High Altitude Pulmonary Edema is when the lungs fill up with fluid as a result of the body adapting to high elevation. It occurs vary rarely below 8,000 feet. The reason the lungs fill up with fluid is a bit complex, and I am not a doctor, but the basic idea is the pulmonary artery (from the heart to the lungs) contracts a bit as people go up in elevation. In a few rare cases, people have only one pulmonary artery. These people are susceptible to HAPE below 8,000 feet. For some reason, the younger you are, the more likely you are to getting HAPE. Being well-conditioned is no defense against HAPE. It is thought that people who are susceptible to HAPE have pulmonary arteries that contract more than average.
The small arterioles of the lungs are peculiarly sensitive to lack of oxygen, which causes them to contract (a vasoconstrictor response). This increases blood pressure in the arterial side of the pulmonary circulation. From then normal 12 to 20 torr, pressure in the pulmonary arteries increases to 30 or 50 torr, or even higher, and is further increased by exertion. This elevated pressure stimulates release of many powerful substances. ... These substances ... (alter) reactions of blood and blood vessels... Some increase the leakiness (permeability) of small vessels.... (From High Altitude; Illness and Wellness, Charles Houston, M.D., 1993)
Procardia acts to relax the pulmonary arteries. This can actually reversed some symptoms of HAPE. It is the only drug that I know of that reverses symptoms of HAPE after they start to develop.
From osmotic pressure, some fluid goes from the alveoli into the lungs. As the lungs fill with fluid, it becomes harder and harder to breathe. After awhile a coma and then death can result. Descent is the best solution, although oxygen can help the symptoms when descent is impossible.
1. Describe the mechanics of breathing. Include the relationship between pressure and volume. How are oxygen and carbon dioxide transported in the blood?
2. What types of physiological problems do humans encounter at high altitudes?
3. What symptoms would mountain climbers exhibit that might be related to altitude? Explain.
4. Compare the air at 18,000 feet (atmospheric pressure 280 mm Hg) to the air at sea level (760 mm Hg). What specific changes in the primary atmospheric gases (nitrogen, oxygen, carbon dioxide) might occur? Are they significant?
5. What is the specific pulmonary response to high altitude? [Assume you are considering a subject at rest.]
6. How will this response affect overall blood gases? What about oxygen loading and unloading from hemoglobin? Explain how you arrived at your conclusions.
7. After breathing at altitude for a few days, the body normally begins producing more 2,3-DPG. What is the significance of this change? How will it affect the pulmonary changes observed?
*adapted from "Into Thin Air"
A Case Study in Physiology by
Department of Biological Sciences
California State University, Sacramento
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