Video System Captures Vital Signs From Face
The technique isn’t new, but engineering researchers in Rice University’s Scalable Health Initiative are making it work under conditions that had stumped earlier systems.
The new version, DistancePPG, can measure a patient’s pulse and breathing just by analyzing the changes in skin color over time. Where other camera-based systems have been challenged by low-light conditions, dark skin tones, and movement, DistancePPG relies on algorithms that correct for those variables.
The team, graduate student Mayank Kumar and professors Ashok Veeraraghavan and Ashutosh Sabharwal, created the system that will let doctors diagnose patients from a distance with special attention paid to those in low-resource settings.
3 Big Challenges
Kumar and his colleagues were aware of an emerging technique that used a video camera to detect nearly imperceptible changes in a person’s skin color due to changes in blood volume underneath the skin. Pulse and breathing rates can be determined from these small changes.
That worked just fine for monitoring white people in bright rooms, he says. But there were three challenges. The first was the technique’s difficulty in detecting color change in darker skin tones. Second, the light was not always bright enough. The third and perhaps hardest problem was that patients sometimes move.
The team solved these challenges by adding a method to average skin-color change signals from different areas of the face and an algorithm to track a subject’s nose, eyes, mouth, and whole face.
“Our key finding was that the strength of the skin-color change signal is different in different regions of the face, so we developed a weighted-averaging algorithm,” Kumar says. “It improved the accuracy of derived vital signs, rapidly expanding the scope, viability, reach, and utility of camera-based vital-sign monitoring.”
By incorporating tracking to compensate for movement—even a smile—DistancePPG perceived a pulse rate to within one beat per minute, even for diverse skin tones under varied lighting conditions.
Kumar, the project’s lead graduate researcher, says DistancePPG will be particularly helpful to monitor premature infants for whom blood pressure cuffs or wired probes can pose a threat. In fact, they were his inspiration.
“This story began in 2013 when we visited Texas Children’s Hospital to talk to doctors and get ideas,” Kumar says. “That was when we saw the newborn babies in the neonatal ICU. We saw multiple wires attached to them and asked, ‘Why?'”
The wires monitored the babies’ pulses, heart rate, “and this and that,” he recalls. “And the wires weren’t a problem. The problem was that the babies would roll, or their mothers needed to take care of them, and the wires would be taken off and put back on.” That, Kumar says, could potentially damage the infants’ delicate skin.
Kumar says he expects the software to find its way to mobile phones, tablets, and computers so people can reliably measure their own vital signs whenever and wherever they choose.
Veeraraghavan is an assistant professor of electrical and computer engineering. Sabharwal is a professor of electrical and computer engineering. The lab’s research appears in the journal Biomedical Optics Express.
The National Science Foundation, the Texas Instruments Fellowship, the Texas Higher Education Coordinating Board, and a Rice University Graduate Fellowship supported the research.
* Image of newborn baby via Shutterstock