A team of researchers at Michigan State University have developed a smartphone-based blood pressure monitoring system that could be an alternative to the traditional blood pressure cuffs. 

Researchers created a 3D-printed phone case with a sensor, data acquisition and transmission circuitry, and a power supply that links onto the back of a smartphone. With the new technology instead of putting a cuff around a patients, the user presses their finger against the a sensor then the external pressure of the underlying artery is steadily increased while the phone measures the applied pressure, which results in variable—amplitude blood volume oscillations, according to a study published by Science Translational Medicine. 

Then the data from the sensor is transmitted to an app on the smartphone via blue tooth, which gives the user feedback to ensure they are applying the right amount for pressure. The app also computes the systolic and diastolic pressure. 

"We targeted a different artery, the transverse palmer arch artery at the fingertip, to give us better control of the measurement," Anand Chandrasekhar, MSU electrical and computer engineering doctoral student and the lead author, said in a statement. "We were excited when we validated this location. Being able to use your fingertip makes our approach much easier and more accessible."

Researchers tested the smartphone system against a finger cuff and found that the two systems had a comparable precision of errors rate, which could mean that cuff-less calibration-free monitoring of systolic and diastolic blood pressure may be feasible via smartphone in the future, wrote the authors of the study. 

Researchers reported the device yielded bias and precision errors of 3.3 and 8.8 mmHg for systolic blood pressure and -5.6 and 7.7 mmHg for diastolic blood pressure over a 40 to 50 mmHg range of blood pressure. 

The researchers also looked at the usability of the device and found that 90 percent of users were able to learn the finger action that was required by the device after one or two practice trials. 

"A key point was to see if users could properly apply the finger pressure over time, which lasts as long as an arm-cuff measurement," Ramakrishna Mukkamala, MSU electrical and computer engineering professor and senior author, said in a statement. "We were pleased to see that 90 percent of the people trying it were able to do it easily after just one or two practice tries."

There is a lot of interest right now in blood pressure monitoring on the phone: Samsung recently added a feature to its health app that uses the Galaxy S9’s optical sensor to directly measure blood pressure, allowing the smartphone to take readings without any external hardware. However another take on the technology, Aura Labs' Instant Blood Pressure app, was fined by the FTC for making inaccurate claims in 2016.