Modern Spirometry Devices
Modern spirometers are generally flow based, measuring the instantaneous exhaled flow (liters/sec.). There are four prevalent types of flow-based spirometers: pneumotacho-graphs, turbines, anemometers, and ultrasounds. Pneumo-tachs measure the pressure differential across a membrane as the subject exhales. These devices are affected by humid-ity and temperature and require daily calibration. Pneumo-tachs are the most prevalent spirometers in medical offices and clinics because of their accuracy.
High-end clinical spirometers can cost upwards of $5000 USD and be comparable in size to a small refrigerator. The patient sits inside an enclosure that controls humidity, tem-perature, and oxygen levels. Portable, ATS-endorsed spi-rometers (about the size of a laptop) generally cost between $1,000-$4,000 USD, and although they are relatively porta-ble compared to their counterparts, they are still bulky, complicated devices (Figure 1).
Low cost peak flow meters exist, which can only measure PEF ($10-$50 USD). They are about the size of a baseball and typically use a mechanical apparatus without any elec-tronics. PEF in isolation, however, is generally considered to be a poor indicator of lung function [28]. Digital home spirometers that report only FEV1 are also commercially available ($50-$200 USD). These meters vary widely in their reporting and archiving of results—some require pa-tients to manually write down the values in journals or have a USB desktop connection. The newest models (e.g., Spi-roTube) can connect to a mobile phone or laptop via Blue-tooth, but cost considerably more, from $900-$3500 USD. In 2011, Gupta et al. presented mobileSpiro, a $100-$200 pneumotach that connects to an Android smart phone [13]. This is one of the first systems that reduce cost by leverag-ing the mobile phone to present feedback and process data.
We note that a number of applications (e.g., mySpirometer, Spirometer Pro) have recently appeared on the iPhone and Android platforms that claim to measure aspects of lung function. However, these applications are advertised as games and have disclaimers warning not to use them for medical assessment.
RELATED WORK
Our work draws motivation from prior research exploring solutions that leverage sensing and computing capabilities of smartphones as well as technologies that leverage audi-ble sensing for improvement in healthcare.