Upper Airway Resistance Syndrome

Sleep-disordered breathing (SDB) encompasses a spectrum of chronic conditions, including snoring, upper airway resistance syndrome (UARS), obstructive sleep apnea (OSA), and central sleep apnea (CSA), along with their subtypes. These disorders have historically been described as abnormal breathing patterns during sleep, with definitions shaped by the recording technologies and clinical understanding available at the time. Despite decades of research, no clear consensus has been established regarding the diagnostic criteria for UARS or whether it constitutes a distinct syndrome separate from OSA. OSA and CSA are typically defined by the number of apneic and hypopneic episodes per hour of sleep, measured as the apnea-hypopnea index (AHI). In contrast, UARS is generally characterized by increased upper airway resistance that causes arousals from sleep due to respiratory effort without significant oxygen desaturation—commonly referred to as respiratory effort–related arousals (RERAs)—and associated daytime symptoms.A more specific definition includes an AHI of less than 5 events per hour, oxygen saturation at or above 92%, and a RERA index of at least 5 events per hour. Another study defines UARS as having an AHI of less than 5 events per hour, a minimum peripheral capillary oxygen saturation (SpO) of 92%, the presence of airflow limitation during at least 5% of total sleep time, and symptoms of daytime sleepiness or fatigue. This activity provides a comprehensive overview of the etiology, epidemiology, clinical presentation, diagnostic evaluation, management strategies, differential diagnosis, and potential complications of UARS. OSA and CSA are addressed in separate discussions.