Altitude and Sleep Apnea: Why Athletes Experience Disrupted Breathing at Night

You've traveled to altitude, done your first day of training, and you're exhausted. But sleep doesn't come easily. When it does, you wake repeatedly—gasping, disoriented, heart pounding. Your training partner reports that your breathing stopped several times during the night. What is happening?

What you are experiencing is periodic breathing at altitude—sometimes called Cheyne-Stokes respiration—and it is one of the most underappreciated challenges in altitude training camps. It is not a sign of underlying illness in most athletes. It is a physiological response to hypoxia that directly impairs the recovery that altitude training demands.

What Is Periodic Breathing?

Periodic breathing is a cyclical pattern of breathing during sleep characterized by:

Hyperventilation: Rapid, deep breaths that over-correct blood oxygen levels
Apnea: Complete cessation of breathing for 5–30 seconds as CO₂ drops and the respiratory drive is inhibited
Arousal or partial awakening: The brain senses hypoxia and triggers an emergency ventilatory response

This cycle repeats—sometimes every 60–90 seconds—throughout the night, fragmenting sleep architecture and preventing the deep, restorative sleep stages (slow-wave sleep and REM) where most physical recovery occurs.

Cheyne-Stokes respiration is the clinical name for the most pronounced form: a crescendo-decrescendo breathing pattern where depth steadily increases, then decreases to apnea, then starts again. It is named after two 19th-century physicians who first described it but is well-established in altitude physiology.

The Physiology: Why Does It Happen?

To understand periodic breathing at altitude, you need to understand the interplay between oxygen (O₂), carbon dioxide (CO₂), and your body's respiratory control system.

The Dual-Chemoreceptor Control System

Breathing at rest is not consciously controlled. It is regulated by chemoreceptors—sensors that monitor blood gas concentrations and send signals to the brainstem respiratory center.

Peripheral chemoreceptors (in the carotid bodies): Primarily sense low oxygen (hypoxemia). They drive ventilation when PO₂ falls.
Central chemoreceptors (in the medulla): Primarily sense CO₂ and pH. They drive ventilation when PCO₂ rises.

At sea level, these two systems work in concert. At altitude, they enter into conflict.

The Instability Loop

When you breathe hypoxic air at altitude, peripheral chemoreceptors detect low O₂ and increase ventilation. This hyperventilation successfully raises O₂ levels—but also washes out CO₂ (hypocapnia), dropping blood CO₂ below the threshold needed to maintain respiratory drive from central chemoreceptors.

With CO₂ low, the brain sends the signal: stop breathing. Apnea ensues. During the apnea, O₂ falls again and CO₂ accumulates. The peripheral chemoreceptors fire again. The cycle repeats.

The core problem is a high loop gain in the respiratory control system—the correction overshoot creates the next perturbation. At sea level, the CO₂ buffer system is large enough to prevent dangerous hypocapnia. At altitude, the reduced barometric pressure compresses this buffer, and the oscillatory instability emerges.

Who Gets Periodic Breathing at Altitude?

Almost everyone who ascends above 2,500 meters will experience some degree of periodic breathing during sleep, at least in the first few nights. Studies using polysomnography (sleep lab recording) at altitude show:

~75% of individuals show significant periodic breathing on night 1 at 3,500 m
~50% still show periodic breathing by night 7, even as other acclimatization markers improve
Incidence is lower at 2,000–2,500 m but still present in many individuals

The hypoxic ventilatory response (HVR) predicts susceptibility: athletes with a strong HVR are more likely to experience pronounced periodic breathing because their corrective hyperventilation is more aggressive, creating a larger CO₂ undershoot.

Individual variation is large. Some athletes sleep perfectly at 2,500 m from night 1; others remain severely disrupted for the entire camp. This is partly genetic, partly related to individual respiratory physiology, and partly influenced by sleeping altitude itself.

How Periodic Breathing Affects Athletic Performance

The impact is substantial and often underestimated:

Sleep Architecture Disruption

Periodic breathing is associated with a reduction in slow-wave sleep (SWS) and REM sleep—the phases most important for hormonal recovery (growth hormone is released primarily during SWS) and cognitive consolidation. Studies at altitude training camps show total SWS can be reduced 50–70% in severe periodic breathers.

Sympathetic Nervous System Activation

Each apnea event triggers a micro-arousal, often with a surge in sympathetic activity (elevated HR, elevated cortisol). Repeated over a night, this creates a stress hormonal environment antagonistic to recovery—the opposite of what altitude training is supposed to produce.

HRV Suppression

Athletes with severe periodic breathing show persistently suppressed HRV at altitude, even after other acclimatization markers (resting SpO₂, resting HR) have normalized. HRV may not recover to baseline until sleep improves—meaning sleep quality, not just hypoxic exposure, drives readiness.

Daytime Fatigue

The subjective experience is familiar to most altitude athletes: waking feeling unrested despite being in bed for 8–9 hours. This fatigue compounds training stress, increasing overreaching risk and impair decision-making during sessions.

Evidence-Based Strategies to Reduce Periodic Breathing

1. Acetazolamide (Diamox)

Acetazolamide is a carbonic anhydrase inhibitor that accelerates renal bicarbonate excretion, lowering blood pH and increasing the CO₂-driven respiratory stimulus. By raising CO₂ sensitivity, it stabilizes the respiratory control loop and reduces or eliminates periodic breathing.

Evidence: Randomized controlled trials consistently show acetazolamide reduces periodic breathing at altitude and improves sleep quality, SpO₂ overnight, and next-day cognitive function.

Dosing for altitude-related sleep disruption: 125–250 mg before sleep (lower doses reduce side effects while preserving most efficacy). Consult a physician; it is a prescription medication in most countries.

Caveats: Acetazolamide causes increased urination (set an alarm for a pre-sleep bathroom visit), mild paresthesias (tingling in hands and feet), and may reduce carbonic anhydrase in red blood cells—a theoretical concern for altitude training adaptation that is not well-supported in the literature at typical doses. Many elite altitude athletes use it for the first 3–5 nights and discontinue once natural acclimatization improves sleep.

2. Sleeping Altitude Reduction

If you are using a Live High, Train Low model, the simplest intervention is sleeping at lower altitude. The severity of periodic breathing is directly proportional to sleeping altitude. Sleeping 200–400 m lower than your daytime altitude can meaningfully reduce overnight desaturation and improve sleep quality.

Athletes on multi-week camps often adjust: sleeping in valley accommodations for the first 7–10 nights, then ascending to full training/sleeping altitude once ventilatory acclimatization is established.

3. Supplemental Oxygen

Small amounts of supplemental oxygen during sleep (1–2 L/min via nasal cannula) raise PO₂ enough to abolish periodic breathing. It is effective and immediate but logistically demanding (oxygen supplies, regulator equipment) and likely disrupts the hypoxic stimulus that drives hematological adaptation.

Practical use: Reserved for athletes with severe sleep disruption unresponsive to acetazolamide, or used selectively before a critical competition or travel day when sleep quality outweighs adaptation concerns.

4. Sleep Position

Sleeping in a semi-reclined position (head of bed elevated 30°) slightly improves upper airway geometry and can reduce the severity of obstructive events that compound hypoxic central apnea. It is a minor intervention but zero cost.

5. Hypoxic Pre-Exposure

Athletes who complete intermittent hypoxic exposure (IHE) protocols in the weeks before their altitude camp often report improved sleep quality at altitude from earlier nights. The pre-conditioning effect on the HVR may reduce the overshoot magnitude that drives periodic breathing.

Distinguishing Altitude Periodic Breathing from Obstructive Sleep Apnea

Athletes with existing obstructive sleep apnea (OSA)—caused by upper airway collapse during sleep—should be aware that altitude worsens their condition significantly. The hypoxia of altitude compounds the oxygen desaturation from obstructive events, leading to more severe nocturnal hypoxemia.

If you have diagnosed OSA or suspect it (habitual snoring, witnessed apneas at sea level, daytime sleepiness), discuss altitude camp planning with a sleep medicine physician. Traveling with a CPAP device, even at altitude where power may be limited, provides meaningful protection.

Practical Monitoring at Camp

Pulse oximetry during sleep: A consumer overnight pulse oximeter can reveal SpO₂ dip patterns consistent with periodic breathing. Repeated desaturation events (SpO₂ dropping below 88–90%, particularly in cyclical patterns) confirm significant periodic breathing. This data is useful for deciding whether pharmacological intervention is warranted.

HRV trends: As noted above, suppressed HRV in the context of normal resting HR and SpO₂ suggests sleep quality is the unresolved variable. Tracking HRV over the camp helps separate "acclimatization fatigue" from "sleep deprivation fatigue."

Morning readiness rating: A simple 1–10 subjective rating of sleep quality, recorded daily, often predicts performance readiness as reliably as wearable data. Don't discard self-report.

Key Takeaways

Periodic breathing at altitude is near-universal above 2,500 m and is physiologically normal, not pathological.
It fragments sleep and suppresses recovery hormones—directly undermining the goals of altitude training.
Acetazolamide at low doses (125 mg before sleep) is the most evidence-backed intervention and is used routinely by elite athletes and high-altitude researchers.
Sleeping at lower altitude during the first week significantly reduces the problem.
Athletes with existing sleep apnea should seek specialist advice before altitude camps.

Managing sleep at altitude is not optional. For a training modality that is explicitly about recovery adaptation, protecting sleep quality is as important as designing the training sessions themselves.

Sleep Better, Train Better at Altitude

Understanding altitude physiology is only half the battle—applying it is the other. Subscribe to the AltitudePerformanceLab newsletter for evidence-based protocols on sleep, recovery, and performance optimization at elevation.

Related reading: Why Sleep Suffers at Altitude (And What Athletes Can Do About It) | Breathing Mechanics at Altitude | Acetazolamide for Altitude: Should Athletes Use It?