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Apple continues to pursue adding accurate blood pressure measurement to the Apple Watch, and now that research includes potentially utilizing a stretchable Watch band.
Apple Watch has always been able to measure heart rates in beats per minute, but it's not been able to include sensors that are sensitive enough to accurately record blood pressure. There are third-party blood pressure apps for Apple Watch, but all of them require an accessory such as a cuff that wraps around the wearer's wrist.
Previously, Apple has researched how to provide accurate and sensitive enough measurements without using a cuff.Now, however, a newly-revealed patent application shows that the company is at least considering using a Watch strap as a blood pressure cuff.
"Stretchable Blood Pressure Cuff," is concerned with how such a cuff could be worn continually, so as to provide a record of blood pressure over time.
"A user may monitor one or more of their physiological parameters by attaching a monitoring device such as a blood pressure monitor to one of their limbs," says the patent application. "The blood pressure monitor may include an inextensible cuff that secures an inflatable bladder against a limb of the user."
This inflatable bladder, Apple explains, could be expanded, "thereby compressing one or more blood vessels in the limb and restricting and/or stopping blood flow through the vessels."
Consequently, the pressures needed to "restrict and/or stop blood flow through the vessels in the limb," can be measured. This means that data could be "used to determine one or more physiological parameters of a user such as blood pressure of the user."
Inflating and deflating the wrist band isn't likely to be something an Apple Watch wearer would appreciate happening twice a minute. But if the cuff usually acted as a regular band, having this facility would mean being able to take measurements without the inconvenience of swapping cuffs or devices.
"A physiological monitoring device such as blood pressure cuff is typically worn during the measurement, and is removed promptly thereafter," says Apple. "In some cases, it might be desirable to wear the monitoring device for longer periods of time such that physiological measurements can be performed at periodically or continuously."
The cuff would work by having "a bladder assembly configured to retain a fluid within an internal chamber."Left: detail from the patent. Right: Apple Watch Series 7 with a Leather Link band
"The bladder assembly can also include a fluid passage that is in fluid communication with the first cell and the second cell and coupled with a reservoir," continues Apple. "The bladder assembly can exchange the fluid with the reservoir and be configured to increase in length when a volume of the fluid in the internal chamber decreases, and decrease in length when the volume of the fluid in the internal chamber increases."
Example drawings in the patent application show one such cuff that resembles the current Leather Link variety of Apple Watch bands.
The patent application is credited to four inventors. That includes the prolific Zijing Zeng, whose many previous related patents or applications includes one for measuring blood pressure without a cuff.