Researchers at the University of Washington have developed a smartphone app, SpiroSmart, which transforms the existing microphone in current smartphones into a spirometer.

In a paper the group presented this week at the 14th Annual International Conference on Ubiquitous Computing, they will show that the app is capable of diagnosing within 5% accuracy for “common measures of lung function”, meaning it already falls within the medical community’s definition of accurate.

“There’s a big need in the pulmonary community to make testing cheaper and more convenient,” said lead researcher Shwetak Patel, a UW assistant professor of computer science and engineering and of electrical engineering. “Other people have been working on attachments for the mobile phone that you can blow into. We said, ‘Let’s just try to figure out how to do it with the microphone that’s already there.’”

Existing spirometers have patients with chronic lung ailments such as asthma, cystic fibrosis and chronic bronchitis blow into a tube with a small turbine that measures the speed of the flow. Patients take a deep breath in, then exhale as hard and fast as they can until they can’t blow any more. The spirometer measures how much and how fast the person can breathe out, which tells doctors whether their airways are narrowed or filled with mucous.

UW researchers found they could model a person’s trachea and vocal tract as a system of tubes to replace the spirometer, and use a phone to analyze the sound of wave frequencies to detect when the breath is resonating in those natural pipes.

“There are resonances that occur in the signal that tells you about how much flow is going through the trachea and the vocal tract, and that’s precisely the quantity that a clinician needs to know,” Patel said.  In a distant way, it is analogous to using an iPhone microphone to play musical instruments.

The team tested the system on 52 mostly healthy volunteers using an iPhone 4S smartphone and its built-in microphone and results showed that the UW research app came within 5.1 percent of a commercial portable spirometer that costs thousands of dollars. Natural variation in how much effort a patient uses to exhale during each test means that about a 3 percent variation is unavoidable.

“The tests are very promising,” said co-author Dr. Margaret Rosenfeld, an associate professor at UW Medicine and a pulmonary specialist at Seattle Children’s Hospital. “Both providers and patients are very excited” about the possibility of home tests, she added.

The group has received a grant from the Coulter Foundation to continue their clinical testing and submit their application to the FDA for formal approval. There is hope to turn SpiroScout into a sustainable business in the long term. You can see a simple demo of how the app is used in the video below.

You can find the paper the group is presenting at UbiComp 2012 here.