Sleep apnea is a common disorder where breathing repeatedly stops and starts during sleep. A key measurement used to understand both the severity of sleep apnea and the effectiveness of its treatment, particularly with a Continuous Positive Airway Pressure (CPAP) machine, is the “Events Per Hour,” also known as the Apnea-Hypopnea Index (AHI). Understanding your AHI is an important step in managing sleep apnea and ensuring therapy is working as intended.
Understanding Events Per Hour
The Apnea-Hypopnea Index (AHI) measures the average number of times per hour that your breathing partially or completely stops during sleep. This index is derived from two types of events: apneas and hypopneas. An apnea refers to a complete cessation of airflow through the nose and mouth, typically lasting for at least 10 seconds.
Conversely, a hypopnea signifies a partial reduction in breathing, where airflow decreases by at least 30% for 10 seconds or longer, often accompanied by a drop in blood oxygen levels. CPAP machines and sleep studies detect these events by monitoring airflow and breathing effort throughout the night. The total number of apneas and hypopneas is then divided by the total sleep time to calculate the AHI.
Interpreting Your Numbers
The AHI number is a standard measure used to classify the severity of sleep apnea. For adults, an AHI below 5 events per hour is considered normal, indicating minimal breathing interruptions during sleep. A diagnosis of mild sleep apnea is given when the AHI ranges from 5 to fewer than 15 events per hour. Moderate sleep apnea is characterized by an AHI between 15 and fewer than 30 events per hour.
Severe sleep apnea is diagnosed when the AHI is 30 or more events per hour. The goal of CPAP therapy is to reduce the AHI to below 5 events per hour to minimize health risks and improve sleep. Some specialists even aim for an AHI below 1 or 2 for optimal results, though any significant reduction from a high baseline is beneficial.
How CPAP Therapy Reduces Events
CPAP therapy works by delivering a continuous stream of positive airway pressure through a mask worn during sleep. This constant airflow acts as a pneumatic splint, gently pushing against the soft tissues in the throat to keep the airway open. By maintaining an open airway, the CPAP machine effectively prevents the collapses and obstructions that cause both apneas and hypopneas.
The consistent pressure prevents the relaxation of throat muscles and the tongue from falling back, which are common causes of airway blockage in obstructive sleep apnea. Consistent use of the CPAP device is important for achieving and maintaining a low AHI. Consistent CPAP use can significantly decrease the AHI, often bringing it down to a normal range.
Addressing High Events Per Hour
If your CPAP machine reports a persistently high AHI despite consistent use, several factors could be contributing to the issue. Mask fit is a common concern; leaks around the mask can reduce the delivered pressure, allowing breathing events to occur. Regularly checking for and addressing mask leaks can improve therapy effectiveness. Incorrect pressure settings on the CPAP machine can also lead to a high AHI, meaning the pressure might be too low to adequately keep the airway open.
Machine maintenance, such as regularly changing filters, is important to ensure optimal performance and proper airflow. Beyond equipment, certain lifestyle factors can influence your AHI, including weight, alcohol consumption, and sleep position. Sleeping on your back can worsen airway collapse. If adjustments to mask fit and maintenance do not lower the AHI, or if you continue to experience symptoms of sleep apnea, it is important to consult with a healthcare provider or sleep specialist. They can assess your therapy, make pressure adjustments, or investigate other underlying causes for the persistent events.