A new smart-phone app can take your pulse and measure your breathing simply by detecting subtle changes in skin color. All you need to do is hold an index finger over a smart phone’s video camera for a few minutes.

Earlier this year, researchers from MIT’s Media Lab showed that a computer could reliably measure heart rate using just a mirror and a webcam. The new app was created by researchers at Worcester Polytechnic Institute seeking to create smart-phone applications that can record basic health information without the need for external sensors, which can be expensive and unwieldy.

When the researchers compared the app with more standard tools for measuring heart and respiratory rates, such as the electrocardiograph and the pulse oximeter, the readings were almost identical. The results will be published in IEEE Transactions on Biomedical Engineering later this fall.

Ki Chon, a biomedical engineer at Worcester Polytechnic Institute and the lead researcher on the study, envisions the technology helping the elderly monitor their vital signs at home or in assisted living facilities. “The app seems to work on the earlobe, too, so the phone could even measure heart rate as people talk on the phone,” he says.

Chon and his colleagues are also collaborating with clinicians at UMass Memorial Medical Center, using the app to monitor patients with atrial fibrillation, a relatively common abnormal heart rhythm that increases a person’s risk of stroke. They’re starting with patients who have already been diagnosed with the disorder, but David McManus, the lead clinician involved, says that the app may also help identify it, particularly in people who experience problems only periodically.

Instead of waiting for symptoms to appear again, patients could use the app to keep a daily record of their heart rhythm, which they could either send to their doctor or bring to their next appointment. “This could be a tremendously powerful tool for monitoring arrhythmia,” McManus says. “There’s no added hardware, and it makes use of a device that a lot of folks have.”

The tricky part for Chon and his team will be getting the app to work on different types of smart phones. The app relies on a combination of green light emitted by the video camera and white light from the flash, and these components vary slightly from phone to phone. Their proof-of-concept study was done on a Motorola Droid. The researchers plan to do more testing before making the app available for download. They’re also testing a smart phone’s ability to measure blood loss, which could help patients and even ambulance crews in emergencies.