ABSTRACT
The sleep apnoea syndrome is characterizezd by frequent cessations of breathing during sleep. It is usually associated with excessive daytime sleepiness. However, in some cases (mainly central sleep apnoea) it may be associated with insomnia. Cessation of breathing during sleep can be partial (decreased tidal volume, hypopnoea) or complete (apnoea), which may result from obstruction of the upper airway (obstructive apnoea), loss of ventilatory effort (central apnoea) or a combination of the two (mixed apnoea). The type of event determines the diagnosis of central or obstructive sleep apnoea. When most of the events are obstructive or mixed, obstructive sleep apnoea (OSA) is diagnosed, whereas for a diagnosis of pure central sleep apnoea (CSA) at least 80% of the events are required to be of central origin (see later). When most of the events are mixed, it is usually diagnosed as OSA. The severity of the syndrome, in both OSA and CSA, is primarily determined by the rate of sleep-disordered breathing events per hour of sleep (RDI or respiratory disturbance index; AHI or apnoea-hypopnoea index) and the magnitude of associated oxygen desaturations. As both hypopnoeas and complete apnoeas result in arousals from sleep, the distinction between them is not considered important from a severity point of view.
