Recently, Apple released the sixth generation of the Apple watch. One of the most talked-about new features was the device’s “revolutionary” blood oxygen feature which “offers users even more insight into their overall wellness”, but how viable is this claim?
Read on to find out:
- A history and summary of the technology underpinning the watch’s new feature: pulse oximetry.
- Whether I think that the ‘revolutionary’ claim can be justified.
- The Apple Watch’s shift towards being a health orientated device.
- New scientific studies to which Apple is contributing.
- Whether measuring oxygen saturation matters to your average fitness enthusiast.
What is pulse oximetry?
The new Apple watch can now estimate oxygen saturation (SpO2). This measure represents the percentage of oxygen being carried by red blood cells from the lungs to the rest of the body.
I was intrigued to find out more about the new feature and how Apple is applying it. ‘Revolutionary’ is a big claim, particularly when pulse oximetry, the underlying technology which measures blood oxygen saturation in this context, is relatively simple and well-established.
Pulse oximetry has been used for over 40 years. The technique was first developed in 1972 by a team of Japanese engineers. They discovered that it was possible to calculate blood oxygen saturation by shining red and infrared light onto the skin, then measuring how much of the light was reflected.
The amount of red and infrared light reflected can be used to determine the amount of light absorbed by the skin. The amount of light which is absorbed changes, according to the how much oxygen is being carried by the haemoglobin (the protein in blood that carries oxygen), in the vessels just beneath the skin surface.
The researchers developed an algorithm to estimate how much oxygen was being carried, based on the ratio of red to infrared light which was reflected. The technique was first tested in a medical setting, with patients, in 1975, then commercialized in 1980.
The Apple Watch 6 uses the same principle, with some notable refinements. To better compensate for variations in skin tone, and to improve accuracy, the watch features four clusters of green, red, and infrared LEDs, along with four photodiodes, which measure light reflected from the skin.
Is the revolutionary claim justified?
While the ‘revolutionary’ claim is difficult to justify based on the fundamental method which is deployed. I wouldn’t be surprised if Apple has made some significant enhancements to the algorithms which are used to calculate oxygen saturation. Fitbit added a SpO2 feature more than two years ago, so Apple must have been working on something.
So what of the “breakthrough wellness and fitness capabilities” claims? Wellness describes the state of being in good health. Still, it’s often used by technology companies to describe a health-related feature, without triggering the risk and liability issues associated with making health claims.
A move towards being a health orientated device
Concerning health, when considered alongside the watch’s existing features, such as fall detection, it certainly seems like Apple is nudging the device towards being more like a clinical monitoring device. Given that the watch now offers pulse oximetry, movement and noise detection, all the pieces seem to be in place to introduce a Sleep Apnoea detection feature, in the future. This possibility is supported by the fact that automatic, periodic background measurements already occur when the user is inactive, including during sleep. You can read more about overnight pulse oximetry for detecting obstructive sleep apnea in a clinical case report.
New studies Apple is involved in
The idea that Apple wants to position the watch as a health device that can help patients to manage their conditions is supported by several studies they are involved in. These aim to explore how blood oxygen levels can be used in future health applications and include:
- Controlling asthma using physiological signals (University of California, Irvine, and Anthem).
- Managing heart failure by investigating metrics, including blood oxygen (University Health Network and the University of Toronto).
- Detecting the early onset of respiratory conditions, such as flu and COVID-19, by measuring heart rate and blood oxygen (Seattle Flu Study and the University of Washington School of Medicine).
Does measuring oxygen saturation matter to your average fitness enthusiast?
Concerning fitness, measuring blood oxygenation probably can’t offer your average fitness enthusiast much useful information. In athletes, changes in arterial blood oxygenation may explain decreases in performance, particularly at altitudes where this value is lowered. Measuring arterial blood oxygenation may also help to predict acute mountain sickness.
Later this year, a feature will be added allowing users to be notified about a drop in VO2 Max. However, I’m more excited about Apple’s move into the home fitness market, with the Fitness + service. I’m fascinated with data and measurement, but it’s unlikely that getting more information, no matter how accurate it is, is going to change the wellbeing and fitness of Apple Watch users. Most people would benefit more from finding new and inspiring ways to foster a more active lifestyle, and the Fitness+ may achieve just that aim.
