Upper Airway Resistance Syndrome: The Condition Between Snoring and Apnea

UARS Defined: Snoring and Daytime Impairment Without an AHI ≥5

Upper airway resistance syndrome (UARS) occupies a diagnostically awkward position: patients suffer the classic symptoms of obstructive sleep apnea — chronic fatigue, non-restorative sleep, morning headaches, cognitive fog, and often loud snoring — yet their formal sleep study results appear normal by conventional OSA criteria. The defining feature of UARS is that airway narrowing during sleep creates increased respiratory effort and sleep fragmentation without causing the oxygen desaturations or complete airway closures that define OSA. The apnea-hypopnea index (AHI), which counts apneas and hypopneas per hour, remains below 5 events per hour in UARS patients — the threshold that has historically defined "normal" in sleep medicine. UARS was first characterized by researchers at Stanford Health Care in the 1990s, who recognized that the AHI was an incomplete measure of sleep-disordered breathing and that a substantial population of symptomatic patients was being systematically missed by standard diagnostic criteria.

Why UARS Is Harder to Diagnose Than OSA

The diagnostic challenge with UARS stems from the very metric that most sleep studies optimize for: the AHI. Standard polysomnography (PSG) and most home sleep test devices are calibrated to detect apneas (complete airflow cessation lasting at least 10 seconds) and hypopneas (partial flow reduction meeting specific oxygen desaturation thresholds). UARS events do not meet these thresholds — they are brief microarousals triggered by increased breathing effort before oxygen levels drop significantly. Because they fall below the detection threshold of standard scoring algorithms, they are simply not counted, and the study appears normal. The result is that UARS patients often receive a clean sleep study report while continuing to suffer debilitating symptoms. Many are misdiagnosed with chronic fatigue syndrome, fibromyalgia, depression, or anxiety — conditions that share overlapping symptom profiles and are frequently comorbid with UARS. Correct diagnosis typically requires either in-lab PSG with esophageal pressure monitoring (the gold standard for detecting respiratory effort) or an experienced sleep physician who recognizes the clinical pattern and interprets the EEG arousal index alongside the AHI.

RERAs: The Respiratory Events That Standard Tests Miss

The events that characterize UARS are called respiratory effort-related arousals, or RERAs. A RERA is defined as a sequence of breaths lasting at least 10 seconds during which increasing respiratory effort leads to an arousal from sleep, but which does not meet the criteria for an apnea or hypopnea. What makes RERAs damaging despite their apparent mildness is their frequency and their timing within the sleep cycle. Each arousal interrupts the current sleep stage, preventing normal progression through the sleep architecture. A patient with 25 RERAs per hour — a RERA index that would be considered moderate-to-severe — experiences the equivalent of being partially awakened more than 200 times during an 8-hour sleep opportunity. The cumulative effect is profound sleep fragmentation: the brain never achieves sustained slow-wave or REM sleep, and restorative processes dependent on those stages — memory consolidation, immune regulation, hormonal secretion, and metabolic clearance — are chronically impaired. The NIH notes that sleep fragmentation from respiratory events is independently associated with cardiovascular risk and metabolic dysfunction, regardless of whether oxygen desaturation occurs.

Treatment Options That Work for UARS

Because UARS is driven by increased upper airway resistance rather than complete obstruction, the same interventions that treat OSA are effective — often at lower therapeutic intensities. CPAP therapy at low pressures (typically 4 to 8 cm H2O, compared to 10 to 15 cm H2O for moderate OSA) effectively eliminates RERAs and resolves daytime symptoms in most UARS patients. Mandibular advancement devices are also well-supported for UARS: by increasing the retropalatal and retroglossal airway space through jaw protrusion, they reduce the resistance that triggers RERAs without requiring the patient to tolerate CPAP pressurization. Clinical experience suggests that UARS patients often achieve excellent symptom relief with MADs at lower advancement settings than OSA patients require, making device tolerance easier. Positional therapy is particularly relevant in UARS, where the condition is often entirely position-dependent — occurring only during supine sleep. Nasal breathing optimization (treating allergic rhinitis, nasal polyps, or septal deviation) also reduces resistance significantly and can be curative in mild cases. The Snorple mouthpiece, which combines jaw advancement with a tongue-stabilizing channel, addresses both the retropalatal and retroglossal resistance contributors that drive UARS.

Why Standard Home Sleep Tests Miss UARS

Home sleep testing (HST) devices have become the dominant modality for sleep apnea screening due to their convenience and lower cost relative to full in-lab polysomnography. However, they have a fundamental limitation for UARS detection: virtually all FDA-cleared home sleep test devices measure airflow and oxygen saturation, but not EEG brain activity or esophageal pressure. This means they can identify apneas and oximetric hypopneas, but they cannot detect the cortical arousals triggered by RERAs, nor can they measure the escalating respiratory effort that defines UARS physiology. A patient with a RERA index of 30 per hour and an AHI of 2 will receive a home sleep test report that reads "normal" or "no significant sleep apnea detected." This is not a failure of interpretation — it is a genuine limitation of what these devices measure. For patients whose symptoms strongly suggest sleep-disordered breathing but whose home sleep tests are normal, requesting an in-lab polysomnography with RERA scoring is the correct next step. Advocating for this testing often requires the patient to explicitly mention UARS to their physician, as many clinicians default to the AHI as the sole diagnostic criterion and may not order RERA analysis unless specifically requested.