Given the currently available information, the most plausible explanation for daytime somnolence in UARS is that sleep disruption from multiple brief arousals occurs as a result of increasingly negative intrathoracic and airway pressure, with the response most likely mediated by mechanoreceptors in the upper airway. Obviously, much more work is needed in this area before any definite conclusions can be reached.
UARS research and even the clinical diagnosis of this syndrome are plagued by the lack of standardization in nomenclature, criteria, and measurement techniques, as is the entire field of sleep-disordered breathing. It can be said, however, that most of the published studies do involve patients who do not meet the standard criteria for OSAS, who do not show significant oxyhemoglobin desaturation during sleep, and who do have EDS, even if mild. buy ventolin inhaler
In 1991, Guilleminault et al used Pes measurements and pneumotachographic airflow assessment to identify repetitive IUAR leading to brief arousals (a 2- to 10-s shift to alpha or fast theta in EEG frequency) in regular heavy snorers with mild daytime sleepiness. The scoring of an event began with the identification of an arousal. If the Pes nadir of one of the two breaths preceding the arousal had the greatest magnitude since the last arousal (the snoring period) and was accompanied by a simultaneous decrease in pneumotachographic airflow, an IUAR event was scored (Fig 1). Additional requirements included a less negative Pes nadir and increased airflow during and two breaths after the arousal, and the absence of another identifiable cause of arousal. Pes nadirs ranging from —29 to —68 cm H2O were seen during these events. Permutations on this basic method have appeared since that time.
One year later, for example, the Stanford group published the results of a study in which patients were selected who did not meet criteria for OSAS and who demonstrated snoring during > 10% of the TST. These patients displayed Pes nadirs that were 1 SD more negative than the mean Pes nadir measured during 30 min of quiet supine wakefulness. The most negative baseline Pes value was —7 cm H2O. An arousal (a 3- to 5-s shift to alpha in EEG frequency) was scored as related to IUAR if the Pes nadir preceding it was more negative than what was seen during baseline wakefulness, and if it was the most negative Pes nadir of the snoring period. A lesser Pes nadir with the breath following the arousal was also required. Of note, oronasal thermistors were used to detect airflow during this study; airflow was not used in the definition of IUAR events.
Figure 1. Two consecutive epochs fromaPSG of a patient with UARS. An esophageal pressure transducer was used to measure the Pes, and a full-face mask connected to a pneumotachograph and differential pressure transducer was used to measure the inspiratory airflow. Three IUAR events are defined as progressively negative Pes with concomitantly decreasing airflow until Pes nadirs are reached, followed directly by EEG arousals, less negative Pes, and increased airflow. Note that oxyhemoglobin saturation (O2 Sat, bottom tracing) does not change significantly. The arrowheads indicate EEG arousals, the closed circles indicate an abrupt increase in airflow, and the arrows indicate the Pes nadirs. Chin = submental EMG; LOC = left oculomyogram; ROC = right oculomyogram; SCM = sternocleidomastoid; INT = intercostal muscle EMG; mic = microphone; Abd = abdominal plethysmography.