Extracellular and Intracellular Fluid Shifts on the Onset of Transcutaneous Auricular Vagus Nerve Stimulation

In this paper, we propose multifrequency body impedance measurement technique for monitoring the onset of vagus nerve stimulation. In response to transcutaneous electrical vagus stimulation, changes occur in body fluids i.e. fluid shifts in extracellular and intracellular media that can be assessed by Cole parameters R_e and R_i before and after stimulus, by measuring single side impedance spectroscopy (from 3 kHz to 1MHz) between wrist and ankle. Following a resting period of 5 minutes in supine position, auricular vagus nerve was stimulated for 3 minutes and BIS performed every 10 seconds, on 23-27 years old, 5 healthy subjects. During the stimulation phase, either an increase or a decrease was observed in extracellular and intracellular fluids. In 3 of the subjects, an ECF decrease of 0.02% per kg was compensated by 0.02 to 0.06% per kg increase in ICF; with a correlation coefficient of -0,70 to -0,79; suggesting fluid shifts between ECF and ICF. With the other 2 subjects, both ECF and ICF decreased by about 0.02% per kg. The study was performed with a limited number of participants; to reach statistically meaningful results measurements will be performed over a larger sample size.