Nobody feels stylish wearing a blood pressure cuff on their arm all day, even if their health and possibly life depends on such continuous monitoring. One alternative may be a pair of Microsoft glasses that can unobtrusively monitor blood pressure as eyeglass wearers go about their daily routines.
The smart glasses developed by Microsoft Research’s Glabella Project use optical pulse sensors to detect the blood flowing through different artery locations in a person’s head. That measurement of pulse transit time—the time delay following each heartbeat as the pressure wave travels between two arterial sites—provides an indirect measure of blood pressure that can be collected without any effort or inconvenience to the wearer. The ease of use could encourage greater compliance from people suffering from health conditions such as hypertension who require continuous blood pressure monitoring outside a hospital setting.
“What inspired the code name of our research project was the general location of one of the sensors in each Glabella device, which is embedded in the nose pad of a regular pair of glasses,” says Christian Holz, a researcher at Microsoft Research in Redmond, Wash. “This allows the sensor to seamlessly blend in with a socially acceptable wearable device and yet continuously sense the wearer’s pulse at a key location.”
The Microsoft researchers filed a patent on the “head-mounted device for capturing pulse data” in June 2017, but the patent application was only published online last month. They also laid out the Glabella glasses design and the results from a pilot study in a white paper published in the September 2017 issue of the Proceedings of the ACM Journal of Interactive, Mobile, Wearable and Ubiquitous Technologies.
Such stealthy monitoring promised by the Glabella Project does not require the wearer to perform manual interventions such as remembering to strap a blood pressure cuff to their arm at certain times each day. It’s also more comfortable and less noticeable than wearing a semi-automated blood pressure cuff that periodically inflates itself. And it does not even require the wearers to perform certain gestures or movements, as is the case with smart watches that similarly aim to measure pulse transit time.
Current prototypes of the glasses are not exactly Warby Parker slim, but they seem comfortable enough for everyday use with a weight of just 45 grams compared with a typical 37 grams for off-the-shelf glasses. Holz and his Microsoft Research colleague, Edward Wang, created a custom design mainboard housed within the frame of regular glasses. A small coin battery keeps the device running all day when fully charged.
They also developed a custom design for the pulse sensors tuned to recognize the reflected signals from the arterial blood at specific locations on the wearer’s head. Current prototypes of the Glabella glasses have tested and compared the performance of two different sensor location combinations: nose pad to superficial temporal artery (in front of the ear) and nose pad to occipital artery (behind the ear). The former seems to deliver a more high-quality signal, but the latter behind the ear “has the potential to be completely invisible” in terms of the glasses form factor, Holz explains.
To give the glasses a test run, the researchers enlisted four relatively young Microsoft employees ranging in age from mid-20s to early 40s for a pilot study. Those four human guinea pigs went about their usual office routines and had conversations while the Glabella glasses recorded their blood pressure behavior. They also manually measured their blood pressure at specific times of day using a standard blood pressure cuff to provide a baseline “ground truth” that the wearable’s measurements could be checked against.
Though the test went well, don’t go looking for the Glabella glasses to appear on store shelves just yet. One challenge is that the Microsoft researchers still need to figure out the most practical approach to calibrating the wearable’s measurements for each individual wearer without requiring the constant blood pressure cuff checks. They plan to evaluate the Glabella glasses in a clinical setting against the baseline of invasive and highly accurate blood pressure measurements involving needles, a study that could involve patients at a university hospital.
The research team is also developing a next version of the glasses with a smaller frame, better power efficiency and improved signal detection. Ideally, they would like to shrink the device to the point where it could become a clip-on that works with anyone’s regular glasses.
Whether it’s Microsoft’s Glabella glasses or another wearable health device that breaks through, convenient and continuous blood pressure monitoring could better connect the dots between blood pressure and factors such as going on a walk or run during daily activities, eating certain foods and taking medical drugs. Such continuous data collection on a large scale could even someday lead to improved medical science understanding of various health conditions based on the blood pressure patterns collected throughout the day from hundreds or thousands of individuals.