The Stanford group used an amalgam of these previous criteria in their 1993 study. The patients had to demonstrate more than 10 transient EEG arousals/h of sleep (a 3- to 15-s shift to alpha in EEG frequency). As before, the breath preceding the arousal had to be associated with a Pes nadir more negative than 1 SD below the mean Pes nadir measured during quiet supine wakefulness. The Pes nadir had to be the most negative of the snoring period, and it had to decrease in magnitude with the breath immediately following the arousal. Natural asthma treatment add comment Polysomnography with a face mask and pneumotachography was performed on the following night. Segments of the tracings were screened randomly to ensure a decreased calculated tidal volume (Vt) in the breath just preceding the arousal. The authors reported a mean (± SD) Vt reduction of 22 ± 6% during that breath. In addition, a declining Vt was noted for only one to three breaths preceding the arousal, rather than a prolonged gradual decline. Based on the results seen in previous sleep-fragmentation subjects following nCPAP therapy, a cutoff of > 10 brief arousals/h was used to define the presence of the syndrome. The patients with improved daytime symptoms all had arousal indexes of < 10/h during nCPAP treatment.
In 1997, Berg et al defined the syndrome in a very different manner. IUAR events were scored when the negative Pes amplitude increased by 20% compared to baseline values for at least 15 s, accompanied by a decrease in airflow of < 50% as measured by a face mask/pneumotachograph. The mean Pes nadir was —15 cm H2O. Most of these events were not accompanied by an oxyhemoglobin desaturation. If the airflow decreased by > 50% for > 10 s accompanied by an oxyhemoglobin desaturation of > 4%, the event was scored as a hypopnea. Arousals were not used to locate or define IUAR events because they were the primary variable being examined. More recently, Lofaso et al looked at the BP response to transient EEG arousals in nonapneic/ nonhypopneic snorers. The subjects had an AHI of < 5, but had > 10 brief arousals/h of sleep by American Sleep Disorders Association (ASDA) criteria. The subjects had Epworth sleepiness scale (ESS) scores of > 10 and had > 10 respiratory events/h. A respiratory event was defined as a flow-limited (flattened) airflow tracing with a concomitant increased Pes nadir, both of which normalized after the event. Essentially, these subjects had UARS, although this term was never specifically used. In a study of the surgical management of UARS, more simplistic criteria were used that consisted of a respiratory disturbance index (RDI) of < 5 and Pes nadirs of < 10 cm H2O during PSG in patients with EDS. Although such criteria seem intuitively reasonable and do not contradict data from earlier, more rigorous studies defining this syndrome, it is not clear that these patient populations are equivalent.