Expiratory and Inspiratory Positive Airway Pressures in Obstructive Sleep Apnea: How Much Pressure is Necessary? A Different Point of View

The pathophysiology of obstructive sleep apnea can be explained by collapse of upper airways secondary to the negative intra-pharyngeal pressure that develops during inspiration [4]. In addition, during sleep, muscles in the mouth relax and tongue and other structures tend to fall toward the back of the mouth causing crowding in the upper airway region with more potential for upper airway obstruction. At end expiration, conditions exist that favor upper airway closure; lung volume is smallest, the pressure in the pharyngeal region is lowest, and dilator neural activity to the upper airways is least, rendering the upper airway unstable and susceptible to collapse [5]. When such conditions are present, inhalation causes the pharyngeal pressure to become slightly sub atmospheric, leading to upper airways obstruction in OSA patients. The primary mechanism for improving upper airway patency during CPAP or BiPAP is related to a mechanical splinting effect due to positive pressure within the oropharyngeal space, which leads to upper airway stabilization, preventing upper airway collapse [5,6]. The increase in lung volume during CPAP and dilator activity, help further to prevent upper airway collapse, but may be less important than the increase in pressure [5].