REVIEW SERIES Sleep ? 2: Pathophysiology of obstructive sleep apnoea/hypopnoea syndrome

Correspondence to: Dr R B Fogel, Division of Sleep Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA 02115, USA; [email protected] . . . . . . . . . . . . . . . . . . . . . . . O bstructive sleep apnoea/hypopnoea syndrome (OSAHS) is a common disorder which affects 2–4% of middle aged women and men in the United States. This disorder is characterised by recurrent sleep induced collapse of the pharyngeal airway leading to hypoxaemia and hypercapnia, with arousal from sleep being required to re-establish airway patency. While the pathophysiology of this disorder remains incompletely understood, much progress has been made since the last review of this topic was published in this journal. We believe that most evidence supports the concept that patients with OSAHS have an anatomical predisposition to airway collapse. However, during wakefulness, protective mechanisms maintain the patency of the pharyngeal airway by increasing the activity of pharyngeal dilator muscles. These protective mechanisms fail during sleep, with subsequent collapse of the pharyngeal airway behind the palate, tongue, or both. In this review we consider the current state of knowledge regarding the pathogenesis of airway obstruction in patients with OSAHS, emphasising those theories that have the most experimental support.