Obstructive-2. central/complex-3. mixed-obstructive sleep apnea (osa)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.central sleep apneacentral sleep apnea is a pattern of breathing characterized by a normal deep inspiratory cycle interchanged with complete cessation of breathing. it is typically caused by problems with how the brain controls breathing rather than an occlusion of the airway.complex sleep apneacomplex 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.periodic breathingperiodic 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). csr is characterized by a cyclic pattern of waxing and waning during periods of apnea, and deep, rapid breathing.