The primary treatment for Obstructive Sleep Apnea (OSA) involves using machines that provide Positive Airway Pressure (PAP) therapy. Continuous Positive Airway Pressure (CPAP) and Automatic Positive Airway Pressure (APAP) are the two most common types. Both machines prevent the collapse of the upper airway during sleep, which causes obstructive sleep apnea. The difference is straightforward: CPAP delivers a single, fixed pressure throughout the night, while APAP automatically adjusts the pressure level as needed using sensors and algorithms.
Understanding Positive Airway Pressure Therapy
Positive Airway Pressure (PAP) therapy is the widely accepted initial treatment for OSA, maintaining a clear path for air to the lungs. The system consists of a bedside machine, a tube, and a mask worn over the nose or nose and mouth. The machine draws in ambient air, which is then pressurized to a specific therapeutic level.
This pressurized air is delivered through the mask and into the upper airway, acting as a pneumatic splint. The constant stream of positive air pressure pushes against the soft tissues in the throat, preventing them from collapsing and causing an apnea event. Keeping the airway open eliminates the breathing pauses and disruptions that characterize sleep apnea.
The fundamental goal of this therapy is to ensure uninterrupted breathing, which restores normal oxygen levels and improves sleep quality. This shared mechanism of delivering pressurized air is why both CPAP and APAP machines are highly effective treatments. The difference lies in how each machine manages the specific pressure level it delivers throughout the night.
CPAP: Delivering a Fixed Pressure
The Continuous Positive Airway Pressure (CPAP) machine is the traditional and most extensively studied form of PAP therapy. A CPAP machine is set to deliver a single, specific pressure level, measured in centimeters of water (cmH2O), which remains constant throughout the night. This fixed pressure is determined during a specialized sleep study called a titration, where a sleep technologist finds the minimum pressure needed to eliminate most obstructive events.
This constant pressure is maintained regardless of changes in the patient’s sleep stage, body position, or the severity of airway obstruction. The simplicity of this fixed setting offers a consistent and reliable flow of air. While some CPAP models include a ramp feature to start at a lower pressure and gradually increase, the therapeutic pressure itself is unvarying for the entire treatment period.
For patients with stable, severe OSA or certain types of central sleep apnea, this consistent pressure is highly effective. The fixed setting ensures the airway is always fully supported at the pressure level proven successful. CPAP machines are simpler and may also be less expensive than their automatically adjusting counterparts.
APAP: Automatic Pressure Adjustment
Automatic Positive Airway Pressure (APAP) machines, sometimes called auto-CPAP, represent a more dynamic form of therapy. These devices utilize sophisticated sensors and proprietary algorithms to monitor the user’s breathing patterns breath-by-breath. The machine detects subtle signs of airway instability, such as flow limitation, snoring, or the beginnings of an apnea or hypopnea event.
When the machine senses an increase in airway resistance, it instantly increases the air pressure to keep the airway open. Conversely, when the airway is stable, the APAP device reduces the pressure to the lowest effective level. This pressure adjustment occurs within a minimum and maximum range prescribed by a healthcare provider, often between 4 and 20 cmH2O.
This ability to adjust pressure in real-time means the APAP machine delivers only the necessary pressure at any given moment. This often results in a lower average pressure throughout the night compared to a fixed CPAP setting. The dynamic response can enhance comfort for some users, making it easier to exhale against the airflow since high pressures are only used when required.
Deciding Between CPAP and APAP
The choice between a CPAP and an APAP machine depends on the specific characteristics of the patient’s OSA and their personal needs. APAP is often preferred for individuals whose pressure requirements fluctuate significantly throughout the night. This includes patients with positional apnea, where obstructions occur mostly when sleeping on the back, or REM-dependent apnea, where breathing disturbances intensify during the REM sleep stage.
APAP is also beneficial for patients whose required pressure changes over time due to factors like weight gain or loss, seasonal allergies, or illness. The automatic adjustment capability means the machine can adapt without needing a new in-lab titration study. Some studies suggest APAP may improve comfort and adherence due to the lower average pressure delivered.
However, CPAP may be the preferred treatment for patients with very stable, severe OSA or those diagnosed with central sleep apnea, which APAP algorithms are not designed to effectively manage. APAP devices are typically more expensive than fixed CPAP machines due to the advanced technology and sensors. Furthermore, APAP machines provide detailed data, including a pressure distribution graph showing pressure changes throughout the night. CPAP generally only records adherence data and basic event statistics.