Transcranial doppler-derived cerebrovascular resistance changes during vagus nerve stimulation in drug-resistant epilepsy

BACKGROUND: Vagus nerve stimulation (VNS) is an established neuromodulation therapy for drug‐resistant epilepsy. Although its clinical efficacy is well documented, its acute effects on cerebral hemodynamics, particularly vascular resistance, are not fully understood. This study aimed to compare cerebral hemodynamic parameters between VNS on and off. METHOD: In this single‐center, prospective, within‐subject pilot study, 12 patients with left‐sided VNS implantation were evaluated. Cerebral blood flow velocities, pulsatility index (PI), and resistive index (RI) were measured from the middle cerebral artery (MCA) and posterior cerebral artery (PCA) using transcranial Doppler ultrasonography (TCD). Measurements were performed under both VNS on and off conditions in a randomized order, with a 3 h interval between assessments. RESULTS: Cerebral blood flow velocities in the MCA and PCA did not differ between VNS on and off conditions. However, PI and RI were observed to be significantly higher in the left MCA when VNS was off (p = 0.008 and p = 0.02, respectively). No significant changes were observed in vascular resistance indices in the right MCA or bilateral PCA. The changes in PI and RI were not influenced by epilepsy focus lateralization. Heart rate did not differ between conditions. CONCLUSION: In this study, VNS was associated with lower PI and RI in the left MCA without altering cerebral blood flow velocities. These findings suggest that VNS may influence distal cerebrovascular resistance may reflect changes in distal vascular resistance in the anterior circulation independent of both large‐vessel flow changes and epilepsy focus lateralization.