Obstructive sleep apnea (OSA) is defined by repetitive interruptions in ventilation caused by the collapse of the pharyngeal region.
Obstructive apnea is characterized by pauses lasting more than 10 seconds with ventilation effort associated. Obstructive hypopnea represents a decrease in ventilation associated with decreased oxygen saturation and awakening. An accepted diagnosis of OSA is the apnea-hypopnea index above 5 and symptoms of excessive daytime sleepiness.
Primary anomaly of these patients is a small pharyngeal anatomical region. Thus during the period of wakefulness a greater resistance opposes ventilation and causes negative pressure during inspiration.
Mechanoreceptors located in the laryngeal area respond to this negative pressure by increasing the activity of muscles that cause dilatation of the airways during wakefulness. But during sleep the collapse of pharyngeal area appears intermittently due to the loss of this compensation mechanism.
During the apnea or hypopnea episode, hypoxemia and hypercapnia stimulate the ventilation effort causing awakening.