Continuous Positive Airway Pressure (CPAP) therapy is the most common and effective treatment for obstructive sleep apnea. This therapy delivers a constant stream of pressurized air to keep the upper airway open during sleep. Many users find the continuous pressure challenging, particularly the effort required to exhale against the incoming airflow. Expiratory Pressure Relief (EPR) is a comfort feature designed to mitigate this sensation and make breathing feel more natural during CPAP use.
What is Expiratory Pressure Relief (EPR)?
Expiratory Pressure Relief (EPR) is a technology built into many modern CPAP devices that adjusts the machine’s output to match the user’s breathing cycle. The device senses the beginning of the exhalation phase. Upon detection, the machine temporarily reduces the air pressure being delivered to the mask. This pressure drop counteracts the feeling of “pushback” that users experience when attempting to breathe out against continuous positive pressure. The purpose of this momentary pressure reduction is to enhance comfort and encourage patient adherence. While EPR is the proprietary name used by ResMed devices, the concept is common across manufacturers, often referred to by names like C-Flex or A-Flex. Devices monitor the user’s breathing pattern in real-time to ensure the pressure reduction is synchronized precisely with the exhalation phase. This dynamic adjustment allows the airway to remain open during inhalation while easing the effort required to exhale.
Understanding the EPR Level Settings
The EPR level setting determines how much pressure relief is provided during exhalation. This feature is adjustable, offering three distinct settings: Level 1, Level 2, or Level 3. Each level corresponds to a specific, measurable reduction in the delivered pressure, quantified in centimeters of water pressure (\(\text{cmH}_2\text{O}\)).
EPR Level Reductions
Level 1 reduces the pressure by \(1 \text{ cmH}_2\text{O}\) from the prescribed therapeutic pressure.
Level 2 provides a reduction of \(2 \text{ cmH}_2\text{O}\) during the exhalation period.
Level 3 lowers the pressure by \(3 \text{ cmH}_2\text{O}\), achieving maximum relief.
These quantifiable levels allow the user and the clinician to fine-tune the balance between comfort and therapeutic effectiveness. For example, if the prescribed pressure is \(10 \text{ cmH}_2\text{O}\) and EPR is set to Level 3, the pressure drops to \(7 \text{ cmH}_2\text{O}\) upon exhalation. The setting can be applied full-time or only during the machine’s ramp-up period.
Balancing Comfort and Therapeutic Effectiveness
The decision to use an EPR level involves a direct trade-off between maximizing user comfort and maintaining the required therapeutic minimum pressure. Higher EPR settings, such as Level 3, offer the greatest relief from the sensation of forced exhalation, which can significantly improve a patient’s willingness to use the device. However, this substantial pressure drop means the airway is being held open by a lower pressure during a portion of the breathing cycle. This temporary reduction in pressure may compromise the stability of the upper airway for some individuals.
If the pressure drops below the level needed to prevent collapse, the effectiveness of the therapy is reduced. This potential reduction in efficacy is monitored by tracking the Apnea-Hypopnea Index (AHI), which measures the number of breathing events per hour. An increase in the AHI score after activating EPR suggests that the level of pressure relief is too aggressive for the user’s condition. Patients should consult their sleep specialist before making adjustments to their EPR setting, ensuring that any changes made to improve comfort do not inadvertently sacrifice the treatment’s primary goal of maintaining an open airway. The optimal setting is the lowest EPR level that still achieves comfortable breathing while keeping the AHI within acceptable clinical limits.