Closed-Loop Multimodal Neuromodulation of Vagus Nerve for Control of Heart Rate*

The use of electrical current to modulate neurons for autonomic regulation requires the ability to both up-regulate and down-regulate the nervous system. An implanted system employing this electrical neuromodulation would also need to adapt to changes in autonomic state in real-time. Stimulation of autonomic nerves at frequencies in the range 1–30 Hz has been a well-established technique for increasing neural activity. Vagus nerve stimulation (VNS) has been shown to be sensitive to frequency adjustments, which can be used to more precisely control the effect as compared to amplitude modulation. Kilohertz frequency alternating current (KHF AC) is a proven technique for blocking action potential conduction to reduce neural activity. Additionally, KHFAC can be reliably modulated by simple amplitude modulation. Although there are many types of commonly used closed-loop controllers, many conventional methods do not respond well to long system delays or discontinuities. Fuzzy logic control (FLC) is a state-based controller that can describe the discontinuities of the system linguistically and then translate the state transition to a continuous output signal. In our preparation, a single bipolar electrode was placed on the vagus nerve and controlled by a fuzzy logic controller to deliver both stimulation and KHFAC to control heart rate. The FLC was able to both change the heart rate to selected values and maintain the heart rate at a constant value in response to a physiological perturbation.