Respiratory Problems of Sleep

The water nymph Ondine, having been jilted by her mortal husband, took from him all automatic functions, requiring him to remember to breathe. When he finally fell asleep, he died. This sad tale serves to remind us of a potential hazard of sleep, and it is not only Ondine's erstwhile lover who has succumbed to some form of 'Ondine's curse', as it was termed by Severinghaus & Mitchell (1962). However, it is now recognized that failure of the drive to the respiratory muscles is not the only hazard of sleep in patients with primary alveolar hypoventilation. No less important is respiratory obstruction occurring in the oropharynx. The key to the patency of the pharyngeal airway is the genioglossus muscle which holds the tongue away from the posterior pharyngeal wall. It has been established that the electromyogram of the genioglossus relates to airway patency in the pharynx (Remmers et al. 1978). Furthermore, the electromyogram of the genioglossus displays phasic activity in time with breathing, peak activity coinciding with inspiration when there is maximal danger of airway obstruction (Harper & Sauerland 1978). Nishino et al. (1984) have shown that electrical activity in the hypoglossal nerve of the cat is impaired by deep anaesthesia and it seems very likely that loss of tone in genioglossus is the cause of pharyngeal obstruction, which is well known to occur during anaesthesia and most forms of coma. The anaesthetist can clear the pharyngeal airway either by extension of the atlanto-occipital joint or by protrusion of the jaw, both of which manoeuvres increase the distance of the superior genial tubercle of the symphysis menti from the cervical vertebrae, and so tend to lift the tongue clear of the posterior pharyngeal wall. Once the tongue has fallen against the posterior pharyngeal wall, the subatmospheric pressure created during inspiration pulls the tongue further back and results in a collapse of the pharynx which may result in total obstruction. On 7 December 1984, the Section of Anaesthetics held an evening meeting to compare and contrast sleep apnoea occurring in three situations arising in different branches of medicine. The methodology of all three papers had much in common and was based on minimally invasive continuous monitoring of respiration and oxygen levels. Respiration monitors used were able to distinguish between central and obstructive apnoea. These observations were correlated with the depth of sleep derived from the electroencephalogram (EEG) and electro-oculogram (EOG). Probably the best understood aspect of the problem is the sleep apnoea syndrome in which breathing ceases for periods of more than 10 seconds throughout the night. This was discussed by Professor David Flenley (this issue, p. 1031). The syndrome can affect people of all ages but is probably commonest in obese male snorers. However, some episodes of sleep apnoea, and more commonly irregular breathing with transient reduction in ventilation not amounting to true apnoea, are very common in older but otherwise healthy subjects over the age of 55. These episodes, which often result in temporary hypoxaemia, occur most frequently during rapid eye movement (REM) sleep in patients with chronic air flow limitation from chronic bronchitis. Hypoventilation during REM sleep in such patients can lead to profound hypoxaemia, particularly in 'blue bloaters' who have cor pulmonale. Nocturnal oxygen administration can prevent these hypoxaemic episodes and accompanying excess pulmonary vasoconstriction. Nocturnal hypoxaemia in 'blue bloaters' can also be prevented by the new French respiratory stimulant, almitrine. Effective treatment for the sleep apnoea syndrome includes nasal positive airway pressure or uveopalatopharyngoplasty. It is now seldom necessary to resort to a permanent tracheostomy which is opened only at night. Sleep apnoea in the elderly has much in common with apnoea in the postoperative period. Dr Gareth Jones and colleagues (this issue, p. 1019) have undertaken continuous monitoring during the first 24 hours after operation and observed a high incidence of obstructive apnoea in patients who had received morphine for relief of postoperative pain. The incidence was much lower in patients who received only regional analgesia. As in the elderly patients, obstructive apnoea occurred during sleep but not at the same level of sleep. REM sleep was never observed during the first 24 hours after operation and the deepest sleep was level 3. Otherwise the pattern of the episodes closely resembled that of patients with obstructive sleep apnoea syndrome. Obstruction, characterized by out-of-phase rib cage and abdominal movements, rapidly resulted in desaturation which was often severe. Eventually the patient would rouse himself and normal unobstructed breathing would be resumed. These episodes are almost certain to be overlooked by conventional monitoring techniques and were first recognized only by the application of continuous monitoring. The continuous administration of oxygen prevented hypoxaemia but not the episodes of obstruction. In contrast to sleep apnoea in the elderly, postoperative episodic apnoea does not seem to be dependent to the same extent on age and obesity. Apnoea was seen in quite young patients of normal weight (Catley et al. 1985) While the characteristics of sleep apnoea in the elderly and in the postoperative period are similar