CPAP machines are the standard treatment for obstructive sleep apnea, a condition where breathing is repeatedly interrupted during sleep. Modern CPAP devices deliver pressurized air and track the user’s breathing patterns throughout the night. This data is converted into a performance indicator called “Events Per Hour” (EPH) or the Apnea-Hypopnea Index (AHI). This metric measures how effectively the therapy is working, allowing users and healthcare providers to monitor sleep quality and make informed decisions about treatment adjustments.
Defining the Events Per Hour Metric
Events Per Hour (EPH) is the simplified term for the Apnea-Hypopnea Index (AHI). The AHI represents the average number of breathing interruptions a person experiences every hour during sleep. It is calculated by dividing the total count of apneas and hypopneas by the total number of hours the machine was in use. The AHI is the primary tool for assessing the success of ongoing therapy, where a lower number indicates more stable breathing. While the machine’s reported AHI is an estimate based on airflow data, it provides a consistent, daily snapshot of treatment effectiveness.
The Types of Events That Are Counted
The events tallied by the CPAP machine fall into two main categories: apneas and hypopneas. An apnea is a complete cessation of airflow, defined as a reduction of 90% or more lasting at least ten seconds. This signifies a full blockage or collapse of the airway. A hypopnea is a partial obstruction or shallow breathing event, defined as a reduction in airflow of 30% or more for at least ten seconds, associated with a drop in blood oxygen or a brief awakening. The machine also tracks central apneas, which occur when the brain fails to signal the muscles to breathe, distinguishing them from obstructive events.
Interpreting the Severity of Your Score
The AHI score is used to classify the severity of sleep apnea for untreated individuals. A score of fewer than five events per hour is considered normal. Mild sleep apnea is diagnosed with a score between five and 15 EPH, moderate is 15 to 30 EPH, and severe is 30 or more EPH. For users undergoing CPAP therapy, the primary goal is to reduce the AHI score to the normal range, ideally below five events per hour. A score consistently below five confirms the treatment is highly effective in minimizing breathing disruptions.
Why Your Score Might Be Changing
It is normal for the AHI score to fluctuate slightly, but a persistent increase requires investigation. The most common cause of a rising score is a mask leak, which prevents the CPAP machine from maintaining necessary air pressure. A poor mask fit, an older cushion, or a mouth leak can compromise the seal. Changes in sleep position, nasal congestion, or the use of alcohol and sedatives can also relax throat muscles and worsen airway collapse. If the score remains elevated despite troubleshooting the equipment and addressing these lifestyle factors, consult a healthcare provider to determine if a pressure adjustment is needed.