Variation in the arousal pattern after obstructive events in obstructive sleep apnea.

The relationship between the severity of obstructive sleep apnea (OSA) (measured by sleep study) and daytime sleepiness is poor. Variation in the degree of arousal accompanying obstructive respiratory events might help explain this poor correlation. Polysomnographic records from patients with OSA were reviewed in order to extract representative examples of apneas and hypopneas (in 10 patients), as well as events both supine and decubitus (in 12 patients). The EEG accompanying each obstructive event was processed with a neural network technique to describe sleep depth on a second-by-second basis. The lengths of any visually evident microarousals were also measured manually. There was considerable interindividual variation in the degree of sleep disturbance using the neural network technique (p < 0.005), but not using the lengths of the visually scored microarousals (p = 0.6). The arousals accompanying apneic events caused greater variability in sleep depth quantified using the neural network technique (p = 0.03), and also lasted longer based on the visual scoring (mean, 12.6; SD, 1.7 s) than the hypopneic events (mean, 9.9; SD, 2.4 s; p = 0.02). There were no significant differences between events occurring supine versus decubitus with either technique (p = 0.7). These differences in arousal magnitude may explain some of the poor correlations between conventional measures of sleep apnea severity and daytime sleepiness.

Value of beat-to-beat blood pressure changes, detected by pulse transit time, in the management of the obstructive sleep apnoea/hypopnoea syndrome.

Two important aspects of a respiratory sleep study are a measure of inspiratory effort and an estimate of the number of arousals. These can be derived from an indirect estimate of beat-to-beat blood pressure (BP), pulse transit time (PTT). This study investigated the reproducibility of inspiratory BP falls (reflecting inspiratory effort), and BP arousals derived from PTT, and the contribution they could make to the management of the obstructive sleep apnoea/hypopnoea syndrome (OSAHS). Overnight PTT was recorded at home in 40 patients being investigated for OSAHS, and a second PTT recording was made in the sleep laboratory with full polysomnography. Patients were divided into three groups according to the severity of their sleep disorder, and a third PTT recording was made at home in 13 patients subsequently established on nasal continuous positive airway pressure (CPAP). The reproducibility between the home and laboratory studies was reasonable (r=0.87 for inspiratory BP falls, r=0.81 for BP arousals). Both derivatives showed a clear progression through the three patient groups, which returned to normal on treatment. The differences between the groups were significant (p<0.001 for inspiratory BP falls, p=0.0014 for BP arousals). Receiver operator characteristic curves, used to compare polysomnography variables and PTT variables, confirmed that the PTT variables were as good as apnoea-hypopnoea index (AHI), >4% arterial oxygen saturation dip rate and electroencephalography micro-arousals at dividing patients into two groups, either requiring nasal CPAP or not requiring CPAP. Pulse transit time can provide a noninvasive estimate of inspiratory effort and a measure of arousals that together document disease severity and response to treatment and may be useful in managing obstructive sleep apnoea/hypopnoea syndrome.

Autonomic markers of arousal during sleep in patients undergoing investigation for obstructive sleep apnoea, their relationship to EEG arousals, respiratory events and subjective sleepiness.

Estimating the degree of sleep fragmentation is an important part of a respiratory sleep study and is conventionally measured using EEG micro arousals or is inferred indirectly from respiratory abnormalities such as apnoeas and desaturations. There is a need for less labour-intensive measures of sleep fragmentation, and transient rises in blood pressure and heart rate may fulfil this role. Forty unselected sleep clinic referrals undergoing investigation for possible obstructive sleep apnoea (OSA) were studied with one night of polysomnography. Three conventional indices of sleep fragmentation (EEG micro arousals, apnoea/hypopnoea index (AHI) and oxygen saturation dip rate (SaO2 dips)) and two autonomic indices (heart rate and blood pressure rises) have been compared. Correlations between these five indices ranged from r=0.38 to r=0.73. Of the two autonomic indices, the correlations for blood pressure rises with SaO2 dips and EEG micro arousals were stronger (r=0.71 and r=0.65, respectively) than those for heart rate rises (0.55 and 0.51). All indices of sleep fragmentation, apart from heart rate rises, were similar in their correlation with subjective sleepiness (r-values 0.21-0.36). Arousals implied from blood pressure rises (using pulse transit time) can be measured easily, are objective, and appear no worse at predicting subjective sleepiness than either EEG micro arousals or AHI. They may therefore provide a useful alternative to manual scoring of micro arousals from the EEG as an index of sleep fragmentation in sleep clinic patients undergoing investigation for possible OSA.

Automatic nasal continuous positive airway pressure titration in the laboratory: patient outcomes.

BACKGROUND: Manual titration of nasal continuous positive airway pressure (NCPAP) treatment for obstructive sleep apnoea (OSA) is time consuming and expensive. There are now "intelligent" NCPAP machines that try to find the ideal pressure for a patient by monitoring a combination of apnoeas, hypopnoeas, inspiratory flow limitation, and snoring. Although these machines usually find similar pressures to skilled technicians, it is not clear if their use in the sleep laboratory influences subsequent acceptance by patients. This study addresses this question. METHODS: One hundred and twenty two patients undergoing a trial of NCPAP were randomly allocated to either manual or automatic (Horizon, DeVilbiss) titration of pressure during their first night on NCPAP in a hospital sleep laboratory. The primary outcome (available on 112 patients) was the acceptance of NCPAP or otherwise six weeks following the initial titration night. Baseline indicators of severity were compared between the groups, as were the pressures selected and the subsequent improvement in the sleepiness of the patients. RESULTS: The initial severity of OSA was not significantly different in the two groups and the mean (SD) NCPAP pressures were similar (manual 8.7 (2.5) cm H2O, automatic 8.2 (2.1) cm H2O). The percentage of patients successfully established on CPAP at six weeks was 64% and 73% for the manual and automatic groups, respectively; 13% and 2%, respectively, in the manual and automatic groups had given up completely (p < 0.05), and there were about equal numbers (23% versus 25%) in the two groups who were still undecided. CONCLUSIONS: The substitution of automatic NCPAP titration for manual titration during the first night of NCPAP in patients with OSA does not reduce the number accepting the treatment at six weeks and may slightly improve it. This has important cost saving potential.

New approaches to monitoring sleep-related breathing disorders.

Conventional approaches to the analysis of sleep and sleep apnea do not describe all of the critical events that result from upper airway narrowing during sleep. The hypersomnolence that drives treatment is mainly due to microarousals, but these are poorly documented with conventional epoch-based sleep staging. The counting of apneas and hypopneas also fails to document other equally important events, such as the arousals due to increased respiratory effort in response to partial upper airway narrowing that may not cause significant hypopnea, hypoxemia, or even snoring. Modifications of conventional polysomnography, such as microarousal detection and analysis of the ribcage/abdominal paradox, may be an improvement. However, no system has been shown to be better than any other at identifying the critical events that produce symptoms of sleep-related breathing disorders, and thus be likely to respond to effective treatment. The time is right to explore innovative ways to characterize sleep-related breathing disorders, such as those derived from the cardiovascular change related to upper airway obstruction and arousal, without the shackles of conventional polysomnography. New monitoring techniques need to identify patients with events that will respond to treatment, not mimic the flawed gold standard of polysomnography.

Use of pulse transit time as a measure of inspiratory effort in patients with obstructive sleep apnoea.

Pulse transit time (PTT) is the time taken for the arterial pulse pressure wave to travel from the aortic valve to a peripheral site. For convenience, it is usually measured from the R wave on the electrocardiogram to the pulse wave arrival at the finger. Pulse transit time is inversely proportional to blood pressure, and the falls in blood pressure which occur with inspiration (pulsus paradoxus) correspond to rises (lengthening) in pulse transit time. In awake normal subjects, the size of these inspiratory rises in pulse transit time correlate well with the degree of inspiratory effort. The aim of this study was to investigate whether inspiratory rises in pulse transit time could provide a quantitative measure of inspiratory effort in patients with obstructive sleep apnoea. Eight patients with obstructive sleep apnoea, attending the laboratory for institution of nasal continuous positive airway pressure, took part in the study. Once asleep, airway pressure was varied between optimal treatment level and minimum pressure, to produce a range of inspiratory efforts whilst continuous recordings of oesophageal pressure and pulse transit time were made. There was an excellent correlation between the size of the swings in oesophageal pressure and the size of the swings in pulse transit time (mean r = 0.94). Pulse transit time may, therefore, provide a clinically useful noninvasive and quantitative measure of inspiratory effort in patients with sleep-related breathing disorders.

Use of the Epworth Sleepiness Scale to demonstrate response to treatment with nasal continuous positive airways pressure in patients with obstructive sleep apnoea.

The Epworth Sleepiness Scale (ESS) was used to measure the degree of daytime sleepiness in two groups of patients with obstructive sleep apnoea (OSA), before and after treatment with nasal continuous positive airways pressure (CPAP). One group (50 patients) were assessed after 2 months CPAP treatment after which the mean ESS fell from 16.4 [standard error of mean (SEM) 0.52] to 7.0 (SEM 0.56). A second group (25 patients) were assessed after 1 yr of treatment: a similar fall in mean ESS was seen from 15.2 (SEM 1.13) before treatment to 6.0 (SEM 0.72). These results imply that the ESS can be used clinically to demonstrate the response of daytime sleepiness in OSA to treatment with CPAP, and that the fall in ESS seen after 2 months is sustained after 1 yr of treatment. It is also possible that this approach could be used to monitor the progress of treatment with CPAP.

Snoring, sleep disturbance, and behaviour in 4-5 year olds.

Parents of 996 children aged 4-5 years identified consecutively from the Oxford health visitor register were asked to complete a questionnaire about breathing disorders during sleep. A total of 782 (78.5%) was returned. Ninety five (12.1%) children were reported to snore on most nights. Habitual snoring was significantly associated with daytime sleepiness, restless sleep, and hyperactivity. The questionnaire responses were used to select two subgroups, one at high risk of a sleep and breathing disorder and a control group. These children (132 in total) were monitored at home with overnight video recording and oximetry, and had formal behavioural assessment using the Conners scale. Seven (7/66) children from the high risk group and none from the control group had obvious sleep disturbance consequent on snoring and upper airway obstruction. Thus our estimate of the prevalence of sleep and breathing disorders in this age group is 7/996 or 0.7%. The high risk group had significantly higher nocturnal movement, oxygen saturation dip rates, and overnight pulse rates than the controls. Maternal but not paternal smoking was associated with the high risk group. Parents and teachers thought those in the high risk group were more hyperactive and inattentive than the controls, but only their parents thought them more aggressive. Significant sleep and breathing disorders occur in about 0.7% of 4-5 year olds. Children whose parents report snoring and sleep disturbance have objective evidence of sleep disruption and show more behaviour problems than controls.