Background -In patients with chronic obstructive pulmonary disease (COPD) periods of hypopnoea occur during rapid eye movement (REM) sleep, but the mechanisms involved are not clear. Methods -Ten patients with stable COPD were studied during nocturnal sleep. Detailed measurements were made ofsurface electromyographic (EMG) activity of several respiratory muscle groups and the accompanying chest wall motion using magnetometers. Results -Hypopnoea occurred in association with eye movements during phasic rapid eye movement (pREM) sleep. During pREM sleep there were reductions in EMG activity of the intercostal, diaphragm, and upper airway muscles compared with non-REM sleep. Episodic hypopnoea due to partial upper airway occlusion ("obstructive" hypopnoea) was seen consistently in four subjects while the others showed the pattern of "central" hypopnoea accompanied by an overall reduction in inspiratory muscle activity. Although activity of the intercostal muscles was reduced relatively more than that of the diaphragm, lateral rib cage paradox (Hoover's sign) was less obvious during pREM-related hypopnoea than during wakefulness or non-REM sleep. Conclusions -Hypopnoea during REM sleep in patients with COPD is associated with reduced inspiratory muscle activity.The pattern of hypopnoea may be either "obstructive" or "central" and is generally consistent within an individual. Relatively unopposed action of the diaphragm on the rib cage during REM sleep is not accompanied by greater lateral inspiratory paradox. (Thorax 1995;50:376-382) Keywords: REM sleep, chronic obstructive pulmonary disease, respiratory muscle activity, hypopnoea.Ventilation during rapid eye movement (REM) sleep is characterised by its variability both within and between subjects."2 In patients with chronic obstructive pulmonary disease (COPD) periods of hypopnoea in REM sleep result in hypoxaemia, but the precise mechanisms are uncertain. In healthy subjects reduced respiratory muscle activity has been shown in REM sleep3-5; this is generally most marked in those respiratory muscles which also have a postural function, with activity of the diaphragm being relatively spared or even increasing. Patients with airways obstruction due to COPD,"8 have been reported to show a similar pattern during REM sleep, but the results have been variable and the numbers of patients studied in detail are few.One potential consequence of discoordinate inspiratory muscle action is recurrent upper airway narrowing or occlusion. Although early work on nocturnal hypoxaemia in patients with COPD suggested that obstructive apnoea was frequently present,9 the population studied was highly selected and later work appeared to refute this conclusion.'0 It has subsequently been shown, however, that the clinical features associated with the obstructive sleep apnoea syndrome can be seen with obstructive hypopnoea rather than complete apnoea. " In patients with COPD it is not clear to what extent diminished activity of the upper airway muscles in REM sleep may result in...

Objective measurements of several sound level indices were made on 32 subjects referred because of snoring and who subsequently underwent uvulopalatopharyngoplasty (UPPP). The measurements were repeated approximately 6 months post-UPPP. The indices were compared with the subjective assessment of snoring by both the subject and his/her bed partner. Correlations between objective and subjective assessments were generally weak and were strongest when the supine posture only was considered. The index which correlated best with subjective assessment was the level which 1% of the sound level samples exceeded.

Thirty-two patients undergoing uvulopalatopharyngoplasty (UPPP) for snoring have been studied prospectively using objective measurement of snoring levels. A significant reduction was found, especially in the supine posture. The quantitative reduction was small and correlations between subjective and objective changes in snoring volume were weak.

SUMMARY Daytime sleepiness and impaired cognitive function can be a consequence of recurrent transient arousal from sleep. Arousal is often associated with abrupt changes in the electroencephalogram (EEG), and such changes can be used as an index of sleep disturbance, but EEG analysis is laborious and requires trained observers. Possible alternative indices of arousal not reliant on EEG analysis were investigated. Recordings were made from 36 sleeping subjects who were being investigated for sleep-related breathing disorders. In each study awakenings and transient arousals according to EEG criteria were compared with activity in five potential indirect indicators of arousal: wrist movement, ankle movement, left and right tibial electromyogram, and phase change in ribcage-abdominal movement. The mean values of sensitivity to arousal ranged from only 25 to 45%. However, their high positive predictive accuracies (PPAs, 68 to 92%) indicated that activity, when present, was usually associated with arousal. Sensitivity to awakenings was higher (71-87%), though PPAs were lower (42 to 63%). For the indicator based on ribcage-abdominal phase, the number of periods of activity showed a significant relation to the number of arousals (r=0.70, P<0.001).It can be concluded that phase changes in chest/abdomen movement are a useful indicator of arousal associated with obstructive apnoea and related conditions. Limb activity has much lower sensitivity for transient arousal, but may be of value in indicating periods of wakefulness.

Laser palatoplasty (LPP) is widely used for the treatment of non-apnoeic snoring, despite the lack of objective data supporting its use. We report measurements of snoring in a prospective study of LPP, and we compare the results with a previous study of uvulopalatopharyngoplasty (UPPP). Twenty patients with an apnoea/hypopnoea index < 20 h-1 underwent LPP for habitual snoring. Overnight sound recordings were compared before and 6 months after operation using three objective indices; L, (the level exceeded by the loudest 1% of sound), L5 (the level exceeded by the loudest 5% of sound) and P50 (% total sleep time above 50 dBA). The subjective impression of snoring severity (Wilcoxon test, P < 0.001), and objective indices L1 and P50 (t-test, P < 0.001) showed significant reductions after LPP. The mean change in L1 was 4.2 dBA, comparable to that we previously reported for UPPP, while P50 was reduced to less than one-third its preoperative value. No other sleep variables changed significantly following LPP. We conclude that LPP results in reduced snoring volume comparable to that following UPPP.