On the potential clinical relevance of the length of arousals from sleep in patients with obstructive sleep apnea

The Tampa Sleep Center, University Community Hospital, Department of Medicine, University of South Florida, Tampa, FL 33613, USA.
Journal of clinical sleep medicine: JCSM: official publication of the American Academy of Sleep Medicine (Impact Factor: 3.05). 04/2006; 2(2):175-80.
Source: PubMed


To assess, in individuals referred for evaluation of obstructive sleep apnea, the potential clinical significance of brief versus longer arousals from sleep.
Full-night polysomnographic tracings from 100 patients referred for evaluation of obstructive sleep apnea were analyzed to delineate the duration of each arousal event. These data were then correlated to the patient's subjective perception of sleepiness as estimated by the Epworth Sleepiness Scale (ESS).
A significant relationship (p < .0001, r(2) = .167) was noted between the frequency of the longer arousals (> 15 seconds) and the ESS. This relationship was significant, but distinctly weaker (p = .004, r(2) = .073), with the shorter arousals (3-15 seconds); moreover, the association with the brief arousals failed to remain significant (p = .678) after controlling for the effect of the longer arousals.
Individuals with obstructive sleep apnea experience frequent respiratory event associated cortical arousals, many of which are greater than 15 seconds in duration. These longer arousals, which, in this study, constituted 18.4% of all arousals and accounted for 37.5% of the total arousal time, correlate more closely with the ESS than does the frequency or time attributable to the more numerous brief arousals. This suggests that these more-prolonged arousal events may have a greater impact on the restorative aspect of sleep, or on the perception thereof.

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    • "The implication is that the cortex is in an altered state for much longer than is apparent from visual inspection of the EEG. Schwartz, et al. (2006) have reported that the Epsworth Sleepiness Score correlates weakly with the frequency of long arousals but does not correlate with the frequency of short arousals. Thus, our observations of an apparent increase in the duration of an aroused state due to the decrease in delta power and the increase in beta power post-arousal could potentially have a significant impact on quantitative assessments of sleep quality. "
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    ABSTRACT: Arousals are often considered to be events which have an abrupt onset and offset, indicating abrupt changes in the state of the cortex. We hypothesized that cortical state, as reflected in electroencephalograph (EEG) signals, exhibits progressive systematic changes before and after a spontaneous, isolated arousal and that the time courses of the spectral components of the EEG before and after an arousal would differ between healthy middle-aged and elderly subjects. We analyzed the power spectrum and Sample Entropy of the C3A2 EEG before and after isolated arousals from 20 middle-aged (47.2±2.0 years) and 20 elderly (78.4±3.8 years) women using polysomnograms from the Sleep Heart Health Study database. In middle-aged women, all EEG spectral band powers <16 Hz exhibited a significant increase relative to baseline at some time in the 21 s before an arousal, but only low- (0.2-2.0 Hz) and high-frequency (2.0-4.0 Hz) delta increased in elderly and only during the last 7 s pre-arousal. Post-arousal, all frequency bands below 12 Hz transiently fell below pre-arousal baseline in both age groups. Consistent with these findings, Sample Entropy decreased steadily before an arousal, increased markedly during the arousal, and remained above pre-arousal baseline levels for ∼30 s after the arousal. In middle-aged, but not in elderly, women the presence of early pre-arousal low delta power was associated with shorter arousals. We propose that this attenuation of the effect of the arousing stimulus may be related to the slow (<1 Hz) cortical state oscillation, and that prolonged alterations of cortical state due to arousals may contribute to the poor correlation between indices of arousals and indices of sleepiness or impaired cognitive function.
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    • "Multiple mechanisms are thought to contribute to sleepiness in patients with sleep-disordered breathing. These include sleep fragmentation [1], hypoxia [2], partial chronic sleep deprivation from sleep time lost due to arousals [3], cytokine dysregulation [4], obesity-associated biology [5] [6], and interactions with individual adaptations [7]. However, treated patients often experience residual daytime sleepiness [8]. "
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