P184. Heart rate variability and its modulation by auricular branch of vagus nerve stimulation in Parkinson’s disease

Abstract

Objective Brainstem nuclei, especially the efferent dorsal motor nucleus of the vagal nerve may degenerate early in the course of Parkinson’s disease (PD). The vagus nerve includes axons which emerge from or converge onto different efferent and afferent brainstem nuclei, all functionally and anatomically interconnected. The auricular branch of the vagus nerve (ABVN) is known to be connected to autonomic regulation of cardiac rhythm. In the present prospective, cross-sectional observational study we tested heart rate variability (HRV) at rest and the influence ABVN stimulation. Methods Fifty patients with PD (age 64 ± 9 years, 21 females Hoehn & Yahr stage 2.3 ± 0.7, UPDRS III 20.9 ± 7.2, disease duration 6.4 ± 4.5 y) and 50 controls (age 64 ± 11 y, 21 females) were investigated. RR intervals were measured on electrocardiograms at normal breathing for 3 min under resting condition and for around 317 min during left or right transcutaneous ABVN stimulation. Several indices of the heart rate variability (HRV) were automatically computed (time and frequency domain): standard deviation of NN intervals (SDNN), RR-intervals/maximal frequency (HFV index), power spectral analysis in the low (ln(LF), 0.05–0.15 Hz) and in the high frequency spectrum (ln(HF), 0.15–0.5 Hz) and the low frequency/high frequency ratio (ln(LF/HF) ratio). Results Most HRV parameters were lower in PD patients compared to controls: SDNN ( p = 0.027), TINN ( p = 0.013), HRV index ( p = 0.003), LF ( p = 0.014) and HF (p = 0.039). The ln(LF/HF) ratio, that is believed to mirror sympathovagal balance did not differ between both groups ( p = 0.137). However, a significant decrease of ln(LF/HF) ratio during right ABVN stimulation in comparison to the resting condition across all subjects was found ( p = 0.002), but not following left ABVN stimulation ( p = 0.238). Other parameters were not significantly influenced by right or left ABVN stimulation. UPDRS III correlated negatively with ln(LF) ( r = −0.369, p = 0.014) and ln(HF) ( r = −0.291, p = 0.050) indicating a (weak) association between impairment in cardiac autonomic modulations and motor deficit. Conclusions Heart rate variability is considerably impaired in PD. Parasympathetic activity seems to be relatively enhanced over sympathetic activity by ABVN stimulation. However, our findings do not point to prominent dysfunction of processing afferent information from ABVN and its connected parasympathetic efferent pathway in PD.