Ion mechanism and parameter analysis of anodal-first waveforms for selective stimulation of C-fiber nerves

Few investigations have been conducted on selective stimulation of small-radius unmyelinated C nerves (C), which is critical to both recoveries of damaged nerves and pain suppressions. The purpose of this study is to understand how an anodal pulse in an anodal-first stimulation could improve C-selectivity over myelinated nociceptive A{delta} nerves (A{delta}), and further clarify the landscape of the solution space. The Hodgkin-Huxley (HH) model and the McIntyre-Richardson-Grill (MRG) model were used for modelling C and A{delta}, respectively to analyze the underlying ion dynamics and the influence of relevant stimulation waveforms, including monopolar, polarity-symmetric, and asymmetric pulses. Results showed that polarity-asymmetric waveforms with preceding anodal stimulations benefit C-selectivity most, underlain by the decrease of the potassium ion current of C. The optimal parameters for C-selectivity have been identified in the low frequency band, which will benefit remarkably the designs of nociceptive nerve selective stimulation.