Abstract— Posture changes initiate a dynamic physiological response that can be used as an indicator of the overall health status. We introduce an inconspicuous mobile wellness monitoring system (imWell) that continuously assesses the dynamic physiological response to posture transitions during activities of daily living. We use Zephyr BioHarness 3 physiological monitor that continually reports heart activity and physical activity via Bluetooth to a personal device. The personal device processes all the data in real-time, recognizes posture transitions from accelerometer data, characterizes dynamic heart response to posture changes, annotates, logs, and uploads heart activity data to our mHealth server. In this paper we present algorithms for detection of posture transitions and heart activity characterization during a sit-to-stand transition. The proposed system was tested on seven healthy subjects performing a predefined protocol. The total average and standard deviation for sit-to-stand transition time is 2.7±0.69 s, resulting in the change of heart rate of 27.369.30 bpm (from 63.39.02 bpm to 90.6610.09 bpm). I. INTRODUCTION Cardiovascular diseases represent the leading cause of death in the United States. The current practices in monitoring health status are expensive, often insufficient, and limited to monitoring in healthcare facilities. Patients usually consult cardiologists only after experiencing first symptoms of deteriorating cardiac status. Cardiologists usually administer exercise stress test to assess cardiac status. Standard stress tests are bike or treadmill exercise supervised by a doctor or a trained technician to determine the level of exercise a patient can tolerate. The tests are usually followed by prescribed therapeutic lifestyle changes including modification of diet and development of an exercise program with a follow-up after several months. However, the clinicians do not have tools to assess the patients’ progress and their compliance to the prescribed therapies. Patients and healthy users lack tools to monitor their own cardiac status and to manage healthy lifestyle. This work was supported in part by the University of Alabama in Huntsville under Grant UAH234343 and NSF CNS-1205439. E. Jovanov is with the Electrical and Engineering Department, University of Alabama in Huntsville, Huntsville, AL 35899 (Phone: 256- 824-5094; fax: 256-824-6803; e-mail: emil.jovanov@uah.edu). M. Milosevic and A. Milenkovic are with the Electrical and Computer Engineering Department, University of Alabama in Huntsville, Huntsville, AL 35899 (e-mail: mladen.milosevic@uah.edu and milenka@uah.edu). Emergence and proliferation of lightweight and wearable physiological sensors enable the design of digital assistants that are capable of continual sensing and processing of cardiac activity and physical activity. A number of new consumer-grade devices for health and wellness monitoring has been introduced [1], [2]. Examples include pedometers that count number of steps and calories, and more sophisticated devices, such as heart and metabolic monitors. On the other side, an increasing number of users actively monitor their own health and fitness status [3]. The availability of affordable wearable devices and their consumer acceptance create new opportunities for individual users and healthcare professionals. Posture changes, such as transitions from sitting to standing, induce a physiological response that can be used to characterize fitness status of the user. Figure 1(b) shows heart rate recorded during a posture transition from sitting to standing for a healthy subject (blue line) and a subject with cardiac condition (red line) The heart rate in the healthy subject quickly increases as a response to the physical activity and then returns to a level that corresponds to the new homeostasis. We hypothesize that characterizing this dynamic response, including a change in the heart rate and time to reach the maximum, can be used to indicate the subject’s cardiac status and overall wellness. Long term monitoring of cardiac health and physical activity during activities of daily living can provide indication of short term and long term changes of cardiac status and fitness. The goal of this project is to develop an inconspicuous wearable cardiac and wellness assistant called imWell (inconspicuous mobile Wellness) for efficient unobtrusive monitoring of physical activity, cardiac health, and overall physical wellness. The imWell system continually records interbeat intervals and processes accelerometer data to recognize posture transitions (Section III.A). For detected sit-to-stand posture transitions the system characterizes dynamic heart response by extracting transition timestamp, duration, heart rate before and after transition, and the time needed to reach the maximum heart rate from the beginning of the transition (Section 0). This way we treat each sit-to-stand posture change, which happens dozens of times per day, as a mini “exercise test”. Analyzing the results of these tests over long period of time, could be used to assess cardiac status and fitness. A Mobile System for Assessment of Physiological Response to Posture Transitions Emil Jovanov, Senior Member, IEEE, Mladen Milosevic, Member, IEEE, Aleksandar Milenković, Senior Member, IEEE, University of Alabama in Huntsville, Huntsville, Alabama, U.S.A