Optimizing IPG-Based Heart Rate Estimation: A Systematic Analysis of Complex Tissue Impedance

Abstract

Impedance Plethysmography is a promising technique for cardiovascular monitoring, yet the optimal excitation frequencies of the applied current and the possibilities of using complex signal components are still not fully investigated. This paper analyzes the results of a 40 participant study to evaluate the influence of injection frequency and choice of signal component. Five simultaneously measured frequencies (3-100 kHz) are used to estimate the participants’ heart rate using an autocorrelation-based algorithm, using both the real and imaginary parts of the complex IPG signal and compared against an oscillometric reference. The paper shows that the real signal component performs similar across all frequencies, with the best performance at 27.3 kHz. Conversely, the imaginary component showed significant frequency dependency, performing best at 51.5 kHz. The findings suggest that using the real component for vital parameter monitoring is the more robust choice, though the imaginary component is more dependent on the correct frequency choice. These results provide design constraints for the next generation of multi-frequency bioimpedance wearables.