(Pocket-lint) - It may be a little late to the party, but the Apple Watch can finally offer SpO2 monitoring through the Apple Watch Series 6

The blood oxygen monitoring feature has become a mainstay in wearables from the likes of Fitbit, Garmin and Withings over the past year, but pulse oximetry is now set to hit the mainstream with Apple's help. 

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So, you're probably wondering what exactly your blood oxygen levels are, why they matter and, frankly, how the Apple Watch Series 6 will keep an eye on them?

Below, we'll be answering all these questions - including how the new Apple Watch feature could even help detect signs of COVID-19.

What is blood oxygen monitoring?

Blood oxygen levels - also known as SpO2 - refer to the percentage of oxygen being carried by red blood cells from the lungs to the rest of the body, as well as how well this oxygenated blood is being delivered.

Using pulse oximetry, which is essentially a simplified way of saying 'non-invasive oxygen saturation monitoring', the Apple Watch Series 6 and other wearables are able to notify the user when their blood oxygen percentage falls below a certain point. 

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Typically, anything above 95% is considered to be 'normal'. However, anything below 92% is a potential indicator of an underlying health issue, such as sleep apnea. 

Fitbit, for example, uses the SpO2 monitor in its wearables to specifically monitor fluctuations and variations in blood oxygen levels during tracked sleep sessions. However, the Apple Watch Series 6 appears to be ready to check on SpO2 levels at any time when the user is still - similar to its ECG tracking function - with readings also only taking 15 seconds. Periodic measurements will also be taken in the background during inactivity and sleep. 

What else can blood oxygen monitoring help with? Well, as noted by John Hopkins Medicine, pulse oximetry can be used to check whether somebody needs help with their breathing (through a ventilator), estimate whether a person is able to take part in strenuous physical activity and, as we mentioned, indicate whether breathing stops temporarily during sleep (sleep apnea).

How does blood oxygen monitoring work?

What was once a test reserved only for dedicated monitors has now found its way onto smartwatches and fitness trackers - so how does it actually work?

Well, traditionally, SpO2 monitors would consist of a clip-on device that the user would place on a finger or toe. It would then use red and infrared light sensors to log the volume of oxygen passing through the finger, for example, and continuously monitor this for changes. 

In the modern sense, of course, this can now be achieved directly from the wrist without any adjustments. Apple, specifically, indicates that it uses four clusters of green, red, infrared LEDs and four photodiodes on the back crystal of the Series 6 in order to measure the light reflected back from the blood.

Can blood oxygen monitoring help detect COVID-19?

With pulse oximetry able to be used to check when somebody needs help with their breathing - and, more specifically, silent hypoxia - this naturally begs the question: can the Apple Watch Series 6 help detect signs of COVID-19?

It has been speculated, such as in this piece by The New York Times from April, that pulse oximetry is able to provide an "early warning system for the kinds of breathing problems associated with Covid pneumonia".

With both blood oxygen fluctuations and heart rate readings able to be taken on-demand with a device like the Apple Watch Series 6, this does, at the very least, suggest vital signs can be checked directly from your smartwatch. 

Of course, though, this is a far-cry from any genuine coronavirus diagnosis - and Apple won't be using its fancy new feature to let you know whether you're even showing signs, either. 

Writing by Conor Allison.