What causes shortness of breath in hikers at high altitudes?

From the Guidelines

Shortness of breath in hikers at high altitudes is primarily caused by decreased oxygen levels in the air, a condition known as hypoxia, as supported by the most recent study in 2024 1. At higher elevations, the atmospheric pressure drops, making it harder for oxygen to enter the bloodstream through the lungs. This triggers a compensatory response where hikers breathe faster and deeper to get more oxygen, resulting in the sensation of breathlessness.

Key Factors Contributing to Shortness of Breath

• Decreased oxygen levels in the air
• Lower atmospheric pressure
• Compensatory response of breathing faster and deeper This condition, often called acute mountain sickness (AMS), typically occurs above 8,000 feet.

Prevention and Management Strategies

• Ascending gradually (no more than 1,000-2,000 feet per day above 8,000 feet) to allow for acclimatization
• Staying hydrated to help the body adapt to the higher altitude
• Considering medications like acetazolamide (Diamox) at 125-250 mg twice daily, starting 24 hours before ascent and continuing for 48 hours after reaching maximum altitude, as recommended by recent guidelines 1 Acetazolamide works by acidifying the blood, which stimulates breathing and improves oxygen levels.

Immediate Relief and Long-term Adaptation

For immediate relief of symptoms, descending to a lower altitude is most effective. The body eventually adapts to higher altitudes through a process called acclimatization, which includes producing more red blood cells to carry oxygen more efficiently, a process that can take several days to complete, as noted in a recent study 1.

From the Research

Causes of Shortness of Breath at High Altitudes

• At high altitudes, the air pressure is lower, which means that there are fewer oxygen molecules available to breathe 2.
• This decrease in oxygen availability can lead to a condition known as acute mountain sickness (AMS), which is characterized by symptoms such as shortness of breath, headache, and nausea 3.
• The exact mechanisms of AMS are not fully understood, but it is thought to be related to the body's inability to adapt to the lower oxygen levels at high altitudes 4.
• Studies have shown that the use of acetazolamide, a medication that helps to increase oxygen levels in the blood, can be effective in preventing AMS and reducing the severity of its symptoms, including shortness of breath 2, 3.

Physiological Responses to High Altitude

• At high altitudes, the body responds to the lower oxygen levels by increasing ventilation, which can lead to an increase in oxygen levels in the blood 2.
• However, this increase in ventilation can also lead to an increase in carbon dioxide levels, which can exacerbate the symptoms of AMS 5.
• The use of medications such as nifedipine, which helps to lower pulmonary artery pressure, has been shown to be ineffective in preventing AMS, suggesting that the condition is not solely related to pulmonary hypertension 4.

Prevention and Treatment of High-Altitude Illnesses

• Slow ascent is the primary prevention strategy for high-altitude illnesses, including AMS and high-altitude pulmonary edema (HAPE) 5, 6.
• Pharmacological agents, such as acetazolamide, can be used to prevent and treat AMS, while medications such as calcium channel blockers and phosphodiesterase inhibitors can be used to treat HAPE 5.
• Dexamethasone should be reserved for the treatment of more severe cases of altitude illnesses, such as cerebral edema 5.