Millions of permanent high-altitude residents, born at high altitude, living normal lives, practicing sports, sleeping well, reproducing, and enjoying entertainment, occasionally descend to sea level, for work or leisure. This is a change where the organism perfectly adapted to chronic hypoxia is suddenly exposed to a hyperoxic environment and needs to adapt to the new circumstance. Although no alarming symptoms and signs such as those that can be seen in acute mountain sickness exist like headaches, nausea, or vomiting, there are signs that show evident changes in the body. One of the most striking is edema of lower limbs that can become more pronounced at 2 weeks of stay. Although there may be an initial edema due to long airplane travel times, this usually goes away within one or two days. However, after around 2 weeks, a positive Godet sign develops in both legs that can be quite impressive. The Godet sign, found by pressing during a few seconds on the skin in front of the tibia, displaces excessive fluid found in the interstitial subcutaneous spaces and gives rise to the formation of an evident concave impression. This sign is usually found in patients suffering from cardiac insufficiency, renal insufficiency, anasarca with low blood protein levels or inflammation. If a sea level physician would evaluate one of the high-altitude residents, at that moment, he would surely think of cardiac insufficiency, and may event start treatment with diuretics or digitalis. Possible mechanisms involve an increase of Sialic acid, found above or borderline of the normal maximum limits found during tests, in 4 subjects. Urine tests also showed an acid pH = 6.0, in spite of been on vegetarian diets, on a recent trip to India. Upon ascent to high altitude, there is central edema and that is why acute mountain sickness, high altitude pulmonary edema and high altitude cerebral edema, occur. Conversely, on descending to sea level, peripheral edema occurs. Going higher, oxygen needs to be transported preferably to the life-sustaining organs: brain, heart, and lungs, whereas going lower there is “excessive” amounts of oxygen and peripheral edema occurs possibly as a defense mechanism to reduce oxygen transport to the life sustaining organs, as it is sensed toxic. The hematologic adaptation with a decrease of the hematocrit to sea level values, is linear and takes around 20 days, going from 3500 m. Hence, once the hematocrit is at the optimal values for sea level, the peripheral edema decreases and is not as evident. Consequently, the Altitude Adaptation Formula stands valid even going down and hence it is best to include the altitude change in the denominator: Adaptation to altitude = time / altitude ∆
