There are many sources of information on acute mountain sickness (AMS). We have compiled some of this information for you to read before your trip to altitude. This information is provided for your information and does not constitute the opinion of a health professional, whom you should consult before your trip.

What is AMS?

AMS is characterized by a set of symptoms linked to the human body’s reactions to the lack of oxygen at high altitude. We consider “high altitude” to be between 3,500m and 5,500m above sea level. Above 5,500m, we are at “extreme altitude”. The effects of altitude can be felt from 2,500 meters upwards, but most people react above 3,000m, with 40% above 4,000m.

Common symptoms of altitude sickness include:

• headache
• Severe fatigue
• Loss of appetite, nausea, vomiting
• Dizziness
• Decreased diuresis (urine output)
• Sleep disorders (apnea, etc.)

In short, AMS is like a “morning after”. It is therefore PRIMORITY to listen to your body and, above all, to talk to a colleague about it AND INFORM your companion. Don’t worry, this won’t necessarily put an end to your expedition; on the contrary, it will allow us to correct the situation so that you can continue your expedition SAFELY.

Why is this happening ? Reduced pressure and oxygen

At sea level, air contains around 21% oxygen, and atmospheric pressure is 1013 hPa. At 3,000 meters, pressure is reduced by around 30%, so less oxygen is available for the lungs and blood. At 5,000 meters, the oxygen available is almost half that at sea level.

The body compensates for the lack of oxygen by speeding up breathing and heart rate. Red blood cells gradually increase to carry more oxygen. But if the ascent is too rapid, the body doesn’t have time to adapt, resulting in altitude sickness.

Factors favouring AMS

• Too rapid an ascent : Gradual acclimatization is essential.
• Altitude reached too quickly: The risk is greater above 2,500 m.
• Intense exertion: Physical exercise aggravates oxygen deficiency.
• Dehydration: Poor hydration accentuates symptoms.
• Individual susceptibility: Some people are more vulnerable than others.

Symptoms of AMS

• Mountain sickness: Headache, nausea, vomiting, starvation, insomnia, fatigue (at 4,000m, 50%).
• Cerebral edema: +blood to the brain, swelling, can be fatal, descend immediately
• Pulmonary edema: Lungs fill with fluid, fatal above 3,600 m

The effects of altitude and the effort required

A gene for adapting to oxygen shortage discovered

In 2015, researchers identified a biological mechanism enabling the heart, and the body in general, to better adapt to the increasing scarcity of oxygen in the atmosphere. “This is the first time we’ve discovered a gene responsible for adapting to high altitude, which is essential for protecting heart function even at sea level”, said Gabriel Haddad, Professor of Pediatrics at Rady Children’s Hospital in San Diego.

This discovery could lead to the development of drugs to combat heart failure, according to researchers at the University of California School of Medicine, whose study appears in the Proceedings of the American Academy of Sciences (PNAS).

They studied the genomes of people living in the Ethiopian highlands. Like those of the Andes and Himalayas, they have undergone major physiological and genetic changes over the millennia, affecting their respiratory and blood systems, unlike the population living at lower altitudes. Sequencing of the Ethiopian genome revealed variations in the EDNRB gene apparently linked to cardiac functions and likely to explain this adaptive capacity, according to a study published in February 2014 in Genome Biology.

Researchers in California have now demonstrated this hypothesis with mice genetically engineered to reproduce this EDNRB variant, which leads to reduced production of the protein endothelin. These rodents were much more resistant to moderate or severe hypoxia, exhibiting better cardiac performance and greater oxygenation of vital organs than normal mice.

The authors’ conclusion: the lowering of endothelin levels, a powerful vasoconstrictor, resulting from this genetic variant helps preserve cardiac function in moderate to severe hypoxia. And this at high altitudes, such as sea level. Even in conditions of extreme hypoxia with only 5% oxygen – less than at the summit of Mount Everest – mice endowed with the mutant gene and therefore producing less endothelin, had significantly better cardiac and respiratory functions than other rodents.

They were able to maintain normal blood pressure and heart rate, and were better able to maintain the flow of oxygen to their vital organs.

But at this level of oxygen depletion, the respiratory capacity of normal mice dropped by 40-50%, and they were unable to maintain their blood pressure. None survived. “Lowering endothelin levels works wonders in mice placed in a low-oxygen environment, suggesting that the EDNRB gene plays a key role in human adaptation to high altitude,” noted Haddad.

According to him, this biological mechanism appears to contribute to the dilation of blood vessels and the proliferation of blood cells.