Gadgets

How Do Smart Watches Measure Blood Pressure

Smart Watch With Stethoscope

According to the Center For Disease Control and Prevention, 116 million Americans live with hypertension (high blood pressure). Further research published by the American Medical Group Foundation estimates that 20% of those living with hypertension don’t know they have it.

Regularly checking blood pressure is key to detecting hypertension early and seeking medical help. Your family physician can check your blood pressure with the traditional cuff reader connected to a monitor. Moreover, you can buy this equipment for home use or pass through the drug store/pharmacy to have a specialist take your blood pressure readings.

However, all these instances are not good enough to measure your blood pressure twice daily as recommended by medical specialists. Besides, the cuffs are uncomfortable for some people, especially those with bigger arms, and may record errors to elevated blood pressure caused by hospital anxiety.

It’s out of this need that health tech companies have developed wearables to help users measure their blood pressure on the go. The smartwatch is one of these wearables whose contribution to monitoring blood pressure is astounding.

But how do smartwatches measure blood pressure?

Quick Answer

Smartwatches use two technologies to measure blood pressure: electrocardiography(ECG) and photoplethysmography(PPG). 

For smartwatches using the ECG technology, a sensor at the back of the watch records the timing and the strength of the electrical signals that make a heartbeat. 

On the other hand, PPG technology uses a light source and a photodetector to quantify volumetric deviation in the blood flowing through the arteries.

This article explores how smartwatches measure blood pressure.

How Smartwatches Measure Blood Pressure

To understand how smartwatches measure blood pressure, we need to know how blood circulates in the body. A heartbeat occurs when the heart pumps blood to the body parts, and the blood returns to the heart after nourishing the body with oxygen.

The heart pumps oxygen-rich blood to the body at a higher pressure than when the blood flows back to the heart. The former is called systolic blood pressure and should be around 120mmHg in a healthy person. 

As the deoxygenated blood flows back to the heart from the body parts, the pressure is known as diastolic blood pressure, and the optimum measurement is 80mmHg. 

Millimeters of Mercury(mmHg) is the measurement unit of blood pressure. 

Note that high blood pressure is expressed as systolic measurement/diastolic measurement. For instance, if your systolic measurement is 120mmHg and your diastolic measurement 77mmHg, your blood pressure reading is 120/77mmHg.

Now moving on to how smartwatches measure blood pressure, these hand-worn smart gadgets use two technologies to monitor the heart rate and, consequently, the blood pressure.

Method #1: Using Electrocardiography (ECG) Technology

Electrocardiography technology is a concept that uses a sensor that monitors the timing and the strength of electrical signals that make a heartbeat. The sensor measures the time taken by a single pulse to travel from the heart to the wrist. This phenomenon is also referred to as pulse transit time (PTT).

A faster PTT is recorded as high blood pressure, while a slow PTT indicates low blood pressure. You’re advised to sit still and elevate the watch-wearing hand to the heart level when using this method. Additionally, wear a cuff on the upper arm to stop blood circulation for a while before measuring the blood pressure.

Furthermore, avoid caffeine and alcohol thirty minutes before measuring the blood pressure because such substances elevate heart rate leading to incorrect readings.

 An example of a smartwatch using ECG technology is the Samsung Galaxy Watch 4, which monitors your blood pressure alongside a Health Monitor App.

Method #2: Using Photoplethysmography (PPG) Technology

Photoplethysmography comprises three words: photo, “plethysmo”, and graph. Photo means light, “plethysmo” means variation in volume in a body part, and the graph is a diagram showing the relationship between two variables.

In other words, photoplethysmography uses a light sensor to determine the volume flowing in the arteries. Changes in volume can cause fluctuations in the heart rate, thereby recording varying blood pressures. 

This method has a limitation in that you need to calibrate the smartwatch using a standard blood pressure monitor initially and after every four weeks to maintain accurate readings. The Apple Watch uses PPG and ECG sensors to monitor blood pressure, alongside third-party apps such as Qardio.

Conclusion

One of the many ways smartwatches have proved helpful is by monitoring blood pressure. These smart gadgets measure your blood pressure using two technologies, namely electrocardiography and photoplethysmography. 

The former involves measuring the timing and strength of electrical signals that make up a heartbeat. At the same time, the latter uses high-efficiency light sensors to detect volume changes in the blood, denoting changes in blood pressure.

Frequently Asked Questions

Is Smartwatches’ blood pressure accurate?

Although blood pressure measured using a smartwatch doesn’t differ considerably from that taken with a standard blood pressure monitor, it’s inaccurate. Elevate your arm to the level of your heart and keep it still to get more accurate results from your smartwatch.

Does the Samsung Galaxy Watch 4 monitor blood pressure?

Yes. The Samsung Galaxy Watch 4 can measure your blood pressure. You, however, need to calibrate it with a standard blood pressure monitor initially and use it alongside the Health Monitor App.

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