kHz-frequency electrical stimulation selectively activates small, unmyelinated vagus afferents.

BACKGROUND: Vagal reflexes regulate homeostasis in visceral organs and systems through afferent and efferent neurons and nerve fibers. Small, unmyelinated, C-type afferents comprise over 80% of fibers in the vagus and form the sensory arc of autonomic reflexes of the gut, lungs, heart and vessels and the immune system. Selective bioelectronic activation of C-afferents could be used to mechanistically study and treat diseases of peripheral organs in which vagal reflexes are involved, but it has not been achieved. METHODS: We stimulated the vagus in rats and mice using trains of kHz-frequency stimuli. Stimulation effects were assessed using neuronal c-Fos expression, physiological and nerve fiber responses, optogenetic and computational methods. RESULTS: Intermittent kHz stimulation for 30 min activates specific motor and, preferentially, sensory vagus neurons in the brainstem. At sufficiently high frequencies (>5 kHz) and at intensities within a specific range (7-10 times activation threshold, T, in rats; 15-25 × T in mice), C-afferents are activated, whereas larger, A- and B-fibers, are blocked. This was determined by measuring fiber-specific acute physiological responses to kHz stimulus trains, and by assessing fiber excitability around kHz stimulus trains through compound action potentials evoked by probing pulses. Aspects of selective activation of C-afferents are explained in computational models of nerve fibers by how fiber size and myelin shape the response of sodium channels to kHz-frequency stimuli. CONCLUSION: kHz stimulation is a neuromodulation strategy to robustly and selectively activate vagal C-afferents implicated in physiological homeostasis and disease, over larger vagal fibers.

Successfully Closing an Acquired Palatal-fistula Using a Turnover Flap from a Previously Transferred Forearm-free-flap.

Palatal fistula between the oral and nasal cavities occurs in about 20% of palatal repairs after oncologic resection. Although healing by secondary intention may be employed as an initial strategy, persistent nonhealing symptomatic fistula necessitates intervention. Folded free flap used for primary repair of palatectomy defects enables placement of epithelialized tissue on both the oral and nasal cavities. In case of acquired palatal fistula, a turnover flap can be easily created, based on the free margin of the folded forearm free flap to serve as a reconstructive lifeboat.