Pure central sleep apnoea syndrome is rare, it is caused by a heterogeneous group of disorders characterised by intermittent loss of respiratory drive during sleep. Causes include cardiac failure (Cheyne-Stokes respiration), cerebral degeneration, and infection or infarction or compression of the brain stem. The loss of the awake drive is critical here, allowing breathing to undershoot and thus promotes instability. OSA can occasionally look like central sleep apnoea when the inspiratory efforts are too weak to see on tracings of chest wall movements, such as in muscular dystrophy or the very obese. Restrictive disorders of the chest wall (e.g. scoliosis or old thoracoplasty) can lead to nocturnal hypoventilation, as can a variety of neuromuscular disorders. The pathogenesis here is thought to be that whilst awake there are compensatory mechanisms available that drop out during sleep, especially REM sleep, causing hypoventilation or complete apnoea. Over time the marked hypoventilation every night produces respiratory drive blunting, that further renders the patient dependent on the awake (or behavioural) drive to breathe. The treatment of these nocturnal hypoventilation syndromes is usually overnight ventilation via a nasal mask. Occasionally protriptyline or other REM suppressant can ward off respiratory failure, but usually only temporarily.
Acknowledgements. An earlier version of this article appeared in Medicine (International) 1995;13(9):372-5