Sleep at Altitude

Contents

1. Thin air changes the night
2. Periodic breathing is a cycle
3. The breathing control loop overshoots
4. Sleep breaks into fragments
5. The pattern may also help
6. Clinicians classify it as central sleep apnea
7. Acclimatization usually brings better nights
8. Residents, visitors and the range of normal

Candace Cooley practiced in Breckenridge, Colorado, from 2011 to 2014, in a mountain town where visitors from sea level often notice the night changing before anything else. The scene is a familiar composite. A woman arrives on a Friday for a weekend of skiing and falls asleep easily. Around two in the morning she wakes abruptly, feeling short of air, Her companion has noticed something stranger: a run of deep breaths, then a silence long enough to be unsettling, then deep breaths again. By morning she feels as though she has barely slept.

The CDC Yellow Book identifies sleep disturbance as the most common complaint of travelers to high altitude, and observes that above roughly 2,700 meters (9,000 feet) some degree of periodic breathing becomes nearly universal.⁶

Thin air changes the night

Air at elevation holds the same share of oxygen as air at the coast; what falls is the pressure that pushes it into the lungs. A review of altitude physiology hosted by the National Institutes of Health explains that as barometric pressure drops, the partial pressure of oxygen drops with it, producing a state physiologists call hypobaric hypoxia, and it lists sleep quality among the functions that sustained hypoxia affects.³

The CDC adds the observation that explains why the night, rather than the day, is the harder part. Oxygen in the blood runs lowest during sleep, which is why a day trip to a high destination with an evening return to lower ground puts far less stress on the body than staying over.⁶

Periodic breathing is a cycle

Periodic breathing describes a repeating pattern rather than a single event. The NIH review describes three to five deep breaths followed by a couple of very shallow ones, or by a complete pause called an apnea, before the sequence begins again.³ It is not confined to climbers on remote peaks. The same review reports that it appears even in healthy people above about 6,000 feet and occurs in most people above 4,000 meters.³ A 2013 review by researchers at the University of Birmingham concluded that periodic breathing is the principal reason sleep is disturbed at altitude, and that it intensifies with the duration and severity of the exposure.²

A science column in The Aspen Times points out that most people who breathe this way are unaware of it; what they register is a night that felt shallow and broken.⁴

Figure

One cycle of periodic breathing

1. 01
   Deep breathsLow oxygen drives deeper, faster breathing, which also clears carbon dioxide from the blood.
2. 02
   Drive fadesWith carbon dioxide already low during sleep, the signal to breathe switches off.
3. 03
   PauseBreaths turn very shallow or stop altogether, and oxygen falls further.
4. 04
   RestartThe body senses the further drop in oxygen and breathing resumes with deep breaths.

The breathing control loop overshoots

At elevation, low oxygen prompts deeper and faster breathing, and that extra breathing clears carbon dioxide from the blood more quickly than usual. During sleep, breathing is steered largely by carbon dioxide and the acidity it creates. The Aspen Times column traces the result: with carbon dioxide already low, the signal to breathe weakens, and breathing can stop for as long as 15 seconds until falling oxygen jolts the sleeper back into rapid, deep breaths.⁴

A 2008 paper indexed in PubMed frames this as an imbalance in the negative feedback loop that governs ventilation, made worse at altitude because the swings in breathing and in oxygen fall half a cycle out of step.¹ A sleep physician interviewed by The Aspen Times in 2024 compared the arrangement to a thermostat and a furnace: the brain senses oxygen and carbon dioxide and tells the lungs to work harder or ease off, and at altitude each correction overshoots.⁹

Sleep breaks into fragments

The cost shows up as fragmentation more than as lost hours. The NIH review describes decompression chamber studies from Operation Everest II in which brief arousals of two to five seconds climbed from an average of 22 an hour at sea level to 161 an hour at a simulated 25,000 feet.³ Total sleep time was reported not to change in that work, but sleep shifted strongly from deeper stages toward lighter ones, and the review notes that people at altitude often wake frequently and do not feel refreshed in the morning.³

The 2016 Aspen Times column singles out slow wave sleep, the deep stage linked to physical restoration and memory processing, as the stage periodic breathing erodes, and it adds that organs such as the brain and heart see reduced oxygen through these nights.⁴

The pattern may also help

Researchers have long asked whether this pattern is purely a disturbance. The 2008 PubMed paper argues that up to roughly 3,000 to 3,500 meters, periodic breathing may be an advantage because it holds oxygen saturation at a relatively high level, while at greater heights frequent arousals lead to severe sleep loss and impaired mental and physical function.¹ The Birmingham review reaches a similar view from a different angle: because periodic breathing may raise rather than lower average oxygen saturation during sleep, it may be an adaptive response rather than a faulty one.²

A study summarized in the NIH review complicates the picture further. In healthy mountaineers who ascended quickly, sleep quality improved with acclimatization as oxygen saturation improved, even though periodic breathing continued, which led the authors to tie poor sleep at altitude more to low oxygen than to the breathing pattern itself.³

Figure

Central and obstructive sleep apnea

	Central	Obstructive
Mechanism	The brain briefly stops sending the signal to breathe	Something blocks the airway outside the lungs
Link to altitude	Can result from high altitude, especially in newcomers	Not caused by altitude
Who it affects	Anyone, including athletic people	Weight and age are factors

Clinicians classify it as central sleep apnea

In clinical vocabulary, altitude periodic breathing sits among the central sleep apneas. The NIH MedGen database defines central sleep apnea caused by high altitude as a syndrome induced by sleeping above 2,000 meters, arising from improper signaling from the brainstem to the breathing muscles, with signs that include snoring, insomnia or excess sleepiness, difficulty concentrating and fatigue.⁵ The physician interviewed by The Aspen Times in 2024 described high altitude periodic breathing as a form of central sleep apnea, distinct from the obstructive form, which comes from a blocked airway and is not caused by altitude.⁹

The two can overlap. The Steamboat Pilot reported that physicians in a Colorado mountain community see sleep apnea grow more severe at elevation, with patients who breathe poorly at night, wake often and feel worn out the next day, and that central sleep apnea turns up there more often than elsewhere.⁸ Nights that look like insomnia can be something else; the 2024 Aspen Times article describes people who stop breathing, wake and blame insomnia without knowing the cause.⁹

Figure

How often altitude periodic breathing appears

people who ascend to 2,500 meters (8,202 feet)

About 1 in 4

people who ascend to 4,000 meters (13,123 feet) or higher

Almost 100%

Acclimatization usually brings better nights

For visitors, the nights usually improve. The CDC says acclimatization improves sleep along with comfort and endurance, that the acute phase of adjustment unfolds over the first three to five days after ascent, and that sleep generally, though not always, gets better as it proceeds.⁶ The Merck Manual notes that most people acclimatize reasonably well to altitudes up to 3,000 meters within a few days, that higher altitudes take longer, and that the gain fades after a few days back at low altitude.⁷ Merck also records that poor sleep was once counted among the symptoms of acute mountain sickness but is no longer one of its diagnostic criteria.⁷ The wider process is covered under altitude acclimatization.

Medical options exist and are matters for a prescriber. The Birmingham review found that acetazolamide reduces periodic breathing by 50 to 80 percent, Merck describes low flow oxygen during sleep as effective but inconvenient, and the CDC warns against respiratory depressants as sleep aids at altitude.²⁷⁶ The CDC also advises that travelers with obstructive sleep apnea or chronic lung disease consult a physician familiar with high altitude medicine before the trip.⁶

Residents, visitors and the range of normal

Not everything resets. The 2016 Aspen Times column argues that while blood chemistry and red cell counts adjust within weeks to months, breathing and sleep at elevation do not return to their sea level pattern, and that residents grow used to the changes rather than free of them.⁴ The Steamboat Pilot article offers the other side: physicians there find that most people, young and old, adapt well and fairly quickly, though some notice they sleep better and feel more energetic at sea level.⁸

Taken together, the research sketches a wide range of normal. A few restless nights after arrival, with brief wakings and the odd sense of breath held in the dark, fall within what physiology predicts for a newcomer, and periodic breathing in that setting is an expected response to thin air rather than a disease. Persistent daytime exhaustion, or broken sleep that does not ease over the first days, sits further from that range. Where one woman’s nights fall on it is a question for her own clinician.