Mirror mirror on the wall, what’s my blood pressure?
You can check a person’s vital signs manually or by attaching sensors to the body. But a student in the Harvard-MIT Health Sciences and Technology program is working on a system that could measure pulse, respiration and blood pressure just by putting a person in front of a low-cost camera such as a laptop computer’s built-in webcam.
Ming-Zher Poh has demonstrated that the system can indeed extract accurate pulse measurements from ordinary low-resolution webcam imagery. Now he’s working on extending the capabilities so it can measure respiration and blood-oxygen levels. Such a system could also be built into a bathroom mirror so that patients who need ongoing monitoring, or just people who want to keep track of their own health, could get pulse, respiration, oxygen saturation and blood-pressure readings routinely while they brush their teeth or wash up, displayed in a corner of the mirror.The system measures slight variations in brightness produced by the flow of blood through blood vessels in the face. Public-domain software is used to identify the position of the face in the image, and then the digital information from this area is broken down into the separate red, green and blue portions of the video image. In tests, the pulse data derived from this set up were compared with the pulse determined by a commercially available FDA-approved blood-volume pulse sensor.The big challenge was dealing with movements of the subject and variations in the ambient lighting. But Poh was able to adapt signal-processing techniques originally developed to extract a single voice from a roomful of conversations, a method called Independent Component Analysis, in order to extract the pulse signal from the “noise” of these other variations.