Finally, a comprehensive list of all wearables that track your oxygen saturation (SpO2)

What is oxygen saturation?

Oxygen saturation (SpO2) is a measurement of the amount of oxygen travelling through your body with your red blood cells. Normal oxygen saturation levels are usually between 95% to 100% for most healthy adults. Any level below this can be concerning and in need of immediate medical attention, because it means that your organs, tissues, and cells aren't getting the oxygen that they need to function properly.

Oxygen saturation levels are impacted by many different conditions including asthma, anaemia and COPD (chronic obstructive pulmonary disease, an inflammatory lung disease).

Other situations that may cause low blood oxygen levels include pus, blood, or water filling the air sacs in the lungs, blood clots in the lung, scarring or loss of lung tissue, sudden exercise (if you have heart or lung disease), not breathing (whilst being profoundly intoxicated), or transitioning from low altitude to high altitude (concentration of oxygen in the air falls as you reach higher altitudes).

What is the science behind it?

To understand how our blood is saturated with oxygen, we must start with the alveoli or air sacs. There are millions of these microscopic air sacs in the lungs which serve an important function: to exchange oxygen and carbon dioxide molecules to and from the bloodstream. As oxygen molecules pass through the alveoli, they bind to haemoglobin which then circulates throughout the body spreading the oxygen. The level of oxygen in your blood depends on a few key factors: how much oxygen you breathe in, how well your alveoli perform, the concentration of haemoglobin in the red blood cells and how well your haemoglobin attracts oxygen.

How do wearables track it?

In wearable devices, Pulse OX is used to determine an individual's oxygen saturation. It is taken by measuring the peripheral oxygen saturation using a form of PPG in which the wearables reflect infrared and red light onto the skin. As the light is absorbed into the skin, it interacts with the oxygenated and deoxygenated haemoglobin. The light is then reflected back to the smartwatch and the difference between the light emitted and the light reflected back is used to determine the blood oxygen level.

Why is it important?

One of the most notable recent events that brought SpO2 to global attention was the global pandemic. COVID-19 has shown us how our lung health and oxygen levels are interconnected and various wearables have been useful in confirming this relationship. In fact, some people with COVID-19 claimed to observe lower levels of SpO2, tracked by their wearable devices, whilst suffering from coronavirus.

Pulse OX monitors are used by many endurance athletes today, especially those who wish to accomplish high altitude feats. It becomes very important, as climbers reach higher altitudes, to ensure that oxygen levels remain above dangerous levels. If not properly monitored, Acute Mountain Sickness from a lack of oxygen can progress into more severe manifestations including high-altitude pulmonary edema (HAPE) and even high-altitude cerebral edema (HACE). If a climber experiences HACE, blood actually flows out from the brain and inner skull pressure rises causing confusion, blurring, loss of vision, and eventually, death. The Death Zone, generally considered to be higher than 8,000 metres above sea level, is the nickname among climbers where there is not enough oxygen in the air to be able to adapt to. In this zone, climbers have to be extremely cautious and ensure their blood oxygen levels don't fall too significantly below safe levels.

Overall, blood oxygen levels are becoming increasingly important to track and can help to inform us when making decisions around our health, and our performance in extreme altitude settings.

Through the Terra API, we provide connections to a range of different devices so that your users can track their pulse OX levels.

Below is a list of the wearables that track blood oxygen levels today:

• Garmin Fenix 7, Fenix 6X, Fenix 5X, Venu, Lily, Approach, Vivoactive 4/4S, Forerunner 245, Forerunner 645, Forerunner 945, Vivosmart 4
• Oura ring Gen 3 (tracking capabilities coming soon)
• Apple watch series 7, watch series 6
• Fitbit Versa series, Charge 5, Sense
• Withings ScanWatch
• Huawei watch GT3, GT2e, GT2 Pro
• Whoop 4.0
• Xiaomi Mi Band 5
• Suunto 9 range

As always, please let me know if I'm missing any!