Self-Synchronized, Continuous Body Weight Monitoring Using Flexible Force Sensors and Ground Reaction Force Signal Processing

Change patterns in body weight are significant indicators of a variety of medical conditions and in some instances, such as congestive heart failure, strong predictors of critical care interventions. The continuous monitoring of body weight can therefore help care givers and patients reduce the risks that are inherent in ignoring body weight changes or in measuring them infrequently. One possible approach to continuous body weight monitoring is to use shoe-integrated sensors. Such approach is however hampered by the lack of patient's adherence to medical protocols and by the detrimental impact of motion artifacts on weight measurements during body movement. The objective of this paper is to show that both problems can be readily addressed by pushing body weight measurement into the background of the patient's daily routine and by adapting piezoresistive flexible force sensors to the specific requirements of accurate body weight measurement during motion. The proposed solution is enabled by two major innovations. The first is a sensor array architecture that helps in collecting the total vertical GRF on each foot during the walk cycle. The second is based on extracting unique features from the waveforms of ground reaction forces (GRFs) as measured by the flexible force sensor array. This paper is dedicated to a full and detailed description of this second innovation that includes the extraction of GRF waveform features using real-time signal processing and the elimination of motion artifacts using accurate estimates of the vertical acceleration of the body's center of mass. A prototype demo system of the proposed solution is described along with testing results using a human subject in various walk conditions. The prototype is comprised of three subsystems: The shoe-integrated flexible sensor array, a sentinel subsystem implemented as a wearable smart watch, and a communication subsystem between sensors and sentinel. The prototype is distinguished with several unique features that ensures its wearability and low cost, including its self synchronizing data collection and the absence of any inertial motion units.