Abstracts

Rationale: Chronotropic incompetence induced by physical exhaustion in people with epilepsy (PWE) may indicate a central disturbance in the central autonomic network (CAN). The underlying neurophysiological mechanisms and clinical modifiers are still unknown. In a pilot study, exercise-induced changes of functional brain network connectivity in the CAN as well as peripheral parasympathetic ("root mean square of the successive differences“ (RMSSD) of heart rate variability) and sympathetic parameters (electrodermal activity (EDA)) of the autonomic nervous system (ANS) were investigated in PWE and healthy age-, sex- and body mass index (BMI)-matched controls.

Methods: 19 PWE (36.8±11.5 yrs, BMI 25.6±4.1, 11 females, 15 patients were seizure free for at least six months) and 19 (35.9±11.3 yrs, BMI 26.1±4.7, 11 females) healthy matched controls performed an exhaustive bicycle ergometer test. Resting state measurements of EDA (meanEDA) and RMSSD (1-lead ECG) were recorded for 5 min before and after exercise. Likewise, 128 channel resting state electroencephalography (EEG) was obtained and functional brain connectivity in 28 regions of interest (ROI) within the CAN was analyzed in alpha frequency band (8-12 Hz) by calculating phase-locking-values (PLV). Non-parametric tests were used for between-group comparisons (Mann-Whitney-U-Test) and within-group comparisons (Wilcoxon-Test). Interrelations between ANS parameters and PLV were analyzed by Spearman rank correlations. Effect sizes were calculated by correlation coefficient r.

Results: MeanEDA increased significantly after exercise in PWE (p=0.000, r=0.869) and healthy controls (p=0.001, r=0.795) and RMSSD decreased after exercise in both groups (p=0.001, r=0.777; p=0.000, r=0.869). No between-group differences were found. PLV in the alpha band of the CAN increased significantly in PWE after exercise (p=0.028, r=0.504), but failed to reach significance in the control group (p=0.071, r=0.415). Correlations between meanEDA and PLV revealed a tendency towards a positive correlation in both groups (PWE: p=0.21, r=0.301; controls p=0.632, r=0.118), which persisted after exercise in the control group (p=0.053, r=0.45), but changed direction in PWE (p=0.274, r=-0.264).

Conclusions: As expected, exhaustive exercises are associated with increased sympathetic (meanEDA) and decreased parasympathetic (RMSSD) activity in both PWE and normal control subjects. Functional connectivity within the CAN did not differ significantly before or after exercise between groups. Since the studied PWE cohort was rather well controlled and most patients did not suffer from a drug resistant epilepsy, patients with more severe forms of drug refractory epilepsies should be investigated in the future as well. Interestingly, the correlation between CAN-based functional connectivity and sympathetic activity (EDA) reversed direction after exhaustive exercise in PWE only, yet without reaching statistical significance. Whether this reveals an epilepsy specific phenomenon of predominantly central sympathetic dysfunction needs to be elucidated in larger studies, possibly even involving patients at risk for sudden unexplained death in epilepsy (SUDEP).

Funding: Please list any funding that was received in support of this abstract.: no funding.