Baroreflex control of muscle sympathetic nerve activity after carotid body tumor resection.

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, 51+/-11 years) and 6 healthy control subjects (2 men and 4 women, 50+/-7 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: 3.68+/-0.93 versus 11.61+/-4.72 ms/mm Hg (phenylephrine, P=0.011) and 2.53+/-1.36 versus 5.82+/-1.94 ms/mm Hg (nitroprusside, P=0.05); sympathetic baroreflex sensitivity: 3.70+/-2.90 versus 7.53+/-4.12 activity/100 beats/mm Hg (phenylephrine, P=0.10) and 3.93+/-4.43 versus 15.27+/-10.03 activity/100 beats/mm Hg (nitroprusside, P=0.028)]. The Valsalva maneuver elicited normal reflex changes in muscle sympathetic nerve activity, whereas heart rate responses were blunted in the patients with bilateral carotid body tumor resection. Maximal sympathetic responses to the cold pressor test did not differ between the two groups. Denervation of carotid sinus baroreceptors as the result of bilateral carotid body tumor resection produces chronic impairment of baroreflex control of both heart rate and sympathetic nerve activity. During the Valsalva maneuver, loss of carotid baroreflex control of heart rate is less well compensated for by the extra carotid baroreceptors than the control of muscle sympathetic nerve activity.