APAP automatically varies the delivered pressure to eliminate apnea, hypopnea, snoring, and airflow limitation.  Upper and lower pressure limits are set by the clinician, often on the basis of a prior failed CPAP/BiLevel PAP (BPAP) titration or the patient’s history of CPAP/BPAP use.  If the APAP unit does not detect obstructive respiratory events, the device lowers the pressure gradually until events recur, at which time the pressure increases again.  That is, the APAP titration device is constantly searching for the lowest effective pressure in any circumstance (e.g., in supine versus lateral sleep; in rapid eye movement (REM) versus nonREM sleep).  The highest pressure is usually needed during supine REM sleep.  The device may also be used for unattended autotitration in the home sleep environment to find an optimal pressure for chronic CPAP treatment.

Auto-BPAP devices automatically detect respiratory events and adjust the delivered IPAP and EPAP to maintain an open airway.

The main disadvantages of unattended APAP titrations performed in the home sleep environment are (1) air leak from the PAP mask and/or the patient’s mouth simulates physiologic events, triggering “false positive” increases in PAP, and (2) APAP’s inability to differentiate between central and obstructive apnea may result in errors in APAP titration.  That is, APAP devices monitor pressure and flow and have no method of determining whether respiratory effort is present during an apnea.  Newer APAP devices have features that attempt to differentiate “clear airway apneas” (central apneas) versus obstructive airway apneas, but hard data validating the newer features is not as well-established as is true for  the older, more-established PAP titration devices.