Fig. 8.

Determinants of how imposed airway obstruction may lead to cyclical obstruction in OSA patients. The figure starts with the OSA patient on sufficient CPAP to ensure a patent airway, optimum airflow and ventilation, blood gases, and stable EEG in NREM sleep. The CPAP level is then quickly removed causing an obstructive apnea with subsequent O₂ desaturation and CO₂ accumulation. At the termination of the airway obstruction, a transient arousal occurs (A), accompanied by a transient ventilatory overshoot, with subsequent return to sleep and another airway obstruction, thereby beginning the cascade of cyclical ventilatory over- and undershoots and obstructions (see text for explanation of factors which determine the resolution of an airway obstruction and therefore the cyclical nature of OSA). [From Younes (753).]