Abstracts

Rationale: Vagus nerve stimulation (VNS) is a treatment option in the case of refractory epilepsy. However, several side effects have been reported, including dyspnea, coughing and bradycardias [JCA 2010: 22;213-222]. Although some patients experience hardly any side effects from the stimulation during rest, they mention a decrease in physical condition during exercise is. The experience of a decrease in physical condition during exercise is reported as shortness of breath when the stimulator is on. It is unclear whether this actually has a laryngeal or respiratory cause, or whether there are cardiac or combined causes as well. The aim of this study is to explore the contribution of these various potential causes to the exercise intolerance reported by several patients treated with a VNS device. Methods: In a case controlled observational study, 5 epilepsy patients who report side effects during exercise are compared to 5 patients without side effects and 5 healthy subjects. All subjects are measured during rest and during a non-maximal ergometry test. During these tests, which both take 20 minutes, respiratory parameters (tidal volume, breathing frequency and minute volume), ECG, 32-channel EEG, pulse oximetry and periodic blood pressure (BP) are measured. Epilepsy patients with VNS are asked to activate the device 3 times during the tests, to study the effects of the stimulation on the aforementioned parameters. Results: At present, 1 patient with and 1 patient without side effects have been included, as well as 4 healthy subjects. In healthy subjects, stable values for the parameters during rest are observed. During the first few minutes of exercise, heart rate and systolic BP increase, while diastolic BP decreases slightly. Thereafter, a steady state is reached. All values are as expected during exercise. In the patients, the same effect of exercise as in healthy subjects occurs. The stimulation does not influence the BP, saturation and respiratory parameters. Heart rate analysis in both patients showed a small but significant increase in inter-beat intervals during stimulation, indicating a slight decrease in heart rate. This happened during both rest and exercise. Conclusions: Preliminary results show that during stimulation of the vagus nerve, small but reproducible slowing of heart rate occurs. No robust conclusion can yet be drawn about the effect of stimulation on respiratory parameters.