The human body and altitude


* El cuerpo humano y la altitud

Humans have the ability to live in mountains, even up to 8000 m, but for this to happen they must first go through a process of acclimatization, i.e., an adaptation of the organism to function in the new environment, something that takes time. A feature of this process is that not all people respond alike. The causes are still mysterious.

The relative proportion of oxygen in the air is almost constant at 21%, to altitudes above 21 000 meters. However pressure falls rapidly. At sea level, standard atmospheric pressure is 1013 hectoPascals, but as we go up it decreases, so that at 5000 meters it is half of normal pressure.


The most common complication for those who climb and are not adapted to the shortage of air is the so-called Mountain Sickness. It was first described in the scientific literature by Thomas Holmes Ravenhill, a physician of the Collahuasi and La Poderosa mines in northern Chile, well ago in 1913 ("Puna Sickness"). Yet it is still a mysterious disease, difficult to diagnose. Only in the 7th International Hypoxia Symposium, held in 1991 in Lake Louise, Canada, consensus was reached that Mountain Sickness consists in headache, along with lack of appetite, nausea, vomiting, dizziness, or trouble to get asleep, after the person has gained altitude.

In 1982, a study by Charles Houston on vacation sites between 2500 m and 2900 m altitude in the mountains of Colorado, USA, showed that of 3906 tourists surveyed, 12% reported Mountain Sickness.

Another study by Buddha Basnyat and colleagues, in 2000, included 228 pilgrims to a holy lake in the Himalayas, at 4300 m, plus a control group at 1300 m, where it was seen that of those in the group that went to the lake, 68% suffered the Sickness.

Jennifer Vardy, John Vardy and Ken Judge published a more detailed study in the July 2006 edition of "Aviation, Space and Environmental Medicine", with 150 tourists in the Solu-Khumbu region, Nepal, where they found that the incidence of Mountain Sickness was of 0% to 2500-3000 m, 10% between 3000 and 4000 m, rising to 15% between 4000 and 4500 m and reached 51% between 4500 and 5000 m.

Bruce Shorts, in an article dated from the year 2000, reports that Mountain Sickness symptoms appear 6-12 hours after ascent, reach a peak within 48 to 72 hours and usually fades by the fifth day. Both the speed of ascent and the altitude to which a person gets, especially the altitude at which one sleeps, worsen the situation.


Apart from this "benign" altitude sickness, in rare cases more serious problems can occur, such as pulmonary edema, which is the infiltration of body fluids into the lungs. It was first reported in 1960 by Charles Houston. Today, the Lake Louise consensus defines High-Altitude Pulmonary Edema as shortness of breath (even without exercise), cough, weakness or loss of athletic ability, chest tightness or congestion, and other clinical signs, which may or may not be accompanied by symptoms of Mountain Sickness, always after the person has gained altitude.

An investigation by Tianyi Wu et al., 2006, found that among 75 000 Chinese workers who were building a railway line to over 4000 m, 0,49% had High-Altitude Pulmonary Edema. Buddha Basnyat and colleagues (2000) found 5% of pilgrims with pulmonary edema at 4300 m.

Bruce Shorts (2000) indicates that this disease appears suddenly, usually at night, between the second and fourth day of arrival. The cold and exercise worsen the situation. Pulmonary edema is the most common cause of death from altitude illnesses. The patient should be drop to a lower altitude quickly to ameliorate. It rarely occurs at less than 2500 m.


The headache can increase up to a serious increase in pressure in the brain, even with bleeding. The Lake Louise consensus defines High-Altitude Cerebral Edema as a change in mental status, or difficulty coordinating movements in a person who has recently gained altitude, with or without symptoms of Mountain Sickness.

The military physician Inder Singh and colleagues reported in 1969 that during the war between China and India, 1,25% of the soldiers who were airborne at 3500 m in the Himalayas, had cerebral edema. Another study, by Peter Hackett, Drummond Rennie and Harry Levine, published in the journal Lancet, of 27 November 1976, showed that 1,8% of the mountaineers who climbed to 4200 m, in the Everest region, had the illness. Wu and colleagues (2006) found 0,26% of workers with cerebral edema at 4500 m.

Shorts explains that this disease often appears on the fifth day, and if left untreated, is fatal. The person must descend immediately. This disease is rare at less than 2500 m.


La Paz city, Bolivia, with its 1,6 million inhabitants is located in a valley that runs from 3000 to 4100 meters above mean sea level. To get an idea of ​​how high you are, just an anecdote: when the beloved airline Braniff, that held the concession granted by the United States of America to this region, bought its first jet aircraft in 1960, Boeing had to develop a special version of the 707 exclusively for this route. One problem was that at arriving at La Paz and opening the airliner's door, at 4100 m, the alarm of the internal pressure of the cabin (which is at 2500 m and should not exceed 3000 m) would sound, and even oxygen masks (calibrated for 4200 m) could be deployed.

A study led by Tom Brutsaert et al., presented in 2000, included 20 players from the club The Strongest (from La Paz), Blooming and Oriente Petrolero (from Santa Cruz), and the Bolivian National Team. Eleven players lived and trained in La Paz (3600 m) and 9 in Santa Cruz (420 m above mean sea level). It was discovered that the oxygen consumption of both groups was greater in Santa Cruz, and therefore the performance improves for all. As expected, oxygen consumption decreases in La Paz, but for the players from the highland plateau this reduction was by only 13%, while for the players from the Bolivian lowland plain the loss was much greater, at 20 %.

Additionally, a survey by Dr. Henry Vargas, which considered 134 international players in 8 matches of the Copa Libertadores and 4 matches of the World Cup, played in La Paz in 2000 and 2001, showed that 64 % had headaches, 42 % complained of fatigue or weakness, 27 % had nausea or decreased appetite, 17 % had sleep disturbances and 12 % dizziness or light-headedness.

As for overall competitive sporting performance, Jorge Flores and Pablo Aguilera Sitic reported that in Bolivian Championship matches between 1995 and 1997, teams from La Paz achieved 225 victories playing at home, and conversely, visitors from the flatlands only won 35 times in this city, that is, the chances were 84 % versus only 16 %.

In international matches, Patrick McSharry and colleagues analyzed statistics of 1460 matches of 10 South American national teams, from the far away year of 1900 through 2004. The results, published in early 2008, showed that when two countries from the same altitude play, the home team has a 54 % chance of winning. However, if one of the national teams is from a high elevated land and the other is not, the one from the heights reaches 83 % chance of victory. They even calculated that for each 1000-m-difference in altitude, one half a goal is scored by the team from the high plateau.

As we can see, the controversy of sport matches at high altitude has a long way to go.

Aldo Loup.

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Originally published in ABC Color, on 17 March 2008. Photograph: This sign in an observation area near the peak of Mount Evans (elevation 4348 m) in Colorado, USA, warns about the symptoms of Mountain Sickness and other risks. Photo credit: Gary Cox, 14 July 2006. With permission from Gary Cox.