How does the Apple Watch Series 6 measure the oxygen level in blood?

In Apple Watch Series 6, the optical heart sensor has been redesigned to add blood oxygen measurement capabilities. Blood oxygen readings can be a useful indicator of wellness especially during Corona Pandemic.

How does the blood oxygen sensor work?

The blood oxygen sensor is built into the back of the Apple Watch. It uses four clusters of red, green and infrared LED lights and four photo-diodes, devices that convert light into an electrical current. The lights shine onto the blood vessels in your wrist and the photo-diodes measure how much light bounces back.

The technology actually is not new. Most probably, you are familiar with pulse oximeters, which measures the oxygen saturation levels of blood. The device is very common in intensive care units of hospitals and was never much noticed by people. Oximeters is probably seen on a fingertip, where a bright light passes all the way through the finger. Human blood will absorb certain wavelengths of light more than others depending on its color. As you know, the oxygen content of blood varies with color. If blood has low oxygen level, blood is a darker red. Parallelly, if blood blood has a higher concentration of oxygen, blood is a brighter red. Hence a pulse oximeter essentially is trying to measure the color of your blood

The Apple Watch Series 6 works on the same principle but it does not pass light all the way through your wrist. The Watch has a bright light; actually more than one light. The device utilize multiple lights to increase the chance of a good measurement that penetrates the skin and reflects off the blood circulating through your blood vessels. Then, with sensors measure reflected light levels to determine the color of the circulating blood.

Why is measuring the oxygen level important?

A person’s blood oxygen level is an indicator of how well the body distributes oxygen from the lungs to the cells. A normal blood oxygen level varies between 75 and 100 mm Hg. A blood oxygen level below 60 mm Hg is considered low and may require oxygen supplementation, depending on a doctor’s decision and the individual case.

Low blood oxygen levels, or hypoxemia, have been linked to Covid-19 because the disease affects your ability to get enough oxygen. As blood oxygen variation is an important indicator in the diagnosis of the disease. Doctors uses SpO2 levels to determine the severity of COVID-19 cases and treat those patients accordingly.

If you like to read how Oximeters work in detail, check here

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