Smartwatches may not be as efficient as thought before: Is a smart ring the solution to detecting Sleep Apnea?

Withings Scanwatch SpO2 measurement

A recent study has discovered that smartwatches have limited capabilities in detecting sleep disturbances. 

The study led by a group of researchers from the Center of Sleep Medicine in Switzerland has found that the level of Oxygen Desaturation (OD) measured from the arm is 2-3% lower than the values obtained from fingertips. 

Under specific circumstances and from the perspective of medical personnel, that is something to be concerned about if smartwatches are the determinants of standard biometric data. Hence, the difference of 2-3% is phenomenal when measuring sleep apnea or sleep disturbances.

What is sleep apnea and its relation to oxygen saturation?

To understand why, it is imperative to understand what sleep apnea is and how it occurs. There are primarily three types of sleep apnea prevalent among the 9-35% of Americans who suffer from this disorder. 

First, Obstructive sleep apnea occurs directly due to the throat muscles being relaxed during deep sleep. As the muscles at the back of the throat relax, the airways become obstructed, with less air flowing in.

This can result in a drop in oxygen level in the blood (Oxygen Desaturation), and the brain awakens the individual from a deep slumber.

Such obstruction in normal airflow and awareness can cause sleep disturbances, and in advanced cases, if the individual does not wake up, this may even result in death due to oxygen deprivation.

Next comes Central sleep apnea, where the brain cannot propagate essential signals to the muscles that contribute to normal breathing in the body. 

Once again, this results in Oxygen Desaturation (OD), and the individual is prone to waking up. Failing to do so ultimately results in death. However, under rare circumstances, individuals can also suffer from both of these states of sleep apnea, also called complex sleep apnea. 

Hence, it is very important to measure the oxygen saturation levels when somebody is sleeping, as failure to do so may have detrimental consequences in terms of physical and mental well-being.

Limitations of smartwatches 

The study described above used products from prominent smart-watch brands like Fitbit, Garmin, etc., and armbands from Humon, Moxy, Portamon, and various other prototypes. As the researchers point out, one caveat to this is that they have used older wearables and not the latest ones for the study.

Detecting sleep apnea in which there is a complete lack of breathing is easier than figuring out a drop in the oxygen level.

Some sensors can monitor breathing frequencies, so that becomes a much easier job. However, sleep hypo-apnea, during which, there is a greater than 30 percent drop in the airflow for more than 10 seconds, is more difficult to measure. This is more important to consider because this ultimately leads to oxygen desaturation in the blood.

However, smartwatches that measure oxygen desaturation rely on data from smaller blood vessels like arterioles, venules, and capillaries.

This data is negatively influenced by the blood circulating within the veins in the arm, which carries deoxygenated blood by default. Hence, the data thus obtained is unreliable.

This is how smartwatches fail to deliver an accurate result for sudden blood oxygen levels, as the interference from the deoxygenated blood in the veins results in false negatives for Obstructive sleep apnea. 

Peripheral capillary oxygen saturation levels

That is why SpO2 levels or, in simpler terms, peripheral capillary oxygen saturation levels become vital in determining the true levels of oxygen desaturation in blood. When measuring a 30% drop in the airflow, it is also imperative to note the SpO2 levels, and the combined data gives a clearer picture of whether there is an actual drop in the blood-oxygen level.

Since these data are constantly interrupted due to the venous flow, SpO2 data from the fingertips can be the ultimate solution.

The venous flow in the fingertips is limited by the ubiquitous and unobstructed presence of numerous capillaries; hence, they are more suitable for detecting Oxygen Desaturation (OD). Products such as the Oura ring and CIRCUL ring use this feature of the fingertips as a means to detect variable respiratory and heart rate.

Samsung Ring wearable
Samsung ring wearable

The infrared light emitted can easily penetrate the skin, and the sensors can readily monitor changes in heart or respiratory rates.

Since the Oura ring can achieve that, this can provide a more accurate representation of the SpO2 data, which is more reliable. Furthermore, Oura has been actively engaged in this space. It recently acquired two patents from Hancock Medical to pursue novel approaches for sleep apnea detection.

Oura ring sleep apnea detection

Although Withings Scanwatch and Fitbit have tried incorporating sleep apnea detection features in their products, they are still awaiting FDA approval. 

This has resulted in a paradigm shift among the engineers employed by Fitbit, and they are trying to develop a ring-like wearable that can measure SpO2 from the fingertips.

Since the ring-like wearable products can pick up data from minute capillaries, this can also provide real-time blood pressure measures that would be more accurate than smart-watch-based products.

Valencell is already working towards obtaining regulatory certification for measuring blood pressure via finger- or ear-based sensors.Withings sleep apnea and stress watch

Smart rings are better equipped for this

A major reason companies like Apple, Fitbit, or Withings have been unable to develop such precise revolutionary features in wearable products is that they rely on “surrogate markers” that can determine the basal frequency of certain physical events, for instance, breathing.

Thus, relying on markers that do not actually measure SpO2 levels or real-time Oxygen saturation is a prime cause why Oura is ahead of the pack regarding sleep apnea detection and monitoring real-time sleep disturbances.

However, the future looks brighter than before for Fitbit and Withings. Fitbit has already filed a patent for a ring-shaped wearable that can detect anomalies or compile biometric data using a photodetector.

The patent exclusively points out SpO2 detectors and a motion sensor that could also contribute to monitoring features like blood pressure, heart rate, sleep activity/disturbances, and lung capacity. 

Although the concept of “reflected light” used to analyze Oxygen Desaturation/ heart rate is another example of implementing data extraction from a surrogate marker, it is still deemed more accurate than smartwatches that acquire data from the arm.

The ring would function just like a clinical pulse oximeter and promises to deliver more in the future.

However, one thing to remember is that the patent talks about software algorithms to analyze the difference between light intensities from the photodetector, to give out a generalized reading for sleep apnea or Oxygen Desaturation levels.

Once again, only time will tell how surrogate markers in the Fitbit ring could detect such intricate measures when considering sleep hypoapnea.

Withings has already come up with a sleep analyzer in the recent past. However, there are also rumors that Withings wishes to delve into the realm of smart ring-based wearable products that would compete against similar products being offered by Fitbit in the near future. 

Although the analyzer claims to detect sleep apnea, the FDA has not yet certified it. However, it has received the CE marking for European markets, and hence, if the rumors are correct, Withings may already be far ahead of Apple, Fitbit, and Garmin in terms of announcing a wearable that can detect sleep apnea.

Final thought

In summary, monitoring sleep apnea, specifically, hypopnea is no small feat unless embedded sensors in smartwatches can be improved.

It requires sophistication, and current technology based on smartwatches is probably inadequate to provide a tangible, yet accurate representation of sleep apnea or sleep disturbances.  

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Sudz Niel Kar
I am a technologist with years of experience with Apple and wearOS products, have a BS in Computer Science and an MBA specializing in emerging tech, and owned the popular site AppleToolBox. In my day job, I advise Fortune 500 companies with their digital transformation strategies and also consult with numerous digital health startups in an advisory capacity. I'm VERY interested in exploring the digital health and fitness-tech evolution and keeping a close eye on patents, FDA approvals, strategic partnerships, and developments happening in the wearables and digital health sector. When I'm not writing or presenting, I run with my Apple Watch Ultra or Samsung Galaxy Watch and closely monitor my HRV and other recovery metrics.


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