Can Any Old Phone Become a Spirometer?

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A smartphone that measures lung sounds? Sure. But now, even dumbphones are getting in on the action.

by Lonnie Stoltzfoos

Technology that was first rolled out in 2012 as a smartphone app has now been adapted so that virtually any telephone connection—cell phone, landline, or internet call—can be used to analyze a person’s pulmonary function in the clinic.

The smartphone app, SpiroSmart, recorded the sound of a person’s exhalations and uploaded the audio file to a central server, which employed multiple regression algorithms to reliably measure lung function by using a physiological model of the vocal tract and by accounting for the sound of reverberation around the user’s head. Most people in low- and middle-income countries do not have access to smartphones, however, so the inventors created SpiroCall, in which a central server analyzes audio data transmitted via cellphone network (GSM) during an ordinary call. Audio submitted via GSM networks is of lower quality, so the inventors tweaked the algorithms to account for those degradations.

The inventors recruited a sample of 50 people to test SpiroCall (age range: 21–67 years; n=30 male; n=20 female). Thirty-two percent of participants reported an existing lung ailment, of whom two-thirds reported asthma. All participants completed spirometry on two FDA-approved clinical spirometers, and on SpiroCall, using a range of telephones devices.

Across the four major measurements of lung function (FVC, FEV1, FEV1%, and PEF), the mean error rate of SpiroCall spirometry was 6.2%, below the clinically accepted error range of 7%–10%. SpiroCall performed best at measuring FEV1%, the most common measure used in clinical diagnosis; the error rate for FEV1% was below 6% across all study conditions.

One remaining challenge for SpiroCall is that health workers need to show users how to exhale properly for the test, and how to hold the phone. The SpiroSmart smartphone app attempts to train the user to conduct the test independently but, to date, SpiroCall will work best under supervision in the clinic.

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