If you’re reviewing your sleep data, you may see “Clear Airway” events labeled as **CA1** or **CA2**. Here’s a simple way to understand what your device is showing:

**Clear Airway Apnea (CA1)**  
A pause in breathing (10+ seconds) where airflow essentially stops **while the airway remains open**.  
These are typically flagged when the flow rate drops to (or near) zero — indicating a **complete cessation (stop)** in airflow.

**Clear Airway Hypopnea (CA2)**  
A partial reduction in breathing (usually a 30%+ drop in airflow for 10+ seconds) with an open airway.  
These are identified when the flow rate shows a **significant reduction**, but not a full stop.

**How Devices Actually Classify Them**  
Most CPAP/APAP devices don’t directly “see” brain signals or effort. Instead, they classify CA1 vs. CA2 based on **flow rate characteristics**:

* Near-zero airflow → labeled as **CA1 (apnea)**
* Reduced (but not absent) airflow → labeled as **CA2 (hypopnea)**

**Key Takeaway**

* **CA1 = complete airflow stop**
* **CA2 = partial airflow reduction**
* Both are “clear airway” (i.e., not caused by obstruction), but the distinction comes from **how much airflow is detected**, not direct measurement of respiratory effort.

**Why it matters**  
A few clear airway events can be normal, especially during sleep transitions. But consistent patterns or elevated counts may be worth digging into further.

*Seeing a lot of CA1 or CA2 in your charts? Drop a screenshot—we’ll help interpret it.*

Clear Airway Apnea (CA1) vs. Clear Airway Hypopnea (CA2) — What’s the Difference?(CPAP Data Explained)