Mobile Phone Based Health Sensing

There are a number of healthcare sensing systems in which external sensors are connected to smartphones. Poh et al. developed a system containing electro-optic sensors worn on the earlobe to provide photoplethysmography (PPG) data on a smartphone [30]. A number of researchers have also evaluated how multiple sensors could be connected to a smartphone via an external board to collect physiological information [7,21]. Bishara et al. have successfully modi-fied the existing on-device camera to perform lens-free hol-ographic microscopy [4]. Pamplona et al. have developed NETRA, a system that combines simple optical compo-nents, like lenses, with high-resolution LCD screens of smartphones to detect human eye impairments [27].
Researchers have also been exploring solutions that require no hardware modification. Grimaldi et al. employed a smartphone’s camera and LED flashlight to measure pulse from the fingertip using photoplethysmography [11]. While this requires users to be in contact with the device, Poh et al. use a tablet’s camera and blind source separation of col-or channels to measure pulse at a distance [29].
Audio Based Health Sensing
Like SpiroSmart, there are several technologies that sense medically relevant quantities using a microphone. Using an in-ear microphone, researchers have shown that one can detect when (and sometimes what) a person is eating [3,25]. Wheeze detection with in-air and throat microphones has shown promising results in diagnosing the severity of asth-ma [14]. Respiratory rate is another vital sign typically sensed with body worn [2] or bedside microphones [17

A few systems have leveraged simple, low-cost micro-phones to analyze signals, such as heart rate and cough. Many systems exist that extract heart rate using a mobile phone [24,40] and, with higher-end microphones, some systems can actually be used to detect certain audible mani-festations of high blood pressure referred to as Korotkoff sounds [1]. In 2011, we presented a solution that uses the microphone on the mobile phone to detect and countcoughs [20]. Similar to SpiroSmart—this was a tool for measuring a medically accepted quantity without the need for specialized equipment.