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Pflugers Archiv : European Journal of... Aug 2023Reflex summation in the expression of left and right aortic baroreflex control of hemodynamic functions was investigated. In anesthetized Sprague-Dawley rats, mean...
Reflex summation in the expression of left and right aortic baroreflex control of hemodynamic functions was investigated. In anesthetized Sprague-Dawley rats, mean arterial pressure (MAP), heart rate (HR), and mesenteric vascular resistance (MVR) were recorded following left, right, and bilateral stimulation of the aortic depressor nerve (ADN). Stimulation frequency was varied between low (1 Hz), moderate (5 Hz), and high (20 Hz). At 1 Hz, left and right ADN stimulation evoked similar depressor, bradycardic and MVR responses, whereas bilateral stimulation induced larger MAP, HR, and MVR reductions compared with stimulations of either side. The sum of the separate and combined stimulation effects on MAP, HR, and MVR was similar, indicating an additive summation. A similar additive summation was observed with HR responses at 5 and 20 Hz. Left-sided and bilateral stimulation produced greater depressor and MVR responses than right-sided stimulation, with responses of the bilateral stimulation mimicking those of the left side. The bilateral MAP or MVR response was smaller than the sum of the separate responses, suggesting an inhibitory summation. In conclusion, reflex summation of the left and right aortic baroreceptor afferent input is differentially expressed in relation to the frequency of the input signal. Summation of baroreflex control of HR is always additive and independent of stimulation frequency. Summation of baroreflex control of MAP is additive when the frequency input is small and inhibitory when the frequency input is moderate to high, with MAP changes mainly driven by parallel baroreflex-triggered changes in vascular resistance.
Topics: Rats; Animals; Pressoreceptors; Rats, Sprague-Dawley; Blood Pressure; Electric Stimulation; Reflex; Baroreflex; Heart Rate
PubMed: 37219603
DOI: 10.1007/s00424-023-02820-0 -
Experimental Physiology Oct 2023What is the topic of this review? We review barosensory vessel mechanics and their role in blood pressure regulation across the lifespan. What advances does it... (Review)
Review
NEW FINDINGS
What is the topic of this review? We review barosensory vessel mechanics and their role in blood pressure regulation across the lifespan. What advances does it highlight? In young normotensive men, aortic unloading mechanics contribute to the resting operating point of the vascular sympathetic baroreflex; however, with advancing age, this contribution is removed. This suggests that barosensory vessel unloading mechanics are not driving the well-documented age-related increase in resting muscle sympathetic nerve activity.
ABSTRACT
An age-associated increase in arterial blood pressure is evident for apparently healthy humans. This is frequently attributed to stiffening of the central arteries and a concurrent increase in sympathetic outflow, potentially mediated by a reduced ability of the baroreceptive vessels to distend. This is supported, in part, by a reduced mechanical component of the vascular sympathetic baroreflex (i.e., a reduction in distension for a given pressure). Previous characterization of the mechanical component has assessed only carotid artery distension; however, evidence suggests that both the aortic and carotid baroreflexes are integral to blood pressure regulation. In addition, given that baroreceptors are located in the vessel wall, the change in wall tension, comprising diameter, pressure and vessel wall thickness, and the mechanics of this change might provide a better index of the baroreceptor stimulus than the previous method used to characterize the mechanical component that relies on diameter alone. This brief review summarizes the data using this new method of assessing barosensory vessel mechanics and their influence on the vascular sympathetic baroreflex across the lifespan.
Topics: Male; Humans; Baroreflex; Blood Pressure; Pressoreceptors; Carotid Arteries; Sympathetic Nervous System; Homeostasis; Heart Rate
PubMed: 37031381
DOI: 10.1113/EP089686 -
The Journal of Maternal-fetal &... Dec 2023Baroreflex is a regulatory mechanism that slows the fetal heart rate. This study aimed to investigate the effects of lipopolysaccharide (LPS)-induced endotoxemia on...
OBJECTIVE
Baroreflex is a regulatory mechanism that slows the fetal heart rate. This study aimed to investigate the effects of lipopolysaccharide (LPS)-induced endotoxemia on fetal baroreceptor sensitivity in preterm fetal sheep.
METHODS
The changes in fetal baroreceptor sensitivity were measured in seven chronically instrumented preterm fetal sheep. Fetal baroreceptor sensitivity was measured in three phases: (A) control phase, defined as the 24 h before the first injection of LPS; (B) acute phase, defined as the 24 h between the first and second injections of LPS; and (C) fetal acidosis phase, defined as the time from the second LPS injection until intrauterine fetal death. Histological examinations of the fetal membrane and umbilical cord were also conducted.
RESULTS
Each fetus developed metabolic acidosis after the second injection of LPS. The fetuses died 24.7 (SD = 6.1) hours after the second injection of LPS. Both the umbilical cord and fetal membranes showed histological evidence of severe inflammation. In total, 163 fetal baroreceptor measurements were performed in this experiment (A, = 77 times; B, = 60 times; C, = 26 times). Fetal baroreceptor sensitivity showed significant differences in all three phases (A: 2.7 [SD = 0.2]; B: 2.5 [SD = 0.2]; and C: 1.5 [SD = 0.2]). Post hoc tests showed that baroreceptor sensitivity in the acidosis phase had decreased significantly compared to that in the control and acute phases (<.001 and =.002, respectively).
CONCLUSIONS
Fetal baroreceptor sensitivity decreased during fetal acidosis induced by LPSs.
Topics: Pregnancy; Female; Humans; Sheep; Animals; Lipopolysaccharides; Pressoreceptors; Fetus; Inflammation; Fetal Diseases; Acidosis; Heart Rate, Fetal
PubMed: 36443245
DOI: 10.1080/14767058.2022.2150392 -
Vascular Apr 2024The bilateral presentation of Carotid Body Tumors (CBT) is rare; the surgical resection of these masses remains the mainstay management due to the malignant potential....
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.
Topics: Humans; Carotid Body Tumor; Female; Male; Middle Aged; Retrospective Studies; Aged; Treatment Outcome; Baroreflex; Pressoreceptors; Risk Factors; Blood Pressure; Heart Rate
PubMed: 36394214
DOI: 10.1177/17085381221140167