Hypoxia and Medicine

Why is Oxygen low at high altitudes?

Public Comments

1. Because it is all pulled close to the earth because of gravity.
2. It's more an issue of low pressure than low levels of oxygen. Higher pressure forces more oxygen through the walls of the alveoli of your lungs quicker than lower pressure.
3. well oxygen gets pulled by earths gravity and Cardon dioxide is higher up there sometimes.
4. It is explained by the ideal gas equation PV=nRT; temperature is directly proportional to pressure, and temperature is low at high altitudes. Therefore pressure is also low at high altitudes.
5. Density of air becomes thinner. So the reduced oxy content.
6. It's a question of density. Gravity pulls the atmosphere towards the earth. But it's a gas and spreads somewhat from the surface. The higher you go, the less dense the air. Go high enough and there is none (space). The higher you go, the less molecules of nitrogen, oxygen, co2, etc per cubic meter. So filling your lungs briings in less molecules of air and thus less oxygen.
7. Well, Adapting to High Altitude There 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 -------------------------------------------------------------------------------- Click here for more information about the Earth's atmosphere -------------------------------------------------------------------------------- The percentage of oxygen in the air at two miles (3.2 km.) is 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 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 , 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 include a lack of appetite, distorted vision, and difficulty with memorizing and thinking clearly. In serious cases, pneumonia-like symptoms (pulmonary edema ) and an abnormal accumulation of fluid around the brain (cerebral edema ) develop, leading to 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 altitudes, 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. Initial inefficient response to low oxygen pressure Later, a more efficient response normally develops as acclimatization takes place. More red blood cells and capillaries are produced to carry more oxygen. The lungs increase in size to facilitate the osmosis of oxygen and carbon dioxide. There is also an increase in the vascular network of muscles which enhances the transfer of gases. Beginning of successful acclimatization to low oxygen pressure However, successful acclimatization rarely results in the same level of physical and mental fitness that was typical of altitudes close to sea level. Strenuous exercise and memorization tasks still remain more difficult. In addition, the rate of miscarriages is usually higher at altitudes above two miles. Increased fitness level after successful acclimatization to low oxygen pressure On returning to sea level after successful acclimatization to high altitude, the body usually has more red blood cells and greater lung expansion capability than needed. Since this provides athletes in endurance sports with a competitive advantage, the U.S. maintains an Olympic training center in the mountains of Colorado. Several other nations also train their athletes at high altitude for this reason. However, the physiological changes that result in increased fitness are short term at low altitude. In a matter of weeks, the body returns to a normal fitness level. Enhanced fitness level for a short period of time after returning to low altitude Who Is Most Likely to Have Hypoxia? Most lowland people begin to develop hypoxia symptoms at 1-2 miles altitude. However, there are some permanent settlements in the Andes Mountains in South America and the Himalaya Mountains in Asia that are at altitudes of 3 miles. Mountain climbers have reached peaks that are over 5 miles high, but only by using tanks of oxygen to assist in breathing. The highest peaks are too high for any human to acclimatize naturally. Climbers at the top of Mt. Logan, Yukon Territory, Canada (19,850 feet altitude) There is considerable variability between individuals and between populations in their ability to adjust to the environmental stresses of high mountain regions. Usually, the populations that are most successful are those whose ancestors have lived at high altitudes for thousands of years. This is the case with some of the indigenous peoples living in the Andes Mountains of Peru and Bolivia as well as the Tibetans and Nepalese in the Himalaya Mountains. The ancestors of many people in each of these populations have lived above 13,000 feet (ca. 4000 meters) for 5,000-10,000 years. Peruvian Indian woman and Tibetan man (Her cheeks are red primarily due to increased blood flow near the skin surface. More red blood cells helps her get oxygen to the tissues of her body.) The implication is that natural selection over thousands of years results in some populations being genetically more suited to the stresses at high altitude. However, different populations respond physiologically to low oxygen pressure in somewhat different ways. The primary solution of Indians from the high mountain valleys in Peru and Bolivia has been to produce more hemoglobin in their blood and to increase their lung expansion capability. The common solution of Tibetans and Nepalese who live at high attitudes generally has been to breathe faster in order to take in more oxygen. However, there is recent evidence that nature is actively selecting for Tibetans who have more oxygenated blood. Cynthia Beall of Case Western Reserve University in Ohio reports that the children of Tibetan women with blood-oxygen concentrations 10% higher than normal are significantly more likely to reach reproductive age themselves. Beall believes that this is confirmation of selection for a "high-oxygen gene." In other words, microevolution resulting in a better adaptation to high altitude is ongoing.