How to measure blood oxygen level with Apple Watch

rear sensor Apple Watch 6

Finally the Apple Watch can now measure the level of oxygen in blood. We had to wait until the series 6 released yesterday afternoon to have this function. Much had been said about whether previous versions of Apple's smartwatch could already perform such a measurement.

And more if we take into account that any finger heart rate monitor of 40 Euros that we find in Amazon or much cheaper in Aliexpress, is also an oximeter in addition to measuring your heart rate. The fact is that finally the new Apple Watch Series 6 incorporates a new rear sensor for this mission. Let's see how it works.

The main novelty of the Apple Watch Series 6 is undoubtedly the ability to measure the level of oxygen in the user's blood. A new feature that could have a real benefit and be able to react in time if you show altered O2 levels if you suffer from diseases such as heart failure, asthma or coronavirus.

How the Apple Watch measures oxygen levels

To make oxygen measurements possible, Apple has changed the arrangement of the sensors on the back of the Apple Watch in Series 6. Now, in addition to the green and infrared LEDs, there are Red LEDs additional and some new photodiodes.

The principle of oxygen measurement is the same or similar to that of pulse measurement: the four LED groups illuminate the underlying skin and vessels, and thus the photodiodes they record backward reflected light and can use algorithms to calculate the amount of oxygen that red blood cells are currently carrying in the body.

This calculation is based on the knowledge that how much more oxygen binds to red blood cells, redder blood appears. The protein responsible for oxygen binding, hemoglobin, contains iron-containing complexes that can bind to oxygen molecules. After bonding, the color changes from dark red to light red, this change can be picked up by the photo diodes of the Apple Watch.

This method has not been devised by Apple far from it. It has been many years since oximeters of hospitals use this system. It is the typical clamp that is placed on the tip of the finger to measure the pulsations, and at the same time the level of oxygen in the blood.

A required application additional on the Apple Watch for measurement. This application guides the user through the measurement and displays the measured data. This information is also added to the health app in the new blood oxygen tab.

Oxygen levels in the blood

oxygen

According to Apple, the optimal level shown should be between 99 and 95 percent.

According to Apple, the normal oxygen saturation in the blood should be 95 to 99 percent, but in some people this limit is slightly lower. Even during sleep, saturation can drop below the 95 percent limit.

Being able to tell how much oxygen is in the blood has important medical connotations, as it could help identify a heart failure, when the heart is unable to pump enough blood to reach the entire body, as in peripartum cardiomyopathy (PPCM). It may also be able to warn of an asthma attack, and could tell if you are experiencing breathing problems related to COVID-19, for example.

Necessary requirements

Obviously, you need a The Apple Watch Series 6, since it is the only Apple Watch capable of measuring oxygen in blood. Will have to be running Watch 7 and the paired iPhone must have installed iOS 14.

Apple has indicated that the oxygen measurement will only be available in some countries, but it has not yet confirmed which countries will have the app that has the ability to measure blood oxygen. When Apple released the Apple Watch Series 4 with the ability to take an ECG, such a feature was not available in many startup countries, due to bureaucratic medical issues in each country.

Like the ECG app, the oxygen app is only activated for users 18 over years. The user must also be 18 years or older to share Apple Watch data with a family member's iPhone.

How to measure blood oxygen with Apple Watch

Before you can take the first action you have to configure the application.

  1. Open the application "Salud" on the iPhone.
  2. Click on the tab Explore.
  3. Choose Breathing.
  4. Choose Oxygen saturation and activate it.
  5. To ensure that the application works reliably, Apple recommends taking the measurement while sitting.

While taking the measurement, you should remain still. The watch must be firmly attached to the wrist and not moved. The measurement takes fifteen seconds, after which it will present a percentage of the oxygen content in the blood.

How to make automatic measurements

The watch can measure the oxygen in the blood in a Automatic, even without having the application open. For the Apple Watch to measure while you sleep, you must activate the sleep plan in the Health app.

Automatic measurement results can be viewed in the app "Salud" in the Respiratory system area. Since red light could be a nuisance in the dark, the app allows you to disable such measurements. You can enable theater mode, for example.

Some measurements may not be exact

If the heartbeat is racing, (150 beats per minute or more), the oxygen level cannot be measured accurately. Another problem would be if there was a tattoo on the wrist at the point where the sensors measure. It could also be the cause of unreliable measurements. Some types and colors of tattoos can completely block the light from the sensors and measurement would not be possible.

If you have the tendency to have a body temperature lower than normal, the properties of blood flow in the skin change, which would also give wrong levels.


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