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Mountain Physiology and High Altitude Illness (HAI) Prevention and Treatment

Alpine Physiology

The external environmental factors change with the increase in elevation. There are:

  1. The amount of oxygen available decreases as the elevation increases: At the peak of Yushan (about 4,000 meters), the amount of oxygen drops to 61.6% of that at sea level, and your physiological performance will not be as good as on flat plains.
  2. The temperature decreases by about 0.6°C for every 100 meters increase in elevation. As the temperature drops, the water vapor pressure in the atmosphere also drops, so that the highland air is much drier than the air at sea level.
  3. Due to the lower air pressure, the volume expands significantly. The higher the elevation, the stronger the solar radiation, such as ultraviolet rays, and the lower the air resistance.

Changes in environmental factors will cause the human body system to experience physiological changes in low oxygen and low pressure, such as blood oxygen saturation lower than that at flat plains.

  1. Respiratory system: You may have rapid breathing to increase blood oxygen saturation. However, the rapid breathing may lead to hyperventilation, which causes alkalemia (weaken red cells' ability to release oxygen), and after water vapor is exhaled, the water content in your body drops, which causes blood viscosity to increase. As the blood flow resistance increases, the flow rate decreases.
  2. Cardiovascular system: As the blood oxygen saturation decreases, your heart rate increases to make up for the lack of oxygen.

The body cavity and chamber and digestive tract may experience flatulence and headaches from gas expansion. These are normal responses to being on high mountains. Most people can continue their mountaineering activities after good adjustments. If they are negligent and do not take appropriate measures, the symptoms may develop into acute mountain sickness and other problems, causing mountaineering safety issues.

Reactions on high mountains

Mountain climbing can be good for promoting physical and mental health and strengthening the heart, lung and blood functions to improve personal strength and endurance, so it is a recreational activity worth promoting. However, according to foreign research reports, high altitude pulmonary edema can occur at 2,440 meters, and cerebral edema can develop at an elevation higher than 2,750 meters. Acute mountain sickness is a common condition at an elevation higher than 3,000 meters.

According to the investigation and research conducted by Dr. Wei-Fong Kao, more than half of the patients during the snow season in Mount Hehuan have symptoms of mountain sickness, and more than 25% of climbers who climb Yushan have gotten acute mountain sickness. Many tourists have experienced symptoms of mountain sickness in Taiwan's alpine areas, and some have even developed into more severe or even life-threatening conditions.

According to studies, many mountain climbing accidents are related to mountain sickness. Due to alpine cerebral edema, you may experience instability in your walk and fall off cliffs. The physical weakness caused by acute mountain sickness or high altitude pulmonary edema may make you move slower, making it difficult to reach the campground before experiencing hypothermia. In the past, people were not too aware of mountain sickness in Taiwan and had often ignored it or mistaken it for other symptoms such as cold or pneumonia, further delaying the opportunity for treatment. Only a full understanding of mountain sickness can lead to prevention to ensure mountaineering safety. We introduce the symptoms, prevention, and treatment for mountain sickness below so that you can refer to the information when you take a trip up the mountains. 

Please refer to the Mountain Sickness Evaluation Form.



Acute mountain sickness

  • Mild: Headache, dizziness, anorexia, insomnia, nausea, peripheral edema, and general fatigue.
  • Moderate: Vomiting, headaches that can not be relieved with regular painkillers, and reduced urine output.
  • Severe: Changes in consciousness, unsteady gait in your walk, difficulty in breathing when taking a break during the trip, rales in lungs, and cyanosis.

High-altitude pulmonary edema

  • Early symptoms: Poor physical performance (often the earliest symptoms), dry cough, fatigue, accelerated heartbeat and breathing.
  • Later symptoms: Breathing difficulties even during the break, cough with phlegm, hemoptysis, extreme weakness and cyanosis.

Alpine brain edema

  • Severe headache (often aggravated by walking, using more strength or lying down), unsteady gait, nausea, vomiting, abnormal judgment, abnormal behavior, hallucination, confusion and even coma.
  • Gait instability is considered the most important and useful early clinical indicator for alpine cerebral edema.


Rules for ascending

Prevention is better than a cure. Ascend gradually to allow your body to have enough time to adapt to changes in altitude. It is the most important rule for preventing mountain sickness.

Rules for general prevention

Carry oxygen cylinders (bottles) or portable pressurized bags. Avoid strenuous activities. Keep yourself warm. Do not smoke. Do not drink alcohol or take sedatives. Eat things rich in carbohydrates. Avoid eating gas-producing foods (such as beans or carbonated drinks).

Prevention with drugs

Prevention with drugs

Prevention with drugs

Diamox (acetazolamide), steroids (dexamethasone) and calcium channel blockers (nifedipine) have proven effective against mountain sickness. People who are allergic to sulfonamides or have glucose-6-phosphate dehydrogenase deficiency (G6PDD) should not take diamox.


  • Before climbing mountains above the elevation of 3,000 meters, you should first spend some time (one night) at areas at an elevation of about 2,500 meters to get your body used to the condition.
  • If you need to travel to places at an elevation of more than 3,000 meters within 24 hours, you should consider taking medication to prevent mountain sickness.




Early detection, diagnosis, and treatment are the keys to successful overall treatment. The main principles are:

  1. Leave the environment at a high elevation (descending). Keep going downhill.
  2. Change the environment that causes symptoms (give oxygen and increase the environmental pressure)
  3. Rest (reduce oxygen consumption)
  4. Medical treatment