The Carotid Sinus Nerve-Structure, Function, and Clinical Implications

The Cholinergic Amelioration of Sepsis-Induced Baroreflex Dysfunction and Brainstem Inflammation Is Negated by Central Adenosine A3 Receptors

Background/Objectives: Sepsis has been shown to depress arterial baroreceptor function, and this effect is counterbalanced by the cholinergic anti-inflammatory pathway. Considering the importance of central adenosine receptors in baroreceptor function, this study tested whether central adenosine A3 receptors (A3ARs) modulate the cholinergic-baroreflex interaction in sepsis and whether this interaction is modulated by mitogen-activated protein kinases (MAPKs) and related proinflammatory cytokines. Methods: Sepsis was induced by cecal ligation and puncture (CLP) and rats were instrumented with femoral and intracisternal (i.c.) catheters. Baroreflex sensitivity (BRS) was measured 24 h later in conscious animals using the vasoactive method, which correlates changes in blood pressure caused by i.v. phenylephrine (PE) and sodium nitroprusside (SNP) to concomitant reciprocal changes in heart rate. Results: The reduction in reflex bradycardic (BRS-PE), but not tachycardic (BRS-SNP), responses elicited by CLP was reversed by i.v. nicotine in a dose-related manner. The BRS-PE effect of nicotine was blunted following intracisternal administration of IB-MECA (A3AR agonist, 4 µg/rat). The depressant action of IB-MECA on the BRS facilitatory action of nicotine was abrogated following central inhibition of MAPK-JNK (SP 600125), PI3K (wortmannin), and TNFα (infliximab), but not MAPK-ERK (PD 98059). Additionally, the nicotine suppression of sepsis-induced upregulation of NFκB and NOX2 expression in the nucleus tractus solitarius (NTS) was negated by A3AR activation. The molecular effect of IB-MECA on NFκB expression disappeared in the presence of SP 600125, wortmannin, or infliximab. Conclusions: The central PI3K/MAPK-JNK/TNFα pathway contributes to the restraining action of A3ARs on cholinergic amelioration of sepsis-induced central neuroinflammatory responses and impairment of the baroreceptor-mediated negative chronotropism.

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.

Vascular mechanoreceptor magnetic activation, hemodynamic evidence and potential clinical outcomes

There is sufficient proof that static magnetic fields (SMFs) of different parameters have a significant effect on the cardiovascular system. The sometimes contradictory, opposite-directional nature of SMF's hemodynamic effect generates uncertainty; therefore, an explanation of the underlying mechanisms is required. Following SMF selective carotid baroreceptors or microvascular net exposure, both high and low blood pressure (BP)/vascular tone starting conditions showed a return to normal. Beyond the previous descriptions of SMF's simple hemodynamic results, the current study aims to clarify the physiology of the SMF BP/vascular tone normalizing effects. The examination of available literature and hemodynamic tracings provided strong evidence that mechanoreceptor magnetic activation is concealed behind SMF vascular tone adjustment (increasing or decreasing as needed), filling in the knowledge gap regarding SMF opposite directional vascular tone normalizing outcomes. It has been proposed that cytoskeletal actin filament rearrangement, mechanically-gated Ca2+ influx, and nitric oxide (NO) activity may strengthen SMF's vascular mechanoreceptor sensing/regulation ability, modifying BP and vascular tone features in a hemodynamic normalizing pattern. It is suggested that baro/mechanoreceptor magnetic activation physiology is a unique mechanism of the magneto-cardiovascular interaction with substantial potential for cardiovascular protection.

Geometric distribution of plaque calcification is associated with postprocedural hypotension after carotid artery stenting

BACKGROUND

Our study aimed to investigate the relationship between the geometric distribution of plaque calcification and the occurrence of postprocedural hypotension following carotid artery stenting (CAS).

METHODS

We retrospectively analyzed data from CAS patients between April 2018 and February 2023. Plaque calcification was evaluated using cross-sectional images obtained from multiplanar reconstructions perpendicular to the longitudinal axis of the internal carotid artery (ICA). The cross-sectional image of the most stenotic ICA was segmented into four quadrants: interior, exterior, ventral, and dorsal. We innovatively defined the geometric classification of plaque calcification based on physiological anatomy as modified calcification location. Postprocedural hypotension was defined as persistent systolic blood pressure at <90 mmHg, requiring intravenous vasopressor infusions that lasted more than 1 hour.

RESULTS

A total of 477 patients were included in the final analysis. Among them, 41 (8.6%) patients experienced postprocedural hypotension after CAS. For the modified geometric method, plaque calcification was found significantly more frequently in the hypotension group compared with the non-hypotension group in the dorsal quadrant. Binary logistic regression analysis showed that modified calcification location on the dorsal side (OR 3.520, 95% CI 1.497 to 8.274, p=0.004) were independently associated with postprocedural hypotension after CAS.

CONCLUSIONS

The presence of plaque calcification on the dorsal side, using the modified geometric method, was found to be associated with a three-fold increased risk of postprocedural hypotension after CAS. These findings may have implications for patient screening, procedure planning, and hospitalization duration expectations.

The ability of Ibutropin to blunt fentanyl-induced respiratory depression is independent of its activation of carotid body chemoafferents

This study examined the effects of intravenous injection of isobutyric tropine ester (Ibutropin) on ventilation in freely-moving sham-operated (SHAM) male Sprague Dawley rats and those with bilateral carotid sinus nerve transection (CSNX). This study also examined the effects of a subsequent injection of fentanyl on ventilatory parameters in both groups of rats. Ibutropin (200 μmol/kg, i.v.) elicited rapid and pronounced increases in breathing frequency, tidal volume, minute ventilation, peak inspiratory and expiratory flows, and inspiratory and expiratory drives in SHAM rats, but substantially smaller responses in CSNX rats. The subsequent injection of fentanyl (75 μg/kg, i.v.) elicited similar ventilatory responses in Ibutropin-treated SHAM and CSNX rats with markedly different changes in end-inspiratory and end-expiratory pauses, expiratory delay, and apneic pause. Moreover, the fentanyl-induced responses in Ibutropin-treated SHAM and CSNX rats were substantially smaller than in rats that were pre-injected with vehicle (saline) rather than Ibutropin. These novel findings suggest that Ibutropin acts at the carotid body-chemoafferent complex to drive ventilation by mechanisms that may involve the rapid entry of this cell-permeant tropine ester into chemoafferent nerve terminals and/or primary glomus cells. A key finding was that the ability of Ibutropin to blunt the adverse effects of fentanyl on breathing does not require functional carotid body chemoreceptor afferent input to brainstem structures controlling breathing. As such, the ability of Ibutropin to greatly diminish the adverse effects of fentanyl on breathing may involve the actions of Ibutropin within central respiratory control centers and/or peripheral structures other than the carotid bodies. SIGNIFICANCE STATEMENT: This study revealed that the ability of Ibutropin to blunt the respiratory depressant effects of fentanyl may involve mechanisms present in central respiratory control centers and/or peripheral structures other than the carotid bodies.

Pathophysiology of syncope: current concepts and their development

Syncope is a symptom in which transient loss of consciousness occurs as a consequence of a self-limited, spontaneously terminating period of cerebral hypoperfusion. Many circulatory disturbances (e.g. brady- or tachyarrhythmias, reflex cardioinhibition-vasodepression-hypotension) may trigger a syncope or near-syncope episode, and identifying the cause(s) is often challenging. Some syncope may involve multiple etiologies operating in concert, whereas in other cases multiple syncope events may be due to various differing causes at different times. In this communication, we address the current understanding of the principal contributors to syncope pathophysiology including examination of the manner in which concepts evolved, an overview of factors that constitute consciousness and loss of consciousness, and aspects of neurovascular control and communication that are impacted by cerebral hypoperfusion leading to syncope. Emphasis focuses on 1) current understanding of the way transient systemic hypotension impacts brain blood flow and brain function; 2) the complexity and temporal sequence of vascular, humoral, and cardiac factors that may accompany the most common causes of syncope; 3) the range of circumstances and disease states that may lead to syncope; and 4) clinical features associated with syncope and in particular the reflex syncope syndromes.

Unveiling novel molecules and therapeutic targets in hypertension - A narrative review

Hypertension is a prevalent non-communicable disease with serious cardiovascular complications, including heart failure, myocardial infarction, and stroke, often resulting from uncontrolled hypertension. While current treatments primarily target the renin-angiotensin-aldosterone pathway, the therapeutic response remains modest in many patients, with some developing resistant hypertension. Newer therapeutic approaches aim to address hypertension from various aspects beyond conventional drugs, including targeting central nervous system pathways, inflammatory pathways, vascular smooth muscle function, and baroreceptors. Despite these advancements, each therapy faces unique clinical and mechanistic challenges that influence its clinical translatability and long-term viability. This review explores the mechanisms of novel molecules in preclinical and clinical development, highlights potential therapeutic targets, and discusses the challenges and ethical considerations related to hypertension therapeutics and their development.

Expression of the cellular prion protein by mast cells in white-tailed deer carotid body, cervical lymph nodes and ganglia

Chronic wasting disease (CWD) is a transmissible and fatal prion disease that affects cervids. While both oral and nasal routes of exposure to prions cause disease, the spatial and temporal details of how prions enter the central nervous system (CNS) are unknown. Carotid bodies (CBs) are structures that are exposed to blood-borne prions and are densely innervated by nerves that are directly connected to brainstem nuclei, known to be early sites of prion neuroinvasion. All CBs examined contained mast cells expressing the prion protein which is consistent with these cells playing a role in neuroinvasion following prionemia.

Baroreflex activation therapy through electrical carotid sinus stimulation

An imbalance between cardiovascular parasympathetic and sympathetic activity towards sympathetic predominance has been implicated in the pathogenesis of treatment-resistant arterial hypertension and heart failure. Arterial baroreceptors control efferent cardiovascular autonomic activity and have, therefore, been recognized as potential treatment targets. Baroreflex activation therapy through electrical carotid sinus stimulation is a device-based approach to modulate cardiovascular autonomic activity. Electrical carotid sinus stimulation lowered blood pressure in various hypertensive animal models and improved cardiac remodeling and survival in preclinical models of heart failure. In human mechanistic profiling studies, electrical carotid sinus stimulation lowered blood pressure through sympathetic inhibition with substantial inter-individual variability. The first-generation device reduced blood pressure in controlled and uncontrolled clinical trials. Controlled clinical trials proving efficacy in blood pressure reduction in patients with hypertension do not exist for the currently available second-generation carotid sinus stimulator. Investigations in heart failure patients showed improved symptoms, quality of life, and natriuretic peptide biomarkers. Electrical carotid sinus stimulation is an interesting technology to modulate cardiovascular autonomic control. However, controlled trials with hard clinical endpoints are required.

Low-intensity focused ultrasound combined with microbubbles for non-invasive downregulation of rabbit carotid body activity in the treatment of hypertension

Targeting the carotid body (CB) is a new approach in treating hypertension. This study investigates the efficacy and safety of ultrasound combined with microbubbles in targeting CB to treat hypertension. Twenty-seven hypertensive rabbits were randomly assigned to three groups: microbubbles only (sham group, n = 11), ultrasound plus microbubbles (LIFU group, n = 11), and bilateral carotid sinus nerve denervation (CSND group, n = 5). Four weeks post-intervention, blood pressure, hypoxic ventilatory response (HVR), blood pressure variability (BPV), heart rate variability (HRV), biochemical indicators, neurohormones, and histopathology were assessed in all groups. The results indicated significant reductions in systolic and diastolic blood pressure in the LIFU and CSND groups post-intervention, along with decreases in BPV, HRV, and catecholamines. HVR results showed a 35.10% reduction in CB activity in the LIFU group compared to the sham group, which was significantly lower than the reduction in the CSND group compared to the sham group (73.85%). Histopathology and transmission electron microscopy confirmed CB damage and cell apoptosis, with immunofluorescence showing a reduction in type I and II cells. In conclusion, LIFU combined with microbubbles can reduce blood pressure by lowering CB and sympathetic nerve activity.

Carotid baroreceptor dysfunction after carotid body tumour resections

OBJECTIVE

Carotid body tumours (CBTs) and baroreceptor failure (BRF) are two distinct but interrelated conditions, affecting the carotid body and its regulatory mechanisms. We aim to describe and quantify BRF after unilateral and bilateral CBT resections.

METHODS

Prospective cohort study. We included all patients with unilateral or bilateral CBT undergoing resection from April 2021 to January 2023. Demographics and CBTs characteristics were analysed; baroreceptor sensitivity assessment was conducted using the Composite Autonomic Severity Score (CASS). Statistical analyses were performed using R. Significance level was set at a 2-tailed α = 0.05.

RESULTS

A total of 30 patients with CBT underwent surgical resection, twenty-three were included in the study (18 unilateral and 5 bilateral CBTs). All 23 (100 %) were females, median age of 60 years. Regarding patients with unilateral CBT; preoperatively, 13 had BRF, the most common dysfunction subtype was mixed. Postoperatively, the most common dysfunction subtype was sympathetic failure. With regards to bilateral CBTs; 2 patients did not have autonomic dysfunction preoperatively. After bilateral surgical resection one patient remained without autonomic dysfunction; however, all other patients persisted with BRF.

CONCLUSION

BRF was present in 13 patients with unilateral CBT and 3 patients with bilateral tumours preoperatively; most will remain with BRF and will only change the characteristics postoperatively. No associations were found between type, severity of BRF and Shamblin classification or laterality. It is paramount that research in this area continues as many features are yet unknown regarding CBT pathogenesis, hence, BRF may be present yet not affect significantly quality of life.

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.

Physiological and clinical impact in the carotid baroreceptor function following the surgical management of bilateral carotid body tumors

OBJECTIVE

The bilateral presentation of Carotid Body Tumors (CBT) is rare; the surgical resection of these masses remains the mainstay management due to the malignant potential. We aim to describe, classify, and quantify baroreceptor failure (BRF) after the surgical management of patients with bilateral CBT to better understand the clinical consequences.

METHODS

Retrospective review of patients that underwent bilateral CBT resection to assess the changes in baroreceptor function. We describe the clinical events associated to BRF after surgery, baseline patient's demographics, characteristics, comorbidities. Additionally, clinical and a quantitative evaluation of baroreceptor sensitivity were conducted using the Composite Autonomic Severity Score (CASS).

RESULTS

From 1986 to 2020, a total 146 CBT resections were performed in 132 patients in our institution. Tumors were removed bilaterally in staged procedures in seven patients with a mean age of 61 years (Standard Deviation 11), six (85%) were females, and there was no family history of paragangliomas. The clinical presentation were palpable masses in 5 (71%), and odynophagia in 2 (29%) cases; malignant histopathology following surgery was found in one case. BRF occurred in one patient after unilateral CBT resection, consisting of bradycardia and a 40 s asystole that was not previously associated to BR sensitivity. Three (43%) patients presented BRF in the immediate postoperative period of the contralateral CBT excision, consisting of volatile hypertensive crisis in two cases, and supraventricular tachycardia in one. All the patients developed (100%) chronic baroreceptor sensitivity symptoms consisting in syncope, vertigo and fatigue in 4 (57%), tachycardia in 2 (28%), and orthostatic headache in one (14%). Autonomic testing showed mixed sympathetic and parasympathetic failure in five (71%), severe sympathetic failure in 1 (14%), and parasympathetic dysfunction in one patient (14%).

CONCLUSIONS

Postoperative autonomic assessment confirmed BRF in all studied patients that underwent staged bilateral CBT resection with mixed, sympathetic, and parasympathetic dysfunction. Further studies are necessary to evaluate the incidence and physiological mechanisms of these sequelae to anticipate possible complications and offer the appropriate perioperative management.

Blood oxygen regulation via P2Y12R expressed in the carotid body

BACKGROUND

Peripheral blood oxygen monitoring via chemoreceptors in the carotid body (CB) is an integral function of the autonomic cardiorespiratory regulation. The presence of the purinergic P2Y12 receptor (P2Y12R) has been implicated in CB; however, the exact role of the receptor in O2 sensing and signal transduction is unknown.

METHODS

The presence of P2Y12R was established by immunoblotting, RT qPCR and immunohistochemistry. Primary glomus cells were used to assess P2Y12R function during hypoxia and hypercapnia, where monoamines were measured by HPLC; calcium signal was recorded utilizing OGB-1 and N-STORM Super-Resolution System. Ingravescent hypoxia model was tested in anaesthetized mice of mixed gender and cardiorespiratory parameters were recorded in control and receptor-deficient or drug-treated experimental animals.

RESULTS

Initially, the expression of P2Y12R in adult murine CB was confirmed. Hypoxia induced a P2Y12R-dependent release of monoamine transmitters from isolated CB cells. Receptor activation with the endogenous ligand ADP promoted release of neurotransmitters under normoxic conditions, while blockade disrupted the amplitude and duration of the intracellular calcium concentration. In anaesthetised mice, blockade of P2Y12R expressed in the CB abrogated the initiation of compensatory cardiorespiratory changes in hypoxic environment, while centrally inhibited receptors (i.e. microglial receptors) or receptor-deficiency induced by platelet depletion had limited influence on the physiological adjustment to hypoxia.

CONCLUSIONS

Peripheral P2Y12R inhibition interfere with the complex mechanisms of acute oxygen sensing by influencing the calcium signalling and the release of neurotransmitter molecules to evoke compensatory response to hypoxia. Prospectively, the irreversible blockade of glomic receptors by anti-platelet drugs targeting P2Y12Rs, propose a potential, formerly unrecognized side-effect to anti-platelet medications in patients with pulmonary morbidities.

A pilot study to assess the origin of the spectral power increases of heart rate variability associated with transient changes in the R-R interval

Spectral analysis of heart rate variability (HRV) is used to assess cardiovascular autonomic function. In the power density spectrum calculated from a time series of the R-R interval (RRI), three main components are distinguished: very-low-frequency (VLF; 0.003-0.04 Hz), low-frequency (LF; 0.04-0.15 Hz), and high-frequency (HF; 0.15-0.4 Hz) components. However, the physiological correlates of these frequency components have yet to be determined. In this study, we conducted spectral analysis of data segments of various lengths (5, 30, 100, and 200 s) of the RRI time series during active standing. Because of the trade-off relationship between time and frequency resolution, the analysis of the RRI data segment shorter than 30 s was needed to identify the temporal relationships between individual transient increases in RRI and the resulting spectral power changes. In contrast, the segment of 200 s was needed to properly evaluate the magnitude of the increase in the VLF power. The results showed that a transient increase in the RRI was tightly associated with simultaneous increases in the powers of the VLF, LF, and HF components. We further found that the simultaneous power increases in these three components were caused by the arterial baroreceptor reflex responding to rapid blood pressure rise.

Acid-Sensing Ion Channels' Immunoreactivity in Nerve Profiles and Glomus Cells of the Human Carotid Body

The carotid body is a major peripheral chemoreceptor that senses changes in arterial blood oxygen, carbon dioxide, and pH, which is important for the regulation of breathing and cardiovascular function. The mechanisms by which the carotid body senses O2 and CO2 are well known; conversely, the mechanisms by which it senses pH variations are almost unknown. Here, we used immunohistochemistry to investigate how the human carotid body contributes to the detection of acidosis, analyzing whether it expresses acid-sensing ion channels (ASICs) and determining whether these channels are in the chemosensory glomic cells or in the afferent nerves. In ASIC1, ASIC2, and ASIC3, and to a much lesser extent ASIC4, immunoreactivity was detected in subpopulations of type I glomus cells, as well as in the nerves of the carotid body. In addition, immunoreactivity was found for all ASIC subunits in the neurons of the petrosal and superior cervical sympathetic ganglia, where afferent and efferent neurons are located, respectively, innervating the carotid body. This study reports for the first time the occurrence of ASIC proteins in the human carotid body, demonstrating that they are present in glomus chemosensory cells (ASIC1 < ASIC2 > ASIC3 > ASIC4) and nerves, presumably in both the afferent and efferent neurons supplying the organ. These results suggest that the detection of acidosis by the carotid body can be mediated via the ASIC ion channels present in the type I glomus cells or directly via sensory nerve fibers.

Expression of the cellular prion protein by mast cells in the human carotid body

Prion diseases are fatal neurologic disorders that can be transmitted by blood transfusion. The route for neuroinvasion following exposure to infected blood is not known. Carotid bodies (CBs) are specialized chemosensitive structures that detect the concentration of blood gasses and provide feedback for the neural control of respiration. Sensory cells of the CB are highly perfused and densely innervated by nerves that are synaptically connected to the brainstem and thoracic spinal cord, known to be areas of early prion deposition following oral infection. Given their direct exposure to blood and neural connections to central nervous system (CNS) areas involved in prion neuroinvasion, we sought to determine if there were cells in the human CB that express the cellular prion protein (PrPC), a characteristic that would support CBs serving as a route for prion neuroinvasion. We collected CBs from cadaver donor bodies and determined that mast cells located in the carotid bodies express PrPC and that these cells are in close proximity to blood vessels, nerves, and nerve terminals that are synaptically connected to the brainstem and spinal cord.

Autonomic cardiovascular control during exercise

The cardiovascular response to exercise is largely determined by neurocirculatory control mechanisms that help to raise blood pressure and modulate vascular resistance which, in concert with regional vasodilatory mechanisms, promote blood flow to active muscle and organs. These neurocirculatory control mechanisms include a feedforward mechanism, known as central command, and three feedback mechanisms, namely, 1) the baroreflex, 2) the exercise pressor reflex, and 3) the arterial chemoreflex. The hemodynamic consequences of these control mechanisms result from their influence on the autonomic nervous system and subsequent alterations in cardiac output and vascular resistance. Although stimulation of the baroreflex inhibits sympathetic outflow and facilitates parasympathetic activity, central command, the exercise pressor reflex, and the arterial chemoreflex facilitate sympathetic activation and inhibit parasympathetic drive. Despite considerable understanding of the cardiovascular consequences of each of these mechanisms in isolation, the circulatory impact of their interaction, which occurs when various control systems are simultaneously activated (e.g., during exercise at altitude), has only recently been recognized. Although aging and cardiovascular disease (e.g., heart failure, hypertension) have both been recognized to alter the hemodynamic consequences of these regulatory systems, this review is limited to provide a brief overview on the action and interaction of neurocirculatory control mechanisms in health.

Long-term exposure to ambient fine particulate matter and carotid intima media thickness at bilateral, left and right in adults from Mexico City: Results from GEA study

BACKGROUND

PM2.5 exposure has been associated with intima-media thickness (cIMT) increase. However, very few studies distinguished between left and right cIMT in relation to PM2.5 exposure.

AIM

To evaluate associations between chronic exposure to PM2.5 and cIMT at bilateral, left, and right in adults from Mexico City.

METHODS

This study comprised 913 participants from the control group, participants without personal or family history of cardiovascular disease, of the Genetics of Atherosclerosis Disease Mexican study (GEA acronym in Spanish), recruited at the Instituto Nacional de Cardiología Ignacio Chávez from June 2008 to January 2013. To assess the associations between chronic exposure to PM2.5 (per 5 μg/m3 increase) at different lag years (1-4 years) and cIMT (bilateral, left, and right) we applied distributed lag non-linear models (DLNMs).

RESULTS

The median and interquartile range for cIMT at bilateral, left, and right, were 630 (555, 735), 640 (550, 750), and 620 (530, 720) μm, respectively. Annual average PM2.5 exposure was 26.64 μg/m3, with median and IQR, of 24.46 (23.5-25.46) μg/m3. Results from DLNMs adjusted for age, sex, body mass index, low-density lipoproteins, and glucose, showed that PM2.5 exposure for year 1 and 2, were positively and significantly associated with right-cIMT [6.99% (95% CI: 3.67; 10.42) and 2.98% (0.03; 6.01), respectively]. Negative associations were observed for PM2.5 at year 3 and 4 and right-cIMT; however only year 3 was statistically significant [-2.83% (95% CI: 5.12; -0.50)]. Left-cIMT was not associated with PM2.5 exposure at any lag year. The increase in bilateral cIMT followed a similar pattern as that observed for right-cIMT, but with lower estimates.

CONCLUSIONS

Our results suggest different susceptibility between left and right cIMT associated with PM2.5 exposure highlighting the need of measuring both, left and right cIMT, regarding ambient air pollution in epidemiological studies.

Vulnerable carotid plaque characteristics on magnetic resonance vessel wall imaging: potential predictors for hemodynamic instability during carotid artery stenting

BACKGROUND

This cross-sectional study sought to explore the possible risk factors assessed with magnetic resonance (MR) vessel wall imaging for hemodynamic instability (HI) during carotid artery stenting (CAS).

METHODS

Patients with carotid stenosis who were referred for CAS from January 2017 to December 2019 were recruited and underwent carotid MR vessel wall imaging. The vulnerable plaque features, including lipid-rich necrotic core (LRNC), intraplaque hemorrhage (IPH), fibrous cap rupture, and plaque morphology, were evaluated. The HI was defined as a drop of systolic blood pressure (SBP) of ≥30 mmHg or the lowest SBP measurement of <90 mmHg after stent implantation. The carotid plaque characteristics were compared between the HI and non-HI groups. The association between carotid plaque characteristics and HI was analyzed.

RESULTS

A total of 56 participants (mean age 68.7±8.3 years; 44 males) were recruited. Patients in the HI group (n=26, 46%) had a significantly greater wall area [median 43.2 (IQR, 34.9-50.5) vs. 35.9 (IQR, 32.3-39.4) mm2; P=0.008], total vessel area (79.7±17.2 vs. 69.9±17.3 mm2; P=0.03), prevalence of IPH (62% vs. 30%; P=0.02), prevalence of vulnerable plaque (77% vs. 43%; P=0.01), and volume of LRNC [median 344.7 (IQR, 155.1-665.7) vs. 103.1 (IQR, 53.9-162.9) mm3; P=0.001] in carotid plaque compared to those in non-HI group (n=30, 54%). Carotid LRNC volume (OR =1.005, 95% CI: 1.001-1.009; P=0.01) and presence of vulnerable plaque (OR =4.038, 95% CI: 0.955-17.070; P=0.06) were significantly and marginally associated with HI, respectively.

CONCLUSIONS

Carotid plaque burden and vulnerable plaque features, particularly a larger LRNC, might be effective predictors for HI during the CAS procedure.

Visualization of the carotid body in situ in fixed human carotid bifurcations using a xylene-based tissue clearing method

The anatomy of the carotid body (CB) and its nerve supply are important, because it is a potential therapeutic target for treatment of various clinical conditions. Visualization of the CB in situ in fixed human anatomical specimens is hampered by obscuring adipose and connective tissues. We developed a tissue clearing method to optimize identification of the CB. We used single sided carotid bifurcations of six human cadavers fixed long term. Visualization of the CB was accomplished by clearing tissue with xylene. Under incident light, carotid bifurcations exhibited a less transparent, darker colored CB; hematoxylin and eosin stained paraffin sections confirmed its identity. Our visualization of the CB in situ in human carotid bifurcations fixed long term enabled targeted resection and subsequent topographic and morphometric measurements of the CB. Our procedure does not interfere with immunohistochemical staining of sections prepared from such specimens.

Organ- and function-specific anatomical organization of vagal fibers supports fascicular vagus nerve stimulation

Vagal fibers travel inside fascicles and form branches to innervate organs and regulate organ functions. Existing vagus nerve stimulation (VNS) therapies activate vagal fibers non-selectively, often resulting in reduced efficacy and side effects from non-targeted organs. The transverse and longitudinal arrangement of fibers inside the vagal trunk with respect to the functions they mediate and organs they innervate is unknown, however it is crucial for selective VNS. Using micro-computed tomography imaging, we tracked fascicular trajectories and found that, in swine, sensory and motor fascicles are spatially separated cephalad, close to the nodose ganglion, and merge caudad, towards the lower cervical and upper thoracic region; larynx-, heart- and lung-specific fascicles are separated caudad and progressively merge cephalad. Using quantified immunohistochemistry at single fiber level, we identified and characterized all vagal fibers and found that fibers of different morphological types are differentially distributed in fascicles: myelinated afferents and efferents occupy separate fascicles, myelinated and unmyelinated efferents also occupy separate fascicles, and small unmyelinated afferents are widely distributed within most fascicles. We developed a multi-contact cuff electrode to accommodate the fascicular structure of the vagal trunk and used it to deliver fascicle-selective cervical VNS in anesthetized and awake swine. Compound action potentials from distinct fiber types, and physiological responses from different organs, including laryngeal muscle, cough, breathing, and heart rate responses are elicited in a radially asymmetric manner, with consistent angular separations that agree with the documented fascicular organization. These results indicate that fibers in the trunk of the vagus nerve are anatomically organized according to functions they mediate and organs they innervate and can be asymmetrically activated by fascicular cervical VNS.

The carotid body: A novel key player in neuroimmune interactions

The idea that the nervous system communicates with the immune system to regulate physiological and pathological processes is not new. However, there is still much to learn about how these interactions occur under different conditions. The carotid body (CB) is a sensory organ located in the neck, classically known as the primary sensor of the oxygen (O2) levels in the organism of mammals. When the partial pressure of O2 in the arterial blood falls, the CB alerts the brain which coordinates cardiorespiratory responses to ensure adequate O2 supply to all tissues and organs in the body. A growing body of evidence, however, has demonstrated that the CB is much more than an O2 sensor. Actually, the CB is a multimodal sensor with the extraordinary ability to detect a wide diversity of circulating molecules in the arterial blood, including inflammatory mediators. In this review, we introduce the literature supporting the role of the CB as a critical component of neuroimmune interactions. Based on ours and other studies, we propose a novel neuroimmune pathway in which the CB acts as a sensor of circulating inflammatory mediators and, in conditions of systemic inflammation, recruits a sympathetic-mediated counteracting mechanism that appears to be a protective response.

Expression of group II and III mGluRs in the carotid body and its role in the carotid chemoreceptor response to acute hypoxia

The carotid body (CB) contributes significantly to oxygen sensing. It is unclear, however, whether glutamatergic signaling is involved in the CB response to hypoxia. Previously, we reported that ionotropic glutamate receptors (iGluRs) and multiple glutamate transporters are present in the rat CB. Except for iGluRs, glutamate receptors also include metabotropic glutamate receptors (mGluRs), which are divided into the following groups: Group I (mGluR1/5); group II (mGluR2/3); group III (mGluR4/6/7/8). We have studied the expression of group I mGluRs in the rat CB and its physiological function response to acute hypoxia. To further elucidate the states of mGluRs in the CB, this study’s aim was to investigate the expression of group II and III mGluRs and the response of rat CB to acute hypoxia. We used reverse transcription-polymerase chain reaction (RT-PCR) to observed mRNA expression of GRM2/3/4/6/7/8 subunits by using immunostaining to show the distribution of mGluR2 and mGluR8. The results revealed that the GRM2/3/4/6/7/8 mRNAs were expressed in both rat and human CB. Immunostaining showed that mGluR2 was localized in the type I cells and mGluR8 was localized in type I and type II cells in the rat CB. Moreover, the response of CB to acute hypoxia in rats was recorded by in vitro carotid sinus nerve (CSN) discharge. Perfusion of group II mGluRs agonist or group III mGluRs agonist (LY379268 or L-SOP) was applied to examine the effect of group II and III mGluRs on rat CB response to acute hypoxia. We found that LY379268 and L-SOP inhibited hypoxia-induced enhancement of CSN activity. Based on the above findings, group II and III mGluRs appear to play an inhibitory role in the carotid chemoreceptor response to acute hypoxia.

Relationship between annular calcification of plaques in the carotid sinus and perioperative hemodynamic disorder in carotid angioplasty and stenting

OBJECTIVE

To investigate the correlation between annular plaque calcification in the carotid sinus and perioperative hemodynamic disorder (HD) in carotid angioplasty and stenting (CAS).

METHODS

The clinical data of 49 patients undergoing CAS due to narrowing of the carotid sinus were retrospectively analyzed. All patients had preoperative carotid computed tomography angiography (CTA) and were divided into HD and non-HD groups based on the occurrence of HD in the perioperative period of CAS. HD was defined as persistent bradycardia (heart rate < 60 beats per min) or persistent hypotension (systolic blood pressure < 90 mmHg) in the perioperative period and lasting for at least 1 h. The baseline data, including the degree of carotid artery stenosis, plaque length, plaque thickness, calcified plaque morphologies (i.e., plaque circumferential angle: < 90° defined as dotted calcification; 90°-180° defined as arcuate calcification; > 180° defined as annular calcification), contralateral carotid artery conditions, balloon diameter, and stent types, were compared between the two groups. Binary logistic regression was used to analyze the risk factors for the occurrence of HD.

RESULTS

Among the 49 patients undergoing CAS, 14 (28.57%) developed perioperative HD, and 35 did not. Annular calcification was more common in the patients in the HD group than in the non-HD group. No significant differences in the probabilities of dotted and arcuate calcifications were found between the two groups (p > 0.05). The duration of continuous dopamine consumption in the HD group was 9-71 h. The average hospital stay of the HD group (10.14 ± 4.17 days) was significantly longer than that of the non-HD group (6.57 ± 1.9 days; p < 0.001). Patients in the HD group had significantly more pronounced lumen stenosis (p = 0.033) and longer plaque length (p = 0.034) than those in the non-HD group. After adjusting for age and sex, multivariate regression analysis showed that the presence of annular plaque calcification was an independent predictor of HD (odds ratio: 7.68, 95% confidence interval: 1.46-40.37, p = 0.016).

CONCLUSIONS

The occurrence of annular plaque calcification in the carotid sinus was an independent risk factor for perioperative HD in CAS. Preoperative carotid CTA assists with the early identification of high-risk patients who may develop HD.

Current trends in carotid body tumors: Comprehensive review

BACKGROUND

Carotid body tumor (CBT) is a rare neoplasm that has been increasingly studied during the last decades; nevertheless, it continues to be a topic of controversy. This review aims to provide an update on the general features of CBT and particularly review different treatment strategies and primary outcomes.

METHODS

Data for this literature review were identified by PubMed, Scopus, and Medline. 93 articles from the initial search were included, as well as 28 relevant studies utilizing the snowballing method; totaling 121 articles about CBT.

RESULTS

Main features such as anatomy, embryology, genetics, clinical presentation, and diagnosis of CBT are presented, followed by evidence of different treatment strategies such as radiotherapy, preoperative embolization, vascular resection, and vascular reconstruction. Main complications are also discussed.

CONCLUSION

This review summarizes the most critical aspects regarding CBT. Future studies should compare different treatments to attain the best surgical results with lower morbidity rates.

Peripheral nerve stimulation and immunity: the expanding opportunities for providing mechanistic insight and therapeutic intervention

Pre-clinical research advances our understanding of the vagus nerve-mediated regulation of immunity and clinical trials successfully utilize electrical vagus nerve stimulation in the treatment of patients with inflammatory disorders. This symbiotic relationship between pre-clinical and clinical research exploring the vagus nerve-based 'inflammatory reflex' has substantially contributed to establishing the field of bioelectronic medicine. Recent studies identify a crosstalk between the vagus nerve and other neural circuitries in controlling inflammation and delineate new neural immunoregulatory pathways. Here we outline current mechanistic insights into the role of vagal and non-vagal neural pathways in neuro-immune communication and inflammatory regulation. We also provide a timely overview of expanding opportunities for bioelectronic neuromodulation in the treatment of various inflammatory disorders.

The Rheology of the Carotid Sinus: A Path Toward Bioinspired Intervention

The association between blood viscosity and pathological conditions involving a number of organ systems is well known. However, how the body measures and maintains appropriate blood viscosity is not well-described. The literature endorsing the function of the carotid sinus as a site of baroreception can be traced back to some of the earliest descriptions of digital pressure on the neck producing a drop in blood delivery to the brain. For the last 30 years, improved computational fluid dynamic (CFD) simulations of blood flow within the carotid sinus have demonstrated a more nuanced understanding of the changes in the region as it relates to changes in conventional metrics of cardiovascular function, including blood pressure. We suggest that the unique flow patterns within the carotid sinus may make it an ideal site to transduce flow data that can, in turn, enable real-time measurement of blood viscosity. The recent characterization of the PIEZO receptor family in the sinus vessel wall may provide a biological basis for this characterization. When coupled with other biomarkers of cardiovascular performance and descriptions of the blood rheology unique to the sinus region, this represents a novel venue for bioinspired design that may enable end-users to manipulate and optimize blood flow.

The inevitability of ATP as a transmitter in the carotid body

Atmospheric oxygen concentrations rose markedly at several points in evolutionary history. Each of these increases was followed by an evolutionary leap in organismal complexity, and thus the cellular adaptions we see today have been shaped by the levels of oxygen within our atmosphere. In eukaryotic cells, oxygen is essential for the production of adenosine 5'-triphosphate (ATP) which is the 'Universal Energy Currency' of life. Aerobic organisms survived by evolving precise mechanisms for converting oxygen within the environment into energy. Higher mammals developed specialised organs for detecting and responding to changes in oxygen content to maintain gaseous homeostasis for survival. Hypoxia is sensed by the carotid bodies, the primary chemoreceptor organs which utilise multiple neurotransmitters one of which is ATP to evoke compensatory reflexes. Yet, a paradox is presented in oxygen sensing cells of the carotid body when during periods of low oxygen, ATP is seemingly released in abundance to transmit this signal although the synthesis of ATP is theoretically halted because of its dependence on oxygen. We propose potential mechanisms to maintain ATP production in hypoxia and summarise recent data revealing elevated sensitivity of purinergic signalling within the carotid body during conditions of sympathetic overactivity and hypertension. We propose the carotid body is hypoxic in numerous chronic cardiovascular and respiratory diseases and highlight the therapeutic potential for modulating purinergic transmission.

3D Reconstruction of the Morpho-Functional Topography of the Human Vagal Trigone

The Vagal Trigone, often referred to as Ala Cinerea, is a triangular-shaped area of the floor of the fourth ventricle that is strictly involved in the network of chardiochronotropic, baroceptive, respiratory, and gastrointestinal control systems of the medulla oblongata. While it is frequently identified as the superficial landmark for the underlying Dorsal Motor Nucleus of the Vagus, this correspondence is not univocal in anatomical literature and is often oversimplified in neuroanatomy textbooks and neurosurgical atlases. As the structure represents an important landmark for neurosurgical procedures involving the floor of the fourth ventricle, accurate morphological characterization is required to avoid unwanted side effects (e.g., bradychardia, hypertension) during neuorphysiological monitoring and cranial nerve nuclei stimulation in intraoperative settings. The aim of this study was to address the anatomo-topographical relationships of the Vagal Trigone with the underlying nuclei. For this purpose, we have conducted an anatomo-microscopical examination of serial sections deriving from 54 Human Brainstems followed by 3D reconstruction and rendering of the specimens. Our findings indicate that the Vagal Trigone corresponds only partially with the Dorsal Motor Nucleus of the Vagus, while most of its axial profile is occupied by the dorsal regions of the Solitary Tract Nucleus. Furthermore, basing on literature and our findings we speculate that the neuroblasts of the Dorsal Motor Nucleus of the Vagus undergo neurobiotaxic migration induced by the neuroblasts of the dorsolaterally located solitary tract nucleus, giving rise to the Ala Cinerea, a topographically defined area for parasympathetic visceral control.

Comparative morphological and molecular studies on the oxygen-chemoreceptive cells in the carotid body and fish gills

Oxygen-chemoreceptive cells play critical roles for the respiration control. This review summarizes the chemoreceptive cells in the carotid body and fish gills from a morphological and molecular perspective. The cells synthesize and secrete biogenic amines, neuropeptides, and neuroproteins and also express many signaling molecules and transcription factors. In mammals, birds, reptiles, and amphibians, the carotid body primordium is consistently formed in the wall of the third arch artery which gives rise to the common carotid artery and the basal portion of the internal carotid artery. Consequently, the carotid body is located in the carotid bifurcation region, except birds in which the organ is situated at the lateral side of the common carotid artery. The carotid body receives branches of the cranial nerves IX and/or X dependent on the location of the organ. The glomus cell progenitors in mammals and birds are derived from the neighboring ganglion, i.e., the superior cervical sympathetic ganglion and the nodose ganglion, respectively, and immigrate into the carotid body primordium, constituting a solid cell cluster. In other animal species, the glomus cells are dispersed singly or forming small cell groups in intervascular stroma of the carotid body. In fishes, the neuroepithelial cells, corresponding to the glomus cells, are distributed in the gill filaments and lamellae. All oxygen-chemoreceptive cells sensitively respond to acute or chronic hypoxia, exhibiting degranulation, hypertrophy, hyperplasia, and upregulated expression of many genes.

Bioelectronic medicine for the autonomic nervous system: clinical applications and perspectives

Bioelectronic medicine (BM) is an emerging new approach for developing novel neuromodulation therapies for pathologies that have been previously treated with pharmacological approaches. In this review, we will focus on the neuromodulation of autonomic nervous system (ANS) activity with implantable devices, a field of BM that has already demonstrated the ability to treat a variety of conditions, from inflammation to metabolic and cognitive disorders. Recent discoveries about immune responses to ANS stimulation are the laying foundation for a new field holding great potential for medical advancement and therapies and involving an increasing number of research groups around the world, with funding from international public agencies and private investors. Here, we summarize the current achievements and future perspectives for clinical applications of neural decoding and stimulation of the ANS. First, we present the main clinical results achieved so far by different BM approaches and discuss the challenges encountered in fully exploiting the potential of neuromodulatory strategies. Then, we present current preclinical studies aimed at overcoming the present limitations by looking for optimal anatomical targets, developing novel neural interface technology, and conceiving more efficient signal processing strategies. Finally, we explore the prospects for translating these advancements into clinical practice.

Eagle's syndrome, elongated styloid process and new evidence for pre-manipulative precautions for potential cervical arterial dysfunction

INTRODUCTION

Safety with upper cervical interventions is a frequently discussed and updated concern for physical therapists, chiropractors and osteopaths. IFOMPT developed the framework for safety assessment of the cervical spine, and this topic has been discussed in-depth with past masterclasses characterizing carotid artery dissection and cervical arterial dysfunction. Our masterclass will expand on this information with knowledge of specific anatomical anomalies found to produce Eagle's syndrome, and cause carotid artery dissection, stroke and even death. Eagle's syndrome is an underdiagnosed, multi-mechanism symptom assortment produced by provocation of the sensitive carotid space structures by styloid process anomalies. As the styloid traverses between the internal and external carotid arteries, provocation of the vessels and periarterial sympathetic nerve fibers can lead to various neural, vascular and autonomic symptoms. Eagle's syndrome commonly presents as neck, facial and jaw pain, headache and arm paresthesias; problems physical therapists frequently evaluate and treat.

PURPOSE

This masterclass aims to outline the safety concerns, assessment and management of patients with Eagle's syndrome and styloid anomalies. By providing evidence of this common anomaly found in almost one-third of the population, hypothesis generation and clinical reasoning with patients presenting with head and neck symptoms can improve.

IMPLICATIONS

Including styloid anomalies as potential hypotheses for patients with head and neck complaints can assist therapists in safe practice and expedite referral. The authors recommend updating the IFOMPT framework to incorporate Eagle's syndrome, a comprehensive autonomic assessment, and palpation of the stylohyoid complex to avoid potentially serious complications from conceivably hazardous interventions.

Anticancer Medications and Sodium Dysmetabolism

Therapeutic advances have revolutionised cancer treatment over the last two decades, but despite improved survival and outcomes, adverse effects to anticancer therapy such as dyselectrolytaemias do occur and need to be managed appropriately. This review explores essential aspects of sodium homeostasis in cancer with a focus on alterations arising from anticancer medications. Sodium and water balance are tightly regulated by close interplay of stimuli arising from hypothalamic osmoreceptors, arterial and atrial baroreceptors and the renal juxtaglomerular apparatus. This delicate balance can be disrupted by cancer itself, as well as the medications used to treat it. Some of the conventional chemotherapeutics, such as alkylating agents and platinum-based drugs, can cause hyponatraemia and, on rare occasions, hypernatraemia. Other conventional agents such as vinca alkaloids, as well as newer targeted cancer therapies including small molecule inhibitors and monoclonal antibodies, can cause hyponatraemia, usually as a result of inappropriate antidiuretic hormone secretion. Hyponatraemia can also sometimes occur secondarily to drug-induced hypocortisolism or salt-wasting syndromes. Another atypical but distinct mechanism for hyponatraemia is via pituitary dysfunction induced by immune checkpoint inhibitors. Hypernatraemia is uncommon and occasionally ensues as a result of drug-induced nephrogenic diabetes insipidus. Identification of the aetiology and appropriate management of these conditions, in addition to averting treatment-related problems, can be lifesaving in critical situations.

Growth Factors in the Carotid Body-An Update

The carotid body may undergo plasticity changes during development/ageing and in response to environmental (hypoxia and hyperoxia), metabolic, and inflammatory stimuli. The different cell types of the carotid body express a wide series of growth factors and corresponding receptors, which play a role in the modulation of carotid body function and plasticity. In particular, type I cells express nerve growth factor, brain-derived neurotrophic factor, neurotrophin 3, glial cell line-derived neurotrophic factor, ciliary neurotrophic factor, insulin-like-growth factor-I and -II, basic fibroblast growth factor, epidermal growth factor, transforming growth factor-α and -β, interleukin-1β and -6, tumor necrosis factor-α, vascular endothelial growth factor, and endothelin-1. Many specific growth factor receptors have been identified in type I cells, indicating autocrine/paracrine effects. Type II cells may also produce growth factors and express corresponding receptors. Future research will have to consider growth factors in further experimental models of cardiovascular, metabolic, and inflammatory diseases and in human (normal and pathologic) samples. From a methodological point of view, microarray and/or proteomic approaches would permit contemporary analyses of large groups of growth factors. The eventual identification of physical interactions between receptors of different growth factors and/or neuromodulators could also add insights regarding functional interactions between different trophic mechanisms.

Phylogenic Determinants of Cardiovascular Frailty, Focus on Hemodynamics and Arterial Smooth Muscle Cells

The evolution of the circulatory system from invertebrates to mammals has involved the passage from an open system to a closed in-parallel system via a closed in-series system, accompanying the increasing complexity and efficiency of life’s biological functions. The archaic heart enables pulsatile motion waves of hemolymph in invertebrates, and the in-series circulation in fish occurs with only an endothelium, whereas mural smooth muscle cells appear later. The present review focuses on evolution of the circulatory system. In particular, we address how and why this evolution took place from a closed, flowing, longitudinal conductance at low pressure to a flowing, highly pressurized and bifurcating arterial compartment. However, although arterial pressure was the latest acquired hemodynamic variable, the general teleonomy of the evolution of species is the differentiation of individual organ function, supported by specific fueling allowing and favoring partial metabolic autonomy. This was achieved via the establishment of an active contractile tone in resistance arteries, which permitted the regulation of blood supply to specific organ activities via its localized function-dependent inhibition (active vasodilation). The global resistance to viscous blood flow is the peripheral increase in frictional forces caused by the tonic change in arterial and arteriolar radius, which backscatter as systemic arterial blood pressure. Consequently, the arterial pressure gradient from circulating blood to the adventitial interstitium generates the unidirectional outward radial advective conductance of plasma solutes across the wall of conductance arteries. This hemodynamic evolution was accompanied by important changes in arterial wall structure, supported by smooth muscle cell functional plasticity, including contractility, matrix synthesis and proliferation, endocytosis and phagocytosis, etc. These adaptive phenotypic shifts are due to epigenetic regulation, mainly related to mechanotransduction. These paradigms actively participate in cardio-arterial pathologies such as atheroma, valve disease, heart failure, aneurysms, hypertension, and physiological aging.

Vasoactive Intestinal Polypeptide in the Carotid Body-A History of Forty Years of Research. A Mini Review

Vasoactive intestinal polypeptide (VIP) consists of 28 amino acid residues and is widespread in many internal organs and systems. Its presence has also been found in the nervous structures supplying the carotid body not only in mammals but also in birds and amphibians. The number and distribution of VIP in the carotid body clearly depends on the animal species studied; however, among all the species, this neuropeptide is present in nerve fibers around blood vessels and between glomus cell clusters. It is also known that the number of nerves containing VIP located in the carotid body may change under various pathological and physiological factors. The knowledge concerning the functioning of VIP in the carotid body is relatively limited. It is known that VIP may impact the glomus type I cells, causing changes in their spontaneous discharge, but the main impact of VIP on the carotid body is probably connected with the vasodilatory effects of this peptide and its influence on blood flow and oxygen delivery. This review is a concise summary of forty years of research concerning the distribution of VIP in the carotid body.

Cranial Nerves: Morphology and Clinical Relevance

This Special Issue entitled "Cranial Nerves: phylogeny, ontogeny, morphology and clinical significance" has been divided into two consecutive volumes. This second volume is devoted to morphology and clinical relevance. Articles in this volume examine these topics from a macroscopic point of view and with a surgical interest. This volume includes articles on oculomotor nerves III, IV, and VI and their course in the orbit; intracranial and extracranial views of the V and VII pairs; and branching patterns of IX, X, XI, and XII pairs with medical significance. Together, these articles provide a general overview of cranial nerves' gross anatomical organization, as well as improving on the knowledge necessary for clinical approaches. Anat Rec, 302:555-557, 2019. © 2019 Wiley Periodicals, Inc.

Carotid Body Baroreceptor Preservation and Control of Arterial Pressure in Eversion Carotid Endarterectomy

The technique of the eversion carotid endarterectomy (ECEA), as an alternative to the conventional endarterectomy with primary or patch angioplasty, is an established technique for managing internal carotid artery stenoses and recently its application has been upgraded through the European Society for Vascular Surgery guidelines (Recommendation 55: Class 1, Level A). However, the typical eversion method has been associated with postoperative hypertension due to loss of the baroreceptor reflex; the standard oblique transection at the bulb performed in the eversion endarterectomy interrupts either the baroreceptor sensoring tissue, which is mostly located in the adventitia at the medial portion of the proximal internal carotid artery, or even the proper Hering nerve, a branch of the glossopharyngeal nerve. These actions deregulate the natural negative feedback of the carotid baroreceptor. Guided by the anatomical location of the baroreceptor sensor we have elaborated a slight modification of the classical ECEA to maintain as much as possible of the viable carotid baroreceptor sensoring surface. By extending the oblique incision distal to the carotid bifurcation in the medial part of the internal carotid artery stem, an eyebrow-like part of the proximal internal carotid artery is maintained and the axis from the sensoring tissue to the nerve of Hering is protected and following the endarterectomy, postoperative arterial blood pressure levels are lower than in the classical ECEA due to the maintenance of the efficiency of the baroreceptor reflex. During the period from September 2016 to November 2018, carotid endarterectomy was performed in 57 patients. Twenty-eight of them underwent the typical ECEA and 29 patients had the modified eyebrow eversion carotid endarterectomy (me-ECEA). The changes of blood pressure baseline during the postoperative course in ECEA and me-ECEA group were analyzed and compared. Postoperative hypertension was defined as an elevation of systolic blood pressure (SBP) greater than 140 mm Hg. Patients who underwent typical ECEA had significantly higher postoperative blood pressure values compared with those who underwent me-ECEA. Actually, the mean postoperative SBP was 172.67 ± 24.59 mm Hg in the typical ECEA group compared with 160.86 ± 12.83 mm Hg in the me-ECEA group ( p  = 0.023). The mean diastolic blood pressure in the ECEA group was 65.42 ± 11.39 mm Hg compared with 58.06 ± 9.06 mm Hg in the me-ECEA group ( p  = 0.009). Our proposed me-ECEA technique seems to be related to lower rates of postoperative hypertension compared with the typical ECEA, probably due to the sparing of the main mass of the baroreceptor apparatus; this improved modification (me-ECEA) of the typical eversion procedure could represent an alternative ECEA technique with its inherent advantages.

The carotid sinus acts as a mechanotransducer of shear oscillation rather than a baroreceptor

The carotid sinus is a dilated area at the base of the internal carotid artery of humans and is located immediately superior to the bifurcation of the internal and external carotid arteries. It is widely accepted, in the fields of medicine and physiology, to function as a baroreceptor in its central control role. This paper presents a hypothesis challenging this paradigm - that the carotid sinus functions by detecting oscillations at the vessel wall which result from shear stress due to vortical flow. This is contrary to conventional thinking which presumes that the carotid sinus responds to blood pressure or wall pressure. Our hypothesis is based on anatomy, physiology and physical properties of fluid which make the sinus the area of highest vorticity. Utilizing magnetic resonance angiograms of undiseased carotid vessels, we computed the oscillatory shear index (OSI) via a computational fluid dynamics simulation of flow. This region of highest OSI coincides with the area where the nerve to the carotid sinus lies within the vessel wall. Accordingly, the hypothesis is that the carotid sinus acts as a mechanotransducer of wall shear stress oscillation and not as a baroreceptor.

Vagal baro- and chemoreceptors in middle internal carotid artery and carotid body in rat

The glossopharyngeal nerve, via the carotid sinus nerve (CSN), presents baroreceptors from the internal carotid artery (ICA) and chemoreceptors from the carotid body. Although neurons in the nodose ganglion were labelled after injecting tracer into the carotid body, the vagal pathway to these baro- and chemoreceptors has not been identified. Neither has the glossopharyngeal intracranial afferent/sensory pathway that connects to the brainstem been defined. We investigated both of these issues in male Sprague-Dawley rats (n = 40) by injecting neural tracer wheat germ agglutinin-horseradish peroxidase into: (i) the peripheral glossopharyngeal or vagal nerve trunk with or without the intracranial glossopharyngeal rootlet being rhizotomized; or (ii) the nucleus of the solitary tract right after dorsal and ventral intracranial glossopharyngeal rootlets were dissected. By examining whole-mount tissues and brainstem sections, we verified that only the most rostral rootlet connects to the glossopharyngeal nerve and usually four caudal rootlets connect to the vagus nerve. Furthermore, vagal branches may: (i) join the CSN originating from the pharyngeal nerve base, caudal nodose ganglion, and rostral or caudal superior laryngeal nerve; or (ii) connect directly to nerve endings in the middle segment of the ICA or to chemoreceptors in the carotid body. The aortic depressor nerve always presents and bifurcates from either the rostral or the caudal part of the superior laryngeal nerve. The vagus nerve seemingly provides redundant carotid baro- and chemoreceptors to work with the glossopharyngeal nerve. These innervations confer more extensive roles on the vagus nerve in regulating body energy that is supplied by the cardiovascular, pulmonary and digestive systems.

Selective denervation of the aortic and carotid baroreceptors in rats

NEW FINDINGS

What is the central question of this study? The traditional surgical approach for sino-aortic denervation in rats leads to simultaneous carotid baroreceptor and chemoreceptor deactivation, which does not permit their individual study in different situations. What is the main finding and its importance? We have described a new surgical approach capable of selective denervation of the arterial (aortic and carotid) baroreceptors, keeping the carotid bodies (chemoreceptors) intact. It is understood that this technique might be a useful tool for investigating the relative role of the baro- and chemoreceptors in several physiological and pathophysiological conditions.

ABSTRACT

Studies have demonstrated that the traditional surgical approach for sino-aortic denervation in rats leads to simultaneous carotid baroreceptor and chemoreceptor deactivation. The present study reports a new surgical approach to denervate the aortic and the carotid baroreceptors selectively, keeping the carotid bodies (peripheral chemoreceptors) intact. Wistar rats were subjected to specific aortic and carotid baroreceptor denervation (BAROS-X) or sham surgery (SHAM). Baroreflex activation was achieved by i.v. administration of phenylephrine, whereas peripheral chemoreflex activation was produced by i.v. administration of potassium cyanide. The SHAM and BAROS-X rats displayed significant hypertensive responses to phenylephrine administration. However, the reflex bradycardia following the hypertensive response caused by phenylephrine was remarkable in SHAM, but not significant in the BAROS-X animals, confirming the efficacy of the surgical procedure to abolish the baroreflex. In addition, the baroreflex activation elicited by phenylephrine increased carotid sinus nerve activity only in SHAM, but not in the BAROS-X animals, providing support to the notion that the baroreceptor afferents were absent. Instead, the classical peripheral chemoreflex hypertensive and bradycardic responses to potassium cyanide were similar in both groups, suggesting that the carotid body chemoreceptors were preserved after BAROS-X. In summary, we describe a new surgical approach in which only the baroreceptors are eliminated, while the carotid chemoreceptors are preserved. Therefore, it is understood that this procedure is potentially a useful tool for examining the relative roles of the arterial baroreceptors versus the chemoreceptors in several pathophysiological conditions, for instance, arterial hypertension and heart failure.

Autonomic Neuromodulation for Preventing and Treating Ventricular Arrhythmias

The cardiac autonomic nervous system (CANS) is associated with modulation of cardiac electrophysiology and arrhythmogenesis. In this mini review, we will briefly introduce cardiac autonomic anatomy and autonomic activity in ventricular arrhythmias (VAs) and discuss novel approaches of CANS modulation for treating VAs. Studies over the decades have provided a better understanding of cardiac autonomic innervation and revealed overwhelming evidence of the relationship between autonomic tone and VAs. A high sympathetic tone and low parasympathetic (vagal) tone are considered as the major triggers of VAs in patients with myocardial ischemia, which can cause sudden cardiac death. In recent years, novel methods of autonomic neuromodulation have been investigated to prevent VAs, and they have been verified as being beneficial for malignant VAs in animal models and humans. The clinical outcome of autonomic neuromodulation depends on the level of cardiac neuraxis, stimulation parameters, and patient's pathological status. Since autonomic modulation for VA treatment is still in the early stage of clinical application, more basic and clinical studies should be performed to clarify these mechanisms and optimize autonomic neuromodulation therapies for patients with VAs in the future.