Objective benefit of laser palatoplasty for non-apnoeic snoring.

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.

Evaluation of activity-based techniques to identify transient arousal in respiratory sleep disorders.

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.

Automated recognition of EEG changes accompanying arousal in respiratory sleep disorders.

Daytime sleepiness and impaired cognitive function can be a consequence of recurrent transient arousal from sleep, associated with abrupt changes in the electroencephalogram (EEG). EEG is normally assessed by trained observers from paper records, but automation offers the advantages of speed and objectivity. We assessed 10 automated indices of EEG activity as potential indicators of arousal. Arousals from light, slow wave and rapid eye movement sleep were studied in 30 subjects. Segments of EEG recorded immediately before and after each arousal were analyzed by automated measurement of 10 EEG indices using a personal computer. We investigated the ability of each index to recognize arousal while rejecting change due to variability during sleep. Nine of the 10 indices showed significant changes with arousal (p < 0.001); the better indices were related to EEG frequency, and 3 were chosen for further study. In these indices, the mean changes with arousal were 3.8 Hz (ZeroCross), 1.7 Hz (Hjorth's Mobility) and 1.2 Hz (FrqMean, an index of central EEG frequency). With none of these three indices were significant differences in performance due to base sleep stage or subject group found. We conclude that detection of arousal is feasible using automated methods that measure simple indices related to the frequency of the EEG waveform.

Objective measurement of the results of uvulopalatopharyngoplasty.

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.

Comparison of methods for assessing snoring.

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.

Respiratory muscle activity and oxygenation during sleep in patients with muscle weakness.

Patients with respiratory muscle weakness show nocturnal hypoventilation, with oxygen desaturation particularly during rapid eye movement (REM) sleep, but evidence in individuals with isolated bilateral diaphragmatic paresis (BDP) is conflicting. The effect of sleep on relative activity of the different respiratory muscles of such patients and, consequently, the precise mechanisms causing desaturation have not been clarified. We have studied eight patients, four with generalized muscle weakness and four with isolated BDP during nocturnal sleep with measurements including oxygen saturation and surface electromyographic (EMG) activity of various respiratory muscle groups. Nocturnal oxygenation correlated inversely with postural fall in vital capacity, an index of diaphragmatic strength. During REM sleep, hypopnoea and desaturation occurred particularly during periods of rapid eye movements (phasic REM sleep). In most subjects, such events were "central" in type and associated with marked suppression of intercostal muscle activity, but two subjects had recurrent desaturation due to "obstructive" hypopnoea and/or apnoea. Expiratory activity of the external oblique muscle was present whilst awake and during non-rapid eye movement (NREM) sleep in seven of the eight subjects in the semirecumbent posture. This probably represents an "accessory inspiratory" effect, which aids passive caudal diaphragmatic motion as the abdominal muscles relax at the onset of inspiration. Expiratory abdominal muscle activity was suppressed in phasic REM sleep, suggesting that loss of this "accessory inspiratory" effect may contribute to "central" hypopnoea. We conclude that, in patients with muscle weakness, nocturnal oxygenation correlates with diaphragmatic strength.(ABSTRACT TRUNCATED AT 250 WORDS)

Respiratory muscle activity during rapid eye movement (REM) sleep in patients with chronic obstructive pulmonary disease.

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 of surface 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.

Automated measurement of the cyclic activity of respiratory muscles.

A microcomputer-based system developed for the automated analysis of the electromyogram (EMG) recorded from respiratory muscles in a variety of situations is described. In addition, an assessment of the performance of the system is presented, along with data relating intercostal EMG activity to ribcage movement in seated subjects. Studies were performed on sixteen normal subjects--non smokers, mean (+/- SD) age 31 (+/- 6) years, mean (+/- SD) mass 78 (+/- 8) kg--of which fifteen studies proved suitable for analysis. Each study lasted for a period of five minutes, during which time recordings of intercostal EMG, ribcage postero-anterior displacement (RCPA) and airflow were made. For every breath taken by each of the subjects, the peak integrated EMG activity (iEMGpeak) was measured both by hand and by the automated system. The automated and manual measurements of iEMGpeak, which ranged from 0.0 to 91.3 microV, differed by only -0.82 +/- 3.34 microV (mean +/- SD). The index iEMGpeak and two additional indices of iEMG activity (iEMGmean, iEMGarea) were evaluated with respect to RCPA, a measure of overall respiratory activity. The indices of iEMG were observed to show an exponential dependence on RCPAamp, the amplitude of ribcage motion. Following a log transformation to linearise the relationship, the correlation of each index with RCPAamp was evaluated; iEMGpeak and iEMGarea correlated similarly with RCPAamp (no significant difference at 5% level), but iEMGmean was found to be a significantly different (p < 0.001) and poorer correlate. We conclude that the automated analysis of respiratory iEMG as described in this paper can provide results showing consistency with manual measurement.(ABSTRACT TRUNCATED AT 250 WORDS)

The use of sound recording and oxygen saturation in screening snorers for obstructive sleep apnoea.

It is desirable to screen snoring patients for obstructive sleep apnoea (OSA) prior to surgical treatment. We postulated that the addition of a sound profile would increase the value of overnight oxygen saturation (SaO2) as a screening method. Thirty-nine polysomnographic studies including sound level measured by calibrated meter were performed on snorers being considered for uvulopalato-pharyngoplasty (UPPP). Polysomnography showed an apnoea/hypopnoea index (AHI) > or = 15 per hour of sleep in seven subjects. Two experienced observers independently, without knowledge of other data, classified paper records of SaO2 alone and SaO2 plus sound level obtained during polysomnography as OSA 'unlikely', 'equivocal' or 'definite'. The addition of sound to SaO2 reduced the number of equivocal results from 14 to six and increased the number classified as 'definite' or 'unlikely'. The sensitivity of oximetry +/- sound increased as the threshold AHI used in the definition of OSA increased; addition of sound improved recognition of mild OSA without impairing specificity.