Multiple brief EEG arousals occur during polysomnography because of respiratory events that may be undetectable by standard oronasal thermistors or abdominal and thoracic strain gauges. Therefore, an increased arousal index in a patient with idiopathic hypersomnia should raise suspicion of UARS. The patients typically demonstrate significantly decreased SWS, 1.2 ± 2% of TST in one study; REM sleep time seems to be less affected. The presence of these features only suggests UARS if IUAR is not clearly demonstrated. flovent inhaler
Surrogate Polysomnographic Markers
The hallmark of IUAR in UARS is an increase in the driving pressure across a partially obstructed upper airway with a constant or decreased airflow. Direct confirmation of this condition requires invasive monitoring, as discussed. Therefore, since the initial discovery of UARS, investigators have tried to identify noninvasive, surrogate polysomnographic markers of IUAR events (Fig 2). Guilleminault and colleagues mentioned brief EEG arousals occurring without identifiable cause (eg, a change in position or other large body movement), a change in the snoring pattern, or a change in breathing pattern (the amplitude or breath duration by impedance plethysmography as compared to a previously established pattern). In a later publication, they cited > 10 alpha EEG arousals/h without another cause as a marker of this syndrome, but warned that the “patient friendly” approach of identifying increasing snoring intensity followed by EEG arousals would produce a significant number of false-negatives. Furthermore, only moderate interobserver agreement was found in a recent study of variability in scoring arousals (k = 0.47). The 14 scorers who participated in this study demonstrated the best agreement for arousals during SWS, the stage most severely curtailed in patients with untreated UARS. Therefore, the scoring criteria that rely heavily on arousals without other concomitant markers may lack reproducibility. In addition, a significant number of brief arousals were demonstrated in a “normal” population by Mathur and Douglas in 1995. They studied 55 patients from a family practice list having a single overnight PSG and they found a mean arousal index of 21 (95% confidence interval 7.0, 56.0) by ASDA criteria.
Figure 2. A noninvasive PSG from a patient with UARS. An IUAR event is suggested by an EEG arousal preceded by crescendo snoring and abdominal and thoracic dyssynchrony by plethysmography. Increased airflow by nasal thermistry follows the onset of arousal. Note that the oxyhemoglobin saturation does not change significantly. The arrowhead indicates an EEG arousal, the thick arrow indicates increased airflow, the thin arrows indicate abdominal and thoracic dyssynchrony, and the closed circles indicate crescendo snoring.