Sometimes people get sick at high altitudes, such as in the mountains. This is called mountain sickness or high-altitude sickness.

What causes this problem?

Lack of oxygen causes high-altitude sickness. As altitude increases, the air becomes "thinner," which means less oxygen is in the atmosphere. You get less oxygen in your lungs with each breath, so the amount of oxygen in your blood declines. (This is called hypoxia) (hi-POKS'e-ah). All people can experience mountain sickness, but it may be more severe in people who have heart or lung problems.

What are the symptoms?

Symptoms usually begin within 48 hours of arriving at high altitude. The higher the altitude, the greater the effects. People can notice effects when they go to an altitude of 7,000 to 8,000 feet. If you have heart disease (such as heart failure) or lung disease (such as emphysema), you may have symptoms at lower altitudes. Symptoms include

• headaches, breathlessness, fatigue
• nausea or vomiting
• inability to sleep
• swelling of the face, hands and feet

Both heart rate and breathing rate increase as the body tries to send more oxygen to its tissues. At very high altitudes, body fluid can leak into the brain (called brain or cerebral edema) or into the lungs (pulmonary edema). Both these conditions can be serious or even life-threatening.

AHA Recommendation

The best way to avoid or lessen the effects of mountain sickness is to increase altitude slowly. Climbers and hikers can take two days to reach 8,000 feet, and then another day for each 1,000 to 2,000 higher feet. This may not be an option for people who travel to a destination at high altitude. Most people can adjust or "acclimatize" to the high altitude within a few days. Here are some tips:

• Avoid strenuous activity for the first day or two.
• Drink extra fluid.
• Be careful of drinking alcohol.  Its effect is magnified at high altitude.
• Your doctor may prescribe medication to help prevent or treat altitude sickness.

If you have a heart or lung condition, consult your physician before going to high altitude. He or she can tell you whether your condition will let your body adjust to the lower oxygen in the atmosphere.