Counted cycles method to quantify the onset response in high-frequency peripheral nerve block

Abstract

The clinical use of high frequency alternating current (HFAC) to block nerve conduction in peripheral nerves is limited due to the large volley of nerve activity generated at the initiation of HFAC. This "onset response" must be characterized in order to determine if it is possible to eliminate it. In this study, preliminary experiments were conducted in an in-vivo animal model using counted cycles of HFAC to investigate and quantify the onset response. Using this method, it is possible to show quantitatively that the onset response has two phases with distinct characteristics. Eliminating the onset response is likely to require addressing each phase independently. It was also possible to show that HFAC establishes a complete block of nerve activity in 50-100 ms.

Reversible Conduction Block in Peripheral Nerve Using Electrical Waveforms

“…

KHFAC block is generally applied through encircling nerve cuff electrodes and produces a localized block of the underlying nerve [3,16] that does not affect the neuromuscular junction;

KHFAC block is nearly instantaneous, as shown in Figure 2. A recent study [4] used a ‘counted cycles’ method to measure the time to achieve complete motor block and found that it could be as rapid as 7.5–14 ms;

KHFAC block shows rapid reversibility (Figure 2) when the KHFAC is terminated [3]. Experiments demonstrate that the nerve completely recovers within 1 s of the cessation of the KHFAC;…”

“…A recent study [4] used a ‘counted cycles’ method to measure the time to achieve complete motor block and found that it could be as rapid as 7.5–14 ms;…”

“…One theory is based on the accumulation of extracellular potassium [30]. However, KHFAC block has been shown to take effect too rapidly to support this theory [4]. Another theory has been that potassium currents flowing out overcome the inward sodium currents and produce block [12].…”

“…One of the primary goals of research in electrical nerve block has been to understand the characteristics of the onset response, and to identify methods for reducing and eliminating this response while still maintaining the desirable characteristics of KHFAC block. The onset response is produced primarily by the response of the nerve to the first few cycles of the KHFAC wave [4]. In addition, lower amplitude KHFAC waves can produce repetitive firing in the nerve, and it is likely that regions of the nerve remote from the blocking site experience this condition.…”

“…Methods of electrical nerve block, as reviewed in this article, typically block nerve conduction in less than 2 s [3]. Methods such as kilohertz frequency alternating current (KHFAC) block have been shown to occur in less than 10 ms [4]. This is much faster than a pharmacologically induced block of nerve conduction, which typically requires several minutes to become fully effective.…”