Single-Electrode, Bidirectional Control of Heart Rate via Vagus Nerve Modulation in Rat Model.

Electrical stimulation of somatic nerves has long been used as a treatment method for a wide range of diseases by increasing activity on a target nerve. Electrical nerve block is an emerging therapy that can provide the same targeted treatment by decreasing activity on the nerve. Here, we demonstrate that both of these techniques can be applied synergistically via a single electrode to achieve precise control of an autonomic system. Two electrodes were placed on the right-side rat vagus nerve. The vagus proximal to the electrodes was crushed, and the left side was cut to isolate the system. The proximal electrode was used to give a perturbing stimulus ramp (0 Hz $\to ~30$ Hz $\to ~0$ Hz) over 10 minutes to roughly mimic the vagal activity seen in an episode of vasovagal syncope. The distal electrode was used to apply either stimulation or kilohertz-frequency electrical nerve block (KHFAC) to the vagus to keep the heart rate at a specified setpoint. The stimulation parameters were decided by a closed-loop fuzzy logic controller. Three different gains for the controller were tried. While each gain showed success in controlling the heart rate, lower gain was sometimes not responsive enough for effective control, and high gain was seen to induce oscillations in the heart rate; a medium gain was seen to be effective without either of these issues. This demonstrates that a single electrode can deliver bimodal neuromodulation of a single nerve, providing a powerful treatment tool against autonomic dysregulation.