Abstract-The large-scale adoption of smartphones during recent years has created many opportunities to improve health monitoring and care delivery. In this work, we demonstrate that motion sensors available in off-the-shelf smartphones can capture physiological parameters of a person during stationary postures, even while being carried in a bag or a pocket. In particular, we develop methods to extract heart and breathing rates from accelerometer data and compare them with measurements obtained with FDA-cleared sensors. We evaluated their accuracy on 12 people across different still body postures (pre-and post-exercise) and were able to reach mean absolute errors of 1.16 beats per minute (STD: 3) and 0.26 breaths per minute (STD: 0.5) when considering different conditions. Furthermore, we evaluated the same methods during regular phone activities, such as when watching a video or listening to a conversation, yielding increased but still comparable error rates for some conditions. Physiological monitoring during daily life offers the possibility of capturing information about a person's health and fitness. This information is useful to base medical diagnoses in real-life conditions (vs. white-coat influenced conditions) and to help track chronic health conditions and effects of therapeutic interventions. While great strides have been made to provide comfortable physiological monitoring, traditional methods still require attaching electrodes to the skin and/or interrupt daily activities. Due to such challenges, people do not feel compelled to track their vital signs and show low adherence with existing physiological monitoring approaches. In order to address these problems, more comfortable and less disruptive methods are needed. In recent work [7] [8], we have demonstrated that motion sensors embedded in head-mounted and wrist-worn wearable devices such as Google Glass and Galaxy Gear can capture heart and breathing rates accurately. While the results were very promising, not everybody uses these types of wearable devices as they may be cumbersome and stigmatizing. Motivated by these challenges, this work explores the possibility of using motion sensors of currently available smartphones while being carried in different locations on the body (e.g., trouser pocket, shoulder bag) and when used during regular phone activities (e.g., watching a video, listening to a conversation), as depicted on Fig. 1 . In the following, we review relevant research in physiological measurement with smartphones. Then, we describe methods to capture heart rate (HR) and breathing rate (BR) from motion data as well as the experimental design to validate them. Finally, we provide a quantitative comparison of our methods with FDA-cleared sensors and concluding remarks. Research is based upon work supported by the National Science Foundation (NSF CCF-1029585), Samsung, and the MIT Media Lab Consortium. Smartphones are now ubiquitous devices and researchers have explored different approaches to leverage their sensors and capture physiological parameters. A commonly explored approach is photoplethysmograpy (PPG). PPG captures the blood volume pulse (BVP) using light reflected from, or transmitted through, the skin [2] . In order to measure PPG, researchers have used the flash and camera of existing smartphones to provide physiological measurements such as HR and BR [11][16]. This approach requires the user to place their finger on the phone in such a way that the flash illuminates the finger while the camera captures color changes. Researchers have also shown that remote cameras and ambient light can also be used to capture the same information [15] , freeing users from having to put their fingers on their phone. However, this method still disrupts daily activity as the user needs to position him/her-self in front of the smartphone camera in order for measurements to be made. An alternate measurement technique for capturing cardiovascular parameters is Ballistocardiography (BCG). BCG captures subtle motions of the body due to shifts in mass of blood as the heart pumps [17] . While original research required the person to lie down on a suspended mattress, technological developments have enabled measurement through other devices that are less disruptive (e.g., weighing scale [10], ear-worn device [6] 978-1-4244-9270-1/15/$31.00 ©2015 IEEE
Hernandez et al. demonstrated REF that motion sensors of a smartphone can be used to recover heart and breathing rates of the users during stationary positions and activities while the smartphone was being carried in a bag or pocket or even during listening on the phone.
Biophone: Physiology monitoring from peripheral smartphone motions
2015 37th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC)
2015 37th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC)
Engineering Computer Science Medicine