease Control and Prevention. https://www.cdc.gov/diabetes/php/data-research/index.html 

3. U.S. Department of Health and Human Services. (n.d.). Diabetes tests & diagnosis – NIDDK. National Institute of Diabetes and Digestive and Kidney Diseases. https://www.niddk.nih.gov/health-information/diabetes/overview/tests-diagnosis 

4. Zheng, R., Xu, Y., Li, M., Wang, L., Lu, J., Wang, T., Xu, M., Zhao, Z., Zheng, J., Dai, M., Zhang, D., Chen, Y., Wang, S., Lin, H., Wang, W., Ning, G., & Bi, Y. (2024). Altitudes and hemoglobin A1C values: An analysis based on two nationwide cross-sectional studies. Diabetes Care, 47(2). https://doi.org/10.2337/dc23-1549 

Acclimation, Altitude Science, Anesthesia, Health, High Altitude, Medicine, Technology

Anesthesia and Altitude

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by Megan Wilson, NP-S

One of the last things anybody wants to go through is a surgical procedure, especially if you happen to be in the mountains on vacation. Unfortunately, life happens, and whether you’re a visitor to high-altitude or a permanent resident, there is a chance you may need surgical care. 

Anesthesia is a requirement for surgical procedures and there are varying levels of anesthetic available. General anesthesia, often referred to as “going off to sleep”, is where you are completely unconscious and anesthetic gases and medications keep you sedated while a machine breathes for you during your procedure. Monitored anesthesia care (MAC), also known as conscious sedation, is when the anesthesiologist keeps you comfortable with meds, but you are still able to breathe on your own. Medications given for surgery affect your ability to breathe, which is why your vital signs (oxygen levels, blood pressure, heart rate) are monitored through a machine by a doctor. 

How is this different at high altitude?

When you head to higher elevations, barometric pressure decreases and causes partial pressure of oxygen to decrease – this makes oxygen harder to effectively get into your lungs and causes hypoxemia/low oxygen levels (Leissner & Mahmood, 2009). This leads to a condition commonly known as altitude sickness, causing headaches and trouble breathing, and in more serious cases, it can also lead to high altitude pulmonary edema (HAPE) and high altitude cerebral edema (HACE). Much like oxygen, anesthetic gases are also affected by barometric pressures, impacting the effectiveness of inhaled anesthetics (Bebic et al., 2021). Additionally, equipment is affected by high altitude – meters on anesthesia machines that monitor gas/oxygen levels tend to under-read at higher elevations (Bebic et al., 2021; Leissner & Mahmood, 2009). Pulse oximetry, which measures your overall oxygen saturation (the percentage of oxygen in your blood) also has limited accuracy at high altitude (Bebic et al., 2021). Providers who practice at higher elevations should be aware of these nuances and treat accordingly. The most important treatment we have to help with the effects of partial pressure at high altitude is supplemental oxygen (Leissner & Mahmood, 2009).  

Unfortunately, there is limited research on the effects of high altitude and anesthesia, and even less on the effects of anesthetic drugs at high altitude vs. sea level (Bebic et al., 2021). With current published data, it is clear that surgical risks increase with elevation. Whether it’s the potential for equipment to malfunction, or novice providers new to high-altitude unaware of the subtleties in treatment, it is critical to be mindful of compromised respiratory status at elevation when considering which anesthetic agents to use for surgery. 

References

Bebic, Z., Brooks Peterson, M., & Polaner, D. M. (2021). Respiratory physiology at high altitude and considerations for pediatric patients. Pediatric Anesthesia, 32(2), 118-125.

https://doi.org/10.1111/pan.14380

Leissner, K. B., & Mahmood, F. U. (2009). Physiology and pathophysiology at high altitude:

Considerations for the anesthesiologist. Journal of Anesthesia, 23(4), 543-553.

https://doi.org/10.1007/s00540-009-0787-7

Acclimation, Altitude Science, Athletic Training, Health, High Altitude, High Altitude Training & Fitness

KYRGYZSTAN VS SUMMIT COUNTY, COLORADO: EXERCISE AT ALTITUDE

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How does the low oxygen environment at altitude affect our ability to exercise?  What is the risk for developing harmful changes in the heart and lungs? Does sleep apnea contribute to these risks? Can supplemental oxygen reverse or reduce these risks and increase our exercise ability at altitude?

An audience of conference participants sit observing a slide in a presentation reading "Cardiac function and PH in 97 Kyrgyz Highlander and 76 Lowlander (50% women).

These important questions have been studied by an international research team conducting tests on residents of the Tien Shan mountain range in Kyrgyzstan, 2500-3500 m (8,200 to 11,482 feet). Dr. Silvia Ulrich presented some of their findings at the Hypoxia 2025 conference in Lake Louise in the Canadian Rocky Mountains this past winter. Using an exercise bike they measured ECG, pulmonary gas exchange and oxygen saturation in healthy highlanders. Participants’ average age was 48 years, 46 % were women, and their average oxygen saturation (SpO2) at rest was 88%. Normal occupations include nomadic herdsmen, hunters and soldiers who usually travel by car or horse, with no prior experience cycling or running. An echocardiogram was performed to assess pulmonary artery pressures (PAP) and right heart function.

Arterial blood gas analysis at baseline showed a normal pH, low oxygen, mildly decreased carbon dioxide and bicarbonate, and higher hemoglobin concentrations. Bicarbonate values were 22-26 moles/L. In Summit county, in the Rocky Mountains of Colorado, with residents living between 2500 to 3300 m bicarbonate values are 17-20 moles/L.

Results showed their peak oxygen uptake, and peak work rate was reduced by one quarter compared to predicted values for lowlanders. Oxygen saturation decreased during exercise. “Exercise limitation was related to an exercise -induced worsening of hypoxemia, high ventilation equivalents for oxygen uptake and carbon dioxide output, a reduced external work efficiency and a lower peak heart rate than predicted for age.” (1) In other words, they had to breathe harder to maintain their oxygen and carbon dioxide at normal values and use more effort for the same musculoskeletal output. Their heart rate did not increase as much as a person from lower altitude doing the same work.

There is little research on exercise capacity in long-term residents at altitude.  Most studies focus on athletes or comparing healthy acclimatized men to recent arrivals. The hypoxic environment is a known risk for pulmonary hypertension, which can lead to exercise intolerance and fatigue that is reversible with descent or oxygen use when diagnosed in a timely manner. Sleep apnea with the accompanying hypoxic episodes adds to this risk. Summit County residents show improvement in both systemic and pulmonary hypertension with supplemental oxygen during sleep, according to local health care providers.

Kyrgyzstan residents studied showed a strong correlation between  the incidence of sleep apnea with hypoxia (time below 90% SpO2), and abnormal pulmonary artery pressures. Echocardiograms compared 97 highlanders with 76 lowlanders who were asymptomatic. Between 6% and 35% had increased PAP depending on which definition is used. 

A slide at a conference presentation on the effect of high-dose SOT on pulmonary artery pressures and cardiac output in highlanders at risk for PH at 3250 meters.

The research team also evaluated their response to supplemental oxygen at altitude and 760m elevation using the six minute walk test. Although the test subjects reported less shortness of breath and had higher measured oxygen levels they were not able to walk further. Supplemental oxygen did reduce pulmonary artery pressures in those at risk when tested at 3,200 m.

A slide from a presentation on an experiment where oxygen levels in residents of high altitude in Kyrgyzstan are measured during a 6-minute walk.

This research was conducted by a crew of scientists who brought all the equipment with them to a basic medical clinic in a village.

Summit County cardiologist Warren Johnson was impressed by the numbers of people with elevated pressures in their lungs. “It could be as high as 30 per cent of adults,” he told local physicians. Symptoms are subtle: decreased exercise tolerance, mild shortness of breath, trouble sleeping, high red blood cell counts. Most people just think they are out of condition or aging.

A study in Spiti Valley India of residents living at 9000-13000 ft found an incidence of three per cent with PH.  Dr Johnson suspects this is a highly adapted population with centuries of mountain living.

Diagnosing this condition early with Echocardiogram can prevent serious disability.  Treatment is as simple as sleeping on oxygen. These measurements and much more are performed on a daily basis at the St. Anthony Summit Hospital, a 34-bed hospital serving five counties in Colorado, located at 2800 m. A parallel study to establish baseline normal values for the healthy population and identify the risk for pulmonary hypertension in asymptomatic mountain residents would be valuable for health care providers who are frequently asked to counsel residents on the risk of living at altitude.

References

Forrer A, Scheiwiller PM, Mademilov M, Lichtblau M, Sheraliev U, Marazhapov NH, Saxer S, Bader P, Appenzeller P, Aydaralieva S, Muratbekova A, Sooronbaev TM, Ulrich S, Bloch KE, Furian M. Exercise Performance in Central Asian Highlanders: A Cross-Sectional Study. High Alt Med Biol. 2021 Dec;22(4):386-394. doi: 10.1089/ham.2020.0211. Epub 2021 Aug 24. PMID: 34432548.

Lichtblau M, Saxer S, Furian M, Mayer L, Bader PR, Scheiwiller PM, Mademilov M, Sheraliev U, Tanner FC, Sooronbaev TM, Bloch KE, Ulrich S. Cardiac function and pulmonary hypertension in Central Asian highlanders at 3250 m. Eur Respir J. 2020 Aug 20;56(2):1902474. doi: 10.1183/13993003.02474-2019. PMID: 32430419.

Acclimation, Acetazolamide, Altitude Science, Child Growth & Development, Diamox, Doc Talk, Health, High Altitude, Medicine, Sleep at Altitude

Sharing at the Chateau: 23rd International Hypoxia Symposium in Lake Louise

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I attended the 23rd International Hypoxia Symposium in Lake Louise, Canada to present some of the research on altitude I’ve been conducting in Colorado. The conference has been going on since 1979, and for the past 26  years the organizers have been Robert Roach and Peter Hackett, world-renowned medical researchers from Colorado. Meeting most of the famous altitude researchers from all over the world was an inspiration.  Personal talks and sharing information were equally important to imbibing the latest knowledge about hypoxia and hemoglobin.

A slide is projected onto a screen over the heads of conference participant, depicting statistics showing infant birthweight in mammals decreasing over increasing elevations.
From Jay Storz’s presentation at the 2025 International Hypoxia Symposia in Lake Louise, Canada

Antarctic Icefish: Life Without Hemoglobin, was presented by Kristen O’Brien, expanding the concept of oxygen distribution in living beings and introducing us to varieties of fish we have never heard of. Her talk was followed by our “Mice and Men” guy, Jay Storz (and colleague Graham Scott), who along with Jon Velotta mentioned in our blogpost on the show “This Podcast Will Kill You” collect the large eared deer mice from peaks such as Blue Sky Mountain to study adaptation to hypoxia in their labs. The talk recognized for first prize was on Altitude Headaches, including a discussion of migraines, by Andrew Charles.

Every evening there was a banquet and speaker.  Astronaut Jessica Meir spent 210 days aboard the space station.  She shared a wide range of challenges such as exercising without gravity, choosing a compatible crew, getting boxes of treats from home, and effects of prolonged weightlessness on your eyes and muscles.

A slide projected onto a conference room screen before participants depicts results for six minute walks on and off oxygen.
Silvia Ulrich presented on Pulmonary Circulation of Central Asian Highlanders at the 2025 International Hypoxia Symposium at Lake Louise, Canada.

The research I would like to see duplicated in Summit County was from Kyrgyzstan, where Silvia Ulrich studied the hearts and lungs of the permanent residents at 9000 feet using the six minute walk as one of her tools.  They did not score higher when studied at sea level! She ran tests for pulmonary hypertension, which could be important here.

Of course, there was a talk on Sleep Disordered Breathing (sleep apnea) by Esther Schwarz, something we pay a great deal of attention to in our own clinic in Frisco, Colorado and have several research projects on the improvement we see with supplemental oxygen. The role of mitochondria in cellular function in hypoxia was presented by Dr. Christian Arias-Reyes, a researcher at Seattle Children’s Hospital who is originally from La Páz, Bolivia.  I met him at the Chronic Hypoxia conference in 2019 when he was a graduate student in Quebec and again in La Páz at this year’s conference. 

A line of people pose in front of a cafe with signs and plants hanging above a stone-tiled street lined with buildings
Altitude experts Dr. Zubieta Calleja, Dr. Christian Arias-Reyes, Dr. Michele Samaja and Dr. Christine Ebert-Santos with colleagues of the Hypoxia Symposia in front of a pizzeria in Coroico, Bolivia.

A deep dive into how our neurons react to hypoxia in the brain by releasing nitric oxide to dilate blood vessels and preserve circulation reenforced the counseling I do here in my clinic to parents whose children have breath holding spells or babies with dips in their oxygen on home monitors. Along with all the millions of children and adults living at 12,000 feet in Bolivia, we can witness that hypoxia does not cause brain damage. (Not to be confused with anoxia, a complete lack of oxygen.)

Lastly, Nobel prize winner and fellow pediatrician Gregg Semenza spoke on research to find a blocking compound against HIF- hypoxia inducible factor, as a cure for some cancers. Gregg’s work was described in our blog on the Nobel prize being awarded to scientists working on hypoxia. HIF deserves its own blogpost! More about cancer and hypoxia at altitude from the Chronic Hypoxia Conference in La Páz.

I was selected to give my presentation, “Colorado Kids Are Smaller” to both conferences. I have been working on this for 20 years. You can read more on our blog where it is titled “Mountain Kids Are Smaller”.  My goal is to get a unique growth chart for children under age two at altitude, to save parents and providers anxiety and money trying to get our kids to “be the same” as those at sea level.

The most useful tidbit of information came on the bus ride back to Calgary. Dr Heimo Mairbaurl, PhD shared that a quarter dose of acetazolamide was sufficient for his acute mountain sickness symptom prevention, 62 mg for a guy over 6 feet tall. Although there was a study on a new possible preventive treatment, prochlorperazine, done on Mount Blue Sky last fall, I still swear by the old drug formerly known as “Diamox”.

Acclimation, Altitude Science, Exposure, Health, High Altitude

ERUCTILE DYSFUNCTION AT ALTITUDE: Low Barometric Pressures Worsen Discomfort for Those Who Can’t Burp

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by Noor Pawar, PA-S


Retrograde Cricopharyngeus Dysfunction and the Impact of Altitude

Lucie Rosenthal’s journey, captured in her viral Reddit video, sheds light on a lesser-known condition: retrograde cricopharyngeus dysfunction, or “no-burp syndrome.” What makes her story particularly fascinating is the intersection of this medical condition with the effects of altitude—a factor that significantly influences our bodies and their functions.

In her video, Lucie joyfully discovers her ability to burp after a procedure that injects Botox into the upper esophageal muscle. However, her initial excitement turns into an uncontrollable experience that raises questions about the body’s mechanisms, especially in relation to altitude. As she recounts the bloating and discomfort that accompanied her condition, it echoes a broader issue faced by many individuals living in higher elevations, where changes in atmospheric pressure can exacerbate gastrointestinal symptoms.

The relationship between altitude and digestive health is an important consideration. At higher elevations, the reduced atmospheric pressure can lead to gas expansion in the stomach and intestines, intensifying feelings of bloating and discomfort. This is particularly relevant for individuals like Daryl Moody, who struggled with no-burp syndrome while also engaging in activities like skydiving. As he ascended, the altitude caused his stomach to inflate like a bag of chips, amplifying his discomfort and highlighting how altitude can complicate existing health issues.

The article emphasizes the growing awareness surrounding retrograde cricopharyngeus dysfunction, especially through online communities like the r/noburp subreddit. These platforms provide vital support for those affected, particularly in regions where altitude impacts digestive health. It’s a testament to how individuals can come together to share experiences and coping strategies, transforming personal struggles into a collective understanding of a shared condition.

The financial barriers mentioned in the article are further complicated for those living in high-altitude areas. With treatments often deemed “experimental” by insurance companies, individuals may face significant out-of-pocket expenses, particularly in regions where healthcare costs are already high.

Historically reports of individuals unable to burp date back centuries. The contemporary acknowledgment of retrograde cricopharyngeus dysfunction reflects an evolving understanding of how environmental factors, such as altitude, can play a crucial role in health. As we continue to learn more about this condition, the need for further research into the effects of altitude on digestive health becomes increasingly apparent.

In summary, Lucie Rosenthal’s story illustrates the complexities of retrograde cricopharyngeus dysfunction, particularly in relation to altitude. The interplay between physiological responses and environmental factors underscores the importance of patient advocacy and community support in addressing these issues. As we navigate our health, understanding how altitude can influence our bodies highlights the need for a comprehensive approach to medical care that considers all aspects of a patient’s environment.

Accessibility, Acclimation, Altitude Science, Athletic Training, Child Growth & Development, Exposure, Genetics, Health, High Altitude, Medicine, Postural Orthostatic Tachycardia Syndrome (POTS)

Thin Air Making You Lightheaded?

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by Joy Plutowski, PA-S2

Feeling lightheaded after going to a high altitude is a key symptom of acute mountain sickness (AMS)—a condition caused by the reduced oxygen available in thin mountain air. AMS often comes with other symptoms like headache, nausea, and fatigue, usually starting after a recent climb to higher elevations.

But what if it’s not just AMS? For people with conditions like postural orthostatic tachycardia syndrome (POTS), which affects blood flow and heart rate, lightheadedness at altitude could be a clue to an underlying issue. While AMS happens because of low oxygen, POTS is tied to a problem with how the nervous system regulates the body. In some cases, going to altitude might even uncover undiagnosed POTS, as symptoms can become more noticeable in these conditions.

Living With POTS

Living with POTS has been a journey of adaptation, requiring constant vigilance and adjustment to manage a complex array of symptoms. Each new environment brings its own challenges, demanding a personalized approach to maintaining stability. My recent clinical rotation in Frisco, Colorado, situated at 9,000 feet above sea level, provided an invaluable opportunity to observe firsthand how altitude influences the physiology of POTS. An overnight stay in Denver for partial acclimatization helped mitigate some initial altitude-related exacerbations, but the first few days at higher elevation were marked by pronounced symptoms, including lightheadedness, tachycardia, and insomnia. Physically demanding activities, such as snowboarding, pushed my body to its limits, resulting in extreme fatigue and heightened tachycardia. Despite these challenges, I observed gradual improvement; by the second week, I had returned to my baseline—if not better than during my time in the heat of Phoenix, Arizona. Interestingly, the colder temperatures of the region seemed to offer symptomatic relief, likely through vasoconstriction that may enhance circulation. These experiences have deepened my understanding of POTS as a highly individualized condition, emphasizing the critical importance of lifestyle modifications, environmental considerations, and a patient-specific approach to management. My journey underscores how adaptability and tailored interventions can significantly improve functionality and quality of life for those navigating the complexities of this syndrome.

What is POTS?

Postural Orthostatic Tachycardia Syndrome (POTS) is a chronic condition characterized by an abnormal increase in heart rate upon standing. It is a form of dysautonomia, involving dysregulation of the autonomic nervous system, which balances the sympathetic (“fight or flight”) and parasympathetic (“rest and digest”) systems. The autonomic nervous system regulates involuntary bodily functions such as heart rate, blood pressure, and digestion. POTS primarily affects women, with symptoms often appearing in their teens or twenties. It is estimated to affect between 1 to 3 million people in the United States, though it is likely underdiagnosed due to lack of awareness. Under normal conditions, standing triggers the body to constrict blood vessels and slightly increase heart rate to counteract gravity’s effects. In POTS, this response is impaired, leading to blood pooling in the lower extremities and reduced blood flow to the brain. The exact cause of POTS is not fully understood, but it is commonly linked to viral infections, autoimmune conditions, genetic predispositions, small fiber neuropathy, impaired norepinephrine regulation, or hypovolemia (low blood volume). Notably, long-COVID, a range of long-term symptoms and conditions resulting from an acute COVID infection, is linked to POTS. Approximately 1% of patients with an acute COVID-19 infection go on to develop orthostatic intolerance (Cheshire, 2024). Studies also show that keeping up with COVID-19 vaccinations can prevent long-COVID.

The hallmark symptom of POTS is an excessive increase in heart rate of over 30 bpm quickly after standing (WP, 2024). Common symptoms include tachycardia, palpitations, dizziness, and fainting (syncope or near-syncope), brain fog, headaches, lightheadedness, and severe fatigue. Less common symptoms include nausea, bloating, abdominal discomfort, shakiness, and exercise intolerance. POTS symptoms are often worsened by factors such as dehydration, heat, prolonged standing, illness, or physical stress. Diagnosing POTS involves a tilt-table test which monitors heart rate and blood pressure during positional changes. Treatment for POTS focuses on improving symptoms and quality of life through lifestyle adjustments. Key components include hydration, increased salt intake, compression garments, graded exercise therapy, and psychological support. Medications such as Fludrocortisone or Midodrine, that both increase blood pressure, may be added if the provider deems it fit. The course of POTS varies widely; some individuals experience significant improvement with treatment, others may have persistent symptoms. Early diagnosis and a multidisciplinary approach can lead to better outcomes.

The Effect of Altitude on the Autonomic Nervous System

Altitude significantly influences the autonomic nervous system due to reduced oxygen levels and atmospheric pressure, which challenge the body’s ability to maintain homeostasis. At higher elevations, the sympathetic nervous system becomes more active, increasing heart rate and blood pressure to compensate for lower oxygen availability. This is because hypoxia alters chemoreceptor and baroreceptor function, leading to increased sympathetic excitation and decreased parasympathetic tone.

During a study at 4300 m, urine norepinephrine levels—a marker of sympathetic activity—peaked 4–6 days after altitude exposure (Mazzeo, 1998). The study compared women in different hormonal phases when exposed to high altitude. The urinary norepinephrine levels heart rates both increased over time in both follicular and luteal phases. The differences between the two were not statistically significant, showing that women experience sympathetic increase at altitude regardless of what phase of their cycle. This was done in comparison to a previous study showing the same findings in men (Mazzeo, 1998). 

A line graph indicating the rise follicular and luteal heart rates in beats per minute as days at altitude increase.
A line graph indicating increasing amounts per 24 hours of urinary norepinephrine.

Other physiological responses include increased ventilation, cardiac output, and heart rate. However, with acclimatization, heart rate and cardiac output typically return to sea-level values within 9–12 days (Hainsworth et al., 2007). Over time, improved oxygen-carrying capacity enhances tolerance to orthostatic stress. All in all, orthostatic tolerance during hypobaric hypoxia involves three mechanisms: cardiovascular control of heart rate and cardiac output, cerebrovascular responses to hypocapnic hypoxia (due to hyperventilation), and elevated sympathetic activity (Blaber et al., 2003). 

For individuals with POTS, altitude-related stresses may exacerbate symptoms. Hypoxia and reduced barometric pressure can worsen fatigue, brain fog, and dizziness by increasing the body’s effort to oxygenate tissues. Reduced oxygen delivery to the brain and tissues may intensify lightheadedness and syncope— which is already common in POTS.

Although acclimatization typically occurs within 1–2 weeks at altitude in healthy individuals, research on acclimatization in POTS patients is limited. Further studies are needed to determine whether individuals with autonomic dysfunction can adapt as effectively as those without.

Living With POTS at Altitude 

Living with POTS at altitude presents unique challenges that require careful management, as patients may find it harder to adapt to the altitude-induced changes in blood oxygenation and pressure regulation. These challenges are compounded by the existing difficulties they face in maintaining autonomic stability. The reduced oxygen levels and increased demands on the cardiovascular system can amplify POTS symptoms, making daily activities more difficult. Patients with POTS generally understand their triggers and have a protocol that was formulated with their provider. Such strategies include staying well-hydrated, using compression garments, increasing salt intake, decreasing alcohol and caffeine consumption, and avoiding sudden changes in posture. Also, gradual exposure to altitude helps the body adapt to the reduced oxygen and barometric pressure, minimizing symptom flares. For individuals with POTS visiting high-altitude environments, strict adherence to their treatment regimen, including lifestyle modifications and potentially pharmacologic interventions, is paramount for managing their condition effectively.

References

Blaber AP, Hartley T, Pretorius PJ (2003) Effect of acute exposure to 3,660 m altitude on orthostatic responses and tolerance. J Appl Physiol 95:591–601

Cheshire WP. (2024) Postural tachycardia syndrome. UpToDate. 

Hainsworth, R., Drinkhill, M. J., & Rivera-Chira, M. (2007). The autonomic nervous system at high altitude. Clinical autonomic research : official journal of the Clinical Autonomic Research Society, 17(1), 13–19

Mazzeo RS, Child A, Butterfield GE, et al. (1998) Catecholamine response during 12  days of high-altitude exposure (4,300 m) in women. J Appl Physiol 84:1151–1157

Joy Plutowski is a second-year PA student born and raised in Arizona. She completed her undergraduate degree in biology at Arizona State University and is now pursuing her master’s at Midwestern University in Glendale, AZ. Before PA school, she worked as a medical scribe for an interventional cardiologist, a field she is interested in pursuing. Currently, she has the wonderful opportunity of completing her pediatrics rotation in Frisco, CO. In her free time, Joy enjoys exploring national parks, playing video games, dancing, and most recently, snowboarding. 

Acclimation, Altitude Science, Exposure, Genetics, Health, High Altitude

Boy Scouts and Skiers: Reducing the Risk of Developing Acute Mountain Sickness

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Thousands of boy scouts travel to Philmont Scout Ranch (PSR) in Cimarron, New Mexico each year in hopes of improving their wilderness survival skills by ascending its rugged, mountainous terrain. Elevations at PSR range from 2011 to 3792 m, in sharp contrast to the lower elevations the boy scouts are used to. Those with a history of daily headaches, gastrointestinal illnesses, and prior acute mountain sickness were found to be most at risk of developing altitude related illnesses while ascending PSR. The incidence of acute mountain sickness was 13.7% at PSR when participants ascended from base camp (2011 m) to 3000m+ as compared to up to 67% in other staged ascent studies [3]. Similarly to PSR, millions of people ascend the Colorado Rocky Mountains during ski season and face the same potential complications. This risk makes it abundantly important to investigate potential ways to prevent the development of altitude related illnesses.

Oxygen from inspired air (air breathed in) flows down its concentration gradient from the alveolar space into the blood, where it is carried primarily bound to hemoglobin and delivered to tissue. At high altitudes, oxygen availability and barometric pressure decrease remarkably, hindering the concentration gradient and increasing the risk of tissue hypoxia [2]. Progressive tissue hypoxia eventually leads to high altitude illnesses (HAI), which are cerebral and pulmonary syndromes resulting from rapid ascent. The likelihood of developing these disease processes can be greatly reduced if the body is given time to acclimate to the increased altitude. This is especially relevant during the holidays, when many are traveling from lower altitudes to higher altitudes abruptly for vacation or to visit with family.

This raises the question: should travelers spend the night in Denver before ascending into the mountains to allow for acclimatization and reduce the risk of HAI?

The rate of acclimatization, or the body’s ability to adjust to and accommodate increased oxygen requirement, is difficult to generalize given rate of ascension is not the only factor that influences the development of HAI. This process can take anywhere from days to potentially months depending on a number of factors including cardiopulmonary comorbidities, a history of HAI, genetics, certain medications, substance usage, and degree of physical exertion amongst others [5].

Despite the multifactorial nature of developing HAI, rate of ascent remains one of the primary risk factors. Studies have shown that spending time at moderate altitude before ascending to higher altitudes in a process called “staged ascent” decreases the likelihood of developing HAI in unacclimatized individuals [4]. A recent study conducted at the U.S. Army Research Institute of Environmental Medicine assessed incidence of acute mountain sickness (AMS, a subcategory of HAI), in unacclimatized individuals who were staged for 2 days at altitudes of 2500 m, 3000 m, and 3500 m respectively before ascending to 4300 m. Another group ascended directly to 4300 m without staging. Ultimately, the incidence of AMS was significantly lower in the staged groups than in the direct ascent group; AMS incidence in the staged groups was up to 67%, while AMS incidence in the direct ascent group was up to 83% [1].

Two graphs, A and B, illustrate the incidence of acute mountain sickness by percent at elevations of 2500m, 3000m, 3500m and a control group, as well as peak acute mountain sickness severity ranked from 0 to 2 for the same elevations and a control group.

Graphs A and B show that the incidence of AMS at 4300 m is reduced when unacclimatized individuals are staged at 2500 m, 3000 m, and 3500 m as compared to those who directly ascended to 4300 m [1].

Given the above information, unacclimatized individuals, skiers and boy scouts alike, may benefit from spending the night in Denver before coming to the mountains, as this mimics staged ascent and thus decreases the incidence of HAI.

Tall, snowy pines rise up out of powdery snow on a ski slope overlooking forests stretching out toward a range of white peaks in the distance under a sunny blue sky.
View from the top of Keystone Resort taken while snowboarding (elevation 3782 m)

References

[1] Beth A. Beidleman et al. “Acute Mountain Sickness is Reduced Following 2 Days of Staging During Subsequent Ascent to 4300m”. In: High Altitude Medicine & Biology 19.4 (2018). Published Online: 21 December 2018, pp. xxx–xxx. doi: 10.1089/ham.2018.0048. 

[2] Chris Imray et al. “Acute Mountain Sickness: Pathophysiology, Prevention, and Treatment”. In: Progress in Cardiovascular Diseases 52.6 (May 2010), pp. 467–484. doi: 10.1016/j.pcad.2009.11.003.

[3] Courtney LL Sharp et al. “Incidence of Acute Mountain Sickness in Adolescents Backpacking at Philmont Scout Ranch”. In: Wilderness and Environmental Medicine 35.4 (2024), pp. 403-408

[4] Andrew M. Luks, Erik R. Swenson, and Peter B¨artsch. “Acute high-altitude sickness”. In: European Respiratory Review 26.143 (Jan. 2017), p. 160096. doi: 10.1183/16000617.0096-2016.

[5] Michael Schneider et al. “Acute mountain sickness: influence of susceptibility, preexposure, and ascent rate”. In: Medicine & Science in Sports & Exercise 34.12 (Dec. 2002), pp. 1886–1891

Matison Miratsky is a physician assistant student who attends Midwestern University in Arizona with plans to go into OB/GYN. Before PA school, she grew up in Denver, Colorado and attended the University of Colorado at Boulder. She worked in an emergency department in Denver, then at a family medicine clinic in Arizona. Her personal interests include snowboarding, watching movies, spending time with family, and cooking.