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What Is Photoplethysmography And What Is It For?

We might need to thoroughly review the activity or the specific state of our heart and other organs at some point in life. That might be the time to do a photoplethysmography.

Elements such as the variation in blood volume resulting from cardiac activity can only be measured with practices such as photoplethysmography.

We invite you to learn much more about this interesting and useful procedure and how its development has led to the fact that today, most sports heart rate monitors marketed on the market no longer have a heart rate band but instead measure our pulsations directly from the wrist.


With photoplethysmography, the volume of a body can be known, establishing the amount of light it reflects. Furthermore, this method has the advantage of being a non-invasive measurement. That is, those measurements do not penetrate the patient’s skin.

Specialists widely use this optical technique for peripheral heart rate monitoring. Likewise, in the last two decades, the use of this procedure for the study of the vasoconstrictor response has become a widely used diagnostic method.


Photoplethysmography (also known as PPG) can provide the value of the heart rate by recording and analyzing a signal of optical origin. This signal is obtained in a vascular conduit and is expressed by the change in blood volume caused by the heart’s pumping. This procedure is used to monitor the heart rate through the analysis of light signals of specific wavelengths.


If you have a heart rate monitor equipped with an optical sensor under the box, you will have seen that it emits a flashing green light when you start it. Now you will understand its function.

The process works like this:

Green LEDs project their light onto the skin and reach the blood circulating in our veins and arteries.
The green light bounces off the blood in the veins.
Finally, the light reflected in the bounce is captured by a photodiode also located under the watch case.
The more blood in the blood vessels, the more light will be reflected, and vice versa. As the amount of blood that circulates, and therefore the amount of reflected light, oscillates depending on our heart’s beat, it is possible to know our heart rate with this procedure.

All the generation of new heart rate monitors equipped with this optical sensor is an excellent tool to know the heart rate based on photoplethysmography.

What is photoplethysmography for?

Although the first optical sensors that appeared on the market were not entirely accurate, the continuous advances in this technology have led to the heart rate monitor models currently on the market being equipped with advanced optical sensors with a high degree of precision.

Photoplethysmography through an App

The procedure for photoplethysmographic readings was performed using a heart rate monitoring application installed on the smartphone, Instant Heart Rate. The software uses the smartphone’s camera lens and light to reflect light on an individual’s finger. It results in variations in color and brightness, which are then extracted from the camera lens and interpreted as variations in the pulse, reflected as both a value numerical (for example, heart rate) and as a photoplethysmographic tracking on the phone screen.