A Study of Upper Airway Resistance Syndrome : Clinical and Polysomnographic Characteristics

Yang, C K; Alex, Clerk

Abstract

OBJECTIVES
Upper airway resistance syndrome(UARS) is a sleep-related breathing disorder characterized by abnormal negative intrathoracic pressure during sleep. Abnormally increased negative intrathoracic pressure results in microarousal and sleep fragmentation which underlay UARS-associated complaints of daytime fatigue and sleepiness. Although daytime dysfunction in patients with UARS is comparable to that of sleep apnea syndrome, UARS has been relatively unnoticed in clinical setting. That is why UARS is apt to be excluded in diagnosing of sleep-related breathing disorders since its respiratory disturbance index and arterial oxygen saturation are within normal limits. The current study presents a summary of clinical and polysomnographic characteristics found in patients with UARS. The present study aims (1) to explore characteristics of patients diagnosed with UARS, (2) to characterize the polysomnographic findings of UARS patients, and (3) to enhance the understanding of UARS through those clinical and laboratory characteristics.
METHODS
This was a retrospective study of 20 UARS patients (male 15, female 5) and 30 obstructive sleep apnea (OSA) patients (male 21, female 9) at the Stanford Sleep Disorders Clinic. We diagnosed patients as having UARS when they met critenia, RDI<5 characteristic findings of an elevated esophageal pressure(<-10 cmH2O), frequent arousals secondary to an elevated esophageal pressure, and symptoms of daytime fatigue and sleepiness. We used polysomnographic value, which is standardized by Williams et al(1974), as normal control. Statiotical test were done with student t-tests.
RESULTS
(1)Mean age of UARS was 41.0+/-14.8 years and OSA was 50.9+/-12.0 years. UARS subject was significantly younger than OSA subject (p<0.05). (2)The total score of Epworth Sleepiness Scale(ESS) was UARS 9.7+/-6.3 and OSAS 11.2+/-6.3. There was no significant difference between two groups. (3)The mean body mass index was UARS 28.1+/-5.7 kg/m2 and OSAS 32.9+/-7.0 kg/m2. UARS had significantly lower mean body man index than OSAS subjects (p<0.05). (4)The polysomnographic parameters of UARS were not significantly different from those of OSA except RDI(p<0.001), SaO2 (p<0.001) and slow wave sleep latency (p<0.05). (5)Compared with normal control. Total sleep time in LIARS subjects was significantly shorter (p<0.001), sleep efficiency index was significantly lower (p<0.001), total awakening percentage was significantly higher (p<0.001), and sleep stage 1 (p<0.001) were significantly higher. (6)OSA patients showed poor sleep quality and distinct abnormal sleep architectures compared with normal control.
CONCLUSIONS
Conclusions from the above results are as follows : (1)UARS patients were younger and had lower body mass index when umpared with OSA patients. (2)The quality of sleep and sleep architectures of the UARS and OSA patients are significantly different from those of normal control. (3)ESS scores and awakening frequencies of UARS are similar with those of OSA, suggesting that daytime dysfunction of UARS patients may be comparable to those of OSA patietns. (4)The RDI and the SaO2, which are important indicators in diagnosing sleep-related breathing disorders, of UARS subjects are close to normal value. (5)According to the above results, we unclude that despite the absence of SaO2 drops and the absence of an elevated number of apnea and hypopnea, subjects developed clinical complaints which were associated with laborious breathing, elevated Pes nadir, and frequently snoring.(6)Accordingly, we suggest including LIARS in the diffterential diagnosis list when sleep related breathing disorder is suspected clinically and overnight polysomnographic findings except snoring and frequent microarousal are within normal limits