PATHOPHYSIOLOGY OF OBSTRUCTIVE SLEEP-APNEA

The pathophysiology of obstructive sleep apnoea (OSA) is complex and i ncompletely understood, A narrowed upper airway is very common among O SA patients, and is usually in adults due to nonspecific factors such as fat deposition in the neck, or abnormal bony morphology of the uppe r airway. Functional impairment of the upper airway dilating muscles i s particularly important in the development of OSA, and patients have a reduction both in tonic and phasic contraction of these muscles duri ng sleep when compared to normals, A variety of defective respiratory control mechanisms are found in OSA, including impaired chemical drive , defective inspiratory load responses, and abnormal upper airway prot ective reflexes, These defects may play an important role in the abnor mal upper airway muscle responses found among patients with OSA. Local upper airway reflexes mediated by surface receptors sensitive to intr apharyngeal pressure changes appear to be important in this respect. A rousal plays an important role in the termination of each apnoea, but may also contribute to the development of further apnoea, because of a reduction in respiratory drive related to the hypocapnia which result s from postapnoeic hyperventilation, A cyclical pattern of repetitive obstructive apnoeas may result.A better understanding of the integrate d pathophysiology of OSA should help in the development of new therape utic techniques.