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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”.

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.