Ear infections occur when fluid builds up in the middle ear behind the eardrum and is infected. This buildup is also common in another condition called otitis media with effusion. Any kind of fluid buildup can be painful and make it hard for children to hear. A new smartphone app 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%. This is on par with current methods used by specialists to detect fluid in the middle ear that involve specialized tools that use acoustics or a puff of air.
The app sends sounds into the ear and measures how those sound waves change as they bounce off the eardrum. The 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.
Researchers tested the algorithm on a variety of smartphones and used different types of paper to make the funnel. The results were consistent regardless of phone or paper type.