Researchers have created a new smartphone app that can detect fluid behind the eardrum by simply using a piece of paper and a smartphone’s microphone and speaker. The smartphone makes a series of soft audible chirps into the ear through a small paper funnel and, depending on the way the chirps are reflected back to the phone, the app determines the likelihood of fluid present with a probability of detection of 85 percent. This is on par with current methods used by specialists to detect fluid in the middle ear, which involve specialized tools that use acoustics or a puff of air.
Once diagnosed, ear infections can be easily treated with observation or antibiotics, and persistent fluid can be monitored or drained by a doctor to relieve symptoms of pain or hearing loss. A quick screening at home could help parents decide whether or not they need to take their child to the doctor.
This app works by sending sounds into the ear and measuring how those sound waves change as they bounce off the eardrum. The team’s system involves a smartphone and a regular piece of paper that the doctor or parent can cut and fold into a funnel. The funnel rests on the outer ear and guides sound waves in and out of the ear canal. When the phone plays a continuous 150 millisecond sound — which sounds like a bird chirping — through the funnel, the sound waves bounce off the eardrum, travel back through the funnel and are picked up by the smartphone’s microphone along with the original chirps. Depending on whether there’s fluid inside, the reflected sound waves interfere with the original chirp sound waves differently.
When there is no fluid behind the eardrum, the eardrum vibrates and sends a variety of sound waves back. These sound waves mildly interfere with the original chirp, creating a broad, shallow dip in the overall signal. But when the eardrum has fluid behind it, it doesn’t vibrate as well and reflects the original sound waves back. They interfere more strongly with the original chirp and create a narrow, deep dip in the signal.
To train an algorithm that detects changes in the signal and classifies ears as having fluid or not, the team tested 53 children between the ages of 18 months and 17 years at Seattle Children’s Hospital. About half of the children were scheduled to undergo surgery for ear tube placement, a common surgery for patients with chronic or recurrent incidents of ear fluid. The other half were scheduled to undergo a different surgery unrelated to ears, such as a tonsillectomy.
Because the researchers want parents to be able to use this technology at home, the team trained parents how to use the system on their own children. Parents and doctors folded paper funnels, tested 25 ears and compared the results. Both parents and doctors successfully detected the six fluid-filled ears. Parents and doctors also agreed on 18 out of the 19 ears with no fluid. In addition, the sound wave curves generated by both parent and doctor tests looked similar.