Tech for your connected self

Sensors explored: Pulse oximeter

Taking a closer look at the tech inside your wearables

Wearables just keep getting smarter. As more and more tech gets crammed into those smartwatches, sports watches and fitness trackers, it's easy to lose track of exactly what that new tech does, and what the devices can actually measure that will be of any use to you.

One thing we are starting to see crop up in more devices is the pulse oximeter. Garmin's put one into one of its sports watches for the first time, Fitbit's done it too and a few years ago Withings packed one into a fitness tracker.

Read this: Stretchable sensors are the next big thing for wearables

So why is putting a pulse oximeter inside of a wearable a big deal? We explore what it is, how it works and what it's going to bring to the wearable party.

What is a pulse oximeter?

Sensors explored: Pulse oximeter

When we talk about pulse oximeters or pulse oximetry, we are delving into the realm of medical tech and talking about a device that's able to measure oxygen levels or oxygen saturation in the blood, plus your heart rate. They can also be used to measure pulse rate too.

That tech usually takes form of a clip-on device that you place on your finger, a toe or even on your ear lobe. It uses red and infrared light sensors to detect your oxygen levels, sensing changes in those levels. It measures the volume of oxygen based on the way the light passes through your finger and delivers the data to the device's screen, which will tell you the percentage of oxygen in your blood.

An oxygen saturation percentage greater than 95% is considered to be a normal reading. If you see a score of 92% or less, then it could be time to further investigate and find out whether it's related to an as yet undetected health issue.

Why you might want to closely monitor oxygen levels

So you know the basics of how the tech works, but why would you want to use a pulse oximeter in the first place – and why would the data it can provide be useful? John Hopkins Medicine explains how measuring oxygen levels through pulse oximetry can offer insights into a range of health related issues.

It can be used to check whether someone needs assistance with their breathing via a ventilator, measure a person's ability to handle intensive physical activities and it can also check whether breathing stops during sleep. This is particularly relevant to sleep apnea, a disorder which if left untreated or undetected could lead to an increase in the risk of high blood pressure, obesity and can even cause a heart attack. It can also be a valuable piece of health data for people suffering from a range of conditions including asthma, pneumonia, heart failure and lung cancer.

The origins of the pulse oximeter

Sensors explored: Pulse oximeter

The first oxygen saturation meter is said to be from as far back as the 1930s, when the exploration of light transmission through skin and the information it could provide really began. It wasn't until the 1960s and 70s when we began to see the pulse oximeter devices shape into the ones that are now used in hospitals, and which can be purchased to carry out those measurements from your home. Hewlett Packard was the first company to make an ear oximeter, which was largely used inside of clinical sleep labs due to its hulking size.

But it was Japanese bioengineer Takuo Aoyagi, in the early 1970s, who first developed a noninvasive way of using the light transmitted through the ear and went on to develop a pulse oximeter. From then up until today, the size of the tech has become smaller and – crucially – cheaper to build, so more people were able to get their hands on it.

Pulse oximeter and wearables you can buy right now

Pulse oximeters are starting to find their way into some big name wearables and that data is being used in very different ways. Arguably it started with the Withings Pulse Ox fitness tracker, which measured blood oxygen levels when you placed your finger on the sensor on the back of the device. But things have changed since then, and now the process of taking those measurements happen much more easily from the wrist.

Garmin's new Fenix 5X Plus is the company's biggest outdoor sports watch yet, and it also introduces something it's calling Pulse Ox Acclimation. This essentially brings a wrist-based pulse oximeter to the 5X Plus to measure oxygen saturation. It uses the data alongside elevation data to analyse how well your body is acclimating to high altitudes.

This is particularly useful for anyone that's into hiking, alpine sports and going on big expeditions. With elevation data you can view how oximeter readings are changing relative to your elevation.

Sensors explored: Pulse oximeter

We've also mentioned Fitbit's interest in measuring oxygen saturation, but unlike Garmin, it's thinking of the potential for using that data in serious health tracking.

Both its Ionic and Versa smartwatches include a light-based SpO2 sensor, which is a pulse oximeter that measures blood oxygen levels. We know that Fitbit wants to tackle sleep apnea in a big way, and the ability to take oxygen measurements from your blood can offer valuable insights relative to exploring a sleep disorder that affects around 18 million Americans. Right now though, that sensor remains untapped and will do until Fitbit feels it's ready to make use of it.

Wearables that could get in on the pulse oximeter action

Sensors explored: Pulse oximeter

Now that the likes of Fitbit and Garmin have embraced pulse oximeter technology, it seems like it's only a matter of time before others join in. There was of course that iFixit teardown of the Apple Watch that claimed to discover an untapped pulse oximeter. Apple, though, didn't claim it could measure blood oxygen levels from its smartwatch.

Despite seemingly putting a nail in the head of its wearables business outside of VR and AR, Microsoft filed patents in 2017 that hint towards a more health-focused device device that looks a lot like a Microsoft Band. It would apparently use a built-in pulse oximeter to measure radial pulse pressure or aortic pulse wave velocity, which is said to correlate with blood pressure. Don't be surprised if Samsung and others are looking at the space too.

Just like measuring heart rate and other biometric data, there will be concerns about the accuracy of this data, but it's clearly a strong sign that both consumer and clinical-grade wearables are starting to surface, breaking away from the usual clip-on style devices to show that there is a growing belief the tech can now work well enough from the wrist.


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