What Is Clear Airway Apnea? Causes, Signs & Treatment

Clear airway apnea is the term positive airway pressure (PAP) machines use when they detect that you stopped breathing even though your airway was open. In medical terms, this is central sleep apnea: instead of your throat collapsing and blocking airflow, your brain temporarily stops sending the signal to breathe. If you are seeing “clear airway” events on your CPAP or BiPAP data report, the machine is telling you that it found pauses where no obstruction was present, which points to a fundamentally different problem than the obstructive events PAP therapy is designed to fix.

How Clear Airway Events Differ From Obstructive Ones

During normal sleep, your chest and abdomen rise and fall together in a coordinated rhythm as the diaphragm and rib-cage muscles contract. When an obstructive apnea happens, the airway physically closes, but the body keeps trying to breathe. That effort creates a telltale out-of-phase motion: the chest pulls inward while the abdomen pushes outward, or vice versa. During a central (clear airway) apnea, there is no movement in the chest or abdomen at all because the brain has not sent the signal for muscles to contract.¹ The airway is patent, the muscles are relaxed, and there is simply no respiratory effort. This is why PAP devices label these events “clear airway” rather than “obstructive.”

What Your PAP Machine Is Actually Measuring

Modern PAP devices estimate whether each apnea event involved obstruction or an open airway by analyzing the airflow signal they deliver. When the machine pushes air and detects the characteristic patterns of a blocked airway, it scores the event as obstructive. When it pushes air and finds no resistance, the event gets labeled “clear airway.” A validation study comparing one current-generation device against in-lab polysomnography found strong overall agreement for the total apnea-hypopnea index, with a correlation of about 0.85. When the device flagged an event as clear airway, the vast majority were genuinely central: only about 16% of device-detected clear airway apneas turned out to be obstructive events when researchers reviewed them manually.²

That means the machine’s clear airway label is right most of the time, but it is not perfect. If your data report shows a handful of clear airway events per night, it could reflect normal variation that the device slightly miscategorizes. A consistently high number, though, warrants a conversation with your sleep specialist, because the underlying cause and the treatment path differ substantially from standard obstructive apnea.

Why the Brain Stops Sending the Signal

Breathing during sleep depends on an automatic feedback loop involving carbon dioxide (CO₂) levels in the blood. When CO₂ rises, chemoreceptors in the brain and large blood vessels trigger a breath. When CO₂ drops too low, the drive to breathe weakens. Central sleep apnea happens when this feedback loop becomes unstable. If ventilation overshoots and pushes CO₂ below a critical threshold, breathing simply stops until CO₂ accumulates enough to restart the cycle.³ The result is a repeating pattern of breathing, overshooting, pausing, and restarting.

This instability tends to be worst during the lighter stages of non-REM sleep, when the chemical drive to breathe has the most influence and the waking neural inputs that stabilize breathing have dropped away. In deeper sleep and REM sleep, other mechanisms help maintain respiratory rhythm, which is why central apneas often cluster in the first half of the night when lighter sleep stages predominate.

Common Causes of Clear Airway Apnea

Central sleep apnea is not a single disease. It is a breathing pattern that can arise from several distinct conditions, each destabilizing the respiratory feedback loop in a different way.

Heart Failure and Cheyne-Stokes Breathing

Heart failure is the most studied trigger. In people with weakened hearts, fluid congestion in the lungs stimulates receptors that ramp up breathing. The overshooting drives CO₂ below the apnea threshold, breathing stops, CO₂ builds back up, and the cycle repeats. This creates a distinctive waxing-and-waning breathing pattern called Cheyne-Stokes respiration, where progressively deeper breaths alternate with central apneas.⁴ People with heart failure who develop this pattern tend to already have CO₂ levels sitting closer to the apnea threshold than normal, so even a small ventilatory increase tips them over.⁵ Reduced blood flow to the brain’s respiratory centers and heightened sensitivity of the chemoreceptors both contribute to this instability.

Opioid Medications

Chronic opioid use is another well-recognized cause. Opioids depress the brainstem respiratory centers, disrupting the normal CO₂ feedback loop and causing both central apneas and an irregular, ataxic breathing pattern during sleep. Research has shown that opioids cause central sleep apnea and can also provoke emergent central apnea in patients already on CPAP for obstructive apnea.⁶ The breathing disturbance tends to resolve when opioid therapy is tapered or discontinued, which makes addressing the medication itself a first-line consideration.

High Altitude

Even healthy people can develop central sleep apnea at high altitude. The low oxygen environment drives heavier breathing, which lowers CO₂ and triggers the same overshoot-pause cycle seen in other forms of central apnea.⁷ At altitude, periodic breathing during sleep alternates between central apneas and brief bursts of hyperventilation in a cyclical pattern.⁸ This is a normal physiological response, not a disease, and it typically resolves over days as the body acclimates.

Brainstem and Neurological Conditions

Structural damage to the brainstem, where the breathing centers live, can directly impair the automatic respiratory drive. Imaging research in patients with cerebral small vessel disease found that the severity of Cheyne-Stokes breathing correlated with microstructural damage in the brainstem specifically.⁹ Stroke, tumors, and congenital malformations affecting this region can all produce central apnea. In children, conditions like Arnold-Chiari malformation and foramen magnum stenosis are recognized causes.¹⁰

Treatment-Emergent Central Apnea

One of the most confusing scenarios for CPAP users is starting therapy for obstructive sleep apnea and then seeing a bunch of clear airway events appear on their data reports. This is treatment-emergent central sleep apnea, and it happens because fixing the obstructive component unmasks or triggers the central instability underneath. Roughly speaking, the CPAP eliminates the throat collapse, which changes the pressure dynamics and CO₂ balance in ways that can push the respiratory system into the overshoot-pause pattern described above.¹¹

The reassuring news is that for most people this is temporary. Research suggests that treatment-emergent central apnea resolves spontaneously in the majority of patients who continue using their CPAP consistently. In a smaller group, the central events persist despite ongoing therapy, and in a minority they appear only after weeks or months of treatment.¹² If your clear airway events are climbing rather than falling after several weeks on CPAP, your sleep physician may need to adjust pressure settings or consider alternative therapy.

Signs and Symptoms

Central sleep apnea does not announce itself the same way obstructive apnea does. The loud snoring and gasping that bed partners notice with obstructive events are often absent or much less dramatic with clear airway apnea, because the airway is not collapsing. Bed partners may notice silent pauses in breathing instead, which can be easy to miss.

The daytime symptoms can also differ in character. While obstructive sleep apnea is famous for producing overwhelming sleepiness, patients with central sleep apnea more frequently complain of insomnia and depression, and frank daytime sleepiness is actually uncommon.¹³ The repeated arousals from central apneas tend to fragment sleep and make it hard to stay asleep rather than producing the deep, unrefreshing sleep pattern of obstructive apnea. People often report waking up multiple times during the night, sometimes with a sensation of breathlessness, and having difficulty returning to sleep. Because the symptom profile overlaps with primary insomnia and mood disorders, central sleep apnea can go unrecognized for a long time.

Treatment Options

Treatment depends heavily on what is driving the central apnea. There is no single fix the way CPAP works for most obstructive cases.

Addressing the Underlying Cause

Whenever possible, treating the root condition is the first step. Optimizing heart failure management with guideline-directed medications and fluid control can reduce Cheyne-Stokes breathing. Tapering opioids can resolve opioid-induced central apnea. Descending from altitude eliminates altitude-related periodic breathing. These approaches target the source of the respiratory instability rather than the breathing pattern itself.

Adaptive Servo-Ventilation

Adaptive servo-ventilation (ASV) is a specialized PAP device that monitors your breathing cycle-by-cycle and delivers variable pressure support to smooth out the waxing-waning pattern. It was initially seen as a promising treatment for central apnea, but a landmark trial called SERVE-HF changed the clinical landscape dramatically. In patients with heart failure and reduced ejection fraction (a weakened pumping ability), ASV was associated with a significantly higher risk of cardiovascular death compared with standard care, with a hazard ratio of 1.34.¹⁴ An on-treatment analysis confirmed this increased risk during periods of actual ASV use.¹⁵

A more recent trial, ADVENT-HF, found that ASV had no significant effect on a composite outcome of death and cardiovascular events in a similar population, with a hazard ratio of 0.95. No safety signal was identified, though the trial also did not show benefit.¹⁶ The tension between these two trials means clinicians remain cautious about prescribing ASV for patients with significant heart failure. In people with central apnea who do not have heart failure with reduced ejection fraction, ASV remains a viable option and often works well for controlling central events and improving sleep quality.

Phrenic Nerve Stimulation

A newer approach uses an implanted device that electrically stimulates the phrenic nerve, which controls the diaphragm, to maintain breathing during sleep. Five-year follow-up data show sustained improvements: the median central apnea index dropped from 23 events per hour at baseline to just 1 at five years, and the overall apnea-hypopnea index fell from 46 to 17.¹⁷ Some residual hypopneas (shallow breaths) persisted, but the dramatic reduction in complete central pauses is encouraging. This device is generally considered for patients who cannot tolerate or do not respond to PAP-based therapies.

Acetazolamide

Acetazolamide is a medication that causes mild metabolic acidosis, effectively raising the CO₂ baseline and moving it further from the apnea threshold. A systematic review and meta-analysis found it substantially reduced the apnea-hypopnea index in central sleep apnea, with a mean reduction of about 23 events per hour. It also improved oxygen levels and sleep efficiency.¹⁸ The same analysis found no significant effect in obstructive sleep apnea, which makes sense given that obstructive events stem from airway anatomy rather than CO₂ feedback instability. Acetazolamide is sometimes used off-label as a bridge therapy or for altitude-related periodic breathing, though long-term use requires monitoring for side effects like tingling, taste changes, and electrolyte shifts.

Why Clear Airway Apnea Matters for Long-Term Health

Central sleep apnea is not a benign curiosity on your CPAP data report. A large retrospective study of veterans found that a quarter of patients with central sleep apnea died during the study period, compared with about 15% of those with obstructive sleep apnea. After adjusting for other health factors, the mortality risk was roughly 50% higher in the central apnea group.¹⁹ Heart failure was a major driver of that increased risk, and the presence of heart failure boosted mortality risk in both groups substantially. This does not mean central apnea itself is killing people: much of the elevated mortality likely reflects the serious underlying conditions (heart failure, stroke, neurological disease) that cause central apnea in the first place. But it underscores why newly discovered clear airway events on a PAP report should be investigated rather than ignored.

Clear Airway Apnea in Infants and Children

Central apnea is not exclusively an adult condition. In newborns and infants, brief central pauses are actually part of normal respiratory development. However, premature infants are especially vulnerable: virtually all babies born before 29 weeks of gestation experience apnea of prematurity, and up to a quarter of those episodes are central in origin.¹⁰ In older children, central sleep apnea tends to occur alongside underlying medical conditions: brain and brainstem malformations, genetic conditions like Prader-Willi syndrome, obesity, and hypothyroidism are all recognized associations. Unlike in adults, pediatric central apnea is rarely idiopathic, which means the diagnostic workup in a child with central events will usually include neuroimaging and screening for underlying conditions that would not be routine in an adult.

When a Few Clear Airway Events Are Normal

Not every clear airway event on your PAP data is a red flag. Occasional central apneas occur in perfectly healthy sleepers, especially during the transition from wakefulness to sleep. The standard diagnostic threshold for central sleep apnea is five or more central events per hour of sleep. A handful of clear airway events scattered across an eight-hour night is generally considered normal and does not require any change in treatment.

Context also matters. If you see a spike in clear airway events on a night when you had alcohol, slept at a higher elevation, or were taking a new medication, those transient triggers may explain the change without indicating a chronic problem. Consistently elevated numbers over multiple nights are a different story and worth discussing with a sleep clinician who can review the raw flow data and, if needed, order an in-lab sleep study to differentiate true central apnea from device artifact. The important thing is not to panic over a single night’s data but also not to dismiss a persistent trend, especially if you have any of the risk factors like heart disease or opioid use that make central sleep apnea more likely and more consequential.