Cardiac monitoring with textile capacitive electrodes in driving applications: Characterization of signal quality and RR duration accuracy

Capacitive ECG sensors in automobiles enable unobtrusive heart rate monitoring as an
indicator of a driver’s alertness and health. This paper introduces a capacitive sensor
with textile electrodes and provides insights into signal quality and RR duration accuracy.
Electrodes of various shapes, sizes, and fabrics were integrated at various positions into
the seat back of a driving simulator car seat. Seven subjects completed identical driving
circuits with their cardiac signals being recorded simultaneously with textile electrodes
and reference Ag-AgCl electrodes. Capacitive ECG signals with observable R peaks (after
filtering) could be captured with almost all pairs of textile electrodes, independently
of design or placement. Signal quality from textile electrodes was consistently lower
compared with reference Ag-AgCl electrodes. Proximity to the heart or even contact with
the body seems to be key but not enough to improve signal quality. However, accurate
measurement of RR durations was mostly independent of signal quality since 90% of
all RR durations measured on capacitive ECG signals had a percentage error below 5%
compared to reference ECG signals. Accuracy was actually algorithm-dependent, where
a classic Pan–Tompkins-based algorithm was interestingly outperformed by an in-house
frequency-domain algorithm.