subject: SOME SLEEP APNOEA SYNDROMES [print this page] Apnoea is defined as no gas flow at the nose or mouth for10 seconds, and a sleep apnoea syndrome is conventionally,and rather arbitrarily, diagnosed if more than 30 suchepisodes occur during the night. Apnoea may be central,when there is no airflow and no chest wall movement;obstructive, when there is no airflow despite chest wallmovement because of upper airways obstruction; or mayresult from both mechanisms.
Obstructive sleep apnoeoObstructive sleep apnoea is much more common thancentral apnoea, occurring perhaps to some degree in up to1 % of the adult male population. The typical features arehypersomnolence by day and upper airways obstructionduring sleep. Many (but not all) patients are obese andhave thick necks; hypertension is common. In severe casesthere is chronic alveolar hypoventilation at night, daytimehypoxia, secondary polycythaemia and cor pulmonale.
Patients often have loud, persistent snoring, and the frequentarousals from apnoeic episodes greatly disturb sleep(although the patient may be unaware of this). Patientsfall asleep by day and may have road and other accidents.There is difficulty in concentrating, particularly in themorning, intellectual impairment, personality change andirritability. Abnormal limb and body movements duringarousals following apnoea (thrashing around in bed),sexual dysfunction and morning headaches are importantfeatures.
During apnoea there are cardiovascular disturbances,particularly bradycardia.In some patients the upper airway is abnormally narrow(e.g. hypertrophy of tonsils and adenoids), but in most noanatomical abnormality is found. In normals the upperairway narrows during sleep and this is more pronouncedin individuals with thick necks. During obstruction the posteriorand lateral walls of the pharynx collapse, occludingthe oropharynx. The collapse of the upper airway is probablydue to a failure to activate the upper airway musculaturesufficiently during inspiration, and the negativepressures generated in the upper airway by the contractionof the respiratory muscles suck in the soft tissues of the oropharynx.
Central sleep apnoea
In central apnoea the patients snore less, are seldom obese,and complain of night-time wakening. The central driveto breathing is abnormal and inspiration may fail to beinitiated. The syndrome may be primary or secondary toorganic lesions of the brainstem.To document sleep apnoea, to determine whether it iscentral or obstructive and to assess the severity of nocturnalhypoxaemia, a formal sleep study in a specialistlaboratory is required.
Sleep in other respiratory disorders
Patients with airways obstruction and hypercapnia may become profoundly hypoxic at night as a result of hypoventilation.Nocturnal hypoxaemia is alsoa clinical problem in patients with advanced kyphoscoliosisor severe respiratory muscle weakness.Sleepdisorderedbreathing in these conditions may causedaytime sleepiness and headache on waking.
