Closed-Loop Electrical Block of Vagus Nerve Scales from Rodent to Porcine Cardiac Models

Objective
Direct current (DC) electrical block of the vagus nerve has shown the ability to downregulate the parasympathetic input to the heart. Previous investigations used static prescribed values, but a main advantage of electrical nerve block is the ability to modulate the block effect in real time. Here we investigate the potential of real-time, closed loop control of heart rate (HR), and how these control schemes translate across species.
Approach
In anesthetized rats and pigs, proximal vagus stimulation was applied on the right side to lower HR and simulate an increase in vagal activity. DC nerve block was applied distally to mitigate this increase in activity and raise the HR. The block amplitudes applied were normalized to a block threshold (BT), or the amount of current to block the nerve completely in 60s. Two static levels of 10% and 50% BT were compared to a closed-loop controlled current.
Main Results
In both the rat and the pig models, the closed-loop nerve block was able to control the heart rate to the desired setpoint. Neither of the static values were able to achieve a reliably consistent level of block, with the controlled trials showing a much tighter spread of HR over time. In the pigs, a higher-gain controller was able to reach the setpoint more quickly. In the rat, the controller reduced both the injected charge and the time to recovery after block. In the pig, the charge was increased, but near-instant recovery times were retained.
Significance
Both the rat and pig models showed success in closed-loop control of HR. Translating from rat to pig models only required minor changes to the controller, indicating that the system is robust. The ease of this translation effort bodes well for potential future translation to human therapies.