Sleep apnea comes in four recognized types: obstructive, central, mixed, and treatment-emergent central sleep apnea (sometimes called complex sleep apnea). Most people have heard of only one or two, but understanding the differences matters because each type has a distinct cause and requires a different treatment approach. An estimated 936 million adults worldwide have some form of sleep apnea, with obstructive sleep apnea accounting for the vast majority of cases.
Obstructive Sleep Apnea (OSA)
Obstructive sleep apnea is by far the most common type. It happens when the soft tissues in your throat, including the tongue and soft palate, physically collapse and block your airway while you sleep. Your brain is still sending the signal to breathe, but air simply can’t get through. Prevalence estimates range from 9% to 38% of adults depending on how it’s measured, and a large U.S. study found that 26% of people between 30 and 70 had at least mild OSA.
During waking hours, the muscles around your airway actively hold it open. People prone to OSA tend to have a narrower airway cross-section or more soft tissue crowding the space. When sleep relaxes those muscles, the airway narrows or closes entirely, causing breathing to stop for seconds at a time, often dozens of times per hour. The hallmark symptoms are loud snoring, gasping awake, and excessive daytime sleepiness.
Severity is measured by the apnea-hypopnea index (AHI), which counts the number of breathing pauses per hour of sleep. Mild OSA is 5 to 15 events per hour, moderate is 15 to 30, and severe is more than 30. Untreated severe OSA carries serious cardiovascular consequences: a 140% increased risk of heart failure, a 60% increased risk of stroke, and a 30% increased risk of coronary heart disease. The standard treatment is a CPAP machine, which delivers steady air pressure through a mask to keep the airway open overnight.
Central Sleep Apnea (CSA)
Central sleep apnea is fundamentally different from OSA. The airway isn’t blocked. Instead, the brain temporarily stops telling the breathing muscles to work. The problem originates in the brainstem, specifically in a cluster of nerve cells responsible for generating the rhythmic signal to inhale. When that signal drops out, you simply miss one or more breathing cycles.
The underlying issue is a disruption in the neurotransmitters that keep the respiratory control system active during sleep. Several conditions can cause this. Congestive heart failure and stroke are the most common triggers, producing a distinctive breathing pattern where breaths gradually speed up, slow down, and then stop entirely before the cycle repeats. Opioid medications can also suppress the brainstem’s breathing drive. Brain tumors, structural brainstem changes, and end-stage kidney disease are less common causes. In rare cases, no cause is found at all, which is called primary or idiopathic central sleep apnea.
CSA shares some symptoms with OSA, like fragmented sleep, fatigue, and waking up short of breath. But people with central sleep apnea are less likely to snore loudly, since the airway itself isn’t collapsing. Treatment focuses on the underlying condition when one exists. Specialized breathing devices that adjust pressure breath-by-breath (adaptive servo-ventilation) are sometimes used instead of standard CPAP, since CPAP alone doesn’t address the brain signaling problem.
Mixed Sleep Apnea
Mixed sleep apnea, as the name suggests, combines features of both obstructive and central types within a single breathing event. A typical episode starts with a central component: the brain fails to send a breathing signal, and there’s no effort to inhale. Then, as the body attempts to resume breathing, the airway is also physically obstructed, adding an obstructive component to the same event.
This dual pattern can make diagnosis tricky because a sleep study needs to capture both the absence of breathing effort and the presence of airway obstruction within the same episodes. Treatment usually begins with addressing the obstructive component using CPAP, since clearing the physical blockage often reduces the overall severity. If central events persist, additional approaches may be layered on.
Treatment-Emergent Central Sleep Apnea
This fourth type, formerly called complex sleep apnea syndrome, is unusual because it only reveals itself during treatment. A person is diagnosed with obstructive sleep apnea, starts using a CPAP machine, and the obstructive events resolve as expected. But central apneas then appear or persist, with at least five central events per hour and more than half of all remaining events being central in nature. In other words, fixing the physical obstruction unmasks a separate brain-signaling problem that wasn’t visible before.
The good news is that in many cases, these central events are transient. They show up during the initial CPAP adjustment period and gradually disappear with continued use over weeks to months. For the subset of people whose central apneas don’t resolve on their own, adaptive servo-ventilation or other advanced breathing devices may be needed. The key distinction from standard central sleep apnea is that treatment-emergent CSA wouldn’t exist without the CPAP treatment itself triggering or revealing the central events.
How the Four Types Compare
- Obstructive: Physical airway collapse during sleep. Most common by a wide margin. Strongly linked to snoring, excess weight, and cardiovascular disease.
- Central: Brain fails to signal breathing muscles. Often associated with heart failure, stroke, or opioid use. Less snoring, more shortness of breath on waking.
- Mixed: Each breathing pause begins as central and transitions to obstructive. Diagnosed when both patterns appear in the same events during a sleep study.
- Treatment-emergent: Central apneas appear only after CPAP treatment resolves obstructive events. Often temporary, but sometimes requires a different device.
All four types share common downstream effects: repeated drops in blood oxygen, fragmented sleep, daytime exhaustion, and increased strain on the heart and blood vessels. The critical first step for any type is a formal sleep study, which records brain activity, breathing effort, airflow, and oxygen levels simultaneously. That data is what separates the types from one another and determines which treatment will actually work.