Impact of the mechanical interface on BCG signals obtained from electronic weighing scales

This work analyzes the reproducibility of the BCG obtained from different weighing scales. First, the natural frequency of three commercial bathroom scales has been characterized by an impulse excitation test. Second, the BCG and the ECG from 5 healthy subjects (27 ± 4 years) have been recorded for 60 s by sequentially standing on these weighing scales connected to the same analog front-end and signal acquisition system. An ensemble average representative of each subject and weighing scale has been obtained by applying Woody's method with the ECG as a timing reference. Consecutive BCG signals obtained from the three scales show consistent systematic intra-subject differences in the timing of the J peak that can reach up to 30 ms. This timing error is relevant because it is about 50 % of the changes induced by typical respiratory maneuvers, such as Valsalva's, used to modulate hemodynamic parameters in correlation studies between changes in J timing with respect to different cardiac fiducial points. Due to its ubiquity, weighing scales are promising devices for monitoring cardiovascular function at home but their frequency response must be accounted for and minimal performance standards should be defined for them.