Sleep apnea is a disorder characterized by pauses in breathing during sleep. The two common forms are Obstructive Sleep Apnea (OSA), caused by a physical blockage, and Central Sleep Apnea (CSA), which involves a failure of the brain’s signals to breathe. Mixed Sleep Apnea (MSA) combines elements of both obstructive and central events within the same individual, making its diagnosis and management complex. Understanding the nature of these combined mechanical and neurological events is the first step toward effective treatment.
Defining Mixed Sleep Apnea
Mixed Sleep Apnea (MSA) is defined by the presence of both central and obstructive breathing events during a sleep study. It is often referred to as Complex Sleep Apnea Syndrome (CompSAS) or Treatment-Emergent Central Apnea (TECA). Diagnosis requires a combination of physical airway collapse and temporary cessation of the brain’s signal to breathe. The central component must meet a specific threshold, typically at least five central apneas per hour of sleep, in addition to the obstructive events.
A significant number of MSA cases are considered treatment-emergent. This means central apneas only become apparent or increase after the patient begins positive airway pressure (PAP) therapy for what was initially diagnosed as pure OSA. The CPAP machine successfully eliminates the obstructive component, but this relief sometimes unmasks an underlying instability in the brain’s respiratory control system. When central events persist or appear following the resolution of the physical blockage, the diagnosis is updated to MSA or TECA.
The Mechanisms of Obstructive and Central Events
Obstructive events occur when the upper airway collapses or becomes blocked, often due to the relaxation of throat muscles during sleep. During an obstructive apnea, the chest and diaphragm muscles continue to strain as the body attempts to draw a breath, but air cannot pass the physical blockage. This effort against a closed airway eventually causes a brief arousal from sleep, allowing the patient to gasp and resume breathing.
Central events, in contrast, are caused by a signaling failure originating in the brainstem, the body’s respiratory control center. In a central apnea, the brain temporarily stops sending signals to the muscles responsible for breathing, including the diaphragm. Because no effort is being made, both airflow and the movement of the chest and abdomen cease simultaneously. This instability is often linked to fluctuations in carbon dioxide levels in the blood, which can trigger temporary cessations of respiratory drive.
Identifying Mixed Sleep Apnea Through Diagnosis
The diagnosis of Mixed Sleep Apnea relies on an overnight laboratory study known as polysomnography (PSG). This sleep study monitors multiple physiological parameters, including brain activity, blood oxygen levels, breathing effort, and airflow. The distinction between central and obstructive events hinges entirely on the measurement of respiratory effort.
Specialized belts placed around the chest and abdomen measure the effort made by the respiratory muscles, while sensors near the nose and mouth record airflow. A clinician identifies an obstructive event when the airflow stops, but the effort belts show continued, strenuous attempts to breathe. Conversely, a central event is identified when both the airflow and the signal from the effort belts cease simultaneously. The diagnosis of MSA is confirmed when the study data shows a mixture of both types of apneas, with the central component reaching a pre-defined level of frequency.
Tailored Treatment Protocols
Treating Mixed Sleep Apnea requires a protocol that addresses both the physical and neurological components of the disorder. The initial step typically involves using Continuous Positive Airway Pressure (CPAP) therapy. CPAP delivers a steady stream of pressurized air to mechanically splint the airway open and resolve the obstructive events. In many cases, central apneas that emerge or persist during CPAP therapy may resolve spontaneously over a few weeks or months as the respiratory system stabilizes. Expectant management, which involves waiting to see if the central events disappear, is often the first approach following CPAP initiation.
If central events persist after the obstructive component is successfully eliminated, treatment shifts to more advanced devices to stabilize the brain’s respiratory drive. Bi-level Positive Airway Pressure (BiPAP) machines deliver two different pressure levels for inhalation and exhalation, and can include a backup breath rate to prevent long pauses. The most specialized device for persistent MSA is Adaptive Servo-Ventilation (ASV). ASV machines continuously monitor the patient’s breathing pattern and dynamically adjust the delivered pressure to stabilize breathing, preventing the over-breathing that can lead to central apneas. The selection between these advanced therapies is made by a sleep specialist based on the patient’s specific ratio of central versus obstructive events and any underlying medical conditions.