Obstructive sleep apnoea/hypopnoea syndrome

The obstructive sleep apnoea/hypopnoea syndrome (OSAHS) is the most common medical cause of sleepiness. It can present at any age but is most common in middle age, when it occurs in around 1–4% of men and 1–2% of women. It occurs rarely in the teens and 20s—a useful differentiator from narcolepsy. Patients usually present with sleepiness which is sometimes irresistible, but often causes difficulty with concentration and work performance rather than sleep attacks. Patients typically find sleepiness most troublesome in monotonous situations such as driving on motorways, reading, and watching television. OSAHS patients usually feel their sleep is undisturbed but do not feel refreshed in the morning. Their partners report loud snoring, apnoeas, and restless sleep. Two thirds of OSAHS patients are men and 50% are obese (body mass index > 30 kg/m²). Retrognathia plays a significant role, particularly in the non-obese.

OSAHS is caused by the throat becoming critically narrow during sleep. Pharyngeal patency is usually achieved by the phasic contraction of upper airway dilating muscles during each inspiration, thus resisting sucking the throat shut as air is sucked in. There is no evidence of upper airway muscle dysfunction in OSAHS, rather the abnormality is anatomical—patients have narrower pharynxes than the normal population when awake. Thus, the physiological relaxation of the palatal and tongue muscles during sleep results in pathological throat narrowing. The patient then struggles to overcome the obstruction until aroused by negative intrathoracic pressure. The brief arousal reactivates the upper airway dilating muscles, and a few unobstructed breaths are taken before sleep resumes and apnoea recurs. This cycle of apnoea, arousal, apnoea, arousal may recur many hundreds …