Answer
Alans feelings of discomfort for his first few days at high altitude ( say 12000 feet) were due to the effects of hypoxia. He had moved from an environment with an atmospheric pressure of about 14,7 to 15.15 psi to live in one that was on 10.91 psi in atmospheric pressure . His headache, drowsiness, fatigue were due to hypoxia. However his body acclimated producing more RBCs and more hemoglobin. This due to the effect of increased levels of erythropoietin on the bone marrow.
After a few days, Alan felt fine because he had only a mild case of acute mountain sickness. He served out his assignment at high altitude. His post- sabbatical medical exam revealed his high RBC count and high hematocrit. This was to be expected. Anyway, this condition would not last. As Alan remained at normal elevation, say 586 feet at Chicago, he would slowly de-acclimatize, and his high hematocrit would return to normal.
Work Step by Step
Alan has been living and working in a high altitude location for about one year. After two day at his new location, Alan began to experience the symptoms of mild acute mountain sickness (AMS) --a kind of altitude sickness. He was short of breath (SOB) and got tired easily. In spite of the initial discomfort, Alan remained at his site. In about two months he felt nearly normal again. So he remained at his high altitude post and completed his sabbatical research. Alan felt better after two months because he had acclimated to the low pressure conditions at his elevated research post. The question does not give the altitude of Alan's post, but travelers, mountain climbers, cyclists and athletes have found that if some- one travels rapidly from seal level ( or a location below 8,000 feet)to a location above 10,000 feet he/she is likely to experience acute mountain sickness within two to three days. The symptoms are dizziness, headaches, dyspnea, and easy fatigability. Alan did not experience all these signs and symptoms(SS) because he probably was at a location below 24,000 feet . But it could have been worse: the seriousness of altitude sickness syndromes increases from mild acute mountain sickness, through severe acute mountain sickness, high altitude cerebral edema (HACE) to high altitude pulmonary edema (HAPE) The last two are life threatening.
The atmospheric pressure of the environment falls as altitude increases. For example, atmospheric pressure at sea level in the US is 14.7 -15.1psi. However, if one travels to Denver (about 5800 ft ) the atmospheric pressure drops to 12.1 psi. The atmospheric pressure in Yellowstone Park (approx. 8,000 ft) is only 10.91 psi and it is even lower on Mt McKinley ( 20,000 ft at 6.7 psi). The concentration of oxygen remains the same 20.96% as at sea level but the atmosphere is rare and all molecules are father apart. Therefore, in any inspiration, fewer molecules of oxygen get into the lungs than at sea level. This results in a decrease in the partial pressure of oxygen both at the alveolar(PAO2) and at the arterial/capillary level PaO2. Because less oxygen gets to the lungs and the blood with each inspiration, this is sensed by both the peripheral and the internal receptors. Because the hypoxia that develops is abnormal and inimical to body functions, mechanisms are deployed to overcome the oxygen deficit.
First the subject increases the ventilation or respiratory rate. This is a natural acute response to hypoxia, but it is not enough. Other compensatory mechanism slowly came into play. Second, the body tries to increase the oxygen carrying capacity of the blood by two devices. The kidneys and the liver increase their production of erythropoietin (EPO), a hormone that acts on the bone marrow to increase erythrocyte and hemoglobin production. Two other developments are also part of the acclimation process. The subject gets rid of water--become relatively dehydrated by in creased urine output. This has the effect of decreasing blood volume and consequently increasing RBC count and hematocrit. One final change enhances the body’s effort to overcome the environmental scarcity of oxygen. The oxygen dissociation curve for hemoglobin shifts to the right; this facilitates the unloading of more oxygen from the RBCs when they pass through the pulmonary capillaries.
These processes would have taken place in Alan's body over the first three days of his stay at high altitude . By the fourth day then he was almost back to normal- but not completely. However, he felt good enough to decide to stay on his mountain for his full sabbatical leave.
After his research assignment was completed, Alan returned to a sea level location (or a near sea level one - for example, Chicago. Chicago is only about an average of 586 feet above sea level, and the atmospheric pressure is about 14.22 psi. If he had been at an elevation like Yellowstone Park , an elevation of 8,000 feet, he would have become acclimatized to living in an atmospheric pressure of 10.91 psi The high hematocrit of his post-sabbatical exam was the product of successful acclimation to living in a hypoxic environment. However, his systems were under stress, and he would slowly de-acclimatize as he remained near sea level. In other words, his high hematocrit would slowly return to normal levels.
