Central parasympathetic excitation in real-time during intra-operative stretch stimulation of the carotid sinus intima in anaesthetised human subjects

Objective: Using the NeuroScope™ system we measured real-time intraoperative changes in central parasympathetic activity in 15 anaesthetised patients undergoing carotid endarterectomy (CEA). We assessed the response to direct stimulation of the carotid sinus before and after removal of atheromatous plaque. Methods: Baseline blood pressure (BP), heart rate (HR), cardiac vagal tone (CVT) and cardiac sensitivity to baroreflex (CSB) were measured 2 days pre-operatively and 2 days post-operatively. Intraoperative measurements were recorded continuously during stretch-stimulation of the internal wall of the carotid sinus with atheromatous plaque in-situ (first rub test) and following atheromatous plaque removal (second rub test). Results: Pre-operative levels of CVT and CSB were low. Before endarterectomy was performed, the first rub test provoked a parasympathetic excitation indicated by an increase in both CVT and CSB. Depression of the rostral ventro-lateral medulla mediated by baroreceptor stimulation was indicated by the following significant changes; 5% drop in diastolic BP, 4% drop in systolic BP and 5% drop in HR. Following endarterectomy, the second rub test provoked no response. Conclusions: The results show that baroreflex function survived dissection and opening of the carotid sinus, but not removal of atheromatous plaque from the intima. It implies that afferent nerves responding to stretch stimulus extend to the luminal surface of the carotid sinus and can be damaged during CEA surgery. Both CVT and CSB are severely low in advanced atherosclerosis. Since the NeuroScope™ system can quantify the output of carotid sinus stimulation; accurate non-invasive routine clinical assessment of baroreflex function is now possible.