What Is Upper Airway Resistance Syndrome?
Chronic Fatigue and Insomnia? It could be UARS.
Have you heard about Upper Airways Resistance Syndrome (UARS)? Do you think you might have it? UARS can be a difficult diagnosis to make. Read on as we deconstruct what UARS is, how to properly diagnose it, and the single best way to treat it.
Definition of UARS
UARS is a subtle form of sleep disordered breathing; it's like a cousin of obstructive sleep apnea (OSA), where the person’s airway narrows during sleep, but often not enough to stop breathing completely. Think of it like periodically trying to breathe through a straw.
To better understand, let’s briefly discuss the types of abnormal respiratory events which can occur during sleep. Apneas are defined as absence of airflow at the nose and mouth for 10 seconds or longer. In OSA, the person stops breathing completely due to total obstruction or closure of the airway.
An obstructive apnea from a sleep study is depicted in the cartoon below. There is no air moving through the sensors in the nostrils that pick up airflow but there is signal in the chest and abdominal belts indicating that the person is trying to breathe:
Hypopneas are episodes of significantly reduced airflow (but they fall short of total airflow cessation) that are associated with either an oxygen desaturation (drop) of at least 3% or a brain awakening (cortical arousal or just "arousal"). Here is an example of a hypopnea with a significant oxygen drop on a sleep study:
Below is a hypopnea based on the "cortical arousal" criteria. This respiratory event was associated with only a 2% oxygen drop so it didn't meet criteria for a hypopneas based on the 3% oxygen rule. But notice that the brain waves (EEG) speeds up where the yellow arrow is. That is the beginning of a micro brain awakening.
A respiratory effort-related arousal (RERA) is defined as a small reduction in airflow (less than a hypopnea) which leads to a cortical arousal but does not result in a significant oxygen desaturation (see cartoon below). Upper Airway Resistance Syndrome is found in a person with significant RERAs and few apneas or hypopneas. Generally having greater than 5 RERAs per hour is considered to be consistent with a diagnosis of UARS.
There's also another way to look at UARS. There is a school of thought that UARS may present when there are long periods of sustained partial airway closure without clear RERAs. The theory is that there are frequent "subcortical" arousals that can't be seen with conventional EEG but lead to sleep fragmentation and non-restorative sleep. The cartoon below depicts an epoch of prolonged and continuous flow limitation, i.e., flattening of the nasal airflow signal that is sometimes associated with UARS:
The gold-standard to accurately diagnose UARS is conventional in-lab polysomnography. That said, home sleep apnea tests that allow the sleep physician to review the raw data can provide strong supportive evidence to also suggest UARS. Since there is no EEG monitoring in these home sleep tests, it's best to classify these events as "probable RERAs." The below cartoon indicates a probable RERA from an Alice NightOne (type 3) home sleep apnea test. There is continuous flow limitation and snoring which abruptly terminates with opening of the airway (yellow arrow). The most logical explanation is that a brain awakening that led to the opening of the airway.
It is important to note that other home sleep apnea test technologies that use peripheral arterial tonography (PAT) and other newer methods that estimate abnormal breathing events based on non-respiratory physiological signals cannot accurately be used to detect or screen for UARS.
UARS & Sleep Fragmentation
UARS fragments sleep by causing excessive cortical arousals. When someone with UARS falls asleep, the muscles of the throat and tongue relax leading to the partial upper airway obstruction described above. Through movement of the chest and abdomen, their body begins to work harder to inhale past this narrowing (airway resistance) and perceives there will not be enough oxygen if the narrowing continues. The brain sends out an alarm (the sympathetic nervous system kicks in) so that the body activates the throat and tongue muscles to widen the airway and prevent oxygen from dropping. Often this is accompanied by an arousal. When the person returns to sleep, the process repeats itself. Many of these awakenings may not be appreciated by the person suffering from UARS, but there can be consequences to having undergone a stress response many times during the night. Repeated respiratory arousals may be associated with the development of sympathetic overdrive, or chronic activation of the fight or flight response, which can lead to a number of the symptoms listed below.
UARS Symptoms:
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Sleep fragmentation |
Chronic fatigue |
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Sleep onset insomnia: trouble falling asleep |
Excessive daytime sleepiness |
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Sleep maintenance insomnia: trouble staying alseep |
Difficulty concentrating, Anxiety, or Depression |
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Regular snoring |
Morning headaches |
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Heavy, labored breathing |
Heartburn |
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Sweating at night, waking in a cold sweat |
Muscle aches or pain |
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Bruxism: clenching or grinding teeth |
Cold extremities |
Who might be at risk for UARS?
It is a common misconception that younger, slim people cannot suffer from sleep disordered breathing. UARS is classically seen in this group. Non-overweight persons may have any of the physical features listed below. Additionally, though frank obstructive sleep apnea is seen more commonly in men than women, UARS is diagnosed in men and women equally, or slightly favoring women.
Causes of Upper Airway Resistance Syndrome
Structural factors that narrow the airway can cause UARS including the following:
- Tissue crowding in the throat such as loose skin or adenoids
- Large tongue, maybe with a grooved appearance at the sides where the tongue presses against the teeth
- Narrow palate. For some people, their dentist may have recommended a palatal expander when they were children.
- Small mandible (lower part of the jaw)
- Deviated septum
- Large nasal turbinates
The Difficulty of Diagnosing UARS
Because those affected by upper airways resistance syndrome are often younger and fit, this subtle form of obstructive sleep apnea may not be considered by their regular doctor when the symptoms call for it. Above all, discussing potential symptoms with your provider is the most important step in the path to diagnosis. A sleep study read by an experienced sleep physician is the only way to diagnose UARS.
An in-lab sleep study is the gold standard for diagnosis. The most sensitive method of detecting increased respiratory effort is to measure esophageal pressure (Pes) during the sleep study. This is done by passing a small, soft fluid-filled catheter (like a pediatric feeding tube) or a flexible balloon catheter through the nose and into the esophagus while the sleep study is being performed. Pes is generally well tolerated, but may be poorly tolerated or refused by some. Despite being the gold standard, esophageal pressure is rarely measured in most clinical sleep laboratories.
However, the appearance of measurements on a home sleep test (HST) may suggest the presence of UARS. As mentioned above, the study may demonstrate a small reduction in airflow without oxygen desaturation but followed by a sudden change in the respiratory pattern which may imply an arousal. Alternatively, crescendo snoring may be observed, terminating with the same abrupt change in respiratory pattern. Finally, the nasal pressure signal worn during HSTs may demonstrate signs of more persistent flow limitation, appearing as flattening of the curve and possibly increased inspiratory time. It has been recognized that flattening of the nasal pressure signal identifies periods of high respiratory effort with reasonable accuracy.
UARS Treatment
As we've established, UARS can significantly detract from quality of life in those suffering with it. There is evidence that sleep quality may actually be worse and daytime fatigue more severe in patients with UARS compared to those with mild obstructive sleep apnea. Symptoms such as fragmented sleep, fatigue, and anxiety or depression may increase over time. The good news is that there is one treatment that has been clearly shown by high-quality scientific research to be effective in treating this potentially debilitating problem: continuous positive airway pressure (CPAP).
Alternative Treatments for UARS
There is some evidence to support alternatives to CPAP as treatment for UARS such as oral appliances and upper airway surgeries. However, these treatment modalities have only been studied in case reports and small case series which don't rise to the level of evidence to give blanket recommendations about their effectiveness. Long-term studies to evaluate treatment are needed to look at the role of CPAP alternatives in the treatment of UARS.
References:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5015642/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4608900/
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