Mobile core hydration sensing using bio-impedance of arm



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A novel arm-wearable mobile core hydration sensor has been designed which works on the principle of Bio-Impedance Vector Analysis (BIVA). Arm impedance is hypothesized to be indicative of core hydration changes. The prototype device is a Flexible PCB that uses gel electrodes for tetrapolar measurement of the arm impedance and uses Bluetooth transmission to transmit the raw data to a base station for data processing, where the resistance and reactance at 50kHz are extracted. The device transmits raw data every 2 seconds, with 2mA average current consumption and measurement error of less than 1% and is ensured to be safe for a wearer by meeting IEC6060-1 safety standards. Device design, evolution, manufacturing, calibration, and validation are discussed in detail. The arm-impedance is analyzed with respect to different arm angles, muscle strain and electrode placement sites, and a Posture control protocol is incorporated to deal with such impacts. Experimental protocols for testing hydration status are explained and the results of a pilot study are presented and analyzed. Physiological signal responses, like Body weight, Heart Rate, and Core temperature, are monitored in the experiment trials, and are used to interpret the results of the hydration study. The pilot study results look promising, and can distinguish between dehydration and euhydration, with arm impedance showing better demarcations than body impedance. Moving forward, this research will be validated by experimentation on multiple subjects.


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