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It can be very beneficial to your health to know that your blood pressure is within normal ranges so that you can get the necessary medical attention if you develop hypertension. Smartwatches come into play here as a key tool for providing you with blood pressure readings at any time. However, things are not as they seem.

Smartwatches use two different methods to track heart rate and, presumably, blood pressure.

Electrocardiography is a technology that monitors the timing and strength of electrical signals that create a heartbeat with the help of a sensor. In smartwatches, the sensor measures the time it takes a single pulse to travel from the heart to the wrist. This is also known as pulse time (PTT).
Smartwatches like Samsung and Fitbit use this technology, using a measure called pulse transit time, which is the time between the contraction of the heart and the time the pulse reaches a certain body part, such as the wrist.
Fitbit vice president of research Eric Friedman says it measures the pulse at a time similar to pulse transit time, but at a slightly different time than Samsung does.

Photoplethysmography is a diagram that gives information about the change in the volume of blood flowing in an area of the body close to the skin and shows the graph and the relationship between the two variables.
Photoplethysmography uses high-efficiency light sensors to show changes in blood pressure by detecting volume changes in blood flowing through arteries. Changes in volume can cause fluctuations in heart rate, resulting in varying blood pressure readings.
This method requires calibrating the smartwatch initially and every four weeks with a standard blood pressure monitor to ensure the accuracy of values.

Why is it difficult to measure blood pressure with a smartwatch?
Although the current sensor in smartwatches is good enough to detect skin temperature, heart rate, and oxygen levels in the blood, it cannot show the same success in blood pressure measurements.
To measure blood pressure, doctors or other healthcare professionals will use a Blood Pressure monitor that temporarily blocks blood flow in the arm, and then measure at what pressure the blood will begin to flow back. The problem with most smartwatches is that they can’t compress and block blood flow.
Entrepreneurs continue their research to measure blood pressure accurately with smartwatches and to ensure that the measurements are at a level that can be used in medicine. Leveraging machine learning-based technologies, some companies and researchers have demonstrated that photoplethysmography (PPG) sensors can provide highly accurate blood pressure measurements as long as the analyzes are done in one go and not used for Blood Pressure.
For decades, the gold standard of blood pressure measurement was based on blocking blood flow, and optical sensors could be great for detecting heart rate, but they’re still in their infancy for monitoring blood pressure.

Should we rely on smartwatches to measure blood pressure?
Experts are still unclear about how reliable the smartwatch-measured blood pressure can be. They note that accurately measuring blood pressure is both more important and more difficult than tracking heart rate and rhythm.

How much should we rely on smartwatches to measure blood pressure? The answer to this question is not yet clear. Accurately measuring blood pressure or any health parameter often requires professional equipment.
Cuffed standard blood pressure monitors and digital blood pressure monitors closely monitor blood movement. These monitors are also recommended by doctors for their fast, reliable, and accurate data. Using a smartwatch to monitor blood pressure levels is still in development.

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