As the barometric pressure decreases, the number of oxygen molecules you inhale with each breath is significantly reduced. The atmospheric oxygen concentration is 21 percent at sea level, but there are around 40 percent fewer oxygen molecules per breath at an altitude of 12,000 feet. Your breathing rate must increase to provide your body with more oxygen. Although the breathing rate increases, there is still not enough oxygen, so your body must go through an adjustment period to get used to less oxygen. Your oxygen adjustment won't be as severe if you increase altitude slowly to give you body time to adjust. A change of altitude might cause you to experience Cheyne-Stokes Respirations, a breathing pattern during sleep characterized by shallow breaths that increase to deep breaths and then decrease rapidly. You might even stop breathing entirely for a few seconds until the process resumes.
Changes in altitude commonly cause high altitude illnesses. You might experience a few symptoms like headache, dizziness or shortness of breath. There are three forms of severe high altitude illness that may occur as a result of change in altitude. Acute Mountain Sickness (AMS) is a common sickness that occurs at elevations above 10,000 feet. Many people will experience AMS, but the severity increases if you climb to high elevations too quickly. Symptoms include headache, dizziness, fatigue, nausea and disturbed sleep. High Altitude Cerebral Edema (HACE) is a more severe form of AMS, caused by the swelling of brain tissue from leaking fluids. Symptoms include disorientation, loss of coordination, hallucination, memory loss and coma. It is a potentially life-threatening illness that requires immediate descent to lower altitude. The third common illness is High Altitude Pulmonary Edema (HAPE), which occurs from fluid buildup in the lungs that prevents the exchange of oxygen. The lack of oxygen can lead to irrational behavior, impaired brain function and even death. Immediate descent and medical assistance are required for treatment of HAPE.
Acclimatization is the slow process through which the body adjusts to the change in atmosphere to allow it to function with decreased oxygen. If you ascend to altitude slowly, your body will have time to acclimatize so that you might not experience altitude illness. The process usually takes from one to three days at each new altitude, so if you plan to climb higher after acclimatizing to one altitude, you will need to acclimatize again once you reach your new altitude. The depth of your breathing will increase so that you get more oxygen with each breath. Pulmonary artery pressure increases to force blood into parts of the lungs that aren't used at sea level. Your body will also produce more red blood cells to carry oxygen throughout the body. You should increase your altitude by only 1,000 feet per day if you go above 10,000 feet, and take a day of rest for every 3,000 feet of ascent.
