Blood pressure is commonly thought of as the most important of all vital signs. Serious problems can be caused by high blood pressure, including heart attack, stroke, or kidney disease. And concerningly, high blood pressure usually does not present with any symptoms that make its presence apparent. Without regular monitoring, it is unlikely that someone would even know that they have this condition. Further, accurate and continuous monitoring of blood pressure is fraught with problems — present solutions, like pressure cuffs, are large and cumbersome, making them very impractical for daily use in a variety of situations.
Lack of accurate monitoring outside of a clinical setting unfortunately leaves many people susceptible to serious diseases that result from a treatable condition. This state of affairs may be in for a change due to recent research conducted by a group at the University of Texas at Austin and Texas A&M University. They have designed an electronic tattoo that is capable of unobtrusively recording blood pressure measurements continuously, and it does so with a high degree of accuracy that rivals or exceeds the best options presently on the market. The virtually weightless tattoo is made from graphene, one of the strongest and thinnest of all materials.
Smartwatch aficionados may wonder what the excitement is all about, because their watch tracks their blood pressure all day, and it is hardly a burden to wear. That may be true, but because smartwatches unavoidably slip around on the wrist, they are incapable of consistently capturing accurate measurements. Further, due to the light-based measurement method that they employ, they also falter in capturing good measurements on users with darker skin tones or larger wrists. These devices have their place, but they are not medical-grade equipment.
The graphene-based sensors designed by the researchers are encased in a soft, stretchy material that is comfortable to wear for long periods. Once it is placed on the skin, it stays put, allowing for consistent, accurate readings to be captured. The sensors operate on the principle of bioimpedance, in which an electrical current is shot into the skin, after which the body's response is measured. This directly measures blood volume, which is correlated with changes in blood pressure.
And how exactly does blood pressure correspond with blood volume, as measured through bioimpedance? The answer to this question is elusive, so rather than put the time and effort into trying to understand these relationships, the team turned to machine learning for help. By training a model to recognize how captured bioimpedance measurements relate to known blood pressure measurements, they were able to create an algorithm that is capable of producing highly accurate blood pressure predictions based on sensor data acquired by the tattoo. An accuracy of 0.2 +/- 4.5 mm Hg for diastolic pressures, and 0.2 +/- 5.8 mm Hg for systolic pressures was achieved.
With typical, infrequent blood pressure readings giving information of limited utility, this new device has the potential to transform many aspects of healthcare. It may one day allow many serious conditions to be prevented from ever occurring through early treatments. There are some limitations to this new method, however. As it currently stands, the tattoo is only effective for about five hours of monitoring. While this is a big step forward, there is still some work yet to be done.