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Current Aging Science Aug 2022This review outlines the normal heart rate and blood pressure response to active standing, the physiological mechanisms governing these, and the effect of ageing on the... (Review)
Review
OBJECTIVES
This review outlines the normal heart rate and blood pressure response to active standing, the physiological mechanisms governing these, and the effect of ageing on the responses.
METHODS
A literature search was conducted to identify articles investigating the normal heart rate and/or blood pressure response to standing.
RESULTS
Heart rate when standing increases and then decreases and recovers to baseline. Blood pressure responses are inverse. Skeletal muscle contraction and the baroreceptor reflex drive this. With ageing, heart rate response attenuates and the initial blood pressure response increases.
DISCUSSION
Normal heart rate and blood pressure responses are attributed to the baroreceptor reflex and skeletal muscle contraction. Decreased muscle strength and baroreceptor sensitivity are associated with ageing, suggesting a possible benefit in improving skeletal muscle strength to maintain an efficient response. Understanding these responses and their variation with ageing is clinically relevant and may be beneficial in improving rehabilitation outcomes.
Topics: Baroreflex; Blood Pressure; Heart Rate; Humans; Muscle Contraction; Pressoreceptors
PubMed: 35440341
DOI: 10.2174/1874609815666220419102648 -
Neuroscience Jun 2022Silent myocardial infarction (MI) is critical for clinical practice with increasing risk for women and the cause remains a medical mystery. Upon the discovery of...
Silent myocardial infarction (MI) is critical for clinical practice with increasing risk for women and the cause remains a medical mystery. Upon the discovery of female-specific Ah-type baroreceptor neurons (BRNs), we hypothesize that glutamate mediates depressor response through afferent-specific expression of particular glutamate receptors (mGluRs) leading descending inhibition of cardiac nociception. In vivo, tail-flick reflex and electromyography were assessed to evaluate glutamate-mediated blood pressure regulation, peripheral and cardiac nociception. The results showed that glutamate decreased mean arterial pressure (MAP) and increased peripheral nociception. Interestingly, glutamate-mediated capsaicin-induced cardiac nociception was strongly reduced in female rats compared with males. Furthermore, Nodose (NG) microinjection of mGluR7 agonist significantly increased MAP in males and slightly decreased that in females. Even though mGluR8 direct activation intensified baroreceptor activation, the sensitivity was similar between sexes. In vitro, the expression profiles of mGluRs were investigated using Western blot and identified BRNs using single-cell qRT-PCR under ischemic conditions. Glutamate in serum, NG and nucleus tractus solitary (NTS) was raised significantly in the model rats of both sexes vs. sham-controls. Female-specific expression of mGluR7 in the baroreflex afferent pathway, especially higher expression in Ah-type BRNs, contributes significantly to cardiac analgesia, which may explain that the pathogenesis of silent MI occurs mainly in female patients. Therefore, higher expression of mGluR7 in female-specific subpopulation of Ah-type BRNs plays a critical role in cardiac analgesia and peripheral nociception.
Topics: Animals; Baroreflex; Estrogens; Female; Glutamates; Humans; Male; Myocardial Infarction; Neurons; Nociception; Pressoreceptors; Rats; Receptors, Metabotropic Glutamate; Solitary Nucleus
PubMed: 35436518
DOI: 10.1016/j.neuroscience.2022.04.008 -
Pflugers Archiv : European Journal of... Jan 2023Recent investigations emphasized the importance of neural control of cardiovascular adjustments in complex behaviors, including stress, exercise, arousal, sleep-wake...
Recent investigations emphasized the importance of neural control of cardiovascular adjustments in complex behaviors, including stress, exercise, arousal, sleep-wake states, and different tasks. Baroreceptor feedback is an essential component of this system acting on different time scales from maintaining stable levels of cardiovascular parameters on the long-term to rapid alterations according to behavior. The baroreceptor input is essentially rhythmic, reflecting periodic fluctuations in arterial blood pressure. Cardiac rhythm is a prominent feature of the autonomic control system, present on different levels, including neuron activity in central circuits. The mechanism of rhythmic entrainment of neuron firing by the baroreceptor input was studied in great detail under anesthesia, but recordings of sympathetic-related neuron firing in freely moving animals remain extremely scarce. In this study, we recorded multiple single neuron activity in the reticular formation of the medulla in freely moving rats during natural behavior. Neurons firing in synchrony with the cardiac rhythm were detected in each experiment (n = 4). In agreement with prior observations in anesthetized cats, we found that neurons in this area exhibited high neuron-to-neuron variability and temporal flexibility in their coupling to cardiac rhythm in freely moving rats, as well. This included firing in bursts at multiples of cardiac cycles, but not directly coupled to the heartbeat, supporting the concept of baroreceptor input entraining intrinsic neural oscillations rather than imposing a rhythm of solely external origin on these networks. It may also point to a mechanism of maintaining the basic characteristics of sympathetic neuron activity, i.e., burst discharge and cardiac-related rhythmicity, on the background of behavior-related adjustments in their firing rate.
Topics: Rats; Animals; Pressoreceptors; Neurons; Medulla Oblongata; Cardiovascular Physiological Phenomena
PubMed: 35396959
DOI: 10.1007/s00424-022-02687-7 -
Nutrients Feb 2022For normal maintenance of blood pressure and blood volume a well-balanced renin-angiotensin-aldosterone system (RAS) is necessary. For this purpose, renin is secreted as... (Review)
Review
For normal maintenance of blood pressure and blood volume a well-balanced renin-angiotensin-aldosterone system (RAS) is necessary. For this purpose, renin is secreted as the situation demands by the juxtaglomerular cells (also called as granular cells) that are in the walls of the afferent arterioles. Juxtaglomerular cells can sense minute changes in the blood pressure and blood volume and accordingly synthesize, store, and secrete appropriate amounts of renin. Thus, when the blood pressure and blood volume are decreased JGA cells synthesize and secrete higher amounts of renin and when the blood pressure and blood volume is increased the synthesis and secretion of renin is decreased such that homeostasis is restored. To decipher this important function, JGA cells (renin cells) need to sense and transmit the extracellular physical forces to their chromatin to control renin gene expression for appropriate renin synthesis. The changes in perfusion pressure are sensed by Integrin β1 that is transmitted to the renin cell's nucleus via lamin A/C that produces changes in the architecture of the chromatin. This results in an alteration (either increase or decrease) in renin gene expression. Cell membrane is situated in an unique location since all stimuli need to be transmitted to the cell nucleus and messages from the DNA to the cell external environment can be conveyed only through it. This implies that cell membrane structure and integrity is essential for all cellular functions. Cell membrane is composed to proteins and lipids. The lipid components of the cell membrane regulate its (cell membrane) fluidity and the way the messages are transmitted between the cell and its environment. Of all the lipids present in the membrane, arachidonic acid (AA) forms an important constituent. In response to pressure and other stimuli, cellular and nuclear shape changes occur that render nucleus to act as an elastic mechanotransducer that produces not only changes in cell shape but also in its dynamic behavior. Cell shape changes in response to external pressure(s) result(s) in the activation of cPLA2 (cytosolic phospholipase 2)-AA pathway that stretches to recruit myosin II which produces actin-myosin cytoskeleton contractility. Released AA can undergo peroxidation and peroxidized AA binds to DNA to regulate the expression of several genes. Alterations in the perfusion pressure in the afferent arterioles produces parallel changes in the renin cell membrane leading to changes in renin release. AA and its metabolic products regulate not only the release of renin but also changes in the vanilloid type 1 (TRPV1) expression in renal sensory nerves. Thus, AA and its metabolites function as intermediate/mediator molecules in transducing changes in perfusion and mechanical pressures that involves nuclear mechanotransduction mechanism. This mechanotransducer function of AA has relevance to the synthesis and release of insulin, neurotransmitters, and other soluble mediators release by specialized and non-specialized cells. Thus, AA plays a critical role in diseases such as diabetes mellitus, hypertension, atherosclerosis, coronary heart disease, sepsis, lupus, rheumatoid arthritis, and cancer.
Topics: Arachidonic Acid; Juxtaglomerular Apparatus; Mechanotransduction, Cellular; Pressoreceptors; Renin
PubMed: 35215399
DOI: 10.3390/nu14040749 -
JACC. Clinical Electrophysiology Feb 2022This study sought to evaluate the role of cardiac afferent reflexes in atrial fibrillation (AF).
OBJECTIVES
This study sought to evaluate the role of cardiac afferent reflexes in atrial fibrillation (AF).
BACKGROUND
Efferent autonomic tone is not associated with atrial remodeling and AF persistence. However, the role of cardiac afferents is unknown.
METHODS
Individuals with nonpermanent AF (n = 48) were prospectively studied (23 in the in-AF group and 25 in sinus rhythm [SR]) with 12 matched control subjects. We performed: 1) low-level lower body negative pressure (LBNP), which decreases cardiac volume, offloading predominantly cardiac afferent (volume-sensitive) low-pressure baroreceptors; 2) Valsalva reflex (predominantly arterial high-pressure baroreceptors); and 3) isometric handgrip reflex (both baroreceptors). We measured beat-to-beat mean arterial pressure (MAP) and heart rate (HR). LBNP elicits reflex vasoconstriction, estimated using venous occlusion plethysmography-derived forearm blood flow (∝1/vascular resistance), maintaining MAP. To assess reversibility, we repeated LBNP (same day) after 1-hour low-level tragus stimulation (in n = 5 in the in-AF group and n = 10 in the in-SR group) and >6 weeks post-cardioversion (n = 7).
RESULTS
The 3 groups were well matched for age (59 ± 12 years, 83% male), body mass index, and risk factors (P = NS). The in-AF group had higher left atrial volume (P < 0.001) and resting HR (P = 0.01) but similar MAP (P = 0.7). The normal LBNP vasoconstriction (-49 ± 5%) maintaining MAP (control subjects) was attenuated in the in-SR group (-12 ± 9%; P = 0.005) and dysfunctional in the in-AF group (+11 ± 6%; P < 0.001), in which MAP decreased and HR was unchanged. Valsalva was normal throughout. Handgrip MAP response was lowest in the in-AF group (P = 0.01). Interestingly, low-level tragus stimulation and cardioversion improved LBNP vasoconstriction (-48 ± 15%; P = 0.04; and -32 ± 9%; P = 0.02, respectively).
CONCLUSIONS
Cardiac afferent (volume-sensitive) reflexes are abnormal in AF patients during SR and dysfunctional during AF. This could contribute to AF progression, thus explaining "AF begets AF." (Characterisation of Autonomic function in Atrial Fibrillation [AF-AF Study]; ACTRN12619000186156).
Topics: Aged; Atrial Fibrillation; Female; Hand Strength; Heart Atria; Humans; Lower Body Negative Pressure; Male; Middle Aged; Pressoreceptors
PubMed: 35210071
DOI: 10.1016/j.jacep.2021.10.010 -
Advances in Physiology Education Jun 2022While the effects of changing heart rate and systemic vascular resistance have been generally understood and appreciated, the effects of changes in left ventricular... (Review)
Review
While the effects of changing heart rate and systemic vascular resistance have been generally understood and appreciated, the effects of changes in left ventricular contractility on end-systolic volume may have been less understood and appreciated and the effects of changes in venous capacitance on end-diastolic volume may have been unknown to many readers. Herein, we have provided a brief review for the medical student and beginning graduate student highlighting these sometimes-complex relationships.
Topics: Blood Pressure; Heart Rate; Heart Ventricles; Humans; Pressoreceptors; Vascular Resistance
PubMed: 35201919
DOI: 10.1152/advan.00160.2021 -
Acta Pharmacologica Sinica Sep 2022Recent studies suggest that melatonin (Mel) plays an important role in the regulation of blood pressure (BP) via the aortic baroreflex pathway. In this study, we...
Recent studies suggest that melatonin (Mel) plays an important role in the regulation of blood pressure (BP) via the aortic baroreflex pathway. In this study, we investigated the interaction between the baroreflex afferent pathway and Mel-mediated BP regulation in rats under physiological and hypertensive conditions. Mel (0.1, 0.3, and 1.0 mg/mL) was microinjected into the nodose ganglia (NG) of rats. We showed that Mel-induced reduction of mean arterial pressure in female rats was significantly greater than that in male and in ovariectomized rats under physiological condition. Consistently, the expression of Mel receptors (MTNRs) in the NG of female rats was significantly higher than that of males. In L-NAME-induced hypertensive and spontaneously hypertensive rat models, MTNRs were upregulated in males but downregulated in female models. Interestingly, Mel-induced BP reduction was found in male hypertensive models. In whole-cell recording from identified baroreceptor neurons (BRNs) in female rats, we found that Mel (0.1 μM) significantly increased the excitability of a female-specific subpopulation of Ah-type BRNs by increasing the Na1.9 current density via a PKC-mediated pathway. Similar results were observed in baroreceptive neurons of the nucleus tractus solitarius, showing the facilitation of spontaneous and evoked excitatory post-synaptic currents in Ah-type neurons. Collectively, this study reveals the estrogen-dependent effect of Mel/MTNRs under physiological and hypertensive conditions is mainly mediated by Ah-type BRNs, which may provide new theoretical basis and strategies for the gender-specific anti-hypertensive treatment in clinical practice.
Topics: Animals; Baroreflex; Blood Pressure; Estrogens; Female; Hypertension; Male; Melatonin; Pressoreceptors; Rats; Rats, Inbred SHR; Rats, Sprague-Dawley
PubMed: 35132193
DOI: 10.1038/s41401-022-00867-w -
Pediatric Cardiology Jun 2022The arterial baroreceptor reflex in children and adolescents has not been well studied in the current literature with a lack of agreed upon normal values, particularly...
The arterial baroreceptor reflex in children and adolescents has not been well studied in the current literature with a lack of agreed upon normal values, particularly in postural orthostatic tachycardia syndrome (POTS) or neurocardiogenic syncope (NCS). We used the sequence method and head-up tilt test (HUTT) to evaluate baroreceptor function in 3 phases: baseline supine position for 10 min, head-up position at 70° for 30 min or until syncope, and post-tilt supine reposition for 10 min. We measured the number of baroreceptor events, baroreceptor effectiveness index (BEI), and the magnitude of sensitivity of the events at each phase of HUTT. We studied 198 individuals (49 normal subjects, 67 POTS, 82 NCS) with age ranges from 8 to 21 years. The data show a statistically significant decrease in slope and BEI in patients with POTS and NCS during the head-up phase, with an increase in activity in the lag 1 and 2 portions of all phases in patients with POTS. This study provides terminology to describe baroreceptor function and identifies the slope and BEI portions of the baroreceptor reflex as the most useful objective measures to differentiate pediatric patients with POTS and NCS from normal subjects.
Topics: Adolescent; Adult; Blood Pressure; Child; Heart Rate; Humans; Postural Orthostatic Tachycardia Syndrome; Pressoreceptors; Syncope, Vasovagal; Tachycardia; Tilt-Table Test; Young Adult
PubMed: 35089394
DOI: 10.1007/s00246-022-02815-1 -
Journal of Integrative Neuroscience Dec 2021Here we use immunohistochemistry to examine the expression of Piezo2 in neurons of the mouse dorsal root ganglia and brain. Whereas Piezo2 is expressed in the large...
Piezo2-peripheral baroreceptor channel expressed in select neurons of the mouse brain: a putative mechanism for synchronizing neural networks by transducing intracranial pressure pulses.
Here we use immunohistochemistry to examine the expression of Piezo2 in neurons of the mouse dorsal root ganglia and brain. Whereas Piezo2 is expressed in the large majority (≥ 90%) of dorsal root ganglia neurons, Piezo2 expression is restricted to select neuron types in specific brain regions, including neocortical and hippocampal pyramidal neurons, cerebellar Purkinje cells and mitral cells of the olfactory bulb. Given the well-established role of Piezo2 as a low-threshold pressure sensor (i.e., ≤5 mmHg) in peripheral mechanosensation, including the regulation of breathing and blood pressure, its expression in central neurons has interesting implications. In particular, we hypothesize that Piezo2 provides neurons with an intrinsic resonance that promotes their entrainment by the normal intracranial pressure pulses (~5 mmHg) associated with breathing and cardiac cycles. The pressure-induced change in neural activity need only be very subtle to increase, for example, the robustness of respiration-entrained oscillations reported previously in widely distributed neuronal networks in both rodent and human brains. This idea of a "global brain rhythm" first arose from the effect of nasal airflow in activating mechanosensitive olfactory sensory neurons, which then synaptically entrain mitral cells within the olfactory bulb and through their projections, neural networks in other brain regions, including the hippocampus and neocortex. Our proposed, non-synaptic, intrinsic mechanism, where Piezo2 tracks the highly predictable and "metronome-like" intracranial pressure pulses-to date generally considered epiphenomena-would have the advantage that a physical force rapidly transmitted throughout the brain also contributes to this synchronization.
Topics: Animals; Biological Clocks; Hippocampus; Intracranial Pressure; Ion Channels; Male; Mice; Mice, Inbred C57BL; Neocortex; Nerve Net; Neurons; Pressoreceptors
PubMed: 34997707
DOI: 10.31083/j.jin2004085 -
BMJ Case Reports Dec 2021We present a case of a 77-year-old man who reported 5 months of syncopal episodes. He was found to have diffuse large B-cell lymphoma encasing the left internal...
We present a case of a 77-year-old man who reported 5 months of syncopal episodes. He was found to have diffuse large B-cell lymphoma encasing the left internal carotid artery but not impeding blood flow. The syncopal episodes resolved after his first cycle of chemotherapy. Recurrent syncope in non-cardiac lymphomas and other head and neck masses is exceedingly rare and may be due to reflex syncope prompted by carotid baroreceptor activation. There are 11 previously described cases of recurrent syncope associated with non-cardiac lymphoma. In all cases, lymphadenopathy abutting the carotid artery was present and the syncopal episodes resolved with treatment. Our case illustrates that malignancy should be considered in patients with unexplained recurrent syncope.
Topics: Aged; Carotid Artery, Internal; Humans; Lymphoma, Large B-Cell, Diffuse; Male; Neoplasm Recurrence, Local; Pressoreceptors; Syncope
PubMed: 34969790
DOI: 10.1136/bcr-2021-244881