Breathing at altitude

What changes up there

The issue isn't that the air is different. It's that there's less pressure. The altitude chapter of the CDC Yellow Book, the U.S. health guide for travelers, gives a reference point: at about 10,000 feet (3,050 m), the pressure of the oxygen you breathe in is 69% of what it is at sea level. On arrival, the oxygen saturation of your blood can drop to between 88% and 91%.

Your body notices and steps up ventilation by itself: you breathe more often and more deeply without deciding to. Getting winded by a small effort isn't poor fitness: it's the expected response.

Acclimatization: time, not technique

According to the same chapter, the body can adjust to moderate low oxygen up to about 17,000 feet (5,200 m), but it needs time. The acute phase takes 3 to 5 days. During it, ventilation increases, oxygenation improves and blood flow to the brain changes. Red blood cell production plays no part in this first stage.

Acclimatizing improves sleep, comfort and endurance at moderate effort. It doesn't bring back peak performance: the CDC says that at high altitude it will always be reduced.

Being fit doesn't protect you: susceptibility is partly genetic, and there's no simple test to predict it. And what counts most is the altitude where you sleep. Any unacclimatized person sleeping at 8,000 feet (2,450 m) or higher can get sick.

Sleeping at altitude

Oxygen runs lowest during sleep. Above about 9,000 feet (2,700 m), the CDC says, periodic breathing during sleep is nearly universal and can interrupt sleep: sleep stages shift and awakenings are frequent.

That's why going high during the day and coming down to sleep is far easier on the body than spending the night up there. The CDC advises avoiding alcohol for the first 48 hours and not using alcohol or opioids to sleep, because they depress breathing.

Breathing exercises don't prevent or treat altitude sickness

Acute mountain sickness is prevented by going up slowly. It's treated by stopping the ascent, descending, oxygen, and medications prescribed by a professional. The CDC chapter doesn't mention breathing exercises among its measures.

One study is often cited the other way, and it's worth reading closely. In 2012, Bilo and colleagues measured healthy people who lived at low elevations: 39 at 14,957 feet (4,559 m) and 28 at 17,717 feet (5,400 m). For 15 minutes they breathed at six breaths a minute, paced by a device. Oxygen saturation rose from about 80% to about 89%.

But the effect lasted about as long as the exercise did. In the group at 5,400 meters, saturation at 30 minutes was no different from the starting value. The study had no control group, didn't measure symptoms of altitude sickness, and didn't test whether breathing this way prevents it. The authors themselves write that prolonged or repeated use remains unexplored.

What it shows is that slow, full breathing gets more out of each breath while you're doing it. It doesn't replace acclimatization, descent or medical care.

How to go up, according to the CDC

• Don't go up all at once. Avoid going from below about 4,000 feet (1,200 m) to sleeping above 9,000 feet (2,750 m) in a single day.
• Above about 9,800 feet (3,000 m), raise your sleeping altitude by no more than 1,650 feet (500 m) a day.
• Add an acclimatization day for every 3,300 feet (1,000 m) gained.
• For the first 48 hours, mild exercise only and no alcohol.
• If your itinerary forces a fast ascent, talk with a health professional beforehand about medication to prevent altitude sickness.
• If you have a heart or lung condition, sleep apnea or diabetes, or you're pregnant, get advice before you travel. For pregnancy, the CDC advises against sleeping above 10,000 feet (3,050 m).

Signs to stop and signs to descend

Acute mountain sickness feels like a hangover: a headache plus nausea, dizziness, fatigue or loss of appetite. It usually starts 2 to 12 hours after you arrive or climb higher, often during the first night. Without further ascent, it generally clears up in 12 to 48 hours.

The CDC's three rules for travelers:

• Know the early symptoms and admit it when you have them.
• Never go up to sleep higher with symptoms, no matter how minor they seem.
• Descend if symptoms get worse while you're resting at the same altitude. Going down 1,000 feet (300 m) or more usually brings improvement.

When it's an emergency

There are two severe forms, uncommon but potentially fatal. In high-altitude cerebral edema, the signs are confusion, extreme drowsiness or loss of coordination when walking. In high-altitude pulmonary edema, there's a cough, chest congestion, and breathlessness that first shows up with exertion and later at rest too.

In either case the CDC is clear: go down immediately and get medical care. Don't wait to see if it passes, and don't try to manage it with breathing.

If you're at altitude, feeling fine and want a quiet moment, you can use a slow pattern with no holds, like Coherent breathing 5-5 or 4-6 breathing, seated. Save long breath holds and fast breathing for when you're back down: that's this site's own caution, not a measured finding.