Blood pressure measurement with app, smartwatch, fitness tracker, and more.

Measuring blood pressure without a cuff

fitness tracker with blood pressure measurement

More and more devices are coming onto the market that can measure blood pressure without the usual cuff. These devices come in the form of a watch or a band. Instead of having to put on a device and watch the cuff inflate, blood pressure can be determined almost effortlessly. The device is usually worn all day, providing constant measurement opportunities, which offers a perfect overview of one's blood pressure.

How does the measurement work?

The devices measure and analyze the pulse wave generated by the heart. The pulse wave transit time (PTT) is determined. The higher the blood pressure, the more tense the vessels are, and the faster the pulse wave travels. This can be imagined like a soccer ball that rolls more easily when it is well inflated. While this method cannot measure blood pressure directly, it can detect changes in blood pressure. Therefore, the devices always require reference measurements. This technology has been researched for many years. Alternatively, photoplethysmographic (PPG) signals are used; for example, the OptiBP app utilizes this approach.

Unlike traditional cuff-based measuring devices, it is irrelevant whether the measurement point is at heart level with these novel devices. To measure, one simply needs to remain still. The devices often also have a sensor that detects movement and indicates it as an error or discards the measurement.

Are the measurement results accurate?

One must fundamentally distinguish between two categories of these devices. There are very simple devices in this field, which are usually very inexpensive. These offer blood pressure measurement but are not certified as medical devices. The results are - well - completely useless. This is a fun feature that determines actual blood pressure as well as a dice roll.

However, there are also devices that are approved as medical devices. In this case, the measurement accuracy has been validated. Examples include Samsung's Galaxy Watch, the Aktiia band, or the OptiBP app.

Here, the device or app usually needs to be calibrated to the individual user. This means measuring with a standard cuff-based device while simultaneously using the device. Usually, two or three measurements are required. This calibration must be repeated regularly - typically monthly. In the meantime, measurements can be taken conveniently and at any time without a cuff.

How well does this work in practice?

Unfortunately, we must temper expectations. We have thoroughly tested both a Samsung Galaxy Watch, the Aktiia band, and the OptiBP app.

The good news: It really works! One can actually see realistic measurement values, and the normal fluctuations in daily blood pressure are clearly visible.

However, the measurements always revolve around the calibration values. In our comparison, we compared the Aktiia band with guideline-compliant home measurements over a week with data from a traditional measuring device. The deviation was 15 mmHg systolic and 4 mmHg diastolic. For the Galaxy Watch 3, we did not conduct such an extensive test series, but in direct comparison with the cuff device and the watch, the differences were sometimes significant. The OptiBP app showed deviations of up to 12 mmHg systolic and 15 mmHg diastolic; after recalibration, the diastolic deviation at least decreased significantly.

For the validation of devices with continuous measurements, the standard DIN EN ISO 81060-3 is provided. Since the devices are worn during everyday activities, they must allow for accurate measurements even during movement and must be able to monitor blood pressure stably and reliably over extended periods. However, Samsung and the manufacturer of Aktiia used the standard DIN EN ISO 81060-2 for validation.

Manufacturers like to advertise studies that are supposed to prove accuracy. One must examine these closely. For example, we have seen a study where test measurements were only conducted shortly after calibration. Unfortunately, this says little about the quality of the measurement results.

Result

If high values are measured during calibration, these will also appear in everyday use. If the calibration values are within the normal range, normal values are more likely to be measured in daily life. This is still too much guesswork, estimation, or rolling dice to be truly useful. Especially with high blood pressure, the values can fluctuate more significantly than the cuffless device's calibration would like to admit.

In practice, we prefer to forgo the Aktiia band because it is uncomfortable to wear and often needs to be removed and put back on due to lack of waterproofing. For this, one receives little helpful measurement results.

The Galaxy Watch is very useful as a smartwatch. However, due to the rather unreliable measurement results, we lost sight of regular measurements - the measurement function was hardly used anymore. When the watch then wanted to be calibrated every month, we preferred to turn off the function entirely rather than have to deal with it once a month for no reason.

The OptiBP app would be straightforward here because one would always have it on hand. However, the ongoing subscription costs of the app are still too high given that the values are still too unreliable.

Conclusion October 2024: Unfortunately, there is still no way around the cuff for high blood pressure patients.

Hybrid of blood pressure watch and smartwatch: Huawei Watch D

Huawei offers the Huawei Watch D, a true smartwatch that also provides blood pressure measurement with an integrated cuff. Since this is a measurement with a cuff - similar to a standard measuring device - what has been said here does not apply. For more information, see our article on blood pressure watches.

Blood pressure measurement with the camera

There are also providers that determine some vital parameters with a 60-second video of the face. This includes blood pressure. This is very innovative, so we looked at the solution from Binah.ai. However, in our test, the measured blood pressure was about 15 mmHg off from the value from the measuring device. Unfortunately, that is the state as of late 2023. Perhaps there will be better results in the future.

Sources:

By Horst Klier. This article is medically reviewed. Last updated by Horst Klier (10/2024).
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