On the activation threshold of nerve fibers using sinusoidal electrical stimulation.

Carpal tunnel syndrome (CTS) diagnosis could be improved by selectively activating different types of nerve fibers traversing the carpal tunnel based on their diameter. The objective of this study was to establish the types of fibers activated by different sinusoidal electrical stimuli. The frequencies selected correspond to those used in an available application known as current perception threshold (CPT). This method has been proposed in the literature to assess the severity of CTS in a patient. CPT operates by varying the amplitude and frequency of stimulating sine wave currents. Subthreshold and supra-threshold responses of nerve fibers were modeled in this study using McNeal's model and Frankanhaeuser-Huxley equations. Simulations were performed in MATLAB to determine the stimulating thresholds for different diameter groups of nerve fibers. The study concluded that large A-beta fibers can be activated alone at the 2000 Hz frequency, the intermediate A-delta fibers can be activated at the 250 Hz frequency in company of A-beta fiber activity, and for fibers with diameter less than 2.5 mum to be activated at the 5 Hz frequency there must be accompanying activity from A-beta and A-delta fibers.