What causes altitude sickness

Overview

Altitude sickness, or acute mountain sickness (AMS), is a common illness that can affect people who travel to higher elevations quickly. It's essentially your body's reaction to the lower atmospheric pressure and reduced oxygen levels found at high altitudes. While most people can acclimatize without issue, rapid ascent without allowing the body sufficient time to adjust can lead to symptoms ranging from mild headaches to severe, life-threatening conditions.

What is Altitude Sickness?

Altitude sickness occurs when you ascend to a higher altitude faster than your body can adapt. The Earth's atmosphere is composed of various gases, including oxygen, and at sea level, the air pressure is higher, meaning there are more oxygen molecules available per breath. As you climb higher, the atmospheric pressure decreases, and the air becomes 'thinner,' containing fewer oxygen molecules. Your body needs oxygen for energy production, and when it doesn't get enough, it can trigger a cascade of symptoms.

The Physiological Cause: Hypoxia

The fundamental cause of altitude sickness is hypoxia, a condition where the body is deprived of adequate oxygen supply. When you reach a higher altitude, the partial pressure of oxygen in the air decreases. This means that even though the percentage of oxygen in the air remains about 21%, the lower atmospheric pressure results in fewer oxygen molecules entering your lungs with each breath. Consequently, less oxygen is transferred into your bloodstream. Your body attempts to compensate by increasing your breathing rate and heart rate, but if the ascent is too rapid, these compensatory mechanisms may not be enough, leading to the symptoms of AMS.

Factors Contributing to Altitude Sickness

Several factors can increase an individual's susceptibility to altitude sickness:

• Rate of Ascent: This is the most significant factor. Ascending too quickly, especially above 8,000 feet (2,500 meters), significantly raises the risk. Sleeping at an altitude above 10,000 feet (3,000 meters) after ascending more than 1,600 feet (500 meters) in a day is often considered a risk.
• Previous History: If you've had altitude sickness before, you are more likely to experience it again.
• Individual Physiology: Some individuals are simply more prone to AMS than others, regardless of their fitness level.
• Physical Exertion: Strenuous physical activity at high altitudes can exacerbate the lack of oxygen and trigger symptoms.
• Dehydration: Being dehydrated can worsen AMS symptoms. It's crucial to stay well-hydrated at altitude.
• Alcohol and Sedatives: Alcohol can impair acclimatization and worsen symptoms. Certain sedatives can also depress breathing, which is detrimental at high altitudes.
• Genetics: Emerging research suggests that genetic factors might play a role in an individual's susceptibility to altitude sickness.

Types and Symptoms of Altitude Sickness

Altitude sickness can manifest in several forms, ranging in severity:

• Acute Mountain Sickness (AMS): This is the most common form. Symptoms usually appear 12 to 24 hours after arriving at a higher altitude and can include headache (often the first symptom), nausea, vomiting, dizziness, fatigue, loss of appetite, and difficulty sleeping.
• High-Altitude Cerebral Edema (HACE): This is a more severe and potentially life-threatening form of AMS where fluid accumulates in the brain. Symptoms include severe headache, confusion, disorientation, loss of coordination (ataxia), drowsiness, and eventually coma.
• High-Altitude Pulmonary Edema (HAPE): This is another severe and life-threatening condition where fluid builds up in the lungs. Symptoms include extreme shortness of breath (even at rest), coughing (sometimes with frothy or pink sputum), chest tightness, rapid breathing, and fatigue.

Prevention and Treatment

The best prevention is a slow and gradual ascent, allowing your body to acclimatize. If you must ascend rapidly, medications like acetazolamide (Diamox) can help speed up acclimatization. Staying well-hydrated, avoiding alcohol and strenuous activity upon arrival, and listening to your body are also crucial. If symptoms develop, descending to a lower altitude is the most effective treatment. Mild symptoms can often be managed with rest and hydration, but severe symptoms require immediate descent and medical attention.