Use of high-frequency peak in spectral analysis of heart rate increment to improve screening of obstructive sleep apnoea

Purpose  

Several studies have correlated the ratio of the very low frequency power spectral density of heart rate increment (%VLFI) with obstructive sleep apnoea syndrome (OSAS). However, patients with impaired heart rate variability may exhibit large variations of heart rate increment (HRI) spectral pattern and alter the screening accuracy of the method.     

Monitoring respiration during sleep

The sleep-related breathing disorders have been categorized in various ways. The most basic schema divides them into obstructive or central apneic events. An American Academy of Sleep Medicine (AASM) Task Force Report published in 1999 defined four separate syndromes associated with abnormal respiratory events during sleep among adults, namely, obstructive sleep apnea-hypopnea syndrome (OSAHS), central sleep apnea-hypopnea syndrome, Cheyne-Stokes breathing syndrome, and sleep hypoventilation syndrome. In this classification, the upper airway resistance syndrome was not regarded as a distinct syndrome; instead, respiratory event-related arousals (RERAs) were considered part of the syndrome of OSAHS.     

Performance vigilance task and sleepiness in patients with sleep-disordered breathing.

Altered vigilance performance has been documented in patients with sleep-related breathing disorders (SRBDs). Sleep fragmentation, sleepiness, respiratory disturbances and nocturnal hypoxaemia have been suggested as the pathogenesis of these deficits, yet it remains difficult to find a good correlation between performance deficits and the above factors. In the present study, which performance measure better characterised SRBD patients and the main factors implicated in these disturbances were examined. The study group consisted of 152 patients and 45 controls, all examined using a performance vigilance task and subjective sleepiness assessment. Speed and accuracy in the psychomotor vigilance task (PVT) were measured in patients and controls. Objective daytime sleepiness was assessed in the patient group using the maintenance of wakefulness test. In comparison with controls, PVT accuracy rather than speed seems to be affected in SRBD patients, with lapses and false responses significantly greater in patients with more severe objective sleepiness and higher apnoea/hypopnoea index. Although slowing and increased variability in reaction time were associated with shorter sleep latency in the maintenance of wakefulness test, subjective sleepiness, sleep fragmentation, nocturnal hypoxaemia and apnoea/hypopnoea index influenced mainly PVT accuracy. It is concluded that vigilance impairment, sleep fragmentation and severity of disease may partially and differentially contribute to the diurnal performance consequences found in sleep-related breathing disorders. Since the psychomotor vigilance task worsening is more marked in accuracy that in speed, measurement of lapses and false responses would better characterise the degree of diurnal impairment in these patients.     

A short daytime test using correlation dimension for respiratory movement in OSAHS.

In order to examine the pathology in patients with obstructive sleep apnoea/hypopnoea syndrome (OSAHS), the nonlinear properties of respiratory movement and breath-to-breath variations during resting wakefulness with eyes closed was investigated. Recording of the respiratory movement using inductive plethysmography was performed on 14 patients with OSAHS and 13 control subjects for 2 h in the supine position during daytime. To calculate the correlation dimension (D2) for respiratory movement, an algorithm proposed by Grassberger and Procaccia was applied. The indices of breath-to-breath variations were estimated. To calculate D2 and breath-to-breath variations, two different segments were selected (200 s each). The value of D2 for respiratory movement in patients with OSAHS was significantly greater than that in control subjects. In the case of > or = 2.0 of D2 for respiratory movement, the sensitivity and specificity of detecting the presence of OSAHS was 85.7% and 76.9%, respectively. On the basis of breath-to-breath variations, only the coefficient of variation of expiratory time for respiratory movement in patients with OSAHS was significantly greater than that in the control subjects. In conclusion, the measurements of correlation dimensions for respiratory movement with a brief period during wakefulness may be a useful index for identifying patients with obstructive sleep apnoea/hypopnoea syndrome.     

Sleep apnoea in heart failure.

Studies from the USA have reported that sleep apnoea is common in congestive heart failure (CHF), with Cheyne-Stokes respiration (CSR) being the most frequent type of sleep-disordered breathing (SDB) in these patients. Within the present study, the authors sought to assess the prevalence and type of SDB among CHF patients in Germany. A total of 203 CHF patients participated in this prospective multicentre study. All patients were stable in New York Heart Association classes II and III and had a left ventricular ejection fraction (LVEF)<40%. The patients were investigated by polygraphy and all data were centrally analysed. Patient enrolment was irrespective of sleep-related symptoms. The majority of patients were male with a mean age of 65 yrs and hospitalised. Of the 203 patients, 145 (71%) had an apnoea/hypopnoea index>10.h(-1), obstructive sleep apnoea (OSA) occurred in 43% (n=88) and CSR in 28% (n=57) of patients. The prevalence of sleep-disordered breathing is high in patients with stable severe congestive heart failure from a European population. As sleep-disordered breathing may have a negative impact on the prognosis of congestive heart failure, a sleep study should be performed in every patient with congestive heart failure and a left ventricular ejection fraction of <40%. This diagnostic approach should probably be adopted for all of these patients irrespective of the presence of sleep-related symptoms.     

Can psychological factors help us to determine adherence to CPAP? A prospective study.

The present study objective was to establish whether pretreatment social cognitive variables may contribute to the explanation of variance in adherence to continuous positive airway pressure (CPAP) treatment for patients with obstructive sleep apnoea/hypopnoea syndrome (OSAHS). A total of 119 of 180 consecutive OSAHS patients were recruited to the study prior to initial CPAP titration. Patients completed psychological measures of health value, health locus of control (incorporating internality, chance, powerful others) and self-efficacy prior to CPAP titration. Objective adherence data were measured by CPAP unit time clocks and collected at 3-month follow-up. Average nightly use was calculated over this period. Logistic regression of prospective predictors of adherence produced a model comprising psychological (health value, internality, powerful others), as well as clinical variables (Epworth score, body mass index, apnoea/hypopnoea index, CPAP pressure). This model explained 24% of the variance in CPAP use, and correctly identified 75% of adherers and 53% of nonadherers. Although the psychological variables explained only a small amount of the overall variance in adherence behaviour, this result provides further support for the hypothesis that psychological variables contribute, in part, to continuous positive airway pressure adherence. Future research should focus on highlighting discrete variables, which may helpfully inform psychologically based interventions aimed at improving the use of continuous positive airway pressure by patients with obstructive sleep apnoea/hypopnoea syndrome at risk of discontinuance.     

Prevalence of sleep-related symptoms in a primary care population - their relation to asthma and COPD.

AIMS: The aim of this study was to clarify the association between obstructive sleep apnoea/hypopnoea syndrome (OSAHS)-related symptoms and physician-diagnosed asthma and COPD. METHODS: 1501 subjects aged 19-90 years completed a structured questionnaire and underwent spirometry and respiratory physician assessment in 10 primary care centres. RESULTS: Frequent snoring was reported in 45.6%, breathing pauses during sleep in 11.0%, and excessive daytime sleepiness in 6.7% of the sample. COPD patients were more likely to report frequent snoring (OR=1.34; 95% CI:1.04-1.71), breathing pauses (OR=1.46; 95% CI:1.01-2.10), and excessive daytime sleepiness (OR=2.04; 95% CI:1.33-3.14). In contrast, there was no significant association between asthma patients and OSAHS-related symptoms. Gender differences were recognised as well. CONCLUSIONS: The increased likelihood for OSAHS-related symptoms in COPD patients, in contrast to patients with asthma, designates them as a target group for the screening of OSAHS in primary care.     

Can heart rate variation rule out sleep-disordered breathing in heart failure?

In patients with obstructive sleep apnoea (OSA), the very low frequency power spectral density index (VLFI) derived from analysis of heart rate correlates with the severity of obstructive apnoeas. VLFI is also associated with Cheyne-Stokes respiration/central sleep apnoea (CSR/CSA) in congestive heart failure (CHF). The present authors have tested the hypothesis that per cent VLFI, derived from a standard Holter ECG recording, can be used to detect the presence of OSA and CSR/CSA in patients with mild-to-moderate CHF. In total, 60 CHF patients underwent polysomnography with monitoring of heart rate. Data from 33 patients were analysed for per cent VLFI. Of the 60 patients, 27 were excluded due to atrial fibrillation, extensive pacing or frequent ventricular extra systoles. Receiver operator characteristic curves were constructed to establish the per cent VLFI that would optimally identify the presence or absence of sleep-disordered breathing. Using an apnoea-hypopnoea index>20 events.h-1 and setting the per cent VLFI at 2.23% yielded a sensitivity of 85%, specificity of 65%, positive predictive value of 61% and a negative predictive value of 87%. The latter increased to 100% when using an apnoea-hypopnoea cut-off of 30 events.h-1. In conclusion, these results suggest that spectral analysis of heart rate may be useful as a "rule-out test" for sleep-disordered breathing in patients with mild-to-moderate congestive heart failure.     

Electroencephalographic spectral analysis: detection of cortical activity changes in sleep apnoea patients.

There are no visible electroencephalographic (EEG) changes at the termination of some apnoeas and hypopnoeas. This study tests the hypothesis that cortical activity fluctuates at apnoea/hypopnoea termination, despite the lack of visible changes. To detect these changes, EEG spectral analysis was performed and centred around the end of apnoeas/hypopnoeas in 15 sleepy patients. Ten second windows were applied and comparisons were conducted between the normalised power of the same frequency bands before and after termination of each apnoea/hypopnoea. Comparisons were performed within patients between apnoeas/hypopnoeas and periods of undisturbed sleep as well as between patients and healthy subjects during sleep. Normalised theta power (4-8 Hz) decreased significantly at apnoea/hypopnoea termination. No significant changes were found between consecutive periods of undisturbed sleep across the 15 patients. During nonrapid eye movement sleep, changes were detected irrespective of arousal visibility. During rapid eye movement sleep, nonarousal apnoeas/hypopnoeas were not accompanied by any significant spectral power changes. Theta power was significantly lower across patients compared to healthy subjects (p=0.03) and was correlated to the apnoea/hypopnoea index (rho=0.6, p=0.008). The authors conclude that electroencephalographic spectral analysis improves detection of changes at apnoea/hypopnoea termination. Further validation is needed to determine whether it improves correlation between nocturnal measures and daytime symptoms.     

The obstructive sleep apnoea/hypopnoea syndrome – An overview

In the last 30 years, there has been an explosion in facilities for the diagnosis and treatment of the obstructive sleep apnoea/hypopnoea syndrome (OSAHS) as well as a rapid advancement in the understanding of its consequences. In the general population, the prevalence of OSAHS is approximately 3–7% in adult men and 2–5% in adult women. OSAHS has been recognised as an independent risk factor for disorders such as hypertension, cardiovascular disease and sleepiness-related accidents. Currently, it is considered to be a systemic disease. This review provides a general overview of OSAHS: its epidemiology, pathophysiology, clinical features, diagnosis and treatment, as well as its consequences for public health.     

Sleep and daytime sleepiness in upper airway resistance syndrome compared to obstructive sleep apnoea syndrome.

This study has investigated differences in the nocturnal sleep and daytime sleepiness among patients with obstructive sleep apnoea syndrome (OSAS), upper airway resistance (UARS), sleep hypopnoea syndrome, and normal control subjects, using sleep scoring and spectral activity analysis of the electroencephalogram (EEG). Twelve nonobese males with UARS aged 30-60 yrs were recruited. These subjects were strictly matched for age and body mass index with twelve OSAS patients, 12 sleep hypopnoea syndrome patients, and 12 normal controls, all male. Daytime sleepiness was evaluated using the Epworth Sleepiness Scale (ESS) and the Multiple Sleep Latency Test (MSLT). The macrostructure of sleep was determined using international criteria and spectral analysis of the sleep EEG was obtained from a central lead. The sleep macrostructure of OSAS and UARS patients was significantly different from that of controls. These patients were also sleepier during the daytime than controls. Complaints of tiredness and daytime sleepiness, ESS and MSLT scores were similar in the different patient groups. Mild dysmorphia was present in all three patient groups. However, nocturnal sleep was significantly different among the different groups. OSAS patients had significantly more awake time during sleep than the UARS patients. The spectral activity of the total sleep time of the patient groups also differed significantly from that of controls. When the sleep spectral activity of UARS and OSAS patients were compared, OSAS patients had less slow wave sleep activity than UARS patients. UARS patients had a significantly higher absolute power in the 7-9 Hz bandwidth than OSAS patients. The absolute delta power over the different sleep cycles was also different between controls and patients, and between UARS and OSAS patients. There are clear differences in the macrostructure and spectral activity of sleep between upper airway resistance and obstructive sleep apnoea syndrome patients, demonstrated by differences in the cortical activity recorded in the central lead during sleep. Despite these nocturnal sleep differences, the tests of subjective daytime sleepiness are not significantly different.     

Diagnostic approaches to respiratory sleep disorders

Sleep disordered breathing (SDB) comprises a number of breathing disturbances occurring during sleep including snoring, the obstructive sleep apnoea/hypopnea syndrome (OSAHS), central sleep apnoea (CSA) and hypoventilation syndromes. This review focuses on sleep disordered breathing and diagnostic approaches in adults, in particular clinical assessment and overnight assessment during sleep. Although diagnostic approaches to respiratory sleep disorders are reasonably straightforward, they do require a degree of clinical acumen when it comes to assessing severity and management options. Diagnosing respiratory sleep disorders on clinical features alone has limitations. Monitoring and measuring respiration during sleep has undergone many advances in the last 40 years in respect of quality and validity, largely regarding OSAHS. Despite the improvement in our diagnostic standards and recognition of sleep disordered breathing, many limitations still need to be overcome. Apart from assessing the individual patient, population screening for sleep disorders continues to preoccupy health professionals and policy makers in many countries. Research in the field is pushing current boundaries in terms of simplifying diagnosis and enhancing screening for sleep disordered breathing in large populations. At present, a number of these newer approaches require further validation.     

High Mallampati score and nasal obstruction are associated risk factors for obstructive sleep apnoea.

Induced nasal obstruction can cause obstructive apnoeas in healthy subjects during sleep, but the relationship between nasal resistance measured during wakefulness and obstructive sleep apnoea syndrome (OSAS) is weak. It was postulated that if the subjects could not breathe through the nose, the oral airway must be used, but if this airway is narrowed as well, then it could precipitate sleep-disordered breathing (SDB). Nasal patency, Mallampati score (MS), neck circumference and body mass index were measured in 202 subjects referred to the authors' hospital to undergo a full-night polysomnography for suspicion of SDB. A significant correlation was found between the MS and apnoea/hypopnoea index measured during sleep. However, the relationship between these parameters was only significant in patients with nasal obstruction. The relative risk of having OSAS with a MS of III or IV was 1.95 for the whole group and 2.45 in patients with nasal obstruction. In conclusion, a high Mallampati score represents a predisposing factor for obstructive sleep apnoea syndrome, especially if it is associated with nasal obstruction. These patients merit special attention from both the sleep physician and the anaesthetist.     

Influence of treatment on leptin levels in patients with obstructive sleep apnoea.

Obstructive sleep apnoea syndrome (OSAS) is a common disorder in obesity. Leptin, an adipocyte-derived signalling factor, plays an important role in metabolic control. There is growing evidence that leptin regulation is altered in OSAS. Therefore, the aim of this study was to test the hypothesis that effective treatment will influence leptin levels in OSAS patients. Serum leptin levels were determined in 86 consecutive patients (aged 57.5 +/- 11.0 yrs) with polysomnographically verified OSAS. In addition, leptin levels were reassessed and treatment efficacy was evaluated by polysomnography after 6 months of therapy. Patients were treated with continuous or bilevel positive airway pressure, a mandibular advancement device or conservatively, depending on the clinical symptoms. Mean serum leptin levels did not change with treatment in the whole study group (7.3 +/- 5.0 versus 7.5 +/- 4.8 ng.mL-1), however, leptin levels decreased in effectively treated patients (8.5 +/- 5.0 versus 7.4 +/- 5.1 ng.mL-1) while they increased in ineffectively treated patients (5.0 +/- 4.0 versus 7.7 +/- 4.1 ng.mL-1). Furthermore, not only was there a significant and independent correlation between the change in leptin levels with treatment and the change in body mass index, but also with the change in apnoea/hypopnoea index. Effective treatment of sleep-disordered breathing may have significant effects on leptin levels in obstructive sleep apnoea syndrome patients. Changes in leptin levels are related to changes in apnoea/hypopnoea index in obstructive sleep apnoea syndrome patients.     

Spectral oscillations of RR intervals in sleep apnoea/hypopnoea syndrome patients.

A recent study has shown that daytime heart rate variability is reduced in obstructive sleep apnoea/hypopnoea syndrome (OSAHS) patients. In the present study, the hypothesis was that sympathovagal balance around apnoeas/hypopnoeas and nocturnal autonomic activity are altered in OSAHS patients. Frequency- and time-domain analyses of RR intervals were performed to monitor sympathovagal activity noninvasively. Fourteen untreated OSAHS patients and seven healthy subjects underwent overnight polysomnography. Low (LF) and total (TF) frequency power increased 2 min around the end of apnoeas/hypopnoeas (LF 229+/-38 ms2 TF 345+/-45 ms2) compared with undisturbed sleep (LF 106+/-18 ms2, TF 203+/-23 ms2). The increase in high frequency (HF) power was not significant. LF increase was proportionally higher than the HF increase (normalised LF (LFn) 67+/-1 units, normalised HF (HFn) 33+/-1 units) compared with undisturbed sleep (LFn 52+/-2 units, HFn 48+/-2 units). RR duration did not change around apnoeas/hypopnoeas (RR 904+/-28 ms). The LF and TF power increase was greater around arousal-inducing (LF 260+/-45 ms2 TF 390+/-65 ms2) compared with self-terminating (LF 161+/-31 ms2, TF 249+/-40 ms2) apnoeas/hypopnoeas; the LF and LFn increases were significant in both groups compared with undisturbed sleep and HF power differences were nonsignificant. RR intervals were longer around self-terminating apnoeas/hypopnoeas (RR 914+/-29 ms); the differences were not significant compared with undisturbed sleep. RR interval spectral power was not influenced by the event type. RR duration decreased (912+/-28 ms) and LF, HF and TF power increased (LF 111+/-16 ms2 , HF 62+/-6 ms , TF 173+/-21 ms2) across patients, compared with healthy controls (RR 1138+/-91 ms, LF 57+/-3 ms2, HF 35+/-3 ms2, TF 91+/-6 ms2). LFn and HFn did not change significantly. Sympathetic activity increases around apnoeas/hypopnoeas. The recurrent nocturnal fluctuations of sympathovagal balance and the overall increase of nocturnal autonomic activity may be of importance in the development of cardiovascular disease in sleep apnoea patients.     

Obstructive sleep apnoea and oral breathing in patients free of nasal obstruction.

Although there is an association between nasal obstruction, oral breathing and obstructive sleep apnoea syndrome (OSAS), it remains unknown whether increased oral breathing occurs in patients with OSAS who are free of nasal obstruction. The present study evaluated the relationship between breathing route and OSAS in patients without nasal obstruction. The breathing route of 41 snorers (25 male; aged 26-77 yrs) with normal nasal resistance was examined during overnight polysomnography using a nasal cannula/pressure transducer and an oral thermistor. In total, 28 patients had OSAS (apnoeics) and 13 patients were simple snorers. Apnoeics had a higher percentage of oral and oro-nasal breathing epochs. Oral and oro-nasal breathing epochs were positively related with apnoea/hypopnoea index (AHI) and duration of apnoeas/hypopnoeas and inversely related to oxygen saturation. Additionally, oro-nasal breathing epochs correlated with body mass index (BMI). In multiple linear regression analysis, oral breathing epochs were independently related only to AHI (r2 = 0.443), and oro-nasal breathing epochs were independently related to AHI (r2 = 0.736) and BMI (r2 = 0.036). In conclusion, apnoeics spent more time breathing orally and oro-nasally than simple snorers, and the apnoea/hypopnoea index is a major determinant of the time spent breathing orally and oro-nasally.     

Evaluation of sleep fragmentation by EEG spectrography in patients with obstructive sleep apnea syndrome]

Sleep fragmentation is considered to have a central role in the pathophysiology of sleep-disordered breathing. However, the evaluation of sleep fragmentation can be very troublesome work. We sought to evaluate sleep fragmentation in 10 patients with obstructive sleep apnea syndrome by utilizing fast-fourier transforms to render their sleep encephalograms as spectrograms (horizontal axis: time, vertical axis: frequency, color: power). Detailed 5-minute spectrograms revealed relatively uniform patterns of change in EEG spectra during and after apnea episodes. In non-REM sleep, delta activity during apnea was followed by alpha and beta activity during resumed breathing. In REM sleep, flat and low-power spectral patterns during apnea were followed by relatively weak alpha and beta activity during resumed breathing. In compressed, 1-hour views of the spectrograms, repeated apnea events appeared as vertical striped patterns of spectral change. These patterns were thought to be representative of sleep fragmentation. The spectrographic display of EEGs may be a very simple and easy method for the evaluation of sleep-fragmentation in sleep disordered breathing.     

Long-term treatment with continuous positive airway pressure improves quality of life in obstructive sleep apnoea syndrome.

Continuous positive airway pressure (CPAP) is an established treatment of obstructive sleep apnoea syndrome (OSAS). While it is known that CPAP reverses the pathological breathing pattern and improves daytime sleepiness, there are no sufficient data on the long-term influence of CPAP on quality of life in patients with OSAS. Thirty-nine patients with polysomnographically verified OSAS (apnoea/hypopnoea index (AHI): (mean+/-SD) 46.8+/-21.8 events x h(-1)) were prospectively studied. All patients answered three quality of life measures (Complaint List, Nottingham Health Profile Part 1 (NHP), and Verbal Analogue-Scale "quality of life") prior to the initiation of CPAP therapy. After a mean of 9 months they were re-evaluated by polysomnography, and completed the questionnaires once again. As expected, CPAP was effective in treating the sleep-related breathing disorder. AHI decreased significantly from (mean+/-SD) 46.8+/-21.8 events x h(-1) to 3.3+/-6.3 events x h(-1), and minimum oxygen saturation increased from 77.1+/-9.3% to 89.9+/-3.4%, while body mass index did not change significantly (31.3+/-5.4 versus 30.8+/-4.8 kg x m(-2)). During long-term treatment with CPAP the Complaint List revealed a significant improvement of the extent of subjective impairment due to physical and general complaints (26.4+/-9.9 versus 20.4+/-11.1), and NHP a significant improvement of emotional reactions (19.8+/-21.7 versus 11.1+/-14.0) and energy (50.8+/-36.6 versus 32.1+/-36.7), but not of pain, physical mobility, sleep, social isolation, and quality of life as assessed by the It is concluded that long-term continuous positive airway pressure therapy is effective in improving not only pathological breathing patterns but also parameters that estimate quality of life in patients with obstructive sleep apnoea syndrome.     

Assisted ventilation for heart failure patients with Cheyne-Stokes respiration.

Patients with chronic congestive cardiac failure (CCF) frequently suffer from central sleep apnoea syndrome (CSAS). Continuous positive airway pressure (CPAP) has been suggested as a treatment. The authors hypothesised that bilevel ventilation might be easier to initiate and superior to CPAP at correcting the sleep-related abnormality of breathing in patients with CCF. After excluding those with a history suggestive of obstructive sleep apnoea, 35 patients with CCF (left ventricular ejection fraction <35%) were screened with overnight oximetry and the diagnosis of CSAS was established with polysomnography in 18. Two 14-day cycles of CPAP (0.85 kPa (8.5 mbar)) or bilevel ventilation (0.85/0.3 kPa (8.5/3 mbar)) in random order, were compared in a crossover study. Sixteen patients (13 males), mean age 62.0+/-7.4 yrs completed the study. The pretreatment apnoea/hypopnoea index of 26.7+/-10.7 was significantly reduced by CPAP and bilevel ventilation to 7.7+/-5.6 and 6.5+/-6.6, respectively. The arousal index fell from 31.1+/-10.0 per hour of sleep to 15.7+/-5.4 and 16.4+/-6.9, respectively. Significant and equal improvements with CPAP and bilevel ventilation were found for sleep quality, daytime fatigue, circulation time and New York Heart Association class. The authors conclude that continuous positive airway pressure and bilevel ventilation equally and effectively improve Cheyne-Stokes respiration in patients with congestive cardiac failure.     

Arousability in sleep apnoea/hypopnoea syndrome patients.

Sleep disruption and daytime sleepiness in obstructive sleep apnoea/hypopnoea syndrome (OSAHS) patients result from recurrent apnoeas/hypopnoeas and arousals from sleep. Around 30% of apnoeas/hypopnoeas are not terminated by visible cortical arousals. The current authors tested the hypotheses that arousal induction is linked to sleep stage, oxygen desaturation, event type, event duration and time of occurrence during the night. Fifteen patients with OSAHS of varying severity were studied and all their apnoeas/hypopnoeas were evaluated. Eight of 15 patients had apnoeas/hypopnoeas in all sleep stages, and all their 610 apnoeas/hypopnoeas were analysed in the between stages comparison; data from all 15 patients were included in other comparisons. Thirty-four per cent of apnoeas/hypopnoeas during slow wave sleep (SWS) were associated with arousal, significantly less than the 77% during nonrapid eye movement (NREM) 1 and 2 and 62% during rapid eye movement (REM) sleep. Arousal induction was not affected by oxygen desaturation, event type, duration or time of the night. The apnoeal/hypopnoea index was 39 x h(-1) in REM 1 and 2, significantly higher compared to 17 x h(-1) in REM or to 11 x h(-1) in SWS sleep. In conclusion, apnoeas/hypopnoeas in slow wave sleep are associated with fewer cortically apparent, visually detected arousals.