Intact blood pressure, but not sympathetic, responsiveness to sympathoexcitatory stimuli in a patient with unilateral carotid body resection

Abstract

Despite rapidly growing interest in the therapeutic resection of the carotid body (CB) chemoreceptors, few physiologic studies exist on the consequences of unilateral CB resection. We present a case of an otherwise healthy postmenopausal female who underwent unilateral CB resection for a paraganglioma. Approximately 4 years postoperatively, she underwent analysis of her sympathetic and hemodynamic responses to hypoxia, lower body negative pressure, cold pressor test (CPT), and ischemic hand grip exercise and postexercise ischemia (IHE/PEI). Hypoxic ventilatory response and baroreflex sensitivity were relatively normal. Hemodynamic responses to IHE/PEI and CPT showed characteristic increases in cardiac output (from 3.9 L/min to 5.2 L/min [IHE/PEI] and 4.9 L/min [CPT]) and blood pressure (from 126/72 mmHg to 161/87 mmHg [IHE/PEI] and 171/93 mmHg [CPT]). However, muscle sympathetic nerve activity (microneurography of the peroneal nerve) decreased from baseline during IHE/PEI and CPT (burst incidence nadir of 45% and 40% of baseline, respectively) and there was no observable change in total peripheral resistance (from 24 mmHg*min/L to 22 mmHg*min/L [IHE/PEI] and 25 mmHg*min/L [CPT]). These findings illustrate intact blood pressure responsiveness despite attenuated sympathoexcitation, possibly due to an increase in cardiac output and/or adaptive inhibitory effect of the baroreflex on peripheral sympathetic activity.

Keywords: Baroreflex sensitivity; carotid chemoreceptor; hypoxic ventilatory response; muscle sympathetic nerve activity.

Figure 1

Magnetic resonance angiography scans pre‐(A) and post‐(B) paraganglioma resection. Imaging revealed the presence of bilateral carotid body paragangliomas, 2.7 cm in diameter on the right, and 0.6 cm in diameter on the left. The patient underwent uneventful elective unilateral resection of the right paraganglioma. (A) Preoperative imaging. (B) Postoperative imaging.

Figure 2

Compressed data from the patient's cold pressor test. Data are shown from quiet baseline prior to cold pressor test, 3 min during cold pressor test, and 3 min of recovery after the cold pressor test. MSNA, muscle sympathetic nerve activity.