Millions of people every year travel to high altitudes for a wide range of reasons including leisure, sports, and long-term relocation. In fact, the number of people traveling to high altitudes is expected to increase with the growth of ecotourism and global adventure travel.
Altitude sickness encompasses a range of pulmonary and cerebral conditions caused by hypoxia, which is oxygen deprivation, due to rapid ascent and poor pre-acclimatization to high altitudes.
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Types of altitude sickness
There are three types of altitude sickness, increasing in severity. These include:
- Acute mountain sickness (AMS)
- High-altitude cerebral edema (HACE)
- High-altitude pulmonary edema (HAPE)
AMS
AMS is the most common form of altitude sickness. Symptoms of AMS include:
- Headache
- Nausea
- Vomiting
- Insomnia
- Fatigue
- Dizziness
- Loss of appetite
HACE
In HACE, the brain ceases to function normally due to an accumulation of excess fluid.
HAPE
HAPE is related to HACE. Fluid enters the lungs due to leaks caused by excessive hypoxia.
Risk factors
Altitude sickness affects 25% to 85% of people traveling to high altitudes. The incidence rate of altitude sickness depends on various factors, including an individual’s age, gender, rate of ascent, home elevation, overall physical health, previous experience at altitude, and their individual susceptibility to altitude sickness.
Stricken with Altitude Sickness in Peru
Gender
The risk of developing altitude sickness between the genders is believed to be equal. However, some observational studies have shown that women have a slightly higher risk than men.
Age
There is little data to suggest that incidence rates increase with age. One uncontrolled study suggested that younger people might be at higher risk, reporting that eighteen to nineteen-year-olds had an incidence rate of 45%, whereas individuals between the ages of 60 and 87 only reported a 16% incidence rate. The information obtained from this study is believed to reflect the higher exercise intensity with younger people.
Exercise
At high altitudes, an individual’s ability to exercise decreases. This is because the ventilatory response that is usually sufficient at sea level to maintain good blood oxygen saturation is no longer possible due to the decreased oxygen levels present at high altitudes. Although those who are already in good physical health are better able to adapt to these changes during rapid ascent, data suggest that their risk of AMS is similar to individuals in poorer physical health.
Physical health
Those with pre-existing diseases should be cautious when considering ascents to high altitudes. Those with heart failure, for example, are not advised to spend time in the hypoxic conditions of high altitudes.
Although it is natural to believe that lung disease will rule out the possibility of high altitude travel, it is possible for individuals to travel to high altitudes following thorough evaluations and adequate prophylactic measures put in place before travel. This ensures that the pre-existing condition is not worsened by the ascent and prevents altitude sickness.
Previous experience at high altitudes
It is more likely that individuals who have previously ascended to high altitudes without experiencing any symptoms of AMS will ascend to high altitudes again at later dates. Those who have had recent exposure to high altitudes are less likely to develop AMS.
Home elevation
People traveling to high altitudes who usually live at sea level are more susceptible to AMS as compared to those who normally live at higher elevations.
Skiing resorts are commonly at an altitude of 3,000 meters, where the partial pressure of oxygen (PO2) is around 70% of the partial pressure at sea level. This partial pressure decreases even further at higher altitudes.
Studies have shown that visitors to a Colorado ski resort who lived at sea level reported a 27% risk of developing AMS as compared to 8.4% of visitors who lived at about 1,000 meters.
Sleeping altitude
The risk of developing AMS increases with sleeping altitude. Data suggests that mountaineers in the Swiss Alps saw a 9% prevalence of AMS at 2,850 meters and 53% at 4,559 meters. However, possibly due to prior experience at high altitudes, these prevalence figures dropped above 5,000 meters, from 51% at 4,500 – 5,000 meters to 34% above 5,000 meters.
Genetic adaptations
Communities that have lived at high altitudes for thousands of years have developed particular genetic characteristics to cope with the conditions, such as higher hemoglobin concentrations or higher ventilator responses. As no specific genetic factors contributing to AMS incidence have been concretely identified, this is an area of particular interest and is the subject of several research studies.
Summary
While the main cause of altitude sickness is poor pre-acclimatization and rapid ascent to high altitudes, there is little to suggest that any particular demographic is significantly more susceptible than the other. No significant differences between men and women or ages have currently been identified, and genetic reasons for suffering from AMS are being actively investigated.
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Further Reading