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As your body makes normal adjustments to adapt to a high altitude, you may experience a few symptoms that are bothersome but are not cause for concern. They include rapid (but still comfortable) breathing, shortness of breath with strenuous exercise, occasional short pauses in breathing while you sleep, and frequent urination. The last two symptoms are caused by a low carbon dioxide level, which triggers adjustments in the brain and kidney.

More serious symptoms are caused by low levels of oxygen in the blood and adjustments that are made by your circulation system.

Acute mountain sickness usuallycauses symptoms at least 8 to 36 hours after ascent.

Symptoms of acute mountain sickness can include:

  • Headache that is not relieved by over-the-counter pain medicine

  • Nausea or vomiting

  • Dizziness or lightheadedness

  • Weakness or fatigue

  • Difficulty sleeping

  • Loss of appetite

High-altitude cerebral edema is considered by many experts to be an extreme form of acute mountain sickness. It usually develops after symptoms of acute mountain sickness. Symptoms of this more severe altitude disease may not be noticed immediately because the illness can begin during the night. Because this low-oxygen injury affects the brain and thought process, a person with high-altitude cerebral edema may not understand that symptoms have become more severe until a traveling companion notices unusual behavior.

Symptoms may include:

  • Worsening headache and vomiting

  • Walking with a staggering gait

  • Confusion

  • Exhaustion

  • Visual hallucinations (seeing things that are not real)

  • Changes in the ability to think

  • Changes in normal behavior

  • Coma (in advanced cases)

High-altitude pulmonary edema, which is the lungs' response to an increase in altitude, may occur with or without other symptoms of altitude illness. A low oxygen concentration can trigger blood vessels in the lungs to constrict (tighten), causing a higher pressure in the lung arteries. This causes fluid to leak from the blood vessels into the lungs. Symptoms of high-altitude pulmonary edema commonly appear at night and can worsen during exertion.

Symptoms of high-altitude pulmonary edema include:

  • Chest tightness or fullness

  • Extreme fatigue

  • Inability to catch your breath, even when resting

  • Blue or gray lips and fingernails

  • Coughing, which may produce pink frothy fluid

  • Fever (temperature is above normal but is less than 101 Fahrenheit)

  • Noises when breathing, such as rattling or gurgling sounds

High-altitude retinal hemorrhage can occur with or without symptoms. It usually is not noticeable unless the area of the eye that provides the most detailed vision (the macula) is involved.

Blurred vision is the main symptom of high-altitude retinal hemorrhage.

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From Health A-Z, Harvard Health Publications. Copyright 2007 by the President and Fellows of Harvard College. All rights reserved. Written permission is required to reproduce, in any manner, in whole or in part, the material contained herein. To make a reprint request, contact Harvard Health Publications. Used with permission of StayWell.

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