Spirometers are commonly used devices that help physicians diagnose and track the progress of various lung conditions. Patients are even using the devices at home to measure their own lung air volume, helping clinicians keep an eye on their disease. Researchers at the University of Washington, UW Medicine and Seattle Children’s hospital were wondering whether it would be possible to indirectly derive air volume measurements from audio recordings of people breathing.
Turns out that by modeling the trachea and vocal tract, the team was able to develop an algorithm that translates audio into air volume with surprising accuracy. Moreover, a standard iPhone has a sufficient microphone to do the recordings and certainly enough computational horsepower to immediately provide the results. According to a study involving 52 people, the SpiroSmart app was within 5.1% accuracy of a commercial spirometer.
Last year Patel’s group used a smartphone to track a person’s coughs throughout the day. Now his graduate students Eric Larson in electrical engineering and Mayank Goel in computer science and engineering have led a 2.5-year project tackling the harder problem of how to get an accurate measure of lung function using nothing but a smartphone.
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.
The 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 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.
Researchers tested the system on 52 mostly healthy volunteers using an iPhone 4S smartphone and its built-in microphone. Results showed that the UW research app, SpiroSmart, 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.
Press release: App lets you monitor lung health using only a smartphone
Project page: SpiroSmart…