Direct current contamination of kilohertz frequency alternating current waveforms

Abstract

Kilohertz Frequency Alternating Current (KHFAC) waveforms are being evaluated in a variety of physiological settings because of their potential to modulate neural activity uniquely when compared to frequencies in the sub-kilohertz range. However, the use of waveforms in this frequency range presents some unique challenges regarding the generator output. In this study we explored the possibility of undesirable contamination of the KHFAC waveforms by direct current (DC). We evaluated current- and voltage-controlled KHFAC waveform generators in configurations that included a capacitive coupling between generator and electrode, a resistive coupling and combinations of capacitive with inductive coupling. Our results demonstrate that both voltage- and current-controlled signal generators can unintentionally add DC-contamination to a KHFAC signal, and that capacitive coupling is not always sufficient to eliminate this contamination. We furthermore demonstrated that high value inductors, placed in parallel with the electrode, can be effective in eliminating DC-contamination irrespective of the type of stimulator, reducing the DC contamination to less than 1 μA. This study highlights the importance of carefully designing the electronic setup used in KHFAC studies and suggests specific testing that should be performed and reported in all studies that assess the neural response to KHFAC waveforms.

Kilohertz frequency nerve block enhances anti-inflammatory effects of vagus nerve stimulation

“…While it is possible for direct current (DC) to contaminate the effects of KES nerve block, it is unlikely because equipment was calibrated prior to starting KES nerve block. Furthermore, DC contamination leads to damage of nervous tissue and can result in uncontrolled and unwanted amounts of either DC stimulation or DC nerve block18.…”

Electrophysiology equipment for reliable study of kHz electrical stimulation

“…low frequency content is introduced) the experiment may be fundamentally compromised (Franke et al . ; Kasten et al . ).…”

Reversible Conduction Block in Peripheral Nerve Using Electrical Waveforms

“…However, DC offsets can be a significant issue, especially in current controlled waveforms, and care needs to be taken to utilize a circuit design that removes the DC offset [28].

There are multiple theories presented regarding the mechanism of KHFAC block [10,29].

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“…The generation of KHFAC waveforms can be difficult to achieve without introducing a slight charge imbalance at the electrode–nerve interface [28]. This could alter the effect of the KHFAC on the nerve so that it is effectively closer to the effect of a DC waveform, with possible implications on long-term effects at both the nerve and electrode.…”