© Shutterstock

What is altitude sickness? -

Altitude sickness is the negative health effect of high altitude, caused by rapid exposure to low amounts of oxygen at high elevation. The condition typically occurs only above 2,500 m (8,000 ft), though some are affected at lower altitudes.

© Shutterstock 

Susceptibility -

People have different susceptibilities to altitude sickness; for some otherwise healthy people, acute altitude sickness can begin to appear at around 2,000 m (6,600 ft) above sea level, such as at many mountain ski resorts.

© Shutterstock 

Can you handle the pressure? -

A ski resort set at an altitude of 2,000 m (6,600 ft) above sea level is the equivalent to a pressure of 80 kilopascals (kPa), or 11.603 pounds per square inch (psi).

© Shutterstock

Acute mountain sickness -

The mildest form of the condition is acute mountain sickness (AMS). Symptoms may include headaches, vomiting, and tiredness. Hikers are sometimes prone to AMS after underestimating the elevation of a mountain walk.

© Shutterstock 

Other symptoms -

AMS can also induce confusion and dizziness, which in turn can lead to disorientation.

© Shutterstock 

Sleep problems -

Campers suffering the effects of AMS are also very likely to experience trouble sleeping.

© Shutterstock 

Tiredness and fatigue -

AMS is the least dangerous of several kinds of altitude illnesses that can occur. It effects many climbers who begin a hike near to sea level and ascend to 4,267 m (14,000 ft) of elevation without scheduling enough rest time.

© Shutterstock 

If in doubt, descend -

Fortunately, symptoms from acute mountain sickness improve if you descend to a lower altitude quickly.

© Shutterstock 

Mild symptoms -

In the case of very mild symptoms, a delay of anywhere between 30 minutes and an hour before further climbing is usually enough to allow the effects to dissipate. But avoid alcohol. Instead, drink lots of water.

© Shutterstock 

High-altitude risks -

At high-altitude, any symptoms of headache, nausea, shortness of breath, or vomiting can be assumed to be as a result of altitude sickness. These should be taken very seriously, since some altitude problems can develop into fatal illnesses.

© Shutterstock 

HACE -

One dangerous reaction to high altitude is a condition called high-altitude cerebral edema (HACE), in which the brain accumulates extra fluid, swells, and stops working properly. It generally appears in patients who have acute mountain sickness and involves disorientation, lethargy, and worsening headache and vomiting among other symptoms. It occurs when the body fails to acclimatize while ascending to a high altitude.

© Shutterstock 

HACE symptoms -

Other symptoms of HACE include exhaustion, walking with a staggering gait, visual hallucinations, and an inability to think properly.

© Shutterstock 

HAPE -

Acute mountain sickness can also progress to high altitude pulmonary edema (HAPE). This is a life-threatening form of non-cardiogenic pulmonary edema (fluid accumulation in the lungs) that occurs in otherwise healthy people at altitudes typically above 2,500 m (8,200 ft).

© Shutterstock 

HAPE symptoms -

The onset of HAPE is indicated by several symptoms, including extreme fatigue, chest tightness, coughing, and telltale noises when breathing (rattling or gurgling sounds). Blue or gray lips or fingernails is another sign.

© Shutterstock 

Major cause of death -

HAPE remains the major cause of death related to high-altitude exposure, with a high mortality rate in the absence of adequate emergency treatment. Climbers on Mount Everest, for example, often experience altitude sickness and have been known to fall victim to the condition.

© Shutterstock

HARH -

Another related illness associated with high altitude is high-altitude retinal hemorrhage (HARH). This can cause eye damage. In fact, a large amount of climbers exhibit retinal hemorrhages during exposure to high altitudes. The short-term effects of HARH include high-altitude retinopathy, change in corneal thickness, and photokeratitis. Long-term effects include pterygium, cataracts, and dry eye syndrome.

© Shutterstock 

Rate of ascent -

As a rule, altitude sickness is more likely to occur in people who have a previous history of the condition. It is more likely if you climb quickly. In fact, the rate of ascent, altitude attained, amount of physical activity at high altitude, as well as individual susceptibility, are contributing factors to the onset and severity of high-altitude illness.

© Shutterstock 

Dehydration -

Dehydration due to the higher rate of water vapor lost from the lungs at higher altitudes may contribute to the symptoms of altitude sickness.

© Shutterstock 

Peripheral edema -

Another primary symptom of altitude sickness is peripheral edema (swelling of hands, feet, and face). While many cases from temporary or minor causes resolve on their own, with no lasting damage, severe swelling can cause permanent damage to nerves, resulting in peripheral neuropathy.

© Shutterstock 

Risk of hypoxemia -

At very high altitude, 3,500 to 5,500 m (11,500 to 18,000 ft), extreme hypoxemia (an abnormally low level of oxygen in the blood) may occur during exercise, during sleep, and in the presence of high altitude pulmonary edema or other acute lung conditions. Severe altitude illness occurs most commonly in this range.

© Shutterstock 

Death Zone -

As with Everest and the world's other highest peaks, K2 (pictured) has a death zone, where oxygen is so limited that the body's cells start to die. Climbers' judgment becomes impaired, and they can experience heart attacks, strokes, or severe altitude sickness.

© Shutterstock

Prevention -

Ascending slowly is the best way to avoid altitude sickness. Gradual changes in altitude will help your body adapt to the low-oxygen environment.

© Shutterstock 

Limit physical exertion -

Limit your physical exertion. Avoid strenuous activity such as skiing and hiking. Of course people adapt at different rates, but as a rule of thumb do not increase your altitude by more than 305 m (1,000 ft) per day.

© Shutterstock 

Altitude acclimatization -

Each time you increase your altitude by 914 m (3,000 ft), spend a second night at this elevation before venturing farther.

© Shutterstock 

Prevention -

At the first sign of mild altitude sickness, stop ascending until symptoms dissipate. If you begin to experience more severe effects, you need to move to a lower altitude as soon as possible. You can treat mild cases with rest and pain relievers.

© Shutterstock 

Oxygen enrichment -

In high-altitude conditions, oxygen enrichment can counteract the hypoxia related effects of altitude sickness. Oxygen from portable gas bottles or liquid containers can be applied directly via a nasal cannula or mask.

© Shutterstock 

Hyperbaric chamber -

For more serious cases of AMS, or where rapid descent is impractical, a Gamow bag (pictured), a portable plastic hyperbaric chamber inflated with a foot pump, can be used to reduce the effective altitude by as much as 1,500 m (5,000 ft).

© Shutterstock

Evacuation -

However, a Gamow bag is generally used only as an aid to evacuate severe AMS patients, not to treat them at altitude.

© Shutterstock

Over-the-counter herbal supplements -

Herbal supplements and traditional medicines are sometimes suggested to prevent high altitude sickness. The results of a study published by the National Library of Medicine provides evidence supporting the use of ginkgo biloba in the prevention of AMS.

© Shutterstock 

Traditional medicines -

Indigenous peoples of the Americas, such as the Aymaras of the Altiplano, have for centuries chewed coca leaves to try to alleviate the symptoms of mild altitude sickness. However, medical evidence to support the effectiveness and safety of this approach is often contradictory and/or lacking.

Sources: (Harvard Health Publishing) (National Health Service) (National Library of Medicine)

See also: Discover the world's most incredible mountain paradises

© Shutterstock