Beneficial Effects of Chronic Hypoxia

Living in Summit County, Colorado has its perks – residents are within a 20 to 40 minute drive to five world class ski resorts, and some of the most beautiful Rocky Mountain trail systems are accessible right out our back door. With the endless opportunities drawing residents outdoors to partake in physical activity, it comes as no surprise that Summit County is considered one of the healthiest communities in the country. However, there may be more than meets the eye when it comes to explaining this, as it also has something to do with the thin air.

As a Summit County native, you have likely heard the term “hypoxia” or “hypoxemia” mentioned a time or two. So what does this mean? Simply put, these words describe the physiological condition that occurs when there is a deficiency in the amount of oxygen in the blood, resulting in decreased oxygen supply to the body’s tissues. When this occurs in the acute setting, it may result in symptoms such as headache, fatigue, nausea, and vomiting. These are common symptoms experienced by those with altitude illness, also known as acute mountain sickness. While these symptoms can cause extreme discomfort and may put a huge damper on a mountain vacation, they are not usually life threatening. However, in a small number of people, development of more serious conditions such as a high altitude pulmonary edema (HAPE) and high altitude cerebral edema (HACE) can occur. The treatment for all conditions related to altitude illness is oxygen, whether via return to lower elevations or by a portable oxygen concentrator that allows you to stay where you are. While altitude illness generally affects those who rapidly travel from sea level to our elevation, it has also been known to affect residents returning home to altitude, usually after a period of two or more weeks away. In a very small subset it can occur after a period of only a day or two. This generally occurs in those with a preexisting illness, where altitude exacerbates the condition.

While the acute effects of altitude can clearly have detrimental effects on one’s physical well-being, there is emerging research demonstrating that chronic hypoxia may actually come with several health benefits. Long time Summit County business owner and community pediatrician, Dr. Chris Ebert-Santos of Ebert Family Clinic in Frisco, has spent quite some time studying the effects of chronic high-altitude exposure, and recently attended and presented at the Chronic Hypoxia Symposium in La Paz, Bolivia, the highest capital city in the world.

It is important to first understand the adaptations that occur in our bodies as a result of long-term hypoxia. The ability to maintain oxygen balance is essential to our survival.

So how do those of us living in a place where each breath we take contains about ⅓ fewer oxygen molecules survive?

Simply put, we beef up our ability to transport oxygen throughout our body. To do this, our bodies, specifically the kidneys, lungs and brain increase their production of a hormone called erythropoietin, commonly known as EPO. This hormone signals the body to increase its production of red blood cells in the bone marrow. Red blood cells contain oxygen binding hemoglobin proteins that deliver oxygen to the body’s tissues. Thus, more red blood cells equal more oxygen-carrying capacity. In addition to increasing the ability to carry oxygen, our bodies also adapt on a cellular level by increasing the efficiency of energy-producing biochemical pathways, and by decreasing the use of oxygen consuming processes2. Furthermore, the response to chronic hypoxia stimulates the production of growth factors in the body that work to improve vascularization2, thus, increased ability for oxygenated blood to reach its destination. 

So, how can these things offer health benefit?

To start, it appears that adaptation to continuous hypoxia has cardio-protective effects, conferring defense against lethal myocardial injury caused by acute ischemia (lack of blood flow) and the subsequent injury caused by return of blood to the affected area3. The exact mechanism of how this occurs is not well understood, but it seems that heart tissue adapts to be better able to tolerate episodes of ischemia, making it more resistant to damage that could otherwise be done by decreased blood flow that occurs during what is commonly known as a heart attack. This same principle applied to ischemic brain damage when tested in rat subjects. Compared to their normoxic counterparts, rats pre-conditioned with hypoxia sustained less ischemic brain changes when subjected to carotid artery occlusion, suggesting neuroprotective effects of chronic hypoxia exposure4.

Additionally, it appears that altitude-adapted individuals may be better equipped to combat a pathological process known as endothelial dysfunction5. This process is a driving force in the development of atherosclerotic, coronary, and cerebrovascular artery disease. Altitude induces relative vasodilation of the body’s blood vessels compared to lowlanders2. A relaxing molecule known as nitric oxide, or NO, assists with causing this dilation, and in turn the resultant dilated blood vessels produce more of this compound5. The molecule has protective effects on the inner linings of blood vessels and helps to decrease the production of pro-inflammatory cytokines that damage the endothelium5. This damage is what kickstarts the cascade that leads to atherosclerosis in our arteries. Thus, a constant state of hypoxia-induced vasodilation may in fact decrease one’s risk of developing occlusive vascular disease. 

The topics mentioned above highlight a few of the proposed mechanisms by which chronic hypoxia may be beneficial to our health. However, do keep in mind that there are potential detrimental effects, including an increased incidence of pulmonary hypertension as well as exacerbation of preexisting conditions such as COPD, structural heart defects and sleep apnea, to name a few6. Research regarding the effects of chronic hypoxia on the human body is ongoing, and given its significance to those of us living at elevations of 9,000 feet and above, it is important to be aware of the impact our physical environment has on our health. Dr. Ebert-Santos is avidly involved in organizations dedicated to better understanding the health impacts of chronic hypoxia, and has several current research projects of her own that may help us to further understand the underlying science.

Kayla Gray is a medical student at Rocky Vista University in Parker, CO. She grew up in Breckenridge, CO, and spent her third year pediatric clinical rotation with Dr. Chris at Ebert Family Clinic. She plans to specialize in emergency medicine, and hopes to one day end up practicing again in a mountain community. She is an avid skier, backpacker, and traveler, and plans to incorporate global medicine into her future practice.

Citations

  1. Theodore, A. (2018). Oxygenation and mechanisms for hypoxemia. In G. Finlay (Ed.), UpToDate. Retrieved May 2, 2019, from https://www-uptodate-com.proxy.rvu.edu/ contents/oxygenation-and-mechanisms-of-hypoxemia?search=hypoxia&source=search_ result&selectedTitle=1~150&usage_type= default&display_rank=1#H467959
  2. Michiels C. (2004). Physiological and pathological responses to hypoxia. The American journal of pathology, 164(6), 1875–1882. doi:10.1016/S0002-9440(10)63747-9. Retrieved May 2, 2019. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1615763/ 
  3. Kolar, F. (2019). Molecular mechanism underlying the cardioprotective effects conferred by adaptation to chronic continuous and intermittent hypoxia. 7th Chronic Hypoxia Symposium Abstracts. pg 4. Retrieved May 2, 2019. http://zuniv.net/symposium7/Abstracts7CHS.pdf
  4. Das, K., Biradar, M. (2019). Unilateral common carotid artery occlusion and brain histopathology in rats pre-conditioned with sub chronic hypoxia. 7th Chronic Hypoxia Symposium Abstracts. pg 5. Retrieved May 2, 2019. http://zuniv.net/symposium7/Abstracts7CHS.pdf
  5. Gerstein, W. (2019). Endothelial dysfunction at high altitude. 7th Chronic Hypoxia Symposium Abstracts. pg 11. Retrieved May 7, 2019. http://zuniv.net/symposium7/Abstracts7CHS.pdf
  6. Hypoxemia. Cleveland Clinic. Updated March 7, 2018. Retrieved May 9, 2019. https://my.clevelandclinic.org/health/diseases/17727-hypoxemia