Baroreflex Control of Muscle Sympathetic Nerve Activity After Carotid Body Tumor Resection

Abstract

Abstract-Bilateral carotid body tumor resection causes a permanent attenuation of vagal baroreflex sensitivity. We retrospectively examined the effects of bilateral carotid body tumor resection on the baroreflex control of sympathetic nerve traffic. Muscle sympathetic nerve activity was recorded in 5 patients after bilateral carotid body tumor resection (1 man and 4 women, 51Ϯ11 years) and 6 healthy control subjects (2 men and 4 women, 50Ϯ7 years). Baroreflex sensitivity was calculated from changes in R-R interval and muscle sympathetic nerve activity in response to bolus injections of phenylephrine and nitroprusside. In addition, sympathetic responses to the Valsalva maneuver and cold pressor test were measured. The integrated neurogram of patients and control subjects contained a similar pattern of pulse synchronous burst of nerve activity. Baroreflex control of both heart rate and sympathetic nerve activity were attenuated in patients as compared with control subjects [heart rate baroreflex sensitivity: 3.68Ϯ0. 4,6,7 and carotid endarterectomy. 8 The resulting clinical syndrome of baroreflex failure is characterized by recurrent bouts of unrestrained sympathetic excitation, manifesting as severe hypertension, headache, and diaphoresis. The findings of excessive rises in plasma catecholamines during these attacks and of exaggerated pressor responses to cold and mental stress in these patients suggest the loss of baroreflexmediated inhibition of efferent sympathetic nerve activity. 4,6 In a previous study, we have demonstrated that although BCBR elicits the full-blown syndrome of baroreflex failure only in a minority of patients, 9 baroreflex control of heart rate is impaired and blood pressure variability is increased in the long term after BCBR. 9,10 Whether BCBR also affects baroreflex control of sympathetic outflow has not yet been established in humans.The aim of this study was to examine the chronic effects of BCBR on the baroreflex control of sympathetic nerve activity. In this cross-sectional, retrospective study of patients with BCBR and age-matched healthy control subjects, sympathetic baroreflex sensitivity was calculated from MSNA responses to (de-)activation of baroreceptors by phenylephrine and nitroprusside bolus injections. In addition, MSNA responses to the Valsalva maneuver and cold pressor test were assessed. Medical Center Nijmegen, the Netherlands, were included in this study. Individual information on tumor size, additional tumor localizations, and surgical details of these 5 patients are shown in the Table. The median interval between the second operation and the study was 6.7 years (range, 4.4 to 20.3 years). Patients were free of diabetes and neurological, cardiovascular, and pulmonary disease. Six healthy subjects (2 men and 4 women) served as control subjects. Full medical history and physical examination including blood pressure measurements revealed no abnormalities. Groups were matched for age (BCBR: 51.2Ϯ10.8 versus control subjects: 50.0Ϯ6.5 years), body mass index (24.8Ϯ1.1 ve...

Recent Insights into Carotid Baroreflex Function in Humans Using the Variable Pressure Neck Chamber

“…More importantly, it has been shown that both baroreceptor populations operate over the same range of arterial pressures . Although these studies have several limitations that are inherent in human experimental investigations, the findings are in general agreement with studies in patients who have undergone bilateral carotid sinus denervation, with the collective results demonstrating the importance of the carotid baroreceptors in the reflex control of ABP (Smit et al 2002;Fadel et al 2003;Timmers et al 2003).…”

Baroreceptors, baroreceptor unloading, and the long-term control of blood pressure

“…In contrast, less than complete sinus denervation decreases baroreflex sensitivity and increases MAP variability but does not result in an elevated MAP (59,64). These observations differ from animal studies that show no chronic effect of carotid sinus denervation on either the level of MAP or the variability of MAP (33,45,56).…”

“…However, the variability of MAP was elevated relative to normal in all four patients at times ranging from 3 mo to 2 yr after surgery. Timmers et al (64) recorded muscle SNA and HR responses to administration of vasoactive drugs in a group of patients who had bilateral carotid body resection 4 -20 years earlier. At the time of the study, none of the patients showed signs of baroreflex failure or were hypertensive, but all showed decreased baroreflex control of HR compared with age-matched controls.…”

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“…However, patients having had bilateral glomus tumor removal are not able to regulate blood pressure adequately, suggesting that aortic baroreceptors may not be able to substitute for carotid sinus baroreceptors. 32 Continuous radial artery blood pressure recordings calibrated on oscillometric brachial artery measurements were used to determine carotid distensibility. Whether peripheral blood pressure measurements introduce uncertainty in computing carotid distensibility is quite unlikely, although we have to acknowledge that differences between peripheral and central arterial pulse waves might occur.…”