The latest patent in Fitbit’s push for wearable blood pressure tech

Fitbit’s patent portfolio in the blood pressure monitoring game just got a little thicker. With the ink barely dry on their latest filing—published on September 21, 2023, and stamped with the snazzy code US 2023/0293028 A1—they’re diving headlong into the Pulse Transit Time (PTT) waters. It’s all part of Fitbit’s master plan to turn your wrist into the ultimate health dashboard.

Blood pressure monitoring is still a developing feature in the wearable tech industry. The majority of mainstream wearables have yet to incorporate this functionality, making it a field ripe for innovation. And the handful of solutions that are out there, mostly come with limitations. This includes the lack of continuous monitoring and cumbersome calibration processes.

Fitbit’s previous blood pressure patents

Before discussing the latest patent, it’s essential to consider Fitbit’s prior work in this area. In December 2021, Fitbit filed a patent focusing on estimating arterial stiffness by measuring pulse wave velocity (PWV) from the wrist. Experts considered this technique promising for continuous, cuffless blood pressure measurements. The title of that patent is “Photoplethysmography-based Pulse Wave Analysis Using a Wearable Device.”

In July 2023, Fitbit filed yet another patent, this time for a finger-based blood pressure monitor. The filing describes a device designed to overcome the limitations of traditional oscillometric blood pressure measurement (OBPM) systems by being less cumbersome and more accurate. The device features a miniaturized and inflatable bladder, which fits inside a hole specifically designed to accommodate a human finger. This design offers a more comfortable and precise measurement process.

The latest patent: PTT-Based blood pressure monitoring

The latest patent discusses Pulse Transit Time (PTT) as a method for continuous, unobtrusive blood pressure measurement. The paperwork goes into lots of detail on the issue of calibration. This has been a significant challenge in the adoption of PTT technology. The patent mentions the use of maneuvers such as the Valsalva or cold pressor test to obtain reliable calibration data.

The patent also outlines other calibration techniques, such as incorporating temperature sensors and altimeters to improve the model’s accuracy. Along with the use of machine learning models and neural networks as potential calibration methods. Such an approach could dynamically adapt to individual variations in blood pressure, making the system more robust and reliable over time. By leveraging machine learning, the patent hints at the possibility of a self-improving system that becomes more accurate with each measurement.

In addition to these calibration techniques, the patent also mentions user-initiated calibration. This would add an extra layer of customization to the process.

Difference between PTT and PWV

When comparing Fitbit’s previous patents with the latest one, there’s a clear trend towards addressing the challenges of blood pressure monitoring. The new patent offers more comprehensive solutions to the calibration issue, which has been a significant hurdle in the technology’s adoption.

PTT and PWV, which was the focus of the 2021 patent, are related but distinct concepts used in cardiovascular monitoring. PTT is the time it takes for a pulse wave to travel between two specific points in the arterial system, often from the heart to a peripheral site like the finger or toe. It is usually measured in milliseconds.

On the other hand, PWV is a measure of how fast the pulse wave travels through the arterial system. It is calculated by dividing the distance between the two points by the PTT and is typically expressed in meters per second.

In essence, PTT gives you the time duration for the pulse wave to travel a certain distance, while PWV tells you the speed of that pulse wave. Both are used for estimating blood pressure, but they offer different perspectives on arterial health.

Comparative insights

Given Fitbit’s series of patents on this topic, it’s evident that the company is working diligently to integrate blood pressure monitoring in their devices. While the technology is still in its infancy, these patents indicate a move towards more user-friendly and reliable blood pressure monitoring solutions in wearables.

Essential reading: Best fitness trackers and health gadgets

Shifting our focus back to the immediate future and Fitbit is dropping not-so-subtle hints about a grand reveal on September 28th. All signs point to the curtain rising on the Fitbit Charge 6.

But don’t hold your breath for blood pressure monitoring to make its debut on this device. The smart money says we’ll see our wrists doubling as sphygmomanometers more commonly in 2024.

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