answer: More Oxygen
Explanation:here are two major kinds of environmental stresses at high altitude for humans. First, there are the alternating daily extremes of climate that often range from hot, sunburning days to freezing nights. In addition, winds are often strong and humidity low, resulting in rapid dehydration. Second, the air pressure is lower. This is usually the most significant limiting factor in high mountain regions.
Air pressure
decreases
as altitude
increases
drawing of the earth's surface and the atmosphere above it showing that with increasing distance from the earth, the gas molecules in the atmosphere are farther apart and the air pressure is lower
The percentage of oxygen in the air at two miles (3.2 km.) is essentially the same as at sea level (21%). However, the air pressure is 30% lower at the higher altitude due to the fact that the atmosphere is less dense--that is, the air molecules are farther apart.
When we breathe in air at sea level, the atmospheric pressure of about 14.7 pounds per square inch (1.04 kg. per cm.2) causes oxygen to easily pass through selectively permeable click this icon to hear the preceding term pronounced lung membranes into the blood. At high altitudes, the lower air pressure makes it more difficult for oxygen to enter our vascular systems. The result is hypoxia click this icon to hear the preceding term pronounced, or oxygen deprivation. Hypoxia usually begins with the inability to do normal physical activities, such as climbing a short flight of stairs without fatigue. Other early symptoms of "high altitude sickness" include a lack of appetite, vomiting, headache, distorted vision, fatigue, and difficulty with memorizing and thinking clearly. In serious cases, pneumonia-like symptoms (pulmonary edema click this icon to hear the preceding term pronounced) due to hemorrhaging in the lungs and an abnormal accumulation of fluid around the brain (cerebral edema click this icon to hear the preceding term pronounced) develop. Pulmonary and cerebral edema usually results in death within a few days if there is not a return to normal air pressure levels. There is also an increased risk of heart failure due to the added stress placed on the lungs, heart, and arteries at high altitudes.
When we travel to high mountain areas, our bodies initially develop inefficient physiological responses. There is an increase in breathing and heart rate to as much as double, even while resting. Pulse rate and blood pressure go up sharply as our hearts pump harder to get more oxygen to the cells. These are stressful changes, especially for people with weak hearts.
