Brainstem cardiovascular regulation during stretch-stimulation of the luminal surface of the carotid sinus in anaesthetised human subjects

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University of Bristol (2001) J Physiol 536P, S010

Communications: Brainstem cardiovascular regulation during stretch-stimulation of the luminal surface of the carotid sinus in anaesthetised human subjects

D. Sigaudo-Roussel, P.O.O. Julu* and M.E. Gaunt†

Department of Neurosurgery, University of Cambridge, Cambridge CB2 2QQ, *Peripheral Nerve and Autonomic Unit, Imperial College of Science, Technology and Medicine, Department of Neurology, Central Middlesex Hospital, London and †Department of Surgery, Addenbrooke's Hospital, Cambridge, UK

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Blood pressure instability after carotid endarterectomy (CEA) is thought to be caused by disturbance of the baroreflex control mechanism during surgery in the carotid sinus region. We investigated the mechanism by which CEA affects baroreceptor function.

Ten patients aged 56-84 years underwent CEA for medical reasons. Informed consents were then obtained to use their data for this study. Under general anaesthesia, heart rate (HR), intra-arterial blood pressure (BP), cardiac vagal tone (CVT) measured in arbitrary units of linear vagal scale (LVS) and cardiac sensitivity to baroreflex (CSB) were monitored and recorded continuously using the NeuroScope system (MediFit Diagnostics Ltd, London) as previously described (Julu et al. 2001). Effects of the following surgical manoeuvres on baroreceptor function were investigated: dissection, clamping of the common carotid artery, restoration of cerebral blood flow through a bypass shunting the carotid sinus, rub test (stretch-stimulation of the intra-arterial carotid sinus area with artheromatous plaque in situ), removal of atheromatous plaque, repeat rub test (plaque removed), clamping of the carotid sinus shunt, and restoration of blood flow through the carotid sinus area.

Systolic BP increased significantly with the initial carotid clamping (means ± S.E.M.) from 122 ± 5 to 145 ± 6 mmHg (P < 0.001, Student’s paired t test; P < 0.05 is significant). The HR increased from 56 ± 2 to 60 ± 2 beats min-1 (P < 0.001). The first rub test with the plaque in situ provoked significant increases in CVT from 2.28 ± 0.8 to 3.7 ± 0.7 units (P < 0.01) and CSB from 1.7 ± 0.3 to 3 ± 0.6 ms mmHg-1 (P < 0.005). These caused significant drops in systolic BP from 145 ± 8 to 137 ± 8 mmHg (P < 0.005) and in heart rate from 61 ± 2 to 58 ± 2 beats min-1 (P < 0.001) after stimulating the carotid sinus area, but no responses to repeat rub test.The results show functioning baroreceptor reflex that survived the dissection and opening of the carotid sinus area (Fig. 1). However, removal of atheromatous plaque altered the reflex, suggesting the interruption of afferent connection of the stretch stimulus from the luminal wall. These findings suggest that afferents of the stretch stimulus extend to the luminal surface of the carotid sinus area and these can be damaged during surgical removal of atheromatous plaques.

figure one
Figure 1. Example of intra-operative data obtained in real-time using the NeuroScope system. Vertical dotted lines indicate BP response to the rub test.
    Julu, P.O.O., Hansen, S. & Jamal, G.A. (2001). J. Physiol. 533.P, 76-77P.

Where applicable, experiments conform with Society ethical requirements.

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