Effects on heart rate from direct current block of the stimulated rat vagus nerve


 Although electrical vagus nerve stimulation has been shown to augment parasympathetic control of the heart, the effects of electrical conduction block have been less rigorously characterized. Previous experiments have demonstrated that direct current (DC) nerve block can be applied safely and effectively in the autonomic system, but additional information about the system dynamics need to be characterized to successfully deploy DC nerve block to clinical practice. The dynamics of the heart rate from DC nerve block of the vagus nerve were measured by stimulating the vagus nerve to lower the heart rate, and then applying DC block to restore normal rate. DC block achieved rapid, complete block, as well as partial block at lower amplitudes. Complete block was also achieved using lower amplitudes, but with a slower induction time. The time for DC to induce complete block was significantly predicted by the amplitude; specifically, the amplitude expressed as a percentage of the current required for a rapid, 60 second induction time. Recovery times after the cessation of DC block could occur both instantly, and after a significant delay. Both blocking duration and injected charge were significant in predicting the delay in recovery to normal conduction. While these data show that broad features such as induction and recovery can be described well by the DC parameters, more precise features of the heart rate, such as the exact path of the induction and recoveries, are still undefined. These findings show promise for control of the cardiac autonomic nervous system, with potential to expand to the sympathetic inputs as well.