Multi-signal electromechanical cardiovascular monitoring on a modified home bathroom scale

A commercially available bathroom scale was modified to enable unobtrusive and robust cardiovascular monitoring in the home. Handlebar electrodes were interfaced to an ultra-low power, two-electrode electrocardiogram (ECG) acquisition circuit providing consistent and clean heartbeat timing information. In addition, the footpad electrodes were used to detect lower-body electromyogram (EMG) and lower-body impedance plethysmogram (IPG) signals using two parallel circuits. The lower-body EMG signal was used as an indication of excessive motion of the subject on the scale. The lower-body IPG signal is related to blood flow through the legs, and will be investigated further in future studies. Finally, the component of bodyweight that varies with time--the ballistocardiogram (BCG) signal--was amplified from the existing strain gauges built into the scale. A preliminary validation was completed on five healthy subjects of varying sizes. The average signal-to-noise ratio (SNR) values computed over all five subjects for the ECG, IPG, and BCG signals were 17.2, 12.0, and 9.0 dB, respectively.