Complex sleep apnea is a form of sleep-disordered breathing where central apneas (pauses in breathing driven by the brain, not a blocked airway) persist or newly appear once obstructive sleep apnea is being treated with CPAP. In other words, you start CPAP therapy to fix one type of apnea, and a different type shows up. It affects roughly 3.5% of patients who begin positive airway pressure therapy, and it’s formally diagnosed when central breathing pauses exceed five per hour while obstructive events have been controlled.
How It Differs From Other Types of Sleep Apnea
Obstructive sleep apnea happens when the muscles in your throat relax and physically block your airway during sleep. Central sleep apnea is the opposite problem: your airway is open, but your brain temporarily stops sending the signal to breathe. Most people with complex sleep apnea start out looking like straightforward obstructive cases. The central component only reveals itself once CPAP opens the airway and the obstructive events disappear.
For a formal diagnosis, the central events must make up more than half of the remaining breathing disruptions on CPAP, or they must produce a clear cyclical pattern of breathing and pausing that fragments sleep. The term “treatment-emergent central sleep apnea” (TECSA) is used interchangeably with complex sleep apnea in many sleep labs.
Why CPAP Itself Can Trigger Central Apneas
The underlying problem is an instability in how your brain regulates breathing. Two main mechanisms are at play. First, CPAP increases the amount of carbon dioxide you exhale with each breath. Carbon dioxide is one of the brain’s primary signals to keep breathing. When levels drop below a certain threshold, the brain briefly stops sending that signal, producing a central apnea. This creates a cycle: the pause lets carbon dioxide build back up, breathing resumes forcefully, carbon dioxide drops again, and another pause follows.
Second, the pressure from CPAP stretches the lungs in a way that activates stretch receptors. These receptors trigger a reflex (called the Hering-Breuer reflex) that temporarily inhibits the next breath. In most people, this effect is minor. In people prone to complex sleep apnea, it’s enough to tip the balance toward repeated central pauses.
What It Feels Like
Complex sleep apnea is tricky because it typically can’t be felt as a distinct condition. Before diagnosis, you experience the same symptoms as obstructive sleep apnea: snoring, gasping awake, daytime fatigue, morning headaches, and difficulty concentrating. The red flag comes after starting CPAP. Despite using the machine consistently, you may still wake up frequently, sleep poorly, and feel unrefreshed in the morning. Your CPAP data may show a persistently high number of breathing events even though the obstructive ones have cleared.
Some people describe feeling like the machine “isn’t working” or notice an odd rhythmic pattern of breathing and pausing that their bed partner can observe. This incomplete response to CPAP is often the first clue that prompts a sleep specialist to look more closely at the data and identify central events.
Does It Resolve on Its Own?
For the majority of people, yes. Studies tracking patients on CPAP over weeks to months show a spontaneous resolution rate between 54% and 86%. One large telemonitoring study following over 133,000 patients found that TECSA appeared in 3.5% of them, resolved on its own in more than half, and persisted in about a quarter. The typical timeline for resolution is two to three months of continued CPAP use.
Because of these numbers, many sleep specialists take a watchful approach: continue CPAP, monitor the data closely, and reassess after a few months. The challenge is that patients whose central apneas don’t resolve tend to abandon therapy at higher rates, since they’re not getting relief from their symptoms.
Treatment When It Persists
When complex sleep apnea doesn’t clear up with ongoing CPAP, the most effective alternative is adaptive servo-ventilation (ASV). Unlike standard CPAP, which delivers a single constant pressure, ASV monitors your breathing pattern in real time and adjusts its pressure breath by breath. When it detects a central pause developing, it increases support to keep you breathing. When your breathing normalizes, it backs off.
A randomized trial comparing the two approaches over 90 days found that ASV brought the overall breathing disturbance index below 10 events per hour in about 90% of patients, compared to 65% with standard CPAP. Central apneas specifically dropped to less than one per hour on ASV, versus nearly five per hour on CPAP. More than 80% of ASV users reported subjective improvement in their symptoms.
An Important Safety Limitation
ASV is not safe for everyone. A major clinical trial found that in patients with symptomatic heart failure and reduced heart pumping function (left ventricular ejection fraction of 45% or below), ASV was associated with increased risk of death. The American Academy of Sleep Medicine issued a safety notice advising against prescribing ASV to this group, and the risk appears to worsen as heart function declines further below that threshold. For people with heart failure, alternative approaches to managing complex sleep apnea need to be explored with a specialist.
Long-Term Health Risks of Untreated Sleep Apnea
When any form of sleep apnea goes unmanaged, the repeated drops in blood oxygen and fragmented sleep take a cumulative toll on the cardiovascular and nervous systems. Untreated sleep apnea increases the risk of heart failure by 140%, stroke by 60%, and coronary heart disease by 30%. People with significant sleep apnea have four times the odds of developing atrial fibrillation compared to those without it.
The brain suffers too. Chronic untreated sleep apnea gradually produces cognitive deficits, poor concentration, and impaired performance. These risks apply broadly to sleep apnea of all types, which is why getting complex sleep apnea properly managed, rather than simply giving up on CPAP when it doesn’t seem to work, matters for long-term health.
How It’s Diagnosed
Complex sleep apnea can only be identified during a sleep study (polysomnography) conducted while you’re on CPAP. A standard diagnostic sleep study without CPAP will show obstructive events but won’t reveal the central component, because the central apneas only emerge once the airway obstruction is treated. This is why it’s sometimes caught during a split-night study, where the first half diagnoses obstructive apnea and the second half introduces CPAP, or during a dedicated CPAP titration night.
If your CPAP machine’s data consistently shows a high number of residual events despite good mask fit and adequate pressure, that’s a strong reason to discuss a follow-up sleep study with your provider. Modern CPAP machines can flag central versus obstructive events in their nightly reports, giving both you and your sleep team an early signal that something beyond obstruction is going on.