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Experimental Physiology Jan 2012After considerable debate and key experimental evidence, the importance of the arterial baroreflex in contributing to and maintaining the appropriate neural... (Review)
Review
After considerable debate and key experimental evidence, the importance of the arterial baroreflex in contributing to and maintaining the appropriate neural cardiovascular adjustments to exercise is now well accepted. Indeed, the arterial baroreflex resets during exercise in an intensity-dependent manner to continue to regulate blood pressure as effectively as at rest. Studies have indicated that the exercise resetting of the arterial baroreflex is mediated by both the feedforward mechanism of central command and the feedback mechanism associated with skeletal muscle afferents (the exercise pressor reflex). Another perhaps less appreciated neural mechanism involved in evoking and maintaining neural cardiovascular responses to exercise is the cardiopulmonary baroreflex. The limited information available regarding the cardiopulmonary baroreflex during exercise provides evidence for a role in mediating sympathetic nerve activity and blood pressure responses. In addition, recent investigations have demonstrated an interaction between cardiopulmonary baroreceptors and the arterial baroreflex during dynamic exercise, which contributes to the magnitude of exercise-induced increases in blood pressure as well as the resetting of the arterial baroreflex. Furthermore, neural inputs from the cardiopulmonary baroreceptors appear to play an important role in establishing the operating point of the arterial baroreflex. This symposium review highlights recent studies in these important areas indicating that the interactions of four neural mechanisms (central command, the exercise pressor reflex, the arterial baroreflex and cardiopulmonary baroreflex) are integral in mediating the neural cardiovascular adjustments to exercise.
Topics: Arteries; Baroreflex; Exercise; Heart; Humans; Sympathetic Nervous System
PubMed: 22002871
DOI: 10.1113/expphysiol.2011.057554 -
The Journal of Physiological Sciences :... Nov 2019A strict adequate perfusion pressure via arterial baroreflex for the delivery of oxygen to the tissues of the body is well established; however, the importance of... (Review)
Review
A strict adequate perfusion pressure via arterial baroreflex for the delivery of oxygen to the tissues of the body is well established; however, the importance of baroreflex for cerebral blood flow (CBF) is unclear. On the other hand, there is convincing evidence for arterial baroreflex function playing an important role in maintaining brain homeostasis, e.g., cerebral metabolism, cerebral hemodynamics, and cognitive function. For example, mild cognitive impairment attenuates the sensitivity of baroreflex, and Alzheimer's disease further decreases it. These clinical findings suggest that CBF and cerebral function are affected by systemic blood pressure regulation via the arterial baroreflex. However, dysfunction of arterial baroreflex is likely to affect CBF regulation as well as the underlying neuronal function, but identifying how this is achieved is arduous since neurological diseases affect systemic as well as cerebral circulation independently. Recent insights into the influence of blood pressure regulation via the arterial baroreflex on cerebral function and blood flow regulation may help elucidate this important question. This review summarizes some update findings regarding direct (autonomic regulation) and indirect (systemic blood pressure regulation) contributions of the arterial baroreflex to the maintenance of cerebral vasculature regulation.
Topics: Animals; Baroreflex; Cerebral Arteries; Cerebrovascular Circulation; Cognition; Humans
PubMed: 31444691
DOI: 10.1007/s12576-019-00704-6 -
European Journal of Applied Physiology Feb 2021We analysed the characteristics of arterial baroreflexes during the first phase of apnoea (φ1).
PURPOSE
We analysed the characteristics of arterial baroreflexes during the first phase of apnoea (φ1).
METHODS
12 divers performed rest and exercise (30 W) apnoeas (air and oxygen). We measured beat-by-beat R-to-R interval (RRi) and mean arterial pressure (MAP). Mean RRi and MAP values defined the operating point (OP) before (PRE-ss) and in the second phase (φ2) of apnoea. Baroreflex sensitivity (BRS, ms·mmHg) was calculated with the sequence method.
RESULTS
In PRE-ss, BRS was (median [IQR]): at rest, 20.3 [10.0-28.6] in air and 18.8 [13.8-25.2] in O; at exercise 9.2[8.4-13.2] in air and 10.1[8.4-13.6] in O. In φ1, during MAP decrease, BRS was lower than in PRE-ss at rest (6.6 [5.3-11.4] in air and 7.7 [4.9-14.3] in O, p < 0.05). At exercise, BRS in φ1 was 6.4 [3.9-13.1] in air and 6.7 [4.1-9.5] in O. After attainment of minimum MAP (MAPmin), baroreflex resetting started. After attainment of minimum RRi, baroreflex sequences reappeared. In φ2, BRS at rest was 12.1 [9.6-16.2] in air, 12.9 [9.2-15.8] in O. At exercise (no φ2 in air), it was 7.9 [5.4-10.7] in O. In φ2, OP acts at higher MAP values.
CONCLUSION
In apnoea φ1, there is a sudden correction of MAP fall via baroreflex. The lower BRS in the earliest φ1 suggests a possible parasympathetic mechanism underpinning this reduction. After MAPmin, baroreflex resets, displacing its OP at higher MAP level; thus, resetting may not be due to central command. After resetting, restoration of BRS suggests re-establishment of vagal drive.
Topics: Adult; Apnea; Baroreflex; Blood Pressure; Exercise; Female; Heart Rate; Humans; Male; Oxygen; Rest; Vagus Nerve
PubMed: 33151437
DOI: 10.1007/s00421-020-04544-w -
Brazilian Journal of Medical and... Apr 2019Frailty is related to a decrease in the physiological reserves, which causes difficulties in maintaining homeostasis. An example of physiological mechanisms for... (Comparative Study)
Comparative Study
Frailty is related to a decrease in the physiological reserves, which causes difficulties in maintaining homeostasis. An example of physiological mechanisms for cardiovascular homeostasis is the baroreflex. The aim of this study was to compare baroreflex among frail, prefrail, and nonfrail individuals, in supine and orthostatic positions. Community-dwelling older adults were evaluated and categorized into frail, prefrail, or nonfrail groups, according to frailty phenotype. The RR interval (RRi) and systolic blood pressure (SBP) series were recorded for 15 min in the supine and 15 min in the orthostatic positions. Mean and variance of RRi and SBP, and baroreflex evaluated by phase, gain (α), and coherence (K2) were determined. A two-way repeated measures ANOVA, with Tukey's post hoc, was applied for group, position, and their interaction effects. The significance level established was 5%. Prefrail and frail participants did not present a significant decrease in mean values of RRi after postural challenge (893.43 to 834.20 ms and 925.99 to 857.98 ms, respectively). Frail participants showed a reduction in RRi variance in supine to orthostatic (852.04 to 232.37 ms2). Prefrail and frail participants showed a decrease in K2 after postural change (0.69 to 0.52 and 0.54 to 0.34, respectively). Frail participants exhibited lower values of K2 (0.34) compared to nonfrail and prefrail participants (0.61 and 0.52, respectively). Baroreflex indicated the presence of decoupling between heart period and SBP in frail and prefrail. Thus, reduced K2 might be a marker of the frailty process.
Topics: Aged; Aged, 80 and over; Baroreflex; Blood Pressure; Female; Frail Elderly; Geriatric Assessment; Humans; Male; Posture; Statistics, Nonparametric
PubMed: 30970083
DOI: 10.1590/1414-431X20198079 -
Sleep Nov 2021Binge alcohol consumption is associated with increased cardiovascular risk. The effects of evening binge alcohol consumption (i.e. 4-5 beverages within 2 h) on the vagal... (Randomized Controlled Trial)
Randomized Controlled Trial
STUDY OBJECTIVES
Binge alcohol consumption is associated with increased cardiovascular risk. The effects of evening binge alcohol consumption (i.e. 4-5 beverages within 2 h) on the vagal components of HRV and cardiovagal baroreflex sensitivity (cvBRS) during sleep remain largely equivocal. The present study examined the effects of evening binge alcohol consumption on nocturnal cardiac vagal tone and baroreflex sensitivity during stage N2, slow wave (SWS), and rapid eye movement (REM) sleep. We hypothesized that evening binge drinking would reduce HRV and cvBRS in each sleep stage.
METHODS
Following a familiarization night within the laboratory, twenty-three participants were examined following a night of binge alcohol consumption and a fluid control (randomized, crossover design). A quality nocturnal beat-to-beat blood pressure signal was obtained in both conditions in 16 participants (seven men, nine women; 25 ± 1 years).
RESULTS
Binge drinking reduced both the high frequency (HF) and time-domain components (i.e. pNN50 and RMSSD) of HRV in stage N2 sleep, SWS, and REM. In addition, cvBRS up-up (vagal activation) was reduced following binge alcohol consumption in stage N2 (21 ± 3 vs. 15 ± 3 ms/mmHg, p = 0.035) and REM (15[11-28] vs. 11[9-18] ms/mmHg, p = 0.009). Binge alcohol consumption reduced cvBRS down-down (vagal withdrawal) in stage N2 (23 ± 2 vs. 14 ± 2 ms/mmHg, p < 0.001), SWS (20[14-30] vs. 14[9-17] ms/mmHg, p = 0.022), and REM (14[11-24] vs. 10[7-15] ms/mmHg, p = 0.006).
CONCLUSIONS
Evening binge alcohol consumption disrupts cardiac vagal tone and baroreflex function during nearly all sleep stages. These findings provide mechanistic insight into the potential role of binge drinking and alcohol abuse on cardiovascular risk.
CLINICAL TRIALS DETAILS
Alcohol and Neural Cardiovascular Control in Binge Drinkers, www.clinicaltrials.gov/ct2/show/NCT03567434, NCT03567434.
Topics: Baroreflex; Blood Pressure; Female; Heart Rate; Humans; Male; Sleep; Vagus Nerve
PubMed: 34015116
DOI: 10.1093/sleep/zsab130 -
JACC. Heart Failure Sep 2022Novel treatments targeting in baroreflex sensitivity (BRS) and chemoreflex sensitivity (CRS) heart failure (HF) are grounded on small prognostic studies, partly...
BACKGROUND
Novel treatments targeting in baroreflex sensitivity (BRS) and chemoreflex sensitivity (CRS) heart failure (HF) are grounded on small prognostic studies, partly performed in the pre-beta-blockade era.
OBJECTIVES
This study assesses the clinical/prognostic significance of BRS and CRS in a large cohort of patients with chronic HF on modern treatments.
METHODS
Outpatients with chronic HF with either reduced (≤40%) or mildly reduced left ventricular ejection fraction (LVEF) (41% to 49%) underwent BRS (SD method) and CRS to hypoxia and hypercapnia (rebreathing technique) assessment and were followed up for a composite endpoint of cardiac death, implantable cardioverter-defibrillator shock, or HF hospitalization.
RESULTS
A total of 425 patients were enrolled (65 ± 12 years of age, LVEF 32% [IQR: 25%-38%], 94% on beta blockers). Patients with decreased BRS (n = 96 of 267, 36%) had lower exercise tolerance and heart rate variability (P < 0.05), whereas those with increased CRS to both hypoxia and hypercapnia (n = 74 of 369, 20%) had higher plasma norepinephrine and central apneas across the 24-hour period (P < 0.01). During a median 50-month follow-up (IQR: 24-94 months), the primary endpoint occurred more often in patients with decreased BRS (log-rank: 11.64; P = 0.001), mainly for increased cardiac deaths/implantable cardioverter-defibrillator shocks, and in those with increased CRS (log-rank: 34.81; P < 0.001), mainly for increased HF hospitalizations. Patients with both abnormal BRS and CRS showed the worst outcome. Reduced BRS (HR: 2.76 [95% CI: 1.36-5.63]; P = 0.005) and increased CRS (HR: 2.91 [95% CI: 1.34-6.31]; P = 0.007) were independently associated with the primary outcome and increased risk stratification when added to standard HF prognosticators (P < 0.05).
CONCLUSIONS
In subjects with HF on modern treatment, abnormal BRS and CRS are frequently observed. BRS and CRS elicit autonomic imbalance, exercise limitation, unstable ventilation, and predict adverse outcomes.
Topics: Baroreflex; Heart Failure; Heart Rate; Humans; Hypercapnia; Hypoxia; Prognosis; Stroke Volume; Ventricular Function, Left
PubMed: 36049816
DOI: 10.1016/j.jchf.2022.02.006 -
International Journal of Environmental... Dec 2022Autonomic dysfunction, such as reduced vagally mediated heart rate variability, has been suggested in headache patients but is still uncertain when considering primary...
Autonomic dysfunction, such as reduced vagally mediated heart rate variability, has been suggested in headache patients but is still uncertain when considering primary headache disorders. This study aims to compare the heart rate and blood pressure variability and baroreflex sensitivity between women with migraine and controls. A migraine (n = 20) and a control group (n = 20) of age-matched women without headache were evaluated. Heart rate variability was analyzed through frequency-domain using spectral analysis presenting variance, low-frequency (LF; 0.04-0.15 Hz) and high-frequency (HF; 0.15-0.4 Hz) bands and by time domain (root mean square of successive R-R interval differences, RMSSD). Blood pressure variability was analyzed with spectral analysis and baroreflex sensitivity with the sequence method. Migraine group had lower heart rate variability characterized by a reduction in total variance, LF oscillations (sympathetic/vagal modulation) and HF oscillations (vagal modulation), and a reduction in SD and RMSSD compared to control group. No difference was found in the blood pressure variability analysis. Regarding baroreflex sensitivity, migraine group had decreased values of total gain, gain down and up compared to control group. Women with migraine exhibited autonomic modulation alterations, expressed by decreased values of heart rate variability and baroreflex sensitivity, but not by differences in blood pressure variability.
Topics: Humans; Female; Autonomic Nervous System; Blood Pressure; Heart; Baroreflex; Heart Rate; Headache; Migraine Disorders
PubMed: 36613082
DOI: 10.3390/ijerph20010763 -
Respiratory Physiology & Neurobiology Nov 2022Despite the relevant presence of nonlinear components on heart period (HP) likely due to cardiorespiratory coupling (CRC), the HP is frequently analyzed in absence of...
PURPOSE
Despite the relevant presence of nonlinear components on heart period (HP) likely due to cardiorespiratory coupling (CRC), the HP is frequently analyzed in absence of concomitant recordings of respiratory movements (RESP). This study aims to assess the cardiovascular dynamics and CRC during postural challenge in athletes and non-athletes via joint symbolic analysis (JSA).
METHODS
A cross-sectional study was conducted in 50 men, aged between 20 and 40 yrs, divided into athletes (n = 25) and non-athletes (n = 25) groups. The electrocardiogram, blood pressure and RESP signals were recorded during 15 min in both supine position (REST) and after active postural maneuver (STAND). From the beat-to-beat series of HP, systolic arterial pressure (SAP) and RESP, we computed the time and frequency domain indexes and baroreflex sensitivity. The JSA was based on the definition of symbolic HP and RESP patterns and on the evaluation of the rate of their simultaneous occurrence in both HP and RESP series.
RESULTS
The JSA analysis was able to identify higher CRC strength at REST in athletes. Moreover, the response of CRC to STAND depended on the time scales of the analysis and was much more evident in athletes than in non-athletes, thus indicating a more reactive autonomic control in athletes.
CONCLUSION
Assessing CRC in athletes via JSA provides additional information compared to standard linear time and frequency domain tools likely due to the more relevant presence of nonlinearities in HP-RESP variability relationship.
Topics: Adult; Autonomic Nervous System; Baroreflex; Blood Pressure; Cross-Sectional Studies; Electrocardiography; Heart Rate; Humans; Male; Young Adult
PubMed: 35835289
DOI: 10.1016/j.resp.2022.103943 -
British Journal of Anaesthesia Sep 2016Baroreflex dysfunction is a common feature of established cardiometabolic diseases that are most frequently associated with the development of critical illness.... (Randomized Controlled Trial)
Randomized Controlled Trial
BACKGROUND
Baroreflex dysfunction is a common feature of established cardiometabolic diseases that are most frequently associated with the development of critical illness. Laboratory models show that baroreflex dysfunction impairs cardiac contractility and cardiovascular performance, thereby increasing the risk of morbidity after trauma and sepsis. We hypothesized that baroreflex dysfunction contributes to excess postoperative morbidity after major surgery as a consequence of the inability to achieve adequate perioperative tissue oxygen delivery.
METHODS
In a randomized controlled trial of goal-directed haemodynamic therapy (GDT) in higher-risk surgical patients, baroreflex function was assessed using the spontaneous baroreflex sensitivity (BRS) method via an arterial line placed before surgery, using a validated sequence method technique (one beat lag). The BRS was calculated during the 6 h postoperative GDT intervention. Analyses of BRS were done by investigators blinded to clinical outcomes. The primary outcome was the association between postoperative baroreflex dysfunction (BRS <6 mm Hg s(-1), a negative prognostic threshold in cardiovascular pathology) and early postoperative morbidity. The relationship between baroreflex dysfunction and postoperative attainment of preoperative indexed oxygen delivery was also assessed.
RESULTS
Patients with postoperative baroreflex dysfunction were more likely to sustain infectious {relative risk (RR) 1.75 [95% confidence interval (CI): 1.07-2.85], P=0.02} and cardiovascular morbidity [RR 2.39 (95% CI: 1.22-4.71), P=0.008]. Prolonged hospital stay was more likely in patients with baroreflex dysfunction [unadjusted hazard ratio 1.62 (95% CI: 1.14-2.32), log-rank P=0.004]. Postoperative O2 delivery was 36% (95% CI: 7-65) lower in patients with baroreflex dysfunction in those not randomly assigned to GDT (P=0.02).
CONCLUSIONS
Baroreflex dysfunction is associated with excess morbidity, impaired cardiovascular performance, and delayed hospital discharge, suggesting a mechanistic role for autonomic dysfunction in determining perioperative outcome.
CLINICAL TRIAL REGISTRATION
ISCRTN76894700.
Topics: Aged; Autonomic Nervous System; Baroreflex; Double-Blind Method; Female; Hemodynamics; Humans; Male; Middle Aged; Morbidity; Postoperative Complications
PubMed: 27543527
DOI: 10.1093/bja/aew257 -
Comparative Biochemistry and... May 2021All vertebrates have baroreflexes that provide fast regulation of arterial blood pressure (P) to maintain adequate tissue perfusion and avoid vascular lesions from...
The baroreflex in aquatic and amphibious teleosts: Does terrestriality represent a significant driving force for the evolution of a more effective baroreflex in vertebrates?
All vertebrates have baroreflexes that provide fast regulation of arterial blood pressure (P) to maintain adequate tissue perfusion and avoid vascular lesions from excessive pressures. The baroreflex is a negative feedback loop, where altered P results in reciprocal changes in heart rate (f) and systemic vascular conductance to restore pressure. In terrestrial environments, gravity usually leads to blood pooling in the lower body reducing venous return, cardiac filling, cardiac output and P. Conversely, in aquatic environments, the hydrostatic pressure of surrounding water mitigates blood pooling and prevents vascular distensions. In this context, we aimed to test the hypothesis that vertebrate species that were exposed to gravity-induced hemodynamic disturbances throughout their evolutionary histories have a more effective barostatic reflex than those that were not. We examined the cardiac baroreflex of fish that perform (Clarias gariepinus and Hoplerythrinus unitaeniatus) and do not perform (Hoplias malabaricus and Oreochromis niloticus) voluntary terrestrial sojourns, using pharmacological manipulations of P to characterize reflex changes in f using a four-variable sigmoidal logistic function (i.e. the "Oxford technique"). Our results revealed that amphibious fish exhibit higher baroreflex gain and responsiveness to hypotension than strictly aquatic fish, suggesting that terrestriality and the gravitational circulatory stresses constitute a relevant driving force for the evolution of a more effective baroreflex in vertebrates. We also demonstrate that strictly aquatic teleosts have considerable baroreflex gain, supporting the view that the baroreflex is an ancient cardiovascular trait that appeared before vertebrates colonized the gravity-dominated realm of land.
Topics: Animals; Baroreflex; Biological Evolution; Blood Pressure; Ecosystem; Fishes; Heart Rate
PubMed: 33545361
DOI: 10.1016/j.cbpa.2021.110916