©Priory Lodge Education Limited 1997 First Published April 1997 Version 1.0

Respiratory Problems During Sleep.

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.

Respiratory physiology of 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:-

• The Ventilatory activity of all respiratory muscles (including the upper airway) is reduced. Consequently, ventilation falls by approximately 10% and upper airway resistance increases, both of which lead to a rise in PaCO2 of 3 - 7 mm Hg. This reduction in ventilatory drive is largely due to the removal of the awake (or behavioural) drive, leaving just the chemical drive from hypercapnia and hypoxia. This behavioural drive is important in preventing ventilation dropping below about 5 litres/min during wakefulness.

• During REM sleep, there is generalised inhibition of skeletal muscles, including the intercostal, accessory and pharyngeal dilators. Thus, ventilation during REM is virtually dependant on diaphragmatic function, and upper airways function is yet more precarious than during SWS.

More
	Obstructive Sleep Apnoea and variants
		Symptoms in Obstructive Sleep Apnoea
		Measuring the Consequences of OSA
		Treatment of OSA
		COPD and OSA
		Central Sleep Apnoea
Back to Chest Medicine On-Line		Suggested Reading	Back to Introduction