Reversible Nerve Conduction Block Using Low Frequency Alternating Currents

Maria I Muzquiz, Purdue University

Abstract

This thesis describes a novel method to reversibly and safely block nerve conduction using a low frequency alternating current (LFAC) waveform at 1 Hz applied through a bipolar extrafascicular elecrode. This work follows up on observations made on excised mammalian peripheral nerves and earthworm nerve cords. An in-situ electrophysiology setup was used to assess the LFAC waveform on propagating action potentials (APs) within the cervical vagus nerve in anaesthetized Sprague-Dawley rats (n = 12). Two sets of bipolar cuff or hook electrodes were applied unilaterally to the cervical vagus nerve, which was crushed rostral to the electrodes to exclude reflex effects on the animal. Pulse stimulation was applied to the rostral electrode, while the LFAC conditioning waveform was applied to the caudal electrode. The efferent volley, if unblocked, elicits acute bradycardia and hypotension. The degree of block of the vagal stimulation induced bradycardia was used as a biomarker. Block was assessed by the ability to reduce the bradycardic drive by monitoring the heart rate (HR) and blood pressure (BP) during LFAC alone, LFAC with vagal stimulation, and vagal stimulation alone. LFAC applied via a hook electrode (n = 7) achieved 86.6 ± 11 % block at current levels 95 ± 38 µAp (current to peak). When applied via a cuff electrode (n = 5) 85.3 ± 4.60 % block was achieved using current levels of 110 ± 65 µAp. Furthermore, LFAC was explored on larger vagal afferent fibers in larger human sized nerve bundles projecting to effects mediated by a reflex. The effectiveness of LFAC was assessed in an in-situ electrophysiological setup on the left cervical vagus in anaesthetized domestic swine (n = 5). Two bipolar cuff electrodes were applied unilaterally to the cervical vagus nerve, which was crushed caudal to the electrodes to eliminate cardiac effects. A tripolar extrafascicular cuff electrode was placed most rostral on the nerve for recording of propagating APs induced by electrical stimulation and blocked via the LFAC waveform.

Degree

M.Sc.

Advisors

Yoshida, Purdue University.

Subject Area

Neurosciences|Medicine|Physiology

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