Starling resistor model of the upper airway

The tendency of the upper airway to collapse is determined by its critical closing pressure, designated as P_crit. When P_crit is below tracheal pressure (P_DS), airway is open without airflow limitation. When P_crit is greater than tracheal pressure (P_DS) but less than nasal pressure (P_US), there is partial airway collapse with maximal inspiratory airflow limitation. When P_crit is above nasal pressure (P_US), there is complete obstructive apnea.