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The cardiovascular system can be influenced by electrically stimulating the vagal nerve. Selectivity for specific cardiac fibers may be limited when stimulating at the cervical level. Our objective was to increase effectiveness and selectivity for cardiovascular effects of vagal nerve stimulation by using local bipolar stimulation in one nerve cross section using a multi-contact cuff instead of less localized stimulation using a tripolar ring electrode. Both types of cuff electrodes were compared with respect to their relative effects on R-R interval (RRI), P-Q interval (PQI), left ventricular contractility (LVC), and left ventricular pressure (P(LV)) in seven pigs. Stimulation using the optimal bipolar configuration on the multi-contact cuff significantly affected RRI, PQI, LVC, and P(LV), whereas stimulation with the ring electrode only significantly affected RRI and PQI. The cardiovascular parameters that could be significantly influenced varied between the bipolar configurations. These novel findings may be relevant for optimizing electrode configurations for clinical cardiac applications of vagal nerve stimulation.

This thesis focuses on sensing cardiovascular signals from the vagus nerve and electrically stimulating the vagus nerve for cardiovascular effects. Sensing cardiovascular signals was attempted on both spontaneous and evoked neural activity. A cardiac-modulated vagus nerve activity pattern was found in spontaneous vagus nerve activity. This pattern may reflect cardiac receptor activity, as it is affected by increased blood pressure and contractility brought about by dobutamine. In evoked vagus nerve responses a component was found that had a long latency, a low stimulation threshold and a high velocity along the nerve. These results led to the hypothesis that the component was an indirect component of a burst of single fibre action potentials, emanating with varying delays from the neural network on the heart. The component was strongly reduced with a tripolar derivation or with the average reference configuration on the centre electrode in a cuff with three rings. It was proposed that this was due to the second order spatial derivative, which reduces a dispersed component when it creates a close to linear field in the cuff. A computer model was used to show that it is possible to record an evoked dispersed component as a result of a burst of single fibre action potentials with varying delays. To further elucidate the origin of the evoked component, two additional experiments were performed in which the recurrent laryngeal nerve was cut. The evoked component disappeared after cutting of the recurrent laryngeal nerve. Arguments are presented for a muscular origin from the larynx or a neuronal origin from the neural network on the heart or the recurrent laryngeal nerve. The physiological origin of the evoked late component remains however as yet unclear. Evoked responses may also originate from the brain stem, but that these are difficult to record. This thesis also described cardiovascular effects of vagus nerve stimulation. A segmented electrode cuff for improving selectivity of vagus nerve stimulation for cardiovascular effects is presented.

The vagal nerve plays a vital role in the regulation of the cardiovascular system. It not only regulates the heart but also sends sensory information from the heart back to the brain. We hypothesize that the evoked vagal nerve compound action potential contains components that are indirect via the brain stem or coming via the neural network on the heart. In an experimental study of 15 pigs, we identified four components in the evoked compound action potentials. The fourth component was found to be an indirect component, which came from the periphery. The latency of the indirect component increased when heart rate and contractility were decreased by burst stimulation (P = 0.01; n = 7). When heart rate and contractility were increased by dobutamine administration, the latency of the indirect component decreased (P = 0.01; n = 9). This showed that the latency of the indirect component of the evoked compound action potentials may relate to the state of the cardiovascular system.

The vagal nerve conveys information from and to many organs, including the heart. The components of the compound action potentials (CAPs) recorded from the vagal nerve give information about the different fiber types present. In this paper, we show that with the average reference recording method an additional component can be measured. This component is missed when using a tripolar recording method. Recordings were made in anesthetized pigs. Results show that there is an indirect component in the CAP of the cervical vagal nerve. This component comes from the periphery most likely from the heart.