Sleep apnea is defined by the presence of at least five episodes per hour of apnea (no airflow for ≥10 seconds) and/or hypopnea (reduction in airflow by at least 30% from baseline for ≥10 seconds accompanied by oxygen desaturation or arousal from sleep) in the presence of nocturnal breathing disturbance symptoms. Obstructive sleep apnea/hypopnea syndrome (OSAHS) is caused by upper airway closure during inspiration, punctuated by brief arousals that terminate apneic episodes. Risk factors for OSAHS include obesity, craniofacial factors such as micrognathia, family history of OSAHS, and male sex. Hypothyroidism and acromegaly are systemic diseases associated with OSAHS. OSAHS increases the risk of multiple cardiovascular conditions, including coronary artery disease, heart failure, stroke, and arrhythmias.

Central sleep apnea (CSA) is characterized by respiratory pauses during sleep related to absence of respiratory effort. CSA is less common than OSAHS but may occur in conjunction with it. CSA is commonly found in heart failure and stroke pts, but may also occur from opioid medications and hypoxia (e.g., breathing at high altitudes).