Engineers at the University of California San Diego are building a small, non-invasive, wearable patch that can replace a slew of medical monitors. The soft, stretchy, polymer sheet, when worn on the neck, is able to continuously monitor blood pressure and heart rate, as well as levels of glucose, lactate, alcohol, and caffeine.
Designed for both inpatient and remote health monitoring, the patch is particularly well suited to monitoring high blood pressure, diabetes, and sepsis — with the later condition being characterized by a sudden drop in blood pressure and corresponding rise in lactate levels. Traditionally, capturing this array of vital sign and chemical level measurements would require the insertion of an arterial catheter and tethers to a number of standalone monitors.
In its current form, the patch is able to measure three parameters simultaneously. Blood pressure and glucose can be measured alongside either lactate, alcohol or caffeine. Blood pressure is acquired by detecting the echo of an ultrasonic wave bounced off of an artery and translating that signal into a blood pressure measurement. The chemical sensors are screen printed onto the patch. The sensor that detects lactate, caffeine and alcohol releases a drug that induces sweating, and the sweat is analyzed for chemical content. The glucose sensor generates a small electrical current that causes the release of interstitial fluid, which can then be assessed for glucose content.
Shrinking a table full of monitors down to the size of a small skin patch was not without its challenges. Each of the sensors requires a hydrogel between it and the skin to make good contact. However, when the sensors are in such close proximity to one another, the different gels can come into contact and cause interference that gives false readings. The engineers got around this problem by using a solid ultrasound gel, which they found to work as well as the liquid version, but cannot leak into the other gels.
An experiment was conducted in which volunteers wore the patch while performing various activities. These activities included combinations of riding a stationary bicycle, consuming alcohol or caffeine, and eating a high-sugar meal. Measurements from the patch were compared with measurements captured by commercial monitoring devices, and the results were found to match closely.
The patch is currently hardwired to a power source as well as a benchtop device that displays the detected measurements. The team is now working to make the patch wireless for more practical real world use.