Central vs Obstructive Sleep Apnea: What's the Difference?

Two Very Different Problems

When you look at your CPAP data, you'll see your breathing events broken down by type. The two most important categories are obstructive apneas (OA) and central apneas (CA). They may look similar on a summary screen, but they have completely different causes, and understanding the difference helps you and your doctor make better treatment decisions.

Obstructive Sleep Apnea: A Mechanical Problem

Obstructive sleep apnea (OSA) is by far the most common type. It accounts for roughly 84% of all sleep apnea diagnoses.

What happens: During sleep, the muscles in your throat relax. In people with OSA, this relaxation causes the soft tissue to collapse inward, physically blocking the airway. Your body is still trying to breathe (your diaphragm and chest muscles are working), but air can't get through the obstruction. After 10 or more seconds, your brain detects the oxygen drop and triggers a brief arousal to restore muscle tone and reopen the airway.

Common causes and risk factors:

• Excess weight, especially around the neck
• Anatomy (large tonsils, narrow airway, recessed jaw)
• Sleeping on your back
• Alcohol or sedative use before bed
• Nasal congestion or allergies

How CPAP treats it: This is exactly what CPAP was designed for. The machine delivers a constant stream of pressurized air that acts as a pneumatic splint, keeping your airway open mechanically. When CPAP pressure is set correctly, obstructive events drop dramatically. If you're still seeing frequent obstructive apneas, the most common culprits are insufficient pressure, mask leak, or both.

Central Sleep Apnea: A Signaling Problem

Central sleep apnea (CSA) is fundamentally different. Your airway is open. The problem is that your brain temporarily stops sending the "breathe" signal to your respiratory muscles.

What happens: During a central apnea, there is no effort to breathe at all. Your diaphragm and chest muscles simply pause. After 10 or more seconds, breathing resumes on its own. Unlike obstructive events, there's no struggle against a blocked airway.

Common causes and associations:

• Heart failure or other cardiac conditions
• Certain medications, particularly opioids
• High altitude
• Stroke or brainstem conditions
• Normal sleep-stage transitions (some central apneas at sleep onset are perfectly normal)
• CPAP therapy itself (more on this below)

Why CPAP alone may not fix it: Since the airway isn't blocked, pushing more air through it doesn't address the root cause. Increasing CPAP pressure for central apneas often makes them worse, not better. This is one reason why knowing your event breakdown matters so much.

Mixed Apneas: Both at Once

Your data may also show mixed apneas. These events start as a central apnea (no breathing effort) and then transition into an obstructive apnea (breathing effort resumes, but the airway is blocked). Mixed events are relatively common and are generally treated like obstructive apneas, since the obstruction component responds to pressure therapy.

Hypopneas: The Middle Ground

For completeness, hypopneas are partial reductions in airflow (at least 30% reduction for 10+ seconds). They can be caused by either partial obstruction or reduced respiratory drive. Most CPAP machines don't distinguish between obstructive and central hypopneas, so they're reported as a single category. Hypopneas are typically the most frequent event type for CPAP users.

Treatment-Emergent Central Sleep Apnea

Here's something that surprises many CPAP users: starting CPAP therapy can actually cause central apneas to appear. This is called treatment-emergent central sleep apnea (TE-CSA), sometimes referred to as complex sleep apnea.

Why it happens: When CPAP eliminates the obstructive events your body has adapted to, it can temporarily destabilize your brain's respiratory control loop. Your carbon dioxide levels change, your chemoreceptors recalibrate, and during that adjustment period, central apneas may increase.

How common is it? Studies suggest that 5 – 15% of patients starting CPAP therapy develop TE-CSA.

The good news: In the majority of cases, TE-CSA resolves on its own within the first few weeks to months of consistent CPAP use. Your brain's respiratory control system adapts to the new normal. This is a well-documented phenomenon, and most sleep physicians will monitor it rather than immediately change therapy.

What to watch for: If you're a new CPAP user seeing central apneas in your data, don't panic. Track the trend over time. If your central apnea index (the number of central apneas per hour) is decreasing week over week, your body is adjusting as expected.

Reading Event Types in CPAP Clarity

When you import your SD card data into CPAP Clarity, the Event Breakdown section on your dashboard shows exactly how many of each event type occurred during your session. Here's what to look for:

• OA (Obstructive Apnea): Airway blockage events. If these dominate your breakdown, focus on pressure optimization and mask seal. A well-fitting mask cushion (opens in new tab) is the foundation of good therapy.
• CA (Central Apnea): Brain signaling events. A few per night is normal for most CPAP users. A sudden increase or consistently high count deserves attention.
• H (Hypopnea): Partial breathing reductions. The most common event type for most people.
• RERA: Subtle disruptions that cause brief arousals. Not included in AHI but still relevant to sleep quality.

The Event Timeline visualization shows when events occurred during the night. Central apneas clustered at sleep onset or during light sleep transitions are typically benign. Central apneas that persist throughout the night, especially at high rates, warrant a conversation with your provider.

Analyze your event breakdown for free →

When Central Apneas Need Medical Attention

A handful of central apneas per night is completely normal, even for healthy sleepers without any sleep disorder. On CPAP, seeing 1 – 3 central apneas per hour is usually not cause for concern.

Talk to your sleep physician if:

• Your central apnea index stays above 5 per hour consistently
• Central apneas are increasing over time rather than decreasing
• You have symptoms of central sleep apnea: frequent nighttime awakenings, morning headaches, chronic fatigue despite good CPAP compliance
• You're on opioid medications, which are strongly associated with central apneas
• You have a history of heart failure or cardiac conditions
• Your central apneas haven't improved after 3 months of consistent CPAP use

Your CPAP data gives you the information you need to have a productive conversation. Bring your event breakdown and trend data to your appointment.

ASV: When CPAP Isn't Enough

For patients with persistent central sleep apnea that doesn't resolve with standard CPAP, the next step is typically an Adaptive Servo-Ventilation (ASV) machine.

How ASV works: Unlike CPAP, which delivers a constant or auto-adjusting pressure, ASV actively monitors your breathing pattern in real time. When it detects a central apnea or reduced breathing effort, it provides a backup breath by increasing pressure support. When your breathing is normal, it backs off. Think of it as a safety net that catches you only when you stop breathing, rather than a constant splint.

Who benefits from ASV:

• Patients with treatment-emergent central apnea that doesn't resolve
• Patients with primary central sleep apnea
• Some patients with Cheyne-Stokes breathing (a specific cyclic breathing pattern)

Important exception: ASV is contraindicated for patients with certain types of heart failure (specifically, those with reduced ejection fraction below 45%). A landmark study (SERVE-HF) found increased cardiovascular mortality in this group when using ASV. Your cardiologist and sleep physician must coordinate care if heart failure is a factor.

ASV machines are more expensive than standard CPAP, typically running $2,000 – $4,000, and insurance coverage varies. The ResMed AirCurve ASV and Philips DreamStation BiPAP autoSV are the most common models.

The Bottom Line

Most CPAP users will see predominantly obstructive events and hypopneas in their data. That's expected. A small number of central apneas is normal and rarely concerning.

If you're new to CPAP and noticing central apneas, give it time. Track the trend, and let your body adapt. If central events persist at high rates or you have risk factors like heart disease or opioid use, bring your data to your sleep physician. Tools like CPAP Clarity make it easy to see exactly what's happening, event by event, night by night.

Understanding your event types is one of the most valuable things you can do as an engaged CPAP user. It turns a single AHI number into a story, and that story helps guide better treatment.