At sea level, 21 percent of the air is oxygen. As altitude increases, oxygen remains at 21 percent, but the amount of air decreases. Less air makes breathing more difficult -- and exercising requires more oxygen, putting climbers at risk of altitude sickness or even death. Altitudes of 8,000 feet above sea level and higher are associated with altitude sickness. For this reason, climbers may need to use supplemental oxygen.
Air is taken in through the lungs, and oxygen is transferred from sacks called alveoli to the red blood cells. Oxygen is delivered to different areas of the body through the circulatory system. Oxygen leaves the alveoli because it is at a higher pressure than the oxygen in the blood. At higher elevations, oxygen has a lower partial pressure -- amount of pressure oxygen would have if no other gases were present in the air. This lower partial pressure reduces the pressure gradient between the lungs and the blood, and oxygen exchange is less efficient.
Exercise activities like climbing increase the amount of oxygen that the body needs. In response, breathing and heart rates increase. Because the air is thinner at higher altitudes, breathing and heart rates must increase at rest just to maintain blood oxygen levels. The volume of blood in the body decreases for the first few weeks of exposure to higher altitudes. As a result, the heart pumps less blood with each beat. As the body acclimates, heart rate increases to compensate for decreased blood volume. Lactic acid -- a waste product of energy use -- accumulates faster at higher elevations. Lactic acid causes muscles to burn and reduces capacity for exercise.
Altitude sickness -- also called acute mountain sickness -- describes a group of physical changes that occur at higher altitudes. It can develop at 6,500 feet above sea level. Symptoms of altitude sickness can begin within a few hours of exposure to high altitude and include dizziness, nausea, headaches, fatigue, diarrhea, vomiting, shortness of breath, nosebleeds, swelling in the limbs, confusion and difficulty sleeping. In severe cases death can occur.
Climbers can use supplemental oxygen in small tanks to facilitate climbing at higher altitudes. Climbers typically use supplemental oxygen at altitudes of 24,000 feet and above. This improves their ability to climb and sleep and allows them to think more clearly. Climbers should carry extra oxygen in case a tank becomes empty or is damaged.
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