OSA is the absence of airflow due to an occlusion in the upper airway that lasts at least 10 seconds in spite of continual effort to breathe. Severity is measured by the Apnea/Hypopnea Index (AHI) – the number of episodes per hour of sleep.

Periodic breathing is defined as alternating periods of hyperventilation with waxing/waning tidal volume and periods of central hypopneas or apneas. There are many forms of periodic breathing, one of which is Cheyne-Stokes Respiration (CSR).

Complex Sleep Apnea is a condition that occurs when a patient is identified as having OSA, but with the application of Continuous Positive Airway Pressure (CPAP) to eliminate the OSA, the patient develops Central Sleep Apnea. The cause of Complex Sleep Apnea is not known at this time.