Smartwatches measure blood oxygen saturation (SpO2) by shining light through your skin and analyzing how much light is absorbed.
Here's a more detailed breakdown:
The Science Behind SpO2 Measurement
Smartwatches utilize a technique called photoplethysmography (PPG) to estimate blood oxygen levels. This involves using light to detect changes in blood volume in the wrist.
How the Smartwatch Works
-
Light Emission: The smartwatch has LEDs (usually green, red, and infrared) on its back that shine light onto the skin of your wrist. These different wavelengths of light are absorbed differently by oxygenated and deoxygenated blood.
-
Light Detection: Photodiodes, which are devices that convert light into electrical current, are also present on the back of the watch. These photodiodes measure the amount of light reflected back to the watch.
-
Data Analysis: The smartwatch's processor analyzes the amount of green, red and infrared light absorbed by your blood. Oxygenated hemoglobin absorbs more infrared light and allows more red light to pass through. Deoxygenated hemoglobin absorbs more red light and allows more infrared light to pass through. By calculating the ratio of red to infrared light absorption, the smartwatch estimates the percentage of oxygenated hemoglobin in your blood (SpO2).
Factors Affecting Accuracy
Several factors can influence the accuracy of SpO2 readings on a smartwatch:
- Skin pigmentation: Darker skin pigmentation can affect light absorption and reflection.
- Movement: Movement during measurement can distort the readings.
- Wrist placement: The watch needs to be snug and properly positioned on the wrist.
- Ambient light: Strong ambient light can interfere with the sensors.
- Skin temperature: Cold skin can restrict blood flow and impact readings.
- Medical Conditions: Certain medical conditions may influence blood flow and accuracy.
Limitations to Consider
It's important to remember that smartwatches are not medical devices. While they can provide an estimate of your SpO2 levels, they should not be used for diagnosing or monitoring medical conditions. If you have concerns about your blood oxygen levels, consult with a healthcare professional.
