Blood Pressure Regulation by the Carotid Sinus Nerve: Clinical Implications for Carotid Body Neuromodulation

Immunohistochemical Detection of PIEZO Ion Channels in the Human Carotid Sinus and Carotid Body

The carotid sinus and the carotid body are major peripheral chemo- and baro(mechano)receptors that sense changes in arterial wall pressure and in oxygen, carbon dioxide, and pH in arterial blood. Recently, it was demonstrated that the PIEZO1 and PIEZO2 mechanoreceptor/mechanotransducers are responsible for the baroreflex in the murine aortic arch (aortic sinus). Furthermore, some experimental evidence suggests that the carotid body could participate in mechanosensing. In this study, we used immunohistochemistry and immunofluorescence in conjunction with laser confocal microscopy to study the distribution of PIEZO1 and PIEZO2 in the human carotid sinus and carotid body as well as in the petrosal ganglion of the glossopharyngeal nerve and the superior cervical sympathetic ganglion. PIEZO1 and PIEZO2 were detected in different morphotypes of sensory nerve formations in the walls of the carotid sinus and carotid artery walls. In the carotid body, PIEZO1 was present in a small population of type I glomus cells and absent in nerves, whereas PIEZO2 was present in both clusters of type I glomus cells and nerves. The most prominent expression of PIEZO1 and PIEZO2 in the carotid body was found in type II glomus cells. On the other hand, in the petrosal ganglion, around 25% of neurons were PIEZO1-positive, and around 85% were PIEZO2-positive; regarding the superior cervical sympathetic ganglion, around 71% and 86% displayed PIEZO1 and PIEZO2, respectively. The results of this study suggest that PIEZO1 and PIEZO2 could be involved in the detection and/or mechanotransduction of the human carotid sinus, whereas the role of the carotid body is more doubtful since PIEZO1 and PIEZO2 were only detected in some nerves and PIEZO2 was present in a small population of type I glomus cells, with PIEZO1 being absent in these cells. However, since immunoreactivity for PIEZO2 was detected in type II glomus cells, researchers should investigate whether these cells play a role in the detection of mechanical stimuli and/or participate in mechanotransduction.

The Effect of Thyroid Lobe Volume on the Common Carotid Artery Blood Flow in Thyroidectomy Position

Background/Objectives: This study investigates the effect of thyroid lobe size on common carotid artery hemodynamics during thyroidectomy. While prior research has reported reduced carotid blood flow during the procedure, the impact of thyroid size remains unclear. We hypothesized that larger thyroid lobes may influence carotid flow dynamics via external compression. Methods: Adult patients undergoing elective thyroidectomy were prospectively included. Doppler ultrasonography measured carotid artery diameters and flow characteristics at three time points: before anesthesia induction, after induction, and after surgical positioning. Regional cerebral oximetry was recorded. Each carotid artery was analyzed separately. Results: Data from 202 carotid arteries (132 patients) were analyzed. Baseline carotid diameters and flow velocities were similar between patients with normal and large thyroid lobes. Anesthesia induction reduced flow velocities in all patients. After surgical positioning, patients with large thyroid lobes had significantly increased peak systolic velocity, leading to an overestimation of carotid blood flow, when using formula-based calculations. Manually traced Velocity Time Integral confirmed the increase in peak systolic velocity and a shortened systolic/diastolic ratio in these patients. Receiver operating characteristic analysis identified a thyroid lobe volume cutoff of 19.7 mL (AUC: 0.93, Sensitivity: 85%, Specificity: 98%). Regional cerebral oxygen saturation remained unchanged (p > 0.05). Conclusions: Larger thyroid lobes are associated with altered carotid flow dynamics during thyroidectomy, emphasizing diastolic flow. While these findings provide insight into thyroid-related hemodynamic changes, their applicability to patients with pre-existing carotid stenosis or peripheral artery disease remains uncertain, as our study population did not include such cases.

Sub-Chronic Peroneal Nerve Stimulation Lowers Ambulatory Blood Pressure in Spontaneously Hypertensive Rats

Objective: Acute electrical stimulation of the common peroneal nerve (cPNS) has been shown to cause an immediate reduction in systolic blood pressure (SBP) in spontaneous hypertense rats (SHR), but the effect of this treatment in sub-chronic ambulatory SBP is unknown. Here we developed an implantable wireless WNClip neural stimulator to test the efficacy of 5-week cPNS as a treatment for hypertension. Results: Daily cPNS 2 Hz monophasic stimulation at threshold for 8 minutes every day for five weeks, reduced SBP in WKY animals by -4 mm Hg, and in SHR animals by -21 mmHg in week 5 (p < 0.01). Ambulatory SBP measured daily recorded approximately twenty-four hours after the cPNS treatment, showed a significant reduction from the first (176.6 ± 24.1 mm Hg; n = 5) to the last week of treatment (165.7± 42.7 mm Hg; n = 4), a -9 mm Hg reduction (p < 0.01). Evaluation of heart rate during the treatment showed no significant difference caused by the daily 8-minute cPNS. Conclusions: Electrical stimulation of the common peroneal nerve induced a reduction in SBP that is comparable to that reportedly achieved pharmacologically by ACE inhibitor Ramipril, or by renal denervation procedures. These results support the notion that neuromodulation of the common peroneal nerve can serve as an alternative treatment for drug resistant hypertension.

Bioelectronic modulation of carotid sinus nerve to treat type 2 diabetes: current knowledge and future perspectives

Bioelectronic medicine are an emerging class of treatments aiming to modulate body nervous activity to correct pathological conditions and restore health. Recently, it was shown that the high frequency electrical neuromodulation of the carotid sinus nerve (CSN), a small branch of the glossopharyngeal nerve that connects the carotid body (CB) to the brain, restores metabolic function in type 2 diabetes (T2D) animal models highlighting its potential as a new therapeutic modality to treat metabolic diseases in humans. In this manuscript, we review the current knowledge supporting the use of neuromodulation of the CSN to treat T2D and discuss the future perspectives for its clinical application. Firstly, we review in a concise manner the role of CB chemoreceptors and of CSN in the pathogenesis of metabolic diseases. Secondly, we describe the findings supporting the potential therapeutic use of the neuromodulation of CSN to treat T2D, as well as the feasibility and reversibility of this approach. A third section is devoted to point up the advances in the neural decoding of CSN activity, in particular in metabolic disease states, that will allow the development of closed-loop approaches to deliver personalized and adjustable treatments with minimal side effects. And finally, we discuss the findings supporting the assessment of CB activity in metabolic disease patients to screen the individuals that will benefit therapeutically from this bioelectronic approach in the future.

Commonalities and differences in carotid body dysfunction in hypertension and heart failure

Carotid body pathophysiology is associated with many cardiovascular-respiratory-metabolic diseases. This pathophysiology reflects both hyper-sensitivity and hyper-tonicity. From both animal models and human patients, evidence indicates that amelioration of this pathophysiological signalling improves disease states such as a lowering of blood pressure in hypertension, a reduction of breathing disturbances with improved cardiac function in heart failure (HF) and a re-balancing of autonomic activity with lowered sympathetic discharge. Given this, we have reviewed the mechanisms of carotid body hyper-sensitivity and hyper-tonicity across disease models asking whether there is uniqueness related to specific disease states. Our analysis indicates some commonalities and some potential differences, although not all mechanisms have been fully explored across all disease models. One potential commonality is that of hypoperfusion of the carotid body across hypertension and HF, where the excessive sympathetic drive may reduce blood flow in both models and, in addition, lowered cardiac output in HF may potentiate the hypoperfusion state of the carotid body. Other mechanisms are explored that focus on neurotransmitter and signalling pathways intrinsic to the carotid body (e.g. ATP, carbon monoxide) as well as extrinsic molecules carried in the blood (e.g. leptin); there are also transcription factors found in the carotid body endothelium that modulate its activity (Krüppel-like factor 2). The evidence to date fully supports that a better understanding of the mechanisms of carotid body pathophysiology is a fruitful strategy for informing potential new treatment strategies for many cardiovascular, respiratory and metabolic diseases, and this is highly relevant clinically.

Perioperative blood pressure and heart rate alterations after carotid body tumor excision: a retrospective study of 108 cases

BACKGROUND

Arising from chemoreceptor cells, carotid body tumors (CBTs) are rare neoplasms associated with hemodynamics. Perioperative changes in blood pressure (BP) and heart rate (HR) are not completely understood.

METHODS

This retrospective, observational, controlled study included all CBT patients from 2013 to 2018 in Peking Union Medical College Hospital. Perioperative changes in BP/HR within or between unilateral/bilateral/control groups were investigated. Perioperative details across Shamblin types were also assessed.

RESULTS

This study included 108 patients (116 excised CBTs). The postoperative systolic BP and HR increased in both unilateral (mean difference of systolic BP = 5.9mmHg, 95% CI 3.1 ~ 8.6; mean difference of HR = 3.7 bpm, 95% CI 2.6 ~ 4.9) and bilateral (mean difference of systolic BP = 10.3mmHg, 95% CI 0.6 ~ 19.9; mean difference of HR = 8.4 bpm, 95% CI 0.5 ~ 16.2) CBT patients compared with the preoperative measures. Compared with control group, the postoperative systolic BP increased (difference in the alteration = 6.3mmHg, 95% CI 3.5 ~ 9.0) in unilateral CBT patients; both systolic BP (difference in the alteration = 9.2mmHg, 95% CI 1.1 ~ 17.3) and HR (difference in the alteration = 5.3 bpm, 95% CI 1.0 ~ 9.6) increased in bilateral CBT patients. More CBT patients required extra antihypertensive therapy after surgery than controls (OR = 2.5, 95% CI 1.14 ~ 5.5). Maximum tumor diameter, intraoperative vascular injury, continuous vasoactive agent requirement, total fluid volume, transfusion, estimated blood loss, operation duration, postoperative pathology, overall complications, and intensive care unit/hospital lengths of stay significantly varied among Shamblin types.

CONCLUSION

CBT excision may be associated with subtle perioperative hemodynamic changes. Perioperative management of CBT patients necessitates careful assessment, full preparation and close postoperative monitoring.