Sleep apnea is a group of disorders characterized by repeated pauses in breathing or periods of shallow breathing during sleep. These events, called apneas, can occur many times an hour and disrupt sleep quality, leading to daytime fatigue and other health issues. One less common form of this condition is Clear Airway Apnea, which is formally known as Central Sleep Apnea (CSA). Unlike other types, CSA is defined by a temporary failure of the brain’s respiratory control system.
The Physiology of Breathing Signal Failure
Central Sleep Apnea occurs when the brain temporarily fails to generate and send the necessary signals to the muscles that control breathing. The respiratory control center, located in the brainstem, is responsible for this automatic function, regulating the rhythm and depth of each breath. The lack of a neurological signal means that the diaphragm and chest muscles receive no instruction to contract. This leads to a pause in respiratory effort, even though the physical airway remains open and unobstructed.
A key underlying mechanism involves the body’s chemoreceptors, which monitor the levels of oxygen and carbon dioxide in the blood. When the carbon dioxide level in the blood falls too low, often due to a period of hyperventilation, the brain’s drive to breathe can drop below a threshold necessary to sustain respiration during sleep. This can lead to a state of temporary hypocapnia, or low carbon dioxide, causing the brain to pause breathing until the carbon dioxide level rises again.
How Central Sleep Apnea Differs from Obstructive Apnea
The distinction between Central Sleep Apnea (CSA) and Obstructive Sleep Apnea (OSA) lies in the cause of the stopped airflow. In OSA, breathing stops because the throat muscles relax and the upper airway collapses, creating a physical blockage. The body’s respiratory muscles, such as the diaphragm and chest wall, continue to try and pull air in against this obstruction.
In contrast, CSA is characterized by a complete absence of both airflow and respiratory effort. The brain is not sending the signal, so the muscles remain inactive and no attempt to breathe is made. The difference in respiratory effort is the primary diagnostic factor observed during a sleep study, known as polysomnography.
During a sleep study, sensors measure the movement of the chest and abdomen to track respiratory effort. In an OSA event, these sensors show continuous or increasing effort against the blocked airway. Conversely, in a CSA event, the sensors show no movement or effort, confirming the lack of a neurological drive.
Underlying Conditions That Trigger Central Apnea
Central Apnea is frequently linked to other underlying medical conditions that affect the brain’s ability to regulate breathing. Congestive heart failure (CHF) is one of the most common associated conditions, particularly when it presents with a distinctive breathing pattern called Cheyne-Stokes respiration. This pattern involves a cyclical waxing and waning of breathing depth, with apneas occurring at the point of weakest ventilation.
Neurological diseases, such as stroke or Parkinson’s disease, can directly damage the brainstem or other areas involved in respiratory control. Additionally, high-altitude exposure can induce a temporary form of CSA, as the lower oxygen concentration causes initial hyperventilation, which lowers carbon dioxide and triggers the apneic threshold.
The use of certain medications, notably opioid pain relievers, can also trigger central apnea. Opioids can depress the central nervous system’s respiratory drive, leading to irregular breathing patterns or periods where the brain simply fails to signal a breath. Treating the underlying condition, such as optimizing heart failure management, is often the first step in effectively managing the associated central apnea.
Management and Treatment Options
Treatment for Central Sleep Apnea focuses on stabilizing the irregular breathing pattern and addressing any underlying medical causes. Specific breathing devices are often utilized to provide ventilatory support during sleep.
Adaptive Servo-Ventilation (ASV) is a device designed for many types of CSA, including Cheyne-Stokes breathing. ASV monitors the patient’s breathing pattern and provides pressure support that automatically adjusts to smooth out the breathing cycle. However, ASV is generally not recommended for patients with heart failure who have a reduced left ventricular ejection fraction.
Continuous Positive Airway Pressure (CPAP) or Bilevel Positive Airway Pressure (BiPAP) devices may be used in certain CSA cases. CPAP can sometimes help by preventing upper airway closure that might otherwise trigger central events. BiPAP machines with a backup rate can ensure a minimum number of breaths per minute, which is particularly useful for central apneas related to medication use or specific types of central drive failure. Supplemental oxygen may also be prescribed to patients with CSA to help maintain blood oxygen saturation levels during sleep.