Category Archives: Altitude Science

Altitude Science, Health, High Altitude, Medicine, Surgery

Thin Air, Thick Blood: Increased Risk for Blood Clots After Surgery at Elevations Above 4000 Feet 

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by Colby Baron, PA-S

Moving to higher elevation often has side effects on the body. To many people, these effects are well managed. They may feel a slight shortness of breath while exercising, an occasional headache relieved by a caffeinated drink, or some dry skin. Others are less fortunate. Their symptoms impact their daily lives. Regardless of how visible one’s symptoms may be, every human body must make physiologic internal changes to adapt to living at higher altitudes.  

The body needs oxygen. While air still contains 21% oxygen in a high altitude environment, the density of the molecules is lower. When you arrive at a mountain town like Frisco, in the Rocky Mountains of Colorado with an elevation of 9,000 feet, the body works to pull whatever oxygen it can find into its system. It not only has to breathe harder to do so but creates more red blood cells so that it can be more efficient in transporting more oxygen to all tissues. While this adjustment works, it has its side effects:  more red blood cell vehicles means more traffic along the blood vessel highways. Such blockage makes the blood more viscous and more prone to forming clots. This is not a a “death trap” for all but can have greater consequences for those already at risk of having a serious clotting event. 

Surgery requires patients to remain immobile in recovery and often involves vascular injuries as the tissue is altered. Blood clots can form in these circumstances. This is managed with anti-platelet and anticoagulation drugs. Orthopedic procedures tend to present with the biggest risk. This is especially true when operating on the knee.  Operations closer to the heart have less risk. Arthroscopic rotator cuff procedures typically only have about a 0.3-0.5% chance of causing any thrombotic issues.  The stakes are altered significantly when altitude is factored into the equation. In a recent study in the Journal of Shoulder and Elbow Surgery published by orthopedic surgeons Matthew Cannefax, Michael T. Burrus, David R. Diduch, and Brian C. Werner, arthroscopic rotator cuff repairs done at elevations above 4,000 feet increased the rate of blood clots by 2 – 3 times as much.   Deep vein thromboses, pulmonary embolisms, and other thrombotic complications lead to improved monitoring and follow up with patients post op.  

My own shoulder surgery was at a lower elevation, requiring  strict immobilization of my arm in a sling for 6 weeks straight, even while asleep. Even if I had wanted to remove my sling, my arm felt weak with significant pain every time I stretched my limits even accidentally. The constant restricted position I was forced to be in rarely felt comfortable. Adding the pain and systemic consequences of a blood clot would have emphasized those hardships even more. Frisco pediatrician Dr. Christine Ebert-Santos had shoulder surgery at 9,000 feet with immediate relief of the constant pain she suffered for 9 months and a rapid uncomplicated recovery. The advantages of receiving care in our home community outweighs the very small risk of increased complications from altitude for most mountain residents. 

References

  1. Journal of Shoulder and Elbow Surgery, Cannefax M, Burrus MT, Diduch DR, Werner BC. Increased risk of venous thromboembolism following arthroscopic rotator cuff repair at high altitude. J Shoulder Elbow Surg. 2017;26(7):e207-e213. doi:10.1016/j.jse.2017.03.012  
  1. American Academy of Orthopaedic Surgeons. Venous thromboembolism in orthopedic surgery. Accessed March 27, 2026. https://www.aaos.org  
  1. Journal of Thrombosis and Haemostasis, Imray C, Booth A, Wright A, Bradwell AR. Thrombosis and coagulation at high altitude. J Thromb Haemost. 2010;8(3):499-504. doi:10.1111/j.1538-7836.2009.03700.

Colby Baron is physician assistant student at Rocky Mountain University in Provo, Utah. Ever since having lifesaving brain surgery when he was 15 years old to repair an idiopathic hemorrhagic stroke, Colby has tried to give back to the medical community any way that he can. As an active individual who loves soccer, board sports, skydiving, hiking, camping, and anything one can do outdoors, he lives an active lifestyle. Such a life has created many great memories but has also been the cause of several orthopedic injuries. He has had a broken leg, a dislocated kneecap, a torn meniscus, a torn labrum, and multiple concussions and sprained ankles. After graduating PA school, he hopes to use these past experiences and time spent in the OR assisting orthopedic surgeons with traumatic and pediatric cases to help others emphatically with their musculoskeletal issues. He feels great passion for this and hopes to positively impact patients and providers throughout his career.  

Acclimation, Altitude Science, Athletic Training, Exposure, Health, High Altitude, High Altitude Training & Fitness, Hyperbaric Therapy, Medicine, Mountaineering

Pressure as Prevention: Can Hyperbaric Oxygen Help You Beat Altitude?

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Pictured above is the highest hyperbaric chamber in the world at the Bolivian Naval Station at Lake Titicaca.

If you’ve ever climbed high enough to feel short of breath, dizzy, or just “off,” you’ve likely experienced the effects of high altitude on the human body. Once you get above about 2,500 meters (8,200 feet), the air gets “thinner”—not because oxygen disappears, but because there’s less pressure pushing oxygen into your body. This particular problem is termed hypobaric hypoxia, and it can turn a beautiful mountain adventure into a medical problem quickly.

Why Altitude Hits So Hard

At elevation, your body is forced to adapt fast—and sometimes it isn’t able to keep up. That’s when altitude illness can develop, ranging from mild to life-threatening ailments:

  • Acute Mountain Sickness (AMS): headache, nausea, fatigue
  • High-Altitude Pulmonary Edema (HAPE): fluid in the lungs, causing shortness of breath
  • High-Altitude Cerebral Edema (HACE): brain swelling, confusion, and potentially coma

These aren’t separate diseases so much as a continuum of worsening hypoxia. Most severe cases can start as mild symptoms and can later progress to more severe presentations. The quicker you can recognize the more subtle symptoms, the better you may be in avoding severe illness. 

What’s Happening Inside the Body?

When oxygen levels drop, the body goes into survival mode:

  • Blood vessels in the lungs constrict → raising pressure (risk of HAPE)
  • Blood vessels in the brain become leaky → swelling (risk of HACE)
  • Inflammatory and hormonal systems ramp up → causing AMS symptoms

In short: your body is trying to compensate in response to the change in environment, but sometimes those compensations backfire.

Enter Hyperbaric Oxygen Therapy (HBOT)…

Now imagine flipping the script. Instead of struggling in thin air, what if you could flood your body with oxygen under pressure? That’s exactly what Hyperbaric Oxygen Therapy (HBOT) does. Inside a pressurized chamber, you breathe 100% oxygen, dramatically increasing how much oxygen dissolves into your blood. In a way you have artificially placed yourself in a lower altitude. 

How HBOT Helps at Altitude

HBOT essentially acts like a “simulated descent”—one of the most important treatments for altitude illness.

It can:

  • Boost oxygen levels in your blood and tissues
  • Improve brain function in hypoxic states
  • Reduce inflammation and oxidative stress
  • Potentially stabilize the blood–brain barrier

In wilderness medicine and EMS settings, portable hyperbaric chambers are already used when immediate descent isn’t possible. They can be lifesaving.

But there’s a catch: The benefits are temporary. Once the pressure is removed, symptoms can return if the person is still at altitude where their symptoms first started.

A New Idea: Can HBOT Be Used Before You Climb?

Here’s where things get interesting. Researchers are now exploring whether HBOT could be used not just as treatment—but as preparation.

The concept: preconditioning

The idea is that repeated exposure to hyperbaric oxygen before ascent might “train” the body to handle low-oxygen environments better—similar to acclimatization.

Potential effects include:

  • Activation of hypoxia-response pathways (like HIF)
  • Improved mitochondrial efficiency (better energy use)
  • Increased antioxidant defenses
  • Enhanced microcirculation

In theory, this could mean: fewer symptoms, better performance, and lower risk of severe altitude illness

What Does the Evidence Say?

Early research is promising, but not definitive.

Some studies suggest:

  • Reduced incidence and severity of AMS
  • Better oxygen saturation at altitude
  • Possible protection against brain and lung edema

But there are still big unknowns:

  • What pressure and duration work best?
  • How long before ascent should HBOT be done?
  • Who benefits most—athletes, mountaineers, or everyone?

For now, HBOT preconditioning is an exciting idea—not standard practice.

What About Athletes and High Performers?

Altitude is a major challenge for:

  • Endurance athletes
  • Military personnel
  • Search and rescue teams
  • Mountaineers

Performance drops quickly due to:

  • Lower VO₂ max
  • Faster fatigue
  • Impaired decision-making

HBOT might help by:

  • Improving oxygen efficiency
  • Preserving cognitive function
  • Delaying fatigue

But again—this is still being studied, and access to HBOT can be limited and expensive.

How Does HBOT Compare to Proven Strategies?

Right now, the gold standard hasn’t changed:

  • Gradual ascent → still the most effective prevention
  • Acetazolamide → helps your body acclimate faster
  • Dexamethasone → used in higher-risk situations

HBOT (for prevention) is still catching up in terms of evidence.

Is HBOT Risk-Free?

Not entirely. While generally safe, it can cause: ear or lung barotrauma (due to pressure-related injury), oxygen toxicity (rare but serious), and can lead to increased oxidative stress with overuse. These risks matter more when using HBOT proactively rather than as a rescue therapy.

Where This Is Headed

HBOT sits at a fascinating intersection of performance, medicine, and physiology.

Future research is looking to focus on finding optimal preconditioning protocols like treatment duration and number of set times. Some other areas also include identifying which patient populations would benefit most from this form of treatment and combining HBOT with other strategies like hypoxic training.

Bottom Line…

Hyperbaric oxygen therapy is already a powerful tool for treating severe altitude illness, especially when descent from altitude isn’t immediately possible.

As a preventive strategy, it shows real promise, but it’s not ready to replace the fundamentals.

For now, your best defense at altitude is still:

  • Climb gradually
  • Know the symptoms and have a buddy!
  • Use proven medications when appropriate (like Acetazolamide)

HBOT may one day become part of the toolkit—but for now, it’s a high-potential frontier, not a first-line solution.

References 

Centers for Disease Control and Prevention. (2023). High-altitude travel and altitude illness. https://www.cdc.gov/travel/page/high-altitude-travel

National Center for Biotechnology Information. (2023). High-altitude illness. In StatPearls. StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK430716/

National Center for Biotechnology Information. (2023). Hyperbaric oxygen therapy. In StatPearls. StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK459172/

PubMed Central. (2020). Hyperbaric oxygen therapy: Mechanisms and clinical applications. https://www.ncbi.nlm.nih.gov/pmc/articles/PMCPubMed Central. (2018). Pathophysiology, prevention, and treatment of high-altitude illness. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC

Wilderness Medical Society. (2019). Wilderness Medical Society clinical practice guidelines for the prevention and treatment of acute altitude illness. Wilderness & Environmental Medicine, 30(4), S3–S18. https://doi.org/10.1016/j.wem.2019.04.006

Hackett, Peter H., & Roach, Robert C.. (2001). High-altitude illness. New England Journal of Medicine, 345(2), 107–114. https://doi.org/10.1056/NEJM200107123450206

Bärtsch, Peter, & Swenson, Erik R.. (2013). Acute high-altitude illnesses. New England Journal of Medicine, 368(24), 2294–2302. https://doi.org/10.1056/NEJMra1214870

Moon, Richard E.. (2019). Hyperbaric oxygen therapy indications. Undersea & Hyperbaric Medicine, 46(3), 425–430.

Milledge, James S., West, John B., & Schoene, Robert B.. (2013). High altitude medicine and physiology (5th ed.). CRC Press.

Dylan Raulie was born and raised in Colorado Springs, Colorado and went out of state for his undergraduate years at Creighton University in Omaha, Nebraska, trading mountains for cornfields and altitude for attitude … from the wind. He got a Bachelor’s of Science in Emergency Medical Services majoring in sirens, stress, and 2 a.m. calls. After studying and learning about what could go wrong with future patients, he would often times avoid trying to become one on his interscholastic rugby team. He worked as a 911 paramedic in Colorado Springs. Between brutal call volumes, lack of sufficient ambulances on the streets, and extreme variety in patient presentations, no day was the same.  He later earned his Master’s in Biomedical Sciences at Rocky Vista University where he developed into being a better student and lifelong learner, which directly influenced his approach as a medical student. On his days off, he is a part-time grappler (in BJJ), but a full-time adventurer, always in motion—physically and mentally.

Acclimation, Altitude Science, Exposure, Health, High Altitude, Technology

From Mountains to Mars: Why High-Altitude Research Matters for Mars Missions

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Thin Air

You step out of your car at roughly 9,000 feet in Frisco, Colorado, and the first thing you notice isn’t the mountain views –it’s your breath. It comes faster, deeper, almost as if your body knows something you don’t: the air pressure here is lower and each breath delivers ~28% fewer oxygen molecules than at sea level1. This “thin air” triggers the same hypoxic (low-oxygen) stress that Mars settlers will face, where every habitat and spacesuit must carefully control both pressure and oxygen1,2,7,8. On Mars, the atmospheric pressure is less than 1% of that on Earth.

Acclimatization

On your first hike, your heart pounds harder than usual. That’s your body’s rapid response: breathing quickens, heart rate rises, and oxygen delivery ramps up to keep the entire body going1,2,4. Within 24-48 hours, your kidneys release erythropoietin (EPO), signaling the bone marrow to make more red blood cells1,3. This raises hemoglobin levels, enhancing oxygen transport. Over the following weeks, blood volume and hemoglobin continue to rise1,2,4. This is acclimatization –which varies between individuals, an important consideration when selecting crew for long-duration Mars missions.

Sleep and Oxygen

At night, breathing becomes fragile. Many people develop “periodic breathing” –brief pauses that fragment sleep. Summit County residents often experience oxygen dips into the high 80% –lower than the ~90% seen in Denver; and far below the typical 96-98% at sea level1. These dips have real implications: hypoxia combined with sleep disruption can affect mood, stress, and cognitive performance, as seen in Antarctic “winter overs,” where low oxygen and isolation caused up to 20% drop in certain cognitive task speeds and increased mood disturbances. Altitude sleep data are useful for researchers to determine extra nighttime buffers and habitat controls. Predicting and mitigating these person-specific patterns is key for astronaut safety and performance4,5.

From Frisco to the Final Frontier

Frisco, Colorado is not just known for its scenic views. This mountain town serves as a “living laboratory”, allowing researchers to track oxygen saturation, breathing, heart rate, sleep, and exercise tolerance in residents and visitors. These insights can help engineers determine how much oxygen a Mars habitat should provide, and how quickly conditions can safely change after landing1,2,7,8. NASA spacecraft air pressures currently range from 8.2 – 14.7 psi, with oxygen comprising 21-32% of that air; parameters informed in part by high-altitude research7,8. At the 7th Chronic Hypoxia Symposium in La Paz, Bolivia at 12,000 feet elevation (3,640 m) the use of insights from high altitude populations to enable the exploration of Space was discussed. The sponsor and organizers were Drs. Gustavo Zubieta-Calleja and his daughter Natalia Zubieta De Urioste who run the Institute of High Altitude Pulmonology and Pathology there. Presenters and attendees came from 16 countries covering topics ranging from molecular biology to genetics.
A presentation on “BioSpaceForming”  identifies chronic hypoxia as a “fundamental tool” that “gives humans and other species an advantage on earth and beyond.” Dr Zubieta explained that the space station is engineered to have the barometric pressure (760 mmHg) and oxygen content of sea level. When the astronauts change into their space suits to work outside the ship they experience a pressure drop of over 200 mm Hg in a laborious process of donning the suit. Seeing that millions of inhabitants are healthy at 486 mm HG in Bolivia, he advocates that maintaining lower pressures and lower oxygen levels in the space station would be economical and promote the health of the astronauts. Several altitude scientists see this as a future that “uncouples biology and physics.

(Photo of Dr Gustavo in front of space slide)

Modeling Mars Conditions

Researchers combine data from high-altitude locations, Antarctic stations, Mars-analog habitats like HI-SEAS in Hawaii to build predictive models. These models provide guidelines for when oxygen supplementation or workload adjustments are needed to optimize safety while completing tasks 4-6,9. They also help develop “operations playbooks” for simulating life on Mars10; set habitat air pressure and oxygen guidelines7,8; define spacesuit safety limits4,6,11; and better understand how the human body responds to spaceflight and space living2,5,9,12,13. For example, extravehicular activity (EVA) suits –spacesuits used for work outside the spacecraft –typically operate at ~4.3 psi with 100% oxygen. While this allows astronauts to breathe in low-pressure environments, prolonged use can lead to overheating, dehydration, and higher risk of injuries11.

The gravitational pull is 38% of that on Earth. Solar and the more dangerous Galactic Cosmic Radiation of Alpha particles from distant supernovae is hundreds of times greater than on Earth, due to the lack of a magnetic field or protective atmosphere. A breeze on Mars could barely move a blade of grass. Global dust storms occur every few years and last months, devastating the surface.

At the 9th  Chronic Hypoxia and First International Space Physiology Symposium in La Paz, Bolivia in 2025 Dr. Akbar Hussain presented his Craterhab design for accommodations in austere high altitude environments and eventually on Mars.

(PHOTO akbar in front of slide with craterhub) 

Astronauts could be acclimatized before embarking on the long journey to distant space in facilities located at 5,000 meters near mines in the Andes.

(Photo of Dr Gustavo in front of space slide)

Limitations

Most high-altitude studies are conducted over weeks to months, while Mars missions could last years and require hundreds of participants to have the skills to be self-sustaining. Due to planetary rotations, travel to Mars is only feasible once every 26 months. Messages from Mars take 7 to 45 minutes to arrive on Earth. Individual differences in acclimatization, long-term cognitive effects, and combined stressors like radiation or microgravity are not fully captured. Longer-duration studies at high-altitudes, combined with simulated Martian habitats and spacesuit trials, are needed to refine safety parameters.

Conclusion

High-altitude research gives scientists a window into human maladaptive and adaptive responses to low-oxygen, low-pressure conditions on Earth, and is directly relevant to anticipating health risks and necessary countermeasures for human habitation on Mars.

References

  1. Ebert-Santos C. High-Altitude Pulmonary Edema in Mountain Community Residents. High Alt Med Biol. 2017 Sep;18(3):278-284. doi: 10.1089/ham.2016.0100. Epub 2017 Aug 28. PMID: 28846035.
  2. Le Roy B, Martin-Krumm C, Pinol N, Dutheil F, Trousselard M. Human challenges to adaptation to extreme professional environments: A systematic review. Neurosci Biobehav Rev. 2023;146:105054. doi:10.1016/j.neubiorev.2023.105054.
  3. Roach RC, Hackett PH. Frontiers of hypoxia research: acute mountain sickness. J Exp Biol. 2001 Sep;204(Pt 18):3161-70. doi: 10.1242/jeb.204.18.3161. PMID: 11581330.
  4. Mairesse O, MacDonald-Nethercott E, Neu D, et al. Preparing for Mars: Human sleep and performance during a 13-month stay in Antarctica. Sleep. 2019;42(1). doi:10.1093/sleep/zsy206.
  5. Pagel JI, Choukèr A. Effects of isolation and confinement on humans—Implications for manned space explorations. J Appl Physiol (1985). 2016;120(12):1449-1457. doi:10.1152/japplphysiol.00928.2015.
  6. Dunn Rosenberg J, Jannasch A, Binsted K, Landry S. Biobehavioral and psychosocial stress changes during three 8–12 month spaceflight analog missions with Mars-like conditions of isolation and confinement. Front Physiol. 2022;13:898841. doi:10.3389/fphys.2022.898841.
  7. Waligora JM, Horrigan DJ, Nicogossian A. The physiology of spacecraft and space suit atmosphere selection. Acta Astronaut. 1991;23:171-177. doi:10.1016/0094-5765(91)90116-M.
  8. Morgenthaler GW, Fester DA, Cooley CG. An assessment of habitat pressure, oxygen fraction, and EVA suit design for space operations. Acta Astronaut. 1994;32(1):39-49. doi:10.1016/0094-5765(94)90146-5.
  9. Sarma MS, Shelhamer M. The human biology of spaceflight. Am J Hum Biol. 2024;36(3):e24048. doi:10.1002/ajhb.24048.
  10. Lim DSS, Abercromby AFJ, Kobs Nawotniak SE, et al. The BASALT research program: Designing and developing mission elements in support of human scientific exploration of Mars. Astrobiology. 2019;19(3):245-259. doi:10.1089/ast.2018.1869.
  11. Stirling L, Arezes P, Anderson A. Implications of space suit injury risk for developing computational performance models. Aerosp Med Hum Perform. 2019;90(6):553-565. doi:10.3357/AMHP.5221.2019.
  12. Cassaro A, Pacelli C, Aureli L, et al. Antarctica as a reservoir of planetary analogue environments. Extremophiles. 2021;25(5-6):437-458. doi:10.1007/s00792-021-01245-w.
  13. Fairén AG, Davila AF, Lim D, et al. Astrobiology through the ages of Mars: The study of terrestrial analogues to understand the habitability of Mars. Astrobiology. 2010;10(8):821-843. doi:10.1089/ast.2009.0440.
  14. Akbar Hussain M, Ayaz Hussain M, Mehdi Hussain M, Fatima R, Carretero R, eds. Craterhab Technology: Adapting Martian Habitat Systems to Combat Chronic Hypoxia in High-Altitude Mining in the Andes – A White Paper. Mareekh Dynamics. Published June 3, 2024. Accessed August 15, 2025. https://www.mareekh.com/post/craterhab-technology-adapting-martian-habitat-systems-to-combat-chronic-hypoxia-in-high-altitude-mi
Accessibility, Acclimation, Altitude Science, Athletic Training, Genetics, Health, High Altitude

Peak Performance: Coach wants a Blood Test

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Iron Deficiency without Anemia in Individuals Living at Altitude 

Madeline Larson, PA-S2

People living at high altitude typically have higher hemoglobin levels compared to those at sea level. This physiological adaptation occurs due to the lower oxygen availability at high elevations which stimulates the production of erythropoietin, a hormone that prompts the bone marrow to produce more red blood cells made famous by the Lance Armstrong blood-doping scandal. Hemoglobin, the protein in red blood cells that carries oxygen, thus increases to enhance the blood’s oxygen-carrying capacity. This adaptation helps individuals efficiently transport oxygen to tissues despite the reduced atmospheric pressure. Over time, this increased hemoglobin level helps maintain adequate oxygen delivery to vital organs, supporting overall health and physical performance in the challenging high-altitude environment.

Despite this natural adaptation of increased hemoglobin levels, people living at high altitude are still susceptible to anemia. Chronic exposure to lower oxygen levels can sometimes lead to a condition where the body’s capacity to produce red blood cells is insufficient to meet increased demands. This can be due to various factors, including inadequate dietary iron, vitamin deficiencies, or underlying health conditions that impair red blood cell production or lifespan. Additionally, individuals who move to high altitudes without sufficient acclimatization may experience a temporary drop in hemoglobin levels until their bodies adjust. Addressing anemia in such environments often involves a combination of dietary adjustments, supplementation, and medical interventions to ensure that the red blood cell count remains adequate to maintain optimal oxygen transport and overall health.

In people living at high altitudes, the threshold for diagnosing anemia is often adjusted to account for the lower oxygen levels in the environment. At high altitudes, the normal range for hemoglobin and hematocrit levels can be higher due to the body’s adaptation to reduced oxygen levels.

For example:

  • Hemoglobin Threshold: At sea level, anemia is commonly defined as a hemoglobin level below 13.0 grams per deciliter (g/dL) in men and 12.0 g/dL in women. In high-altitude areas, these thresholds might be higher. For instance, at elevations above 2,500 meters (8,200 feet), a hemoglobin level of around 14.0 g/dL in men and 13.0 g/dL in women might be considered the lower limit of normal.
  • Hematocrit Threshold: Similarly, normal hematocrit levels are adjusted. At sea level, anemia is typically diagnosed with hematocrit levels below 39% in men and 36% in women. At high altitudes, these values might be adjusted to about 42% for men and 40% for women.

These adjustments are necessary because high-altitude residents tend to have higher hemoglobin and hematocrit levels as a physiological response to lower oxygen availability. If someone at high altitude presents with symptoms of anemia but has hemoglobin or hematocrit levels within the high-altitude normal range, further evaluation might be needed to assess their overall health and adapt to the specific altitude.

Understanding Iron Deficiency Without Anemia: What You Need to Know

Iron is an essential mineral that plays a crucial role in various bodily functions, most notably in the production of hemoglobin, which is vital for oxygen transport in the blood. While many people are familiar with iron deficiency anemia, where low iron levels lead to a reduced number of red blood cells, there is another, often overlooked, condition: iron deficiency without anemia. Understanding this condition is important for addressing health issues that can arise even in the absence of anemia. 

What is Iron Deficiency Without Anemia?

Iron deficiency without anemia occurs when the body’s iron levels are insufficient, but the quantity of red blood cells and their capacity to carry oxygen remain within normal ranges. Essentially, it’s a state where iron stores are low, but the body has not yet progressed to a point where anemia develops. This can make it a bit tricky to diagnose since standard blood tests for anemia might not immediately show abnormalities.

Symptoms and Effects

The symptoms of iron deficiency without anemia can be subtle and may vary from person to person. Common signs include:

  • Fatigue and Weakness: Even without anemia, low iron can lead to feelings of tiredness and decreased energy levels. Coaches notice that some competitive athletes benefit from addressing iron deficiency without anemia.
  • Frequent Headaches: Iron is involved in various enzymatic processes in the body, and a deficiency might contribute to headaches or migraines.
  • Cold Hands and Feet: Poor circulation or lower iron levels can result in feeling unusually cold.
  • Brittle Nails and Hair: Iron deficiency can affect the health and strength of nails and hair.
  • Restless Legs Syndrome: Some people with low iron levels experience uncomfortable sensations in their legs, particularly at night.

Causes of Iron Deficiency Without Anemia

Several factors can contribute to iron deficiency without leading to anemia:

  • Dietary Intake: Inadequate consumption of iron-rich foods, such as red meat, legumes, and fortified cereals, can lead to low iron levels.
  • Increased Iron Requirements: Certain life stages and conditions, such as pregnancy, heavy menstrual periods, or intense physical activity, can increase iron needs.
  • Absorption Issues: Conditions like celiac disease or inflammatory bowel disease can impair iron absorption.
  • Chronic Inflammation: Chronic illnesses or inflammatory conditions can affect iron metabolism and utilization, even if anemia does not develop.

Diagnosis and Testing

Diagnosing iron deficiency without anemia typically involves a combination of tests and assessments:

  • Serum Ferritin Levels: Ferritin is a protein that stores iron in the body. Low levels can indicate depleted iron stores, even if anemia is not present.
  • Serum Iron and Transferrin Saturation: These tests measure the amount of circulating iron and how well it is being transported in the blood.
  • Complete Blood Count (CBC): While a normal CBC might not show anemia, it can help rule out other conditions.

Treatment and Management

Addressing iron deficiency without anemia often involves dietary and lifestyle changes:

  • Iron-Rich Diet: Incorporate foods high in iron, such as lean meats, leafy green vegetables, nuts, and seeds. Iron from animal sources (heme iron) is generally more easily absorbed than plant-based iron (non-heme iron).
  • Vitamin C Intake: Consuming vitamin C-rich foods like oranges, strawberries, and bell peppers can enhance the absorption of non-heme iron.
  • Iron Supplements: In some cases, a healthcare provider may recommend iron supplements. It’s important to follow dosing instructions carefully, as excessive iron intake can have adverse effects.
  • Address Underlying Causes: If an underlying condition is contributing to iron deficiency, treating that condition is crucial for resolving the deficiency.

Conclusion

While long-term adaptation to high altitude allows individuals to increase their iron available for erythropoiesis due to higher demand, those who have not adapted or are vulnerable due to exercise or pregnancy, are at risk of depleting their iron stores. Iron deficiency without anemia is a condition that requires attention to prevent potential health issues and improve overall well-being. 

Resources & References:

Alkhaldy HY, Hadi RA, Alghamdi KA, Alqahtani SM, Al Jabbar ISH, Al Ghamdi IS, Bakheet OSE, Saleh RAM, Shehata SF, Aziz S. The pattern of iron deficiency with and without anemia among medical college girl students in high altitude southern Saudi Arabia. J Family Med Prim Care. 2020 Sep 30;9(9):5018-5025. doi: 10.4103/jfmpc.jfmpc_730_20. PMID: 33209838; PMCID: PMC7652112.

Kaylee Sarna, Gary M Brittenham, Cynthia M Beall, Detecting anaemia at high altitude, Evolution, Medicine, and Public Health, Volume 2020, Issue 1, 2020, Pages 68–69, https://doi.org/10.1093/emph/eoaa011

Martina U. Muckenthaler, Heimo Mairbäurl, and Max Gassmann. Iron metabolism in high-altitude residents. 2020 Jan 9: https://journals.physiology.org/doi/pdf/10.1152/japplphysiol.00019.2020

Acclimation, Altitude Science, Child Growth & Development, Diabetes, Doc Talk, Health, High Altitude, Wildlife

Ducks, Mice and Sea Turtles Teach Us About High Altitude

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You may be surprised to learn that the University of California San Diego has been on the forefront of high altitude and hypoxia research since 1968. I recently attended the 9th Annual Center for Physiologic Genomics of Low Oxygen Summit (CPGLO) led by Tatum Simonson PhD where I gave a short presentation on Growth At Altitude. I met Dr John West who joined the university in 1968 after a Mount Everest research expedition with Sir Edmund Hillary in 1960.  He also consulted for NASA serving on the advisory committee for Spacelab. He studied medicine and physiology at the University of Adelaide.

Dr. Chris and Dr. John West

The featured speaker was Isha Jain PhD from the University of San Francisco.  Her research on mice shows how chronic hypoxia can mitigate and possibly cure some conditions, such as the devasting condition of mitochondrial disease.  Colleen Julian PhD, from the University of Colorado, gave a talk on “Surviving Birth at Altitude: Genetic and Physiologic Insights”.        

Other short presentations included a scientist from Florida who spoke of studying waterfowl who migrate at very high altitude as well as diving deep into the water to fish, thus adapted to two very different low oxygen environments.    Among the poster presentations were a study on the effects of hypoxia on mitochondrial function in fibroblasts from loggerhead sea turtles  presented by B. Gabriela Arango from the University of California Berkeley and a study on sleep apnea in self-identified Latinos.

Gabriela Arango from University of California Berkeley with her sea turtle research poster.

Acknowledging that chronic hypoxia may increase the risk of depression and suicide, the benefits include decreased incidence of obesity and diabetes and lower cholesterol/LDL with decreased or unchanged hypertension.   These scientists study animals to help us understand the effects of our environment on our health. At conferences like this, we discuss how what I see as a clinician  could be related to their study on the cellular and genomic levels.      

                            

Dr Chris and Gabriela meeting again- they both presented research at the Hypoxia 2025 conference in Lake Louise, Canada
Gabriela Arango and Dr. Chris were excited to meet again after both presented at the Hypoxia 2025 conference in Lake Louise, Canada in February
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

Altitude Science, Health, Hyperbaric Therapy, Medicine

WHEN OXYGEN IS TOXIC

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Why Too Much Oxygen Can Be Deadly: The Hidden Molecular Consequences of Hyperoxia

by Nic Rolph, PA-S

Oxygen keeps us alive—but in excess, it can quietly unravel critical cellular functions. A groundbreaking study by Baik et al. (2023) in Molecular Cell shines a light on why hyperoxia (too much oxygen) is toxic, and reveals a hidden mechanism behind its damaging effects.

The Mystery of Oxygen Toxicity

We’ve long known that both oxygen deprivation (hypoxia) and oxygen overload (hyperoxia) are harmful. While hypoxia research has led to major discoveries like the Nobel Prize-winning work on HIF (Hypoxia-Inducible Factors), hyperoxia has remained less understood—until now.

Baik and colleagues tackled a fundamental biological question: Why is oxygen toxic at the molecular level?

The Culprit: Fragile Iron-Sulfur Proteins

Using a combination of genome-wide CRISPR screening, proteomics, and in vivo experiments, the researchers identified a specific class of proteins highly vulnerable to excess oxygen: iron-sulfur cluster (Fe-S)-containing proteins.

These clusters act like tiny biochemical power stations inside proteins, but they’re extremely sensitive to oxidation. Under hyperoxic conditions, certain Fe-S proteins degrade, compromising several key cellular pathways:

  • Diphthamide synthesis – crucial for accurate protein translation.
  • De novo purine biosynthesis – needed for DNA and RNA building blocks.
  • Nucleotide excision repair (NER) – repairs damaged DNA.
  • Mitochondrial electron transport chain (ETC) – essential for energy production.

A Vicious Cycle of Oxygen Damage

Perhaps the most striking discovery was the feedback loop of cellular damage:

  1. Hyperoxia damages the ETC, lowering oxygen consumption;
  2. this increases local tissue oxygen levels even more,
  3. which leads to more damage—a self-amplifying loop Baik et al. called “cyclic oxygen toxicity.”

This cycle can explain why supplemental oxygen—while lifesaving—is also associated with complications in neonatal care, ICU patients, and chronic diseases.

From Petri Dishes to Lungs

The team validated their findings in human cells, mice, and even primary lung tissue. In a mouse model of hyperoxic lung injury, the same Fe-S proteins degraded rapidly—especially those in the ETC. Mice with preexisting ETC defects (like the Ndufs4 KO model) showed extreme sensitivity, confirming the ETC as the “weakest link” in the oxygen toxicity chain.

Bigger Picture: Aging, Disease, and Therapy

This study suggests that hyperoxia might contribute to a wide range of diseases—from premature infant lung injury and ischemia-reperfusion damage to neurodegenerative and mitochondrial disorders. It also offers a potential explanation for why antioxidant therapies have largely failed: superoxide isn’t the only villain—molecular oxygen itself may be enough to destabilize these proteins.

Rethinking Oxygen Therapy

Given these findings, clinicians may need to rethink how we use oxygen in medical settings. Rather than focusing solely on delivering “more oxygen,” we might need to tailor therapy to a patient’s oxygen-processing capacity—especially in those with mitochondrial or genetic vulnerabilities.

What’s Next?

Future research may explore:

  • Therapeutic hypoxia to interrupt the damage cycle.
  • Genetic screening to identify patients vulnerable to oxygen toxicity.
  • New drugs to stabilize Fe-S proteins in oxidative environments.

Takeaway

Oxygen is life-sustaining—but Baik et al. reveal it’s also a molecular saboteur under the wrong conditions. This landmark study not only explains the elusive biology of oxygen toxicity but opens new doors for safer therapies and deeper understanding of metabolic diseases.

Note from Dr. Christine Ebert-Santos, MD, MPS of Ebert Family Clinic in the Colorado Rocky Mountains at 9000’/2743m: newborns, children with respiratory infections or high altitude pulmonary edema, and people with sleep apnea are advised to use oxygen at high altitude. The level of oxygen saturation achieved with this treatment is well below normal sea-level values, so unlikely to cause any negative effects.

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.