OFDM-based electrical impedance spectroscopy technique for pacemaker-induced fibrosis detection implemented in an ARM microprocessor

Fibrosis represents an open issue for medium to long-term active implants, such as pacemakers, given that this biological medium surrounds the stimulation electrodes and can impact or modify the performances of the system. For this reason, Embedded Impedance Spectroscopy (EIS) techniques have been investigated these last years to sense the fibrosis. The following article introduces a new technique for EIS derived from multi-carrier digital communication methods. Due to its properties of flat spectrum and fast generation the Orthogonal-Frequency Division Multiplexing (OFDM) technique for EIS represents an efficient and a low foot-print alternative compared to the classical sweep frequency technique. This article focuses on this approach and also proposes a solution that reduces the effect of high crest factor typically found in OFDM systems. An embedded implementation is also presented. This designed prototype is used here to characterize the impedance spectrum of a pacemaker's electrode achieving an accuracy of 99% when measuring with 64 OFDM subcarriers and with a sampling frequency of 12 kHz.