When you travel to a higher altitude environment, your body must make certain physiological adaptations in order to handle the significant decrease in oxygen.
Your heart is one such organ that makes immediate changes, as it works to maintain delivery of the amount of oxygen needed by your tissues and organs. As such, you could experience and increase in breathing and a rapid heart rate as you enter higher altitudes.
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High altitude is commonly defined as 8,000 feet in elevation. However, heart rate can be affected any time a person travels to an elevation higher than they are accustomed to. For reference, Denver, Colorado — also called the "mile-high city" — sits at 5,000 feet.
Rapid Heart Rate With Altitude
Oxygen is necessary for all cellular life in your body. Your heart's sole function is to provide your organs and tissues with oxygenated blood and to return deoxygenated blood to your lungs so that it can become oxygenated again. How often it needs to beat is partly dependent upon the density of oxygen present in the surrounding air.
The atmosphere is 21 percent oxygen at any elevation. However, the air is thinner at higher altitudes, so you are unable to pull the same amount of oxygen in your lungs with each breath. As a result, with initial exposure to high altitude, breathing rate increases to bring more oxygen into your body and your heart rate immediately speeds up to help carry the oxygen throughout the body, according to an August 2014 article published by Diabetes Care.
Long-Term Acclimatization
When you are exposed to higher altitudes for a long period, your body acclimatizes and your resting heart rate decreases. It takes about two weeks to complete the acclimatization process. Because of this process, many athletes will arrive at a location a few days prior to their competition or event in order to perform at their regular abilities.
If moving after a long period at high altitude to a lower altitude, there is a typical slight decrease in heart rate as the heart has become more efficient, but the acclimatization period is not nearly as extensive.
High Altitude Sickness
High altitude sickness — often called mountain sickness — often occurs from not receiving enough oxygen. Symptoms can show up within 12 hours of arriving at the high altitude environment, but in some cases, develop over the first few days.
High-altitude sickness can cause headaches, nausea, sleep problems and swelling. In some situations, altitude sickness can be serious — fluid can accumulate in your brain or in your lungs, leading to a condition called high altitude pulmonary edema.
High altitude pulmonary edema can be a life-threatening condition, according to the Colorado Academy of Family Physicians. Symptoms can include shortness of breath, hallucinating, pink phlegm, rapid heartbeat and confusion. Seek immediate medical attention if you have these symptoms.