Otoacoustic emissions (OAEs) are sounds generated from the cochlea. The sounds are transmitted across the middle ear to the external ear canal, and can be recorded in the outer ear. A present OAE indicates an essentially normally functioning inner ear. OAEs can be used to screen hearing, as in newborn hearing screenings (NBHS) or as a diagnostic measure to cross check other audiological findings.
It is common practice for high-income, first-world countries to have universal newborn hearing screening programs that may include the use of OAEs. Early identification and intervention are known to mitigate the negative effects of hearing loss on neurodevelopment. However, OAE equipment is expensive, which can limit its use in low- and middle-income countries.
Chan and colleagues designed and tested clinically a low-cost OAE probe made from off-the-shelf earbuds and microphone, with a material cost of about $10 in U.S. currency. The design sends two pure-tone signals using each of the earbuds. The earbuds are not placed in the ear, but rather, near the smartphone. The distortion product OAE is then measured using a microphone attached to the probe head. Data are analyzed using algorithms that run on the smartphone. These real-time algorithms run on the smartphone to perform calibration, noise detection, and automatic pass or refer testing for hearing screening.
The authors conducted a study on 201 ears of patients between one week and 20 years of age. Distortion product OAEs were first measured using a commercial OAE device, followed with the smartphone system using the same probe tip. Both devices were calibrated to emit the two tones at 65- and 55-dB SPL respectively, and measurements were obtained for the 2, 3, 4 and 5 kHz bands.
Across these age groups, the authors’ system obtained accuracies ranging from 84 percent to 100 percent, while the commercial device obtained accuracies ranging from 75 percent to 96 percent. Sensitivity with the experimental device was as good as or better than the commercial device, with specificity being slightly lower in the smartphone system when compared to the commercial device.
The authors concluded that the key advantage of using off-the-shelf earbuds and smartphones is that custom electronics do not need to be manufactured, which significantly lowers development costs. They note, however, the cost of OAE devices is only one factor associated with addressing the complex public-health problem of hearing screening in low- and middle-income countries.
There are other factors involved including establishing strong partnerships, support for follow-ups, and the cost of regulatory clearance. Financial support is required to fund the screening staff/other health-care workers who would be administering the test. To increase its use globally, the authors have open-sourced their hardware and software code to allow anyone to download and recreate the smartphone device.
In summary, the low-cost OAE system that uses off-the-shelf earbuds was as sensitive as commercial equipment. Early detection of hearing loss is challenging in low- and middle-income countries due to lack of access to affordable hearing-screening tools. Compared with commercial OAE devices that cost thousands of dollars, the frugal earbud-based OAE system has the potential to increase access to hearing screening in resource-constrained environments.
Learn more at the reference below or go Behind the Paper.
Chan J, Ali N, Najafi A, Meehan A, Mancl LR; Gallagher E; Bly R; Gollakota S. (2022) An off-the-shelf otoacoustic emission probe for hearing screening via a smartphone. Nat Biomed Eng 6(11):1203-1213.
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