There are three types of sleep apnea: obstructive sleep apnea (OSA), central sleep apnea (CSA), and complex sleep apnea syndrome, which is a combination of the first two. Obstructive sleep apnea is by far the most common, accounting for roughly 48% of participants in one large cohort study, while central sleep apnea affected fewer than 1% of the same population. Each type has a different underlying cause, which changes how it’s diagnosed and treated.
Obstructive Sleep Apnea
Obstructive sleep apnea happens when the airway physically collapses or narrows during sleep. The section of your throat between the hard palate and the voice box is made entirely of soft tissue and muscles, with no bone or cartilage to hold it open. When you fall asleep, the muscles that normally keep this passage open relax, and in people with OSA, the airway narrows enough to block airflow partially or completely.
Several factors make this collapse more likely. A naturally narrow airway is more prone to obstruction than a wider one. Your tongue plays a key role: a muscle at the base of the tongue normally responds to changes in air pressure by stiffening and pulling the airway open, but this reflex weakens during sleep. Lung volume matters too. When lung volume drops, the diaphragm shifts upward, reducing the downward pull on airway structures and making them floppier.
The hallmark symptom of OSA is loud, chronic snoring, often punctuated by gasping or choking sounds when breathing restarts. During an obstructive episode, your chest and abdomen move out of sync as your body tries to force air past the blockage. This effort distinguishes OSA from central sleep apnea on a sleep study. Daytime sleepiness, morning headaches, and difficulty concentrating are common consequences because the repeated awakenings prevent deep, restorative sleep.
Risk factors include excess weight (especially around the neck), a large tongue or tonsils, a recessed jaw, nasal congestion, and aging. Men are more commonly affected, though the gap narrows after menopause. Alcohol and sedatives relax throat muscles further and can worsen episodes.
Central Sleep Apnea
Central sleep apnea is a fundamentally different problem. The airway stays open, but the brain temporarily stops sending signals to the muscles that control breathing. During a central apnea episode, the chest and abdomen go completely still because there is no effort to breathe at all.
CSA is closely tied to other medical conditions. The brainstem, which controls heart rate and breathing, can be disrupted by heart failure, stroke, or neurological disorders. Opioid medications also suppress the brainstem’s respiratory drive and are a well-recognized trigger. Sleeping at high altitude can cause a form of central apnea as well, because lower oxygen levels destabilize the body’s breathing control system.
One specific pattern, called Cheyne-Stokes breathing, is most commonly linked to congestive heart failure or stroke. In this pattern, breathing gradually deepens, then gradually fades until it stops altogether for a few seconds before the cycle starts again. It reflects instability in the feedback loop between carbon dioxide levels in the blood and the brain’s breathing center.
People with CSA often report waking up short of breath rather than with the gasping or choking typical of OSA. Snoring can occur but is usually less prominent. Because CSA is rarer and its symptoms overlap with those of the underlying condition causing it, it often goes undiagnosed longer.
Complex Sleep Apnea Syndrome
Complex sleep apnea syndrome, sometimes called treatment-emergent central sleep apnea, is the third type. It starts as obstructive sleep apnea, but when the airway obstruction is treated (typically with a CPAP machine), central apneas appear or persist. Essentially, once the physical blockage is removed, an underlying problem with the brain’s breathing signals becomes visible.
In the Sleep Heart Health Study cohort, about 2.7% of participants had predominantly obstructive apnea with a central component, placing complex sleep apnea between OSA and pure CSA in prevalence. It’s significant because standard treatment for obstructive apnea doesn’t fully resolve it, and recognizing it changes the approach.
How Severity Is Measured
Regardless of type, sleep apnea severity is graded using the apnea-hypopnea index (AHI), which counts how many times per hour your breathing stops or significantly slows during sleep. The scale breaks down as follows:
- Mild: 5 to fewer than 15 events per hour
- Moderate: 15 to 30 events per hour
- Severe: more than 30 events per hour
These numbers come from a sleep study, either conducted overnight in a lab or through a home testing device. The AHI alone doesn’t distinguish between obstructive and central events. That distinction requires monitoring chest and abdominal movement during the study to determine whether breathing effort is present (obstructive) or absent (central) during each pause.
How Treatment Differs by Type
The type of sleep apnea you have directly determines which treatments work. CPAP, which delivers a steady stream of pressurized air to keep the airway open, is the standard first-line treatment for obstructive sleep apnea. It works well precisely because the problem is mechanical: the air pressure acts as a splint for the collapsible portion of the throat.
For central sleep apnea, CPAP can help in some cases, but a different device called adaptive servo-ventilation (ASV) is often more effective. ASV continuously adjusts the air pressure and breathing support breath by breath, compensating for the brain’s inconsistent signaling. In a controlled trial comparing the two approaches for complex sleep apnea, ASV brought the AHI below 10 in roughly 90% of patients, compared to about 65% with CPAP alone.
Treating the underlying condition is equally important for CSA. Optimizing heart failure treatment, adjusting opioid medications, or descending from high altitude can reduce or eliminate central apneas without any device at all. For obstructive sleep apnea, weight loss, oral appliances that reposition the jaw, and surgery to widen the airway are alternatives or additions to CPAP depending on the severity and anatomy involved.