©Priory Lodge Education Limited
John R Stradling MD FRCP, Consultant Physician and
Senior Clinical Lecturer.
Osler Chest Unit, Oxford, England.
It has become abundantly clear that disorders of breathing during sleep can have profound effects, only some of which are apparent during wakefulness. There is significant interaction between sleep and breathing in both directions: sleep changes the way we breath, and problems with breathing can profoundly fragment sleep.
Sleep is not homogeneous and is conventionally divided into two states - non rapid eye movement (NREM) sleep and rapid eye movement sleep (REM) - which can be distinguished on behavioural and electrophysiological criteria. NREM sleep is further divided into stages 1 - 4; stages 3 and 4 represent the deeper levels of sleep (that are thought to be required to refresh the brain) and together are known as slow wave sleep (SWS). Periods of NREM and REM sleep alternate cyclically through the night at intervals of 90 - 120 minutes. The minimum amount of sleep that can be tolerated without adverse side effects varies between individuals, but the mean is approximately 6 - 7 hours.
There are two clinically important changes in ventilatory control and mechanics that normally accompany sleep:-