Oxygen concentration in the air decreases at high altitudes. Breathing becomes faster and deeper to supply enough oxygen to tissues. This occurs at least above 8000 feet but is more prominent at altitudes higher than 15000 feet. In central sleep apnea due to high altitude, the breathing pattern may imitate Cheyne-Stokes breathing (crescendo - decrescendo breathing, followed by pauses). This type of apnea resolves by itself when the altitude decreases.
