Digital biomarkers for sleep apnoea
Common, substantially underdiagnosed, and diagnosed through a test inconvenient enough to be part of the reason it goes undetected.
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Sleep apnoea is common, substantially underdiagnosed, and diagnosed through a test that is expensive and inconvenient enough to be part of the reason it goes undetected. That combination has made it one of the most active areas for digital measurement, and one where consumer devices have moved unusually close to a regulated clinical role.
The measures collected here describe breathing disturbance during sleep and its consequences. The apnoea hypopnoea index, which counts breathing interruptions per hour of sleep, remains the defining clinical measure. Around it sit oxygen desaturation measures, breathing rate, and the sleep continuity measures that describe how fragmented the resulting night was.
What distinguishes this condition from most in this library is that a digital measure has been designed to detect the disease itself rather than to describe its consequences. Consumer wearable features intended to notify users of possible sleep apnoea have reached regulatory clearance, which places them in a different category from measures that track a condition already diagnosed. That also raises the stakes on accuracy, since the population being screened is largely unaware they have anything wrong.
Digital biomarkers used in sleep apnoea research
How these measures are used
Screening and case finding is the fastest growing use. A wearable that flags possible sleep apnoea and routes the person towards a diagnostic test addresses the underdiagnosis problem directly, and this is the primary way consumer devices are entering the clinical pathway in this condition.
In trials, the apnoea hypopnoea index is used as an endpoint in studies of positive airway pressure, positional therapy, weight loss and pharmacological approaches. It is one of the few measures in this library used as a primary endpoint by essentially every registered trial that has adopted it, which reflects its status as the accepted definition of disease severity.
Adherence to positive airway pressure is a second continuous measure of practical importance, since therapy that is prescribed but not used has no effect. Studies routinely pair objective measures with daytime sleepiness questionnaires, because reduction in breathing events that does not relieve daytime symptoms is an incomplete result.
What the evidence supports today
The reference standard is polysomnography, and home sleep apnoea testing is an accepted clinical alternative with a substantial validation literature. Against that background, consumer wearable detection has progressed further than in most conditions, with sleep apnoea notification features receiving regulatory clearance.
Clearance for a notification feature is a narrower claim than it can appear. These features are cleared to identify signs of possible moderate to severe sleep apnoea over a monitoring period and to prompt the user to seek assessment. They are not cleared to diagnose, to grade severity, or to determine whether treatment is working, and none of them replaces a diagnostic study.
The apnoea hypopnoea index itself has known limitations that predate digital measurement. It counts events without weighting their duration or the depth of desaturation, and it correlates only moderately with symptoms. It remains the accepted endpoint because it is standardised, not because it captures everything that matters.
Common questions
Can a smartwatch detect sleep apnoea?
Some devices have cleared features that identify signs consistent with moderate to severe sleep apnoea over a period of nights and prompt the user to seek assessment. That is a screening prompt, not a diagnosis, and confirmation still requires a sleep study.
What is the apnoea hypopnoea index?
The number of apnoeas and hypopnoeas, meaning complete and partial interruptions of breathing, per hour of sleep. It is the standard measure of disease severity and the usual primary endpoint in treatment trials, despite counting events without accounting for how long they last or how much oxygen desaturation they cause.
Does a home sleep test give the same result as a laboratory study?
Not identically. Home testing typically records fewer channels and often estimates recording time rather than measuring actual sleep, which can produce a lower index than a laboratory study on the same person. It is an accepted diagnostic route in appropriate patients, with those differences understood.
Why measure adherence to positive airway pressure?
Because it is the main determinant of whether treatment works, and because it is measured objectively by the device itself. A trial reporting improvement in breathing events without reporting hours of nightly use has left out the variable most likely to explain the result.
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