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Liu C, Yu H, Xia H, Wang Z, Li B, Xue H, Jin S, Xiao L, Wu Y, Guo Q. Butyrate attenuates sympathetic activation in rats with chronic heart failure by inhibiting microglial inflammation in the paraventricular nucleus. Acta Biochim Biophys Sin (Shanghai) 2024. [PMID: 38863438 DOI: 10.3724/abbs.2024092] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/13/2024] Open
Abstract
Sympathetic activation is a hallmark of heart failure and the underlying mechanism remains elusive. Butyrate is generated by gut microbiota and influences numerous physiological and pathological processes in the host. The present study aims to investigate whether the intestinal metabolite butyrate reduces sympathetic activation in rats with heart failure (HF) and the underlying mechanisms involved. Sprague-Dawley rats (220‒250 g) are anaesthetized with isoflurane, and the left anterior descending artery is ligated to model HF. Then, the rats are treated with or without butyrate sodium (NaB, a donor of butyrate, 10 g/L in water) for 8 weeks. Blood pressure and renal sympathetic nerve activity (RSNA) are recorded to assess sympathetic outflow. Cardiac function is improved (mean ejection fraction, 22.6%±4.8% vs 38.3%±5.3%; P<0.05), and sympathetic activation is decreased (RSNA, 36.3%±7.9% vs 23.9%±7.6%; P<0.05) in HF rats treated with NaB compared with untreated HF rats. The plasma and cerebrospinal fluid levels of norepinephrine are decreased in HF rats treated with NaB. The infusion of N-methyl-D-aspartic acid (NMDA) into the paraventricular nucleus (PVN) of the hypothalamus of HF model rats increases sympathetic nervous activity by upregulating the NMDA receptor. Microglia polarized to the M2 phenotype and inflammation are markedly attenuated in the PVN of HF model rats after NaB administration. In addition, HF model rats treated with NaB exhibit enhanced intestinal barrier function and increased levels of GPR109A, zona occludens-1 and occludin, but decreased levels of lipopolysaccharide-binding protein and zonulin. In conclusion, butyrate attenuates sympathetic activation and improves cardiac function in rats with HF. The improvements in intestinal barrier function, reductions in microglia-mediated inflammation and decreases in NMDA receptor 1 expression in the PVN are all due to the protective effects of NaB.
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Affiliation(s)
- Chang Liu
- Department of Physiology, Hebei Medical University, Shijiazhuang 050017, China
| | - Hao Yu
- Department of Physiology, Hebei Medical University, Shijiazhuang 050017, China
| | - Hongyi Xia
- Department of Physiology, Hebei Medical University, Shijiazhuang 050017, China
| | - Ziwei Wang
- Department of Reproduction, the Second Hospital of Hebei Medical University, Shijiazhuang 050017, China
| | - Bolin Li
- Department of Physiology, Hebei Medical University, Shijiazhuang 050017, China
| | - Hongmei Xue
- Department of Physiology, Hebei Medical University, Shijiazhuang 050017, China
| | - Sheng Jin
- Department of Physiology, Hebei Medical University, Shijiazhuang 050017, China
| | - Lin Xiao
- Department of Physiology, Hebei Medical University, Shijiazhuang 050017, China
| | - Yuming Wu
- Department of Physiology, Hebei Medical University, Shijiazhuang 050017, China
- Hebei Collaborative Innovation Center for Cardio-Cerebrovascular Disease, Shijiazhuang 050017, China
- The Key Laboratory of Neural and Vascular Biology, Ministry of Education, Shijiazhuang 050017, China
- Hebei Key Laboratory of Cardiovascular Homeostasis and Aging, Shijiazhuang 050017, China
| | - Qi Guo
- Department of Physiology, Hebei Medical University, Shijiazhuang 050017, China
- Experimental Center for Teaching, Hebei Medical University, Shijiazhuang 050017, China
- Hebei Key Laboratory of Cardiovascular Homeostasis and Aging, Shijiazhuang 050017, China
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Gimhani D, Shanks J, Pachen M, Chang JWH, Ramchandra R. Sympathetic transduction of cardiac sympathetic nerve activity in healthy, conscious sheep. J Physiol 2024; 602:619-632. [PMID: 38329227 DOI: 10.1113/jp285079] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2023] [Accepted: 01/16/2024] [Indexed: 02/09/2024] Open
Abstract
Sympathetic transduction is the study of how impulses of sympathetic nerve activity (SNA) affect end-organ function. Recently, the transduction of resting bursts of muscle SNA (MSNA) has been investigated and shown to have a role in the maintenance of blood pressure through changes in vascular tone in humans. In the present study, we investigate whether directly recorded resting cardiac SNA (CSNA) regulates heart rate (HR), coronary blood flow (CoBF), coronary vascular conductance (CVC), cardiac output (CO) and mean arterial pressure. Instrumentation was undertaken to record CSNA and relevant vascular variables in conscious sheep. Recordings were performed at baseline, as well as after the infusion of a β-adrenoceptor blocker (propranolol) to determine the role of β-adrenergic signalling in sympathetic transduction in the heart. The results show that after every burst of CSNA, there was a significant effect of time on HR (n = 10, ∆: +2.1 ± 1.4 beats min-1 , P = 0.002) and CO (n = 8, ∆: +100 ± 150 mL min-1 , P = 0.002) was elevated, followed by an increase in CoBF (n = 9, ∆: +0.76 mL min-1 , P = 0.001) and CVC (n = 8, ∆: +0.0038 mL min-1 mmHg-1 , P = 0.0028). The changes in HR were graded depending on the size and pattern of CSNA bursts. The HR response was significantly attenuated after the infusion of propranolol. Our study is the first to explore resting sympathetic transduction in the heart, suggesting that CSNA can dynamically change HR mediated by an action on β-adrenoceptors. KEY POINTS: Sympathetic transduction is the study of how impulses of sympathetic nerve activity (SNA) affect end-organ function. Previous studies have examined sympathetic transduction primarily in the skeletal muscle and shown that bursts of muscle SNA alter blood flow to skeletal muscle and mean arterial pressure, although this has not been examined in the heart. We investigated sympathetic transduction in the heart and show that, in the conscious condition, the size of bursts of SNA to the heart can result in incremental increases in heart rate and coronary blood flow mediated by β-adrenoceptors. The pattern of bursts of SNA to the heart also resulted in incremental increases in heart rate mediated by β-adrenoceptors. This is the first study to explore the transduction of bursts of SNA to the heart.
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Affiliation(s)
- Dilsha Gimhani
- Department of Physiology, University of Auckland, Auckland, New Zealand
| | - Julia Shanks
- Department of Physiology, University of Auckland, Auckland, New Zealand
| | - Mridula Pachen
- Department of Physiology, University of Auckland, Auckland, New Zealand
| | - Joshua W-H Chang
- Department of Physiology, University of Auckland, Auckland, New Zealand
| | - Rohit Ramchandra
- Department of Physiology, University of Auckland, Auckland, New Zealand
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D'Souza AW, Yoo JK, Bhai S, Sarma S, Anderson EH, Levine BD, Fu Q. Attenuated peripheral oxygen extraction and greater cardiac output in women with posttraumatic stress disorder during exercise. J Appl Physiol (1985) 2024; 136:141-150. [PMID: 38031720 PMCID: PMC11219012 DOI: 10.1152/japplphysiol.00161.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2023] [Revised: 11/20/2023] [Accepted: 11/20/2023] [Indexed: 12/01/2023] Open
Abstract
Posttraumatic stress disorder (PTSD) is associated with an increased risk of developing cardiovascular disease, especially in women. Evidence indicates that men with PTSD exhibit lower maximal oxygen uptake (V̇o2max) relative to controls; however, whether V̇o2max is blunted in women with PTSD remains unknown. Furthermore, it is unclear what determinants (i.e., central and/or peripheral) of V̇o2max are impacted by PTSD. Therefore, we evaluated the central (i.e., cardiac output; Q̇c) and peripheral (i.e., arteriovenous oxygen difference) determinants of V̇o2max in women with PTSD; hypothesizing that V̇o2max would be lower in women with PTSD compared with women without PTSD (controls), primarily due to smaller increases in stroke volume (SV), and therefore Q̇c. Oxygen uptake (V̇o2), heart rate (HR), Q̇c, SV, and arteriovenous oxygen difference were measured in women with PTSD (n = 14; mean [SD]: 43 [11] yr,) and controls (n = 17; 45 [11] yr) at rest, and during an incremental maximal treadmill exercise test, and the Q̇c/V̇o2 slope was calculated. V̇o2max was not different between women with and without PTSD (24.3 [5.6] vs. 26.4 [5.0] mL/kg/min; P = 0.265). However, women with PTSD had higher Q̇c [P = 0.002; primarily due to greater SV (P = 0.069), not HR (P = 0.285)], and lower arteriovenous oxygen difference (P = 0.002) throughout exercise compared with controls. Furthermore, the Q̇c/V̇o2 slope was steeper in women with PTSD relative to controls (6.6 [1.4] vs. 5.7 [1.0] AU; P = 0.033). Following maximal exercise, women with PTSD exhibited slower HR recovery than controls (P = 0.046). Thus, despite attenuated peripheral oxygen extraction, V̇o2max is not reduced in women with PTSD, likely due to larger increases in Q̇c.NEW & NOTEWORTHY The current study indicates that V̇o2max is not different between women with and without PTSD; however, women with PTSD exhibit blunted peripheral extraction of oxygen, thus requiring an increase in Q̇c to meet metabolic demand during exercise. Furthermore, following exercise, women with PTSD demonstrate impaired autonomic cardiovascular control relative to sedentary controls. We interpret these data to indicate that women with PTSD demonstrate aberrant cardiovascular responses during and immediately following fatiguing exercise.
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Affiliation(s)
- Andrew W D'Souza
- Neurovascular Research Laboratory, School of Kinesiology, Western University, London, Ontario, Canada
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, Dallas, Texas, United States
- Department of Internal Medicine, The University of Texas Southwestern Medical Center, Dallas, Texas, United States
| | - Jeung-Ki Yoo
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, Dallas, Texas, United States
- Department of Internal Medicine, The University of Texas Southwestern Medical Center, Dallas, Texas, United States
| | - Salman Bhai
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, Dallas, Texas, United States
- Department of Neurology, The University of Texas Southwestern Medical Center, Dallas, Texas, United States
| | - Satyam Sarma
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, Dallas, Texas, United States
- Department of Internal Medicine, The University of Texas Southwestern Medical Center, Dallas, Texas, United States
| | - Elizabeth H Anderson
- Department of Psychiatry, The University of Texas Southwestern Medical Center, Dallas, Texas, United States
- Veterans Affairs North Texas Health Care System, Dallas, Texas, United States
| | - Benjamin D Levine
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, Dallas, Texas, United States
- Department of Internal Medicine, The University of Texas Southwestern Medical Center, Dallas, Texas, United States
| | - Qi Fu
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, Dallas, Texas, United States
- Department of Internal Medicine, The University of Texas Southwestern Medical Center, Dallas, Texas, United States
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D'Souza AW, Hissen SL, Manabe K, Takeda R, Washio T, Coombs GB, Sanchez B, Fu Q, Shoemaker JK. Age- and sex-related differences in sympathetic vascular transduction and neurohemodynamic balance in humans. Am J Physiol Heart Circ Physiol 2023; 325:H917-H932. [PMID: 37594483 DOI: 10.1152/ajpheart.00301.2023] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/23/2023] [Revised: 08/14/2023] [Accepted: 08/15/2023] [Indexed: 08/19/2023]
Abstract
Bursts of muscle sympathetic nerve activity (MSNA) and the ensuing vasoconstriction are pivotal determinants of beat-by-beat blood pressure regulation. Although age and sex impact blood pressure regulation, how these factors affect the central and peripheral arcs of the baroreflex remains unclear. In 27 young [25 (SD 3) yr] males (YM; n = 14) and females (YF; n = 13) and 23 older [71 (SD 5) yr] males (OM; n = 11) and females (OF; n = 12), femoral artery blood flow, blood pressure, and MSNA were recorded for 10 min of supine rest. Sympathetic baroreflex sensitivity (i.e., central arc) was quantified as the relationship between diastolic blood pressure and MSNA burst incidence. Signal averaging was used to determine sympathetic vascular transduction into leg vascular conductance (LVC) for 12 cardiac cycles following MSNA bursts (i.e., peripheral arc). Older adults demonstrated attenuated sympathetic transduction into LVC (both P < 0.001) following MSNA bursts, and smaller increases in sympathetic transduction as a function of MSNA burst size and firing pattern compared with young adults (range, P = 0.004-0.032). YM (r2 = 0.36; P = 0.032) and OM (r2 = 0.51; P = 0.014) exhibited an inverse relationship between the central and peripheral arcs of the baroreflex, whereas females did not (YF, r2 = 0.03, P = 0.621; OF, r2 = 0.06, P = 0.445). MSNA burst incidence was inversely related to sympathetic transduction in YM and OF (range, P = 0.03-0.046) but not in YF or OM (range, P = 0.360-0.603). These data indicate that age is associated with attenuated sympathetic vascular transduction, whereas age- and sex-specific changes are present in the relationship between the central and peripheral arcs of the baroreflex regulation of blood pressure.NEW & NOTEWORTHY Sympathetic vascular transduction is attenuated in older compared with young adults, regardless of biological sex. Males, but not females (regardless of age), demonstrate an inverse relationship between central (sympathetic baroreflex sensitivity) and peripheral (sympathetic vascular transduction) components of the baroreflex arc. Young males and older females exhibit an inverse relationship between resting sympathetic outflow and sympathetic vascular transduction. Our results indicate that age and sex exert independent and interactive effects on sympathetic vascular transduction and sympathetic neurohemodynamic balance in humans.
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Affiliation(s)
- Andrew W D'Souza
- Neurovascular Research Laboratory, School of Kinesiology, Western University, London, Ontario, Canada
| | - Sarah L Hissen
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, Dallas, Texas, United States
- Internal Medicine, The University of Texas Southwestern Medical Center, Dallas, Texas, United States
| | - Kazumasa Manabe
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, Dallas, Texas, United States
- Internal Medicine, The University of Texas Southwestern Medical Center, Dallas, Texas, United States
| | - Ryosuke Takeda
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, Dallas, Texas, United States
- Internal Medicine, The University of Texas Southwestern Medical Center, Dallas, Texas, United States
- Laboratory of Neuromuscular Biomechanics, School of Health and Sport Sciences, Chukyo University, Toyota, Japan
| | - Takuro Washio
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, Dallas, Texas, United States
- Internal Medicine, The University of Texas Southwestern Medical Center, Dallas, Texas, United States
| | - Geoff B Coombs
- Neurovascular Research Laboratory, School of Kinesiology, Western University, London, Ontario, Canada
| | - Belinda Sanchez
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, Dallas, Texas, United States
- Internal Medicine, The University of Texas Southwestern Medical Center, Dallas, Texas, United States
| | - Qi Fu
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, Dallas, Texas, United States
- Internal Medicine, The University of Texas Southwestern Medical Center, Dallas, Texas, United States
| | - J Kevin Shoemaker
- Neurovascular Research Laboratory, School of Kinesiology, Western University, London, Ontario, Canada
- Department of Physiology and Pharmacology, Western University, London, Ontario, Canada
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Bigalke JA, Durocher JJ, Greenlund IM, Keller-Ross M, Carter JR. Blood pressure and muscle sympathetic nerve activity are associated with trait anxiety in humans. Am J Physiol Heart Circ Physiol 2023; 324:H494-H503. [PMID: 36800506 PMCID: PMC10259854 DOI: 10.1152/ajpheart.00026.2023] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/18/2023] [Revised: 02/14/2023] [Accepted: 02/14/2023] [Indexed: 02/19/2023]
Abstract
Chronic anxiety is prevalent and associated with an increased risk of cardiovascular disease. Prior studies that have reported a relationship between muscle sympathetic nerve activity (MSNA) and anxiety have focused on participants with anxiety disorders and/or metabolic syndrome. The present study leverages a large cohort of healthy adults devoid of cardiometabolic disorders to examine the hypothesis that trait anxiety severity is positively associated with resting MSNA and blood pressure. Resting blood pressure (BP) (sphygmomanometer and finger plethysmography), MSNA (microneurography), and heart rate (HR; electrocardiogram) were collected in 88 healthy participants (52 males, 36 females, 25 ± 1 yr, 25 ± 1 kg/m2). Multiple linear regression was performed to assess the independent relationship between trait anxiety, MSNA, resting BP, and HR while controlling for age and sex. Trait anxiety was significantly correlated with systolic arterial pressure (SAP; r = 0.251, P = 0.018), diastolic arterial pressure (DAP; r = 0.291, P = 0.006), mean arterial pressure (MAP; r = 0.328, P = 0.002), MSNA burst frequency (BF; r = 0.237, P = 0.026), and MSNA burst incidence (BI; r = 0.225, P = 0.035). When controlling for the effects of age and sex, trait anxiety was independently associated with SAP (β = 0.206, P = 0.028), DAP (β = 0.317, P = 0.002), MAP (β = 0.325, P = 0.001), MSNA BF (β = 0.227, P = 0.030), and MSNA BI (β = 0.214, P = 0.038). Trait anxiety is associated with increased blood pressure and MSNA, demonstrating an important relationship between anxiety and autonomic blood pressure regulation.NEW & NOTEWORTHY Anxiety is associated with development of cardiovascular disease. Although the sympathetic nervous system is a likely mediator of this relationship, populations with chronic anxiety have shown little, if any, alteration in resting levels of directly recorded muscle sympathetic nerve activity (MSNA). The present study is the first to reveal an independent relationship between trait anxiety, resting blood pressure, and MSNA in a large cohort of healthy males and females devoid of cardiometabolic comorbidities.
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Affiliation(s)
- Jeremy A Bigalke
- Department of Health and Human Development, Montana State University, Bozeman, Montana, United States
- Department of Psychology, Montana State University, Bozeman, Montana, United States
- Department of Kinesiology and Integrative Physiology, Michigan Technological University, Houghton, Michigan, United States
| | - John J Durocher
- Department of Kinesiology and Integrative Physiology, Michigan Technological University, Houghton, Michigan, United States
- Department of Biological Sciences and Integrative Physiology and Health Sciences Center, Purdue University Northwest, Hammond, Indiana, United States
| | - Ian M Greenlund
- Department of Psychology, Montana State University, Bozeman, Montana, United States
- Department of Kinesiology and Integrative Physiology, Michigan Technological University, Houghton, Michigan, United States
- Department of Cardiovascular Medicine, Mayo Clinic, Rochester, Minnesota, United States
| | - Manda Keller-Ross
- Division of Physical Therapy and Rehabilitation Science, University of Minnesota, Minneapolis, Minnesota, United States
| | - Jason R Carter
- Department of Health and Human Development, Montana State University, Bozeman, Montana, United States
- Department of Kinesiology and Integrative Physiology, Michigan Technological University, Houghton, Michigan, United States
- Robbins College of Health and Human Sciences, Baylor University, Waco, Texas, United States
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Jenkins ZM, Castle DJ, Eikelis N, Phillipou A, Lambert GW, Lambert EA. Autonomic nervous system function in women with anorexia nervosa. Clin Auton Res 2022; 32:29-42. [PMID: 34762216 DOI: 10.1007/s10286-021-00836-z] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Accepted: 10/28/2021] [Indexed: 01/31/2023]
Abstract
PURPOSE Abnormalities in autonomic function have been observed in people with anorexia nervosa. However, the majority of investigations have utilised heart rate variability as the sole assessment of autonomic activity. The current study utilised a variety of methodologies to assess autonomic nervous system function in women with a current diagnosis of anorexia, a past diagnosis of anorexia who were weight-restored, and healthy controls. METHODS The sample included 37 participants: 10 participants with anorexia, 17 weight-restored participants (minimum body mass index > 18.5 for minimum of 12 months) and 10 controls. Assessments of autonomic function included muscle sympathetic nerve activity (MSNA) using microneurography, heart rate variability, baroreflex sensitivity, blood pressure variability, head-up tilt table test, sudomotor function and assessment of plasma catecholamines. RESULTS MSNA (bursts/min) was significantly decreased in both anorexia (10.22 ± 6.24) and weight-restored (17.58 ± 1.68) groups, as compared to controls (23.62 ± 1.01, p < 0.001 and p = 0.033, respectively). Participants with anorexia had a significantly lower standard deviation in heart rate, lower blood pressure variability and decreased sudomotor function as compared to controls. Weight-restored participants demonstrated decreased baroreflex sensitivity in response to head-up tilt as compared to controls. CONCLUSION Women with a current or previous diagnosis of anorexia have significantly decreased sympathetic activity, which may reflect a physiological response to decreased energy intake. During the state of starvation, women with anorexia also displayed decreased sudomotor function. The consequences of a sustained decrease in MSNA are unknown, and future studies should investigate autonomic function in long-term weight-restored participants to determine whether activity returns to normal.
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Affiliation(s)
- Zoe M Jenkins
- Iverson Health Innovation Research Institute and School of Health Sciences, Swinburne University of Technology, Melbourne, Australia. .,Department of Mental Health, St Vincent's Hospital Melbourne, PO Box 2900, Fitzroy, VIC, 3065, Australia. .,Department of Psychiatry, University of Melbourne, Melbourne, Australia.
| | - David J Castle
- Department of Mental Health, St Vincent's Hospital Melbourne, PO Box 2900, Fitzroy, VIC, 3065, Australia.,Centre for Complex Interventions, Centre for Addictions and Mental Health, Toronto, Canada.,Department of Psychiatry, University of Toronto, Toronto, Canada
| | - Nina Eikelis
- Iverson Health Innovation Research Institute and School of Health Sciences, Swinburne University of Technology, Melbourne, Australia
| | - Andrea Phillipou
- Department of Mental Health, St Vincent's Hospital Melbourne, PO Box 2900, Fitzroy, VIC, 3065, Australia.,Department of Psychiatry, University of Melbourne, Melbourne, Australia.,Centre for Mental Health and School of Health Sciences, Swinburne University of Technology, Melbourne, Australia.,Department of Mental Health, Austin Health, Melbourne, Australia
| | - Gavin W Lambert
- Iverson Health Innovation Research Institute and School of Health Sciences, Swinburne University of Technology, Melbourne, Australia
| | - Elisabeth A Lambert
- Iverson Health Innovation Research Institute and School of Health Sciences, Swinburne University of Technology, Melbourne, Australia
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Bigalke JA, Carter JR. Sympathetic Neural Control in Humans with Anxiety-Related Disorders. Compr Physiol 2021; 12:3085-3117. [PMID: 34964121 DOI: 10.1002/cphy.c210027] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Numerous conceptual models are used to describe the dynamic responsiveness of physiological systems to environmental pressures, originating with Claude Bernard's milieu intérieur and extending to more recent models such as allostasis. The impact of stress and anxiety upon these regulatory processes has both basic science and clinical relevance, extending from the pioneering work of Hans Selye who advanced the concept that stress can significantly impact physiological health and function. Of particular interest within the current article, anxiety is independently associated with cardiovascular risk, yet mechanisms underlying these associations remain equivocal. This link between anxiety and cardiovascular risk is relevant given the high prevalence of anxiety in the general population, as well as its early age of onset. Chronically anxious populations, such as those with anxiety disorders (i.e., generalized anxiety disorder, panic disorder, specific phobias, etc.) offer a human model that interrogates the deleterious effects that chronic stress and allostatic load can have on the nervous system and cardiovascular function. Further, while many of these disorders do not appear to exhibit baseline alterations in sympathetic neural activity, reactivity to mental stress offers insights into applicable, real-world scenarios in which heightened sympathetic reactivity may predispose those individuals to elevated cardiovascular risk. This article also assesses behavioral and lifestyle modifications that have been shown to concurrently improve anxiety symptoms, as well as sympathetic control. Lastly, future directions of research will be discussed, with a focus on better integration of psychological factors within physiological studies examining anxiety and neural cardiovascular health. © 2022 American Physiological Society. Compr Physiol 12:1-33, 2022.
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Affiliation(s)
- Jeremy A Bigalke
- Department of Psychology, Montana State University, Bozeman, Montana, USA
| | - Jason R Carter
- Department of Psychology, Montana State University, Bozeman, Montana, USA.,Department of Health and Human Development, Montana State University, Bozeman, Montana, USA
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Esler M. Pivotal role of the sympathetic nerves of the human heart in mental stress responses and triggered cardiovascular catastrophes. Auton Neurosci 2021; 237:102925. [PMID: 34896690 DOI: 10.1016/j.autneu.2021.102925] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2021] [Revised: 11/09/2021] [Accepted: 11/15/2021] [Indexed: 11/28/2022]
Abstract
Mental stress can trigger cardiac catastrophes, explicitly evident during national disasters such as earthquakes. Activation of the cardiac sympathetic outflow and inhibition of the cardiac vagus are important mediating mechanisms. This manuscript describes efforts by the Human Neurotransmitters Research Laboratory of the Baker Institute in Melbourne to develop investigative methods to study the sympathetic nerves of the human heart, and to apply these in mental stress research. With laboratory mental stress, activation of the adrenal medulla was found to occur, accompanied by a regionalized sympathetic nervous response directed to the heart, but sparing the sympathetic outflow to the skeletal muscle vasculature. Patients with panic disorder are at increased cardiovascular risk. They exhibit high-level sympathetic activation during a panic attack, sometimes accompanied by coronary artery spasm. Patients with sudden ventricular arrhythmias causing collapse in the community were found to have as the predisposing substrate high baseline cardiac sympathetic activity, from previously unrecognized mild heart failure; it was surprising at the time that we did not find critical coronary artery stenosis as the substrate. In some the arrhythmia event had a behavioural trigger. In Takotsubo cardiomyopathy ("Broken Heart Syndrome") the myocardial stunning appears to represent a catecholamine cardiomyopathy, from astronomically high plasma adrenaline concentrations, rather than be caused by activation of the cardiac sympathetic nerves. Some diseases (essential hypertension, heart failure, panic disorder) have forms of sympathetic neural enhancement which contribute to cardiovascular risk: reuptake of noradrenaline by sympathetic nerves after release is faulty and single sympathetic fibres fire in multiple salvos within a single cardiac cycle. Paradoxically, obesity-hypertension does not share in this sympathetic neural augmentation, which is present only in normal-weight hypertensive patients, providing the possible basis for an observed "Obesity Paradox" (longer survival in obesity-hypertension than in normal weight hypertension). Community-wide specific prevention of cardiovascular triggering is not currently possible, due to there being no available simple screening tests which could be applied to the community at-large for the commonest substrates, silent coronary artery disease and mild heart failure. Standard medical preventive measures for coronary atherosclerosis will of course be helpful. Targeted prevention of triggering can be done in those with a detected predisposing substrate, such as genetic Long QT Syndrome, and in survivors of a serious triggered event, who need detailed, appropriate testing.
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Affiliation(s)
- Murray Esler
- Baker Heart and Diabetes Institute, PO Box 6492, Melbourne, VIC 3004, Australia.
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Klassen SA, Joyner MJ, Baker SE. The impact of ageing and sex on sympathetic neurocirculatory regulation. Semin Cell Dev Biol 2021; 116:72-81. [PMID: 33468420 PMCID: PMC8282778 DOI: 10.1016/j.semcdb.2021.01.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2020] [Revised: 12/30/2020] [Accepted: 01/04/2021] [Indexed: 02/07/2023]
Abstract
The sympathetic nervous system represents a critical mechanism for homoeostatic blood pressure regulation in humans. This review focuses on age-related alterations in neurocirculatory regulation in men and women by highlighting human studies that examined the relationship between muscle sympathetic nerve activity (MSNA) acquired by microneurography and circulatory variables (e.g., blood pressure, vascular resistance). We frame this review with epidemiological evidence highlighting sex-specific patterns in age-related blood pressure increases in developed nations. Indeed, young women exhibit lower blood pressure than men, but women demonstrate larger blood pressure increases with age, such that by about age 60 years, blood pressure is greater in women. Sympathetic neurocirculatory mechanisms contribute to sex differences in blood pressure rises with age. Muscle sympathetic nerve activity increases with age in both sexes, but women demonstrate greater age-related increases. The circulatory adjustments imposed by MSNA - referred to as neurovascular transduction or autonomic (sympathetic) support of blood pressure - differ in men and women. For example, whereas young men demonstrate a positive relationship between resting MSNA and vascular resistance, this relationship is absent in young women due to beta-2 adrenergic vasodilation, which offsets alpha-adrenergic vasoconstriction. However, post-menopausal women demonstrate a positive relationship between MSNA and vascular resistance due to a decline in beta-2 adrenergic vasodilatory mechanisms. Emerging data suggest that greater aerobic fitness appears to modulate neurocirculatory regulation, at least in young, healthy men and women. This review also highlights recent advances in microneurographic recordings of sympathetic action potential discharge, which may nuance our understanding of age-related alterations in sympathetic neurocirculatory regulation in humans.
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Affiliation(s)
- Stephen A Klassen
- Human and Integrative Physiology and Clinical Pharmacology Laboratory, Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, MN, USA
| | - Michael J Joyner
- Human and Integrative Physiology and Clinical Pharmacology Laboratory, Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, MN, USA
| | - Sarah E Baker
- Human and Integrative Physiology and Clinical Pharmacology Laboratory, Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, MN, USA.
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10
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Incognito AV, Teixeira AL, Shafer BM, Nardone M, Vermeulen TD, Foster GE, Millar PJ. Muscle sympathetic single-unit responses during rhythmic handgrip exercise and isocapnic hypoxia in males: the role of sympathoexcitation magnitude. J Neurophysiol 2021; 126:170-180. [PMID: 34133241 DOI: 10.1152/jn.00678.2020] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
A small proportion of postganglionic muscle sympathetic single units can be inhibited during sympathoexcitatory stressors in humans. However, whether these responses are dependent on the specific stressor or the level of sympathoexcitation remains unclear. We hypothesize that, when matched by sympathoexcitatory magnitude, different stressors can evoke similar proportions of inhibited single units. Multiunit and single-unit muscle sympathetic nerve activity (MSNA) were recorded in seven healthy young males at baseline and during 1) rhythmic handgrip exercise (40% of maximum voluntary contraction) and 2) acute isocapnic hypoxia (partial pressure of end-tidal O2 47 ± 3 mmHg). Single units were classified as activated, nonresponsive, or inhibited if the spike frequency was above, within, or below the baseline variability, respectively. By design, rhythmic handgrip and isocapnic hypoxia similarly increased multiunit total MSNA [Δ273 ± 208 vs. Δ254 ± 193 arbitrary units (AU), P = 0.84] and single-unit spike frequency (Δ8 ± 10 vs. Δ12 ± 13 spikes/min, P = 0.12). Among 19 identified single units, the proportions of activated (47% vs. 68%), nonresponsive (32% vs. 16%), and inhibited (21% vs. 16%) single units were not different between rhythmic handgrip and isocapnic hypoxia (P = 0.42). However, only 9 (47%) single units behaved with concordant response patterns across both stressors (7 activated, 1 nonresponsive, and 1 inhibited during both stressors). During the 1-min epoch with the highest increase in total MSNA during hypoxia (Δ595 ± 282 AU, P < 0.01) only one single unit was inhibited. These findings suggest that the proportions of muscle sympathetic single units inhibited during stress are associated with the level of sympathoexcitation and not the stressor per se in healthy young males.NEW & NOTEWORTHY Subpopulations of muscle sympathetic single units can be inhibited during mild sympathoexcitatory stress. We demonstrate that rhythmic handgrip exercise and isocapnic hypoxia, when matched by multiunit sympathoexcitation, induce similar proportions of single-unit inhibition, highlighting that heterogeneous single-unit response patterns are related to the level of sympathoexcitation independent of the stressor type. Interestingly, only 47% of single units behaved with concordant response patterns between stressors, suggesting the potential for functional specificity within the postganglionic neuronal pool.
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Affiliation(s)
- Anthony V Incognito
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada
| | - André L Teixeira
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada
| | - Brooke M Shafer
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada
| | - Massimo Nardone
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada
| | - Tyler D Vermeulen
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada
| | - Glen E Foster
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada
| | - Philip J Millar
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada.,Toronto General Research Institute, Toronto General Hospital, Toronto, Ontario, Canada
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11
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Rankin GD, Kabéle M, Brown R, Macefield VG, Sandström T, Bosson JA. Acute Exposure to Diesel Exhaust Increases Muscle Sympathetic Nerve Activity in Humans. J Am Heart Assoc 2021; 10:e018448. [PMID: 33942621 PMCID: PMC8200707 DOI: 10.1161/jaha.120.018448] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Background Diesel exhaust (DE) emissions are a major contributor to ambient air pollution and are strongly associated with cardiovascular morbidity and mortality. Exposure to traffic‐related particulate matter is linked with acute adverse cardiovascular events; however, the mechanisms are not fully understood. We examined the role of the autonomic nervous system during exposure to DE that has previously only been indirectly investigated. Methods and Results Using microneurography, we measured muscle sympathetic nerve activity (MSNA) directly in the peroneal nerve of 16 healthy individuals. MSNA, heart rate, and respiration were recorded while subjects rested breathing filtered air, filtered air with an exposure mask, and standardized diluted DE (300 µg/m3) through the exposure mask. Heart rate variability was assessed from an ECG. DE inhalation rapidly causes an increase in number of MSNA bursts as well as the size of bursts within 10 minutes, peaking by 30 minutes (P<0.001), compared with baseline filtered air with an exposure mask. No significant changes occurred in heart rate variability indices during DE exposure; however, MSNA frequency correlated negatively with total power (r2=0.294, P=0.03) and low frequency (r2=0.258, P=0.045). Heart rate correlated positively with MSNA frequency (r2=0.268, P=0.04) and the change in percentage of larger bursts (burst amplitude, height >50% of the maximum burst) from filtered air with an exposure mask (r2=0.368, P=0.013). Conclusions Our study provides direct evidence for the rapid modulation of the autonomic nervous system after exposure to DE, with an increase in MSNA. The quick increase in sympathetic outflow may explain the strong epidemiological data associating traffic‐related particulate matter to acute adverse cardiovascular events such as myocardial infarction. Registration URL: https://www.clinicaltrials.gov; Unique identifier: NCT02892279.
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Affiliation(s)
- Gregory D Rankin
- Department of Public Health and Clinical Medicine Section of Medicine/Respiratory Umeå University Umeå Sweden
| | - Mikael Kabéle
- Department of Public Health and Clinical Medicine Section of Medicine/Respiratory Umeå University Umeå Sweden
| | - Rachael Brown
- School of Medicine Western Sydney University Sydney NSW Australia
| | - Vaughan G Macefield
- Human Autonomic Neurophysiology Laboratory School of Medicine Baker Heart and Diabetes Institute Melbourne Vic. Australia.,Department of Physiology School of Biomedical Sciences The University of Melbourne Melbourne Vic. Australia
| | - Thomas Sandström
- Department of Public Health and Clinical Medicine Section of Medicine/Respiratory Umeå University Umeå Sweden
| | - Jenny A Bosson
- Department of Public Health and Clinical Medicine Section of Medicine/Respiratory Umeå University Umeå Sweden
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12
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Floras JS. From Brain to Blood Vessel: Insights From Muscle Sympathetic Nerve Recordings: Arthur C. Corcoran Memorial Lecture 2020. Hypertension 2021; 77:1456-1468. [PMID: 33775112 DOI: 10.1161/hypertensionaha.121.16490] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Multiunit recordings of postganglionic sympathetic outflow to muscle yield otherwise imperceptible insights into sympathetic neural modulation of human vascular resistance and blood pressure. This Corcoran Lecture will illustrate the utility of microneurography to investigate neurogenic cardiovascular regulation; review data concerning muscle sympathetic nerve activity of women and men with normal and high blood pressure; explore 2 concepts, central upregulation of muscle sympathetic outflow and cortical autonomic neuroplasticity; present sleep apnea as an imperfect model of neurogenic hypertension; and expose the paradox of sympathetic excitation without hypertension. In awake healthy normotensive individuals, resting muscle sympathetic nerve activity increases with age, sleep fragmentation, and obstructive apnea. Its magnitude is not signaled by heart rate. Age-related changes are nonlinear and differ by sex. In men, sympathetic nerve activity increases with age but without relation to their blood pressure, whereas in women, both rise concordantly after age 40. Mean values for muscle sympathetic nerve activity burst incidence are consistently higher in cohorts with hypertension than in matched normotensives, yet women's sympathetic nerve traffic can increase 3-fold between ages 30 and 70 without causing hypertension. Thus, increased sympathetic nerve activity may be necessary but is insufficient for primary hypertension. Moreover, its inhibition does not consistently decrease blood pressure. Despite a half-century of microneurographic research, large gaps remain in our understanding of the content of the sympathetic broadcast from brain to blood vessel and its specific individual consequences for circulatory regulation and cardiovascular, renal, and metabolic risk.
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Affiliation(s)
- John S Floras
- Sinai Health and University Health Network Division of Cardiology, Toronto General Hospital Research Institute, and the Department of Medicine, University of Toronto
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13
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Zwack CC, McDonald R, Tursunalieva A, Cooray A, Lambert GW, Lambert EA. Does autonomic nervous system dysfunction influence cardiovascular disease risk in young adults with intellectual disability? Am J Physiol Heart Circ Physiol 2020; 320:H891-H900. [PMID: 33566748 DOI: 10.1152/ajpheart.00807.2020] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
People with intellectual disability (ID) experience cardiometabolic-related morbidity and mortality. However, it has been suggested that this population presents and lives with underestimated cardiovascular risk factors at a younger age, hence affecting their overall health and quality of life and contributing to early mortality. We assessed autonomic nervous system function in subjects with ID (n = 39), aged 18-45 yr, through measures of sudomotor function, heart rate and systolic blood pressure variability, and cardiac baroreflex function. Traditional clinical cardiovascular measurements and a biochemical analysis were also undertaken. We found that young adults with ID presented with sudomotor dysfunction, impaired cardiac baroreflex sensitivity, and systolic blood pressure variability, when compared with age-matched control subjects (n = 38). Reduced hand and feet electrochemical skin conductance and asymmetry were significantly associated with having a moderate-profound ID. Autonomic dysfunction in individuals with ID persisted after controlling for age, sex, and other metabolic parameters. Subjects in the ID group also showed significantly increased blood pressure, body mass index, and waist/hip circumference ratio, as well as increased plasma hemoglobin A1c and high-sensitivity C-reactive protein levels. We conclude that autonomic dysfunction is present in young adults with ID and is more marked in those with more severe disability. These finding have important implications in developing preventative strategies to reduce the risk of cardiovascular disease in people with ID.NEW & NOTEWORTHY Adults with intellectual disability experience higher risk of premature death than the general population. Our investigation highlights increased cardiovascular risk markers and autonomic dysfunction in young adults with intellectual disability compared with control adults. Autonomic dysfunction was more marked in those with a more severe disability but independent of cardiovascular parameters. Assessment of autonomic nervous system (ANS) function may provide insight into the mechanisms of cardiometabolic disease development and progression in young adults with intellectual disability.
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Affiliation(s)
- Clara C Zwack
- Iverson Health Innovation Research Institute and School of Health Sciences, Faculty of Health, Arts and Design, Swinburne University of Technology, Hawthorn, Victoria, Australia
| | - Rachael McDonald
- Iverson Health Innovation Research Institute and School of Health Sciences, Faculty of Health, Arts and Design, Swinburne University of Technology, Hawthorn, Victoria, Australia
| | - Ainura Tursunalieva
- Department of Econometrics and Business Statistics, Monash University, Clayton, Victoria, Australia
| | - Amali Cooray
- Iverson Health Innovation Research Institute and School of Health Sciences, Faculty of Health, Arts and Design, Swinburne University of Technology, Hawthorn, Victoria, Australia
| | - Gavin W Lambert
- Iverson Health Innovation Research Institute and School of Health Sciences, Faculty of Health, Arts and Design, Swinburne University of Technology, Hawthorn, Victoria, Australia
| | - Elisabeth A Lambert
- Iverson Health Innovation Research Institute and School of Health Sciences, Faculty of Health, Arts and Design, Swinburne University of Technology, Hawthorn, Victoria, Australia
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14
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Hamaoka T, Murai H, Takata S, Hirai T, Sugimoto H, Mukai Y, Okabe Y, Tokuhisa H, Takashima SI, Usui S, Sakata K, Kawashiri MA, Sugiyama Y, Nakatsumi Y, Takamura M. Different prognosis between severe and very severe obstructive sleep apnea patients; Five year outcomes. J Cardiol 2020; 76:573-579. [PMID: 32620307 DOI: 10.1016/j.jjcc.2020.06.010] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/07/2020] [Revised: 04/26/2020] [Accepted: 05/25/2020] [Indexed: 11/27/2022]
Abstract
BACKGROUND Obstructive sleep apnea (OSA) is characterized by augmented sympathetic nerve activity. In our previous study, patients with OSA and an apnea-hyperpnea index (AHI)>55events/h showed increased single-unit muscle sympathetic nerve activity compared to patients with OSA and AHI of 30-55events/h. However, the prognostic impact in these patients remains unclear. METHODS Ninety-one OSA patients were included. All patients who had indication for continuous positive airway pressure (CPAP) were treated with CPAP. Patients were divided into three groups: mild/moderate OSA (S), AHI<30events/h (n=44); severe OSA (SS), AHI 30-55events/h (n=29); and very severe OSA (VSS), AHI>55events/h (n=18). The primary endpoint was a composite outcome composed of death, cardiovascular events, stroke, and heart failure with hospitalization. RESULTS In the 5-year follow-up, the primary event rate in the SS group [3 events (7%)] was the same as that in the S group [3 events (10%)]. However, the VSS group showed a significantly higher primary event rate among the three groups [6 events (33%), p<0.05]. In Cox regression analysis, the VSS group had the highest hazard ratio compared to other risk factors. CONCLUSIONS CPAP was effective for preventing cardiovascular disease in patients with severe OSA, however patients with very severe OSA still had a high event rate, indicating that CPAP treatment might be insufficient to reduce the OSA-related risk burden in patients with very severe OSA. Additional systemic medical treatment for CPAP might be needed in patients with very severe OSA.
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Affiliation(s)
- Takuto Hamaoka
- Department of Cardiovascular Medicine, Kanazawa University Graduate School of Medical Sciences, Kanazawa, Japan
| | - Hisayoshi Murai
- Department of Cardiovascular Medicine, Kanazawa University Graduate School of Medical Sciences, Kanazawa, Japan; Kanazawa Municipal Hospital, Kanazawa, Japan.
| | | | - Tadayuki Hirai
- Department of Cardiovascular Medicine, Kanazawa University Graduate School of Medical Sciences, Kanazawa, Japan
| | - Hiroyuki Sugimoto
- Department of Cardiovascular Medicine, Kanazawa University Graduate School of Medical Sciences, Kanazawa, Japan
| | - Yusuke Mukai
- Department of Cardiovascular Medicine, Kanazawa University Graduate School of Medical Sciences, Kanazawa, Japan
| | - Yoshitaka Okabe
- Department of Cardiovascular Medicine, Kanazawa University Graduate School of Medical Sciences, Kanazawa, Japan
| | - Hideki Tokuhisa
- Department of Cardiovascular Medicine, Kanazawa University Graduate School of Medical Sciences, Kanazawa, Japan
| | - Shin-Ichiro Takashima
- Department of Cardiovascular Medicine, Kanazawa University Graduate School of Medical Sciences, Kanazawa, Japan
| | - Soichiro Usui
- Department of Cardiovascular Medicine, Kanazawa University Graduate School of Medical Sciences, Kanazawa, Japan
| | - Kenji Sakata
- Department of Cardiovascular Medicine, Kanazawa University Graduate School of Medical Sciences, Kanazawa, Japan
| | - Masa-Aki Kawashiri
- Department of Cardiovascular Medicine, Kanazawa University Graduate School of Medical Sciences, Kanazawa, Japan
| | - Yu Sugiyama
- Kanazawa Municipal Hospital, Kanazawa, Japan
| | | | - Masayuki Takamura
- Department of Cardiovascular Medicine, Kanazawa University Graduate School of Medical Sciences, Kanazawa, Japan
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15
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Ott EP, Jacob DW, Baker SE, Holbein WW, Scruggs ZM, Shoemaker JK, Limberg JK. Sympathetic neural recruitment strategies following acute intermittent hypoxia in humans. Am J Physiol Regul Integr Comp Physiol 2020; 318:R961-R971. [PMID: 32267729 DOI: 10.1152/ajpregu.00004.2020] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
We examined the effect of acute intermittent hypoxia (IH) on sympathetic neural firing patterns and the role of the carotid chemoreceptors. We hypothesized exposure to acute IH would increase muscle sympathetic nerve activity (MSNA) via an increase in action potential (AP) discharge rates and within-burst firing. We further hypothesized any change in discharge patterns would be attenuated during acute chemoreceptor deactivation (hyperoxia). MSNA (microneurography) was assessed in 17 healthy adults (11 male/6 female; 31 ± 1 yr) during normoxic rest before and after 30 min of experimental IH. Prior to and following IH, participants were exposed to 2 min of 100% oxygen (hyperoxia). AP patterns were studied from the filtered raw MSNA signal using wavelet-based methodology. Compared with baseline, multiunit MSNA burst incidence (P < 0.01), AP incidence (P = 0.01), and AP content per burst (P = 0.01) were increased following IH. There was an increase in the probability of a particular AP cluster firing once (P < 0.01) and more than once (P = 0.03) per burst following IH. There was no effect of hyperoxia on multiunit MSNA at baseline or following IH (P > 0.05); however, hyperoxia following IH attenuated the probability of particular AP clusters firing more than once per burst (P < 0.01). Acute IH increases MSNA by increasing AP discharge rates and within-burst firing. A portion of the increase in within-burst firing following IH can be attributed to the carotid chemoreceptors. These data advance the mechanistic understanding of sympathetic activation following acute IH in humans.
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Affiliation(s)
- Elizabeth P Ott
- Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri
| | - Dain W Jacob
- Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri
| | - Sarah E Baker
- Department of Anesthesiology, Mayo Clinic, Rochester, Minnesota
| | | | | | - J Kevin Shoemaker
- School of Kinesiology, University of Western Ontario, London, Ontario, Canada
| | - Jacqueline K Limberg
- Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri.,Department of Anesthesiology, Mayo Clinic, Rochester, Minnesota
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16
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Ott EP, Baker SE, Holbein WW, Shoemaker JK, Limberg JK. Effect of varying chemoreflex stress on sympathetic neural recruitment strategies during apnea. J Neurophysiol 2019; 122:1386-1396. [PMID: 31389742 DOI: 10.1152/jn.00319.2019] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
We sought to examine the effect of varying chemoreflex stress on sympathetic neural recruitment strategies during end-expiratory apnea. We hypothesized that increases in the firing frequency and probability of low-threshold axons at the asphyxic "break point" would be exaggerated during hypoxia and attenuated during hyperoxia. Multiunit muscle sympathetic nervous system activity (MSNA) (peroneal nerve microneurography) was measured in 10 healthy male subjects (31 ± 2 yr, 25 ± 1 kg/m2). Individuals completed maximal voluntary end-expiratory apnea under normoxic, hypoxic (inspired O2 fraction: 0.17 ± 0.01), and hyperoxic (inspired O2 fraction: 0.92 ± 0.03) conditions. Action potential (AP) patterns were examined from the filtered raw signal with wavelet-based methodology. Multiunit MSNA was increased (P ≤ 0.05) during normoxic apnea, because of an increase in the frequency and incidence of AP spikes (243 ± 75 to 519 ± 134 APs/min, P = 0.048; 412 ± 133 to 733 ± 185 APs/100 heartbeats, P = 0.02). Multiunit MSNA increased from baseline (P < 0.01) during hypoxic apnea, which was due to an increase in the frequency and incidence of APs (192 ± 59 to 952 ± 266 APs/min, P < 0.01; 326 ± 89 to 1,212 ± 327 APs/100 heartbeats, P < 0.01). Hypoxic apnea also resulted in an increase in the probability of a particular AP cluster firing more than once per burst (P < 0.01). Hyperoxia attenuated any increase in MSNA with apnea, such that no changes in multiunit MSNA or frequency or incidence of AP spikes were observed (P > 0.05). We conclude that increases in frequency and incidence of APs during apnea are potentiated during hypoxia and suppressed when individuals are hyperoxic, highlighting the important impact of chemoreflex stress in AP discharge patterns. The results may have implications for neural control of the circulation in recreational activities and/or clinical conditions prone to apnea.NEW & NOTEWORTHY Our results demonstrate that, compared with normoxic end-expiratory apnea, hypoxic apnea increases the frequency and incidence of action potential spikes as well as the probability of multiple firing. We further show that this response is suppressed when individuals are hyperoxic. These data highlight the potentially important role of chemoreflex stress in neural firing and recruitment and may have implications for neural control of the circulation in recreational and/or clinical conditions prone to apnea.
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Affiliation(s)
- Elizabeth P Ott
- Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri
| | - Sarah E Baker
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota
| | - Walter W Holbein
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota
| | - J Kevin Shoemaker
- School of Kinesiology, University of Western Ontario, London, Ontario, Canada
| | - Jacqueline K Limberg
- Department of Nutrition and Exercise Physiology, University of Missouri, Columbia, Missouri.,Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota
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17
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Doherty CJ, King TJ, Incognito AV, Lee JB, Shepherd AD, Cacoilo JA, Slysz JT, Burr JF, Millar PJ. Effects of dynamic arm and leg exercise on muscle sympathetic nerve activity and vascular conductance in the inactive leg. J Appl Physiol (1985) 2019; 127:464-472. [PMID: 31246555 DOI: 10.1152/japplphysiol.00997.2018] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
The influence of muscle sympathetic nerve activity (MSNA) responses on local vascular conductance during exercise are not well established. Variations in exercise mode and active muscle mass can produce divergent MSNA responses. Therefore, we sought to examine the effects of small- versus large-muscle mass dynamic exercise on vascular conductance and MSNA responses in the inactive limb. Thirty-five participants completed two study visits in a randomized order. During visit 1, superficial femoral artery (SFA) blood flow (Doppler ultrasound) was assessed at rest and during steady-state rhythmic handgrip (RHG; 1:1 duty cycle, 40% maximal voluntary contraction), one-leg cycling (17 ± 3% peak power output), and concurrent exercise at the same intensities. During visit 2, MSNA (contralateral fibular nerve microneurography) was acquired successfully in 12/35 participants during the same exercise modes. SFA blood flow increased during RHG (P < 0.0001) and concurrent exercise (P = 0.03) but not cycling (P = 0.91). SFA vascular conductance was unchanged during RHG (P = 0.88) but reduced similarly during concurrent and cycling exercise (both P < 0.003). RHG increased MSNA burst frequency (P = 0.04) without altering burst amplitude (P = 0.69) or total MSNA (P = 0.26). In contrast, cycling and concurrent exercise had no effects on MSNA burst frequency (both P ≥ 0.10) but increased burst amplitude (both P ≤ 0.001) and total MSNA (both P ≤ 0.007). Across all exercise modes, the changes in MSNA burst amplitude and SFA vascular conductance were correlated negatively (r = -0.43, P = 0.02). In summary, the functional vascular consequences of alterations in sympathetic outflow to skeletal muscle are most closely associated with changes in MSNA burst amplitude, but not frequency, during low-intensity dynamic exercise.NEW & NOTEWORTHY Low-intensity small- versus large-muscle mass exercise can elicit divergent effects on muscle sympathetic nerve activity (MSNA). We examined the relationships between changes in MSNA (burst frequency and amplitude) and superficial femoral artery (SFA) vascular conductance during rhythmic handgrip, one-leg cycling, and concurrent exercise in the inactive leg. Only changes in MSNA burst amplitude were inversely associated with SFA vascular conductance responses. This result highlights the functional importance of measuring MSNA burst amplitude during exercise.
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Affiliation(s)
- Connor J Doherty
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada
| | - Trevor J King
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada
| | - Anthony V Incognito
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada
| | - Jordan B Lee
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada
| | - Andrew D Shepherd
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada
| | - Joseph A Cacoilo
- Department of Kinesiology, University of Guelph-Humber, Toronto, Ontario, Canada
| | - Joshua T Slysz
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada
| | - Jamie F Burr
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada
| | - Philip J Millar
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada.,Toronto General Research Institute, Toronto General Hospital, Toronto, Ontario, Canada
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18
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Incognito AV, Doherty CJ, Nardone M, Lee JB, Notay K, Seed JD, Millar PJ. Evidence for differential control of muscle sympathetic single units during mild sympathoexcitation in young, healthy humans. Am J Physiol Heart Circ Physiol 2019; 316:H13-H23. [DOI: 10.1152/ajpheart.00675.2018] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Two subpopulations of muscle sympathetic single units with opposite discharge characteristics have been identified during low-level cardiopulmonary baroreflex loading and unloading in middle-aged adults and patients with heart failure. The present study sought to determine whether similar subpopulations are present in young healthy adults during cardiopulmonary baroreflex unloading ( study 1) and rhythmic handgrip exercise ( study 2). Continuous hemodynamic and multiunit and single unit muscle sympathetic nerve activity (MSNA) data were collected at baseline and during nonhypotensive lower body negative pressure (LBNP; n = 12) and 40% maximal voluntary contraction rhythmic handgrip exercise (RHG; n = 24). Single unit MSNA responses were classified as anticipated or paradoxical based on whether changes were concordant or discordant with the multiunit MSNA response, respectively. LBNP and RHG both increased multiunit MSNA burst frequency (∆5 ± 3 bursts/min, P < 0.001; ∆5 ± 8 bursts/min, P = 0.005), burst amplitude (∆5 ± 7%, P = 0.04; ∆13 ± 14%, P < 0.001), and total MSNA (∆302 ± 191 AU/min, P = 0.001; ∆585 ± 556 AU/min, P < 0.001). During LBNP and RHG, 43 and 64 muscle single units were identified, respectively, which increased spike frequency (∆9 ± 11 spikes/min, P < 0.001; ∆10 ± 19 spikes/min, P < 0.001) and the probability of multiple spike firing (∆10 ± 12%, P < 0.001; ∆11 ± 26%, P = 0.001). During LBNP and RHG, 36 (84%) and 39 (61%) single units possessed anticipated firing responses (∆12 ± 10 spikes/min, P < 0.001; ∆19 ± 19 spikes/min, P < 0.001), whereas 7 (16%) and 25 (39%) single units exhibited paradoxical reductions (∆−3 ± 1 spikes/min, P = 0.003; ∆−4 ± 5 spikes/min, P < 0.001). The observation of divergent subpopulations of muscle sympathetic single units in healthy young humans during two mild sympathoexcitatory stressors supports differential control at the fiber level as a fundamental characteristic of human sympathetic regulation. NEW & NOTEWORTHY The activity of muscle sympathetic single units was recorded during cardiopulmonary baroreceptor unloading and rhythmic handgrip exercise in young healthy humans. During both stressors, the majority of single units (84% and 61%) exhibited anticipated behavior concordant with the integrated muscle sympathetic response, whereas a smaller proportion (16% and 39%) exhibited paradoxical sympathoinhibition. These results support differential control of postganglionic muscle sympathetic fibers as a characteristic of human sympathetic regulation during mild sympathoexcitatory stress. Listen to this article's corresponding podcast at https://ajpheart.podbean.com/e/differential-control-of-sympathetic-outflow-in-young-humans/ .
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Affiliation(s)
- Anthony V. Incognito
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada
| | - Connor J. Doherty
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada
| | - Massimo Nardone
- Department of Kinesiology, University of Guelph-Humber, Toronto, Ontario, Canada
| | - Jordan B. Lee
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada
| | - Karambir Notay
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada
| | - Jeremy D. Seed
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada
| | - Philip J. Millar
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada
- Toronto General Research Institute, Toronto, Ontario, Canada
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19
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Reyes LM, Usselman CW, Davenport MH, Steinback CD. Sympathetic Nervous System Regulation in Human Normotensive and Hypertensive Pregnancies. Hypertension 2018. [DOI: 10.1161/hypertensionaha.117.10766] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Affiliation(s)
- Laura M. Reyes
- From the Program for Pregnancy and Postpartum Health, Faculty of Kinesiology, Sport and Recreation, Women and Children’s Health Research Institute (L.M.R., C.W.U., M.H.D., C.D.S.) and Alberta Diabetes Institute (M.H.D.), University of Alberta, Edmonton, Canada
| | - Charlotte W. Usselman
- From the Program for Pregnancy and Postpartum Health, Faculty of Kinesiology, Sport and Recreation, Women and Children’s Health Research Institute (L.M.R., C.W.U., M.H.D., C.D.S.) and Alberta Diabetes Institute (M.H.D.), University of Alberta, Edmonton, Canada
| | - Margie H. Davenport
- From the Program for Pregnancy and Postpartum Health, Faculty of Kinesiology, Sport and Recreation, Women and Children’s Health Research Institute (L.M.R., C.W.U., M.H.D., C.D.S.) and Alberta Diabetes Institute (M.H.D.), University of Alberta, Edmonton, Canada
| | - Craig D. Steinback
- From the Program for Pregnancy and Postpartum Health, Faculty of Kinesiology, Sport and Recreation, Women and Children’s Health Research Institute (L.M.R., C.W.U., M.H.D., C.D.S.) and Alberta Diabetes Institute (M.H.D.), University of Alberta, Edmonton, Canada
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20
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Ramchandra R, Hood SG, Xing D, Lambert GW, May CN. Mechanisms underlying the increased cardiac norepinephrine spillover in heart failure. Am J Physiol Heart Circ Physiol 2018; 315:H340-H347. [PMID: 29701999 DOI: 10.1152/ajpheart.00069.2018] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Patients with heart failure (HF) have increased levels of cardiac norepinephrine (NE) spillover, which is an independent predictor of mortality. We hypothesized that this increase in NE spillover in HF depends not only on increases in sympathetic nerve activity (SNA) but also on changes in the mechanisms controlling NE release and reuptake. Such changes would lead to differences between the increases in directly recorded SNA and NE spillover to the heart in HF. Experiments were conducted in conscious sheep implanted with electrodes to record cardiac SNA (CSNA). In addition, arterial pressure and cardiac NE spillover were determined. In HF, the levels of both CSNA (102 ± 8 vs. 45 ± 8 bursts/min, P < 0.05) and cardiac NE spillover (21.6 ± 3.8 vs. 3.9 ± 0.8 pmol/min, P < 0.05) were significantly higher than in normal control animals. In HF, baroreflex control of cardiac NE spillover was impaired, and when CSNA was abolished by increasing arterial pressure, there was no reduction in cardiac NE spillover. A decrease in cardiac filling pressures in the HF group led to a significant increase in CSNA, but it significantly decreased cardiac NE spillover. In HF, the levels of cardiac NE spillover were enhanced above those expected from the high level of SNA, suggesting that changes in mechanisms controlling NE release and reuptake further increase the high level of NE at the heart, which will act to enhance the deleterious effects of increased CSNA in HF. NEW & NOTEWORTHY This is the first study, to our knowledge, to compare direct recordings of cardiac sympathetic nerve activity with simultaneously measured cardiac norepinephrine (NE) spillover. Our results indicate that in heart failure, increased cardiac sympathetic nerve activity is a major contributor to the increased NE spillover. In addition, there is enhanced NE spillover for the levels of synaptic nerve activity.
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Affiliation(s)
- Rohit Ramchandra
- Florey Institute of Neuroscience and Mental Health, University of Melbourne , Parkville, Victoria , Australia.,Department of Physiology, University of Auckland , New Zealand
| | - Sally G Hood
- Florey Institute of Neuroscience and Mental Health, University of Melbourne , Parkville, Victoria , Australia
| | - Daniel Xing
- Florey Institute of Neuroscience and Mental Health, University of Melbourne , Parkville, Victoria , Australia
| | - Gavin W Lambert
- Faculty of Health, Arts and Design, Swinburne University of Technology , Melbourne, Victoria , Australia
| | - Clive N May
- Florey Institute of Neuroscience and Mental Health, University of Melbourne , Parkville, Victoria , Australia
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21
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Wenner MM. Sympathetic activation in chronic anxiety: not just at the "height" of stress. Editorial Focus on "Relative burst amplitude of muscle sympathetic nerve activity is an indicator of altered sympathetic outflow in chronic anxiety". J Neurophysiol 2018; 120:7-8. [PMID: 29668387 DOI: 10.1152/jn.00220.2018] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Affiliation(s)
- Megan M Wenner
- Department of Kinesiology and Applied Physiology, University of Delaware , Newark, Delaware
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22
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Holwerda SW, Luehrs RE, Gremaud AL, Wooldridge NA, Stroud AK, Fiedorowicz JG, Abboud FM, Pierce GL. Relative burst amplitude of muscle sympathetic nerve activity is an indicator of altered sympathetic outflow in chronic anxiety. J Neurophysiol 2018. [PMID: 29537916 DOI: 10.1152/jn.00064.2018] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Relative burst amplitude of muscle sympathetic nerve activity (MSNA) is an indicator of augmented sympathetic outflow and contributes to greater vasoconstrictor responses. Evidence suggests anxiety-induced augmentation of relative MSNA burst amplitude in patients with panic disorder; thus we hypothesized that acute stress would result in augmented relative MSNA burst amplitude and vasoconstriction in individuals with chronic anxiety. Eighteen participants with chronic anxiety (ANX; 8 men, 10 women, 32 ± 2 yr) and 18 healthy control subjects with low or no anxiety (CON; 8 men, 10 women, 39 ± 3 yr) were studied. Baseline MSNA and 24-h blood pressure were similar between ANX and CON ( P > 0.05); however, nocturnal systolic blood pressure % dipping was blunted among ANX ( P = 0.02). Relative MSNA burst amplitude was significantly greater among ANX compared with CON immediately preceding (anticipation) and during physiological stress [2-min cold pressor test; ANX: 73 ± 5 vs. CON: 59 ± 3% arbitrary units (AU), P = 0.03] and mental stress (4-min mental arithmetic; ANX: 65 ± 3 vs. CON: 54 ± 3% AU, P = 0.02). Increases in MSNA burst frequency, incidence, and total activity in response to stress were not augmented among ANX compared with CON ( P > 0.05), and reduction in brachial artery conductance during cold stress was similar between ANX and CON ( P = 0.92). Relative MSNA burst amplitude during mental stress was strongly correlated with state ( P < 0.01) and trait ( P = 0.01) anxiety (State-Trait Anxiety Inventory), independent of age, sex, and body mass index. Thus in response to acute stress, both mental and physiological, individuals with chronic anxiety demonstrate selective augmentation in relative MSNA burst amplitude, indicating enhanced sympathetic drive in a population with higher risk for cardiovascular disease. NEW & NOTEWORTHY Relative burst amplitude of muscle sympathetic nerve activity in response to acute mental and physiological stress is selectively augmented in individuals with chronic anxiety, which is a prevalent condition that is associated with the development of cardiovascular disease. Augmented sympathetic burst amplitude occurs with chronic anxiety in the absence of common comorbidities. These findings provide important insight into the relation between anxiety, acute stress and sympathetic activation.
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Affiliation(s)
- Seth W Holwerda
- Department of Health and Human Physiology, University of Iowa , Iowa City, Iowa.,Abboud Cardiovascular Research Center, University of Iowa , Iowa City, Iowa
| | - Rachel E Luehrs
- Department of Health and Human Physiology, University of Iowa , Iowa City, Iowa
| | - Allene L Gremaud
- Department of Health and Human Physiology, University of Iowa , Iowa City, Iowa
| | - Nealy A Wooldridge
- Department of Health and Human Physiology, University of Iowa , Iowa City, Iowa
| | - Amy K Stroud
- Department of Psychiatry, University of Iowa , Iowa City, Iowa
| | - Jess G Fiedorowicz
- Department of Psychiatry, University of Iowa , Iowa City, Iowa.,Department of Epidemiology, University of Iowa , Iowa City, Iowa.,Department of Internal Medicine, University of Iowa , Iowa City, Iowa.,Abboud Cardiovascular Research Center, University of Iowa , Iowa City, Iowa
| | - Francois M Abboud
- Department of Internal Medicine, University of Iowa , Iowa City, Iowa.,Department of Molecular Physiology and Biophysics, University of Iowa , Iowa City, Iowa.,Abboud Cardiovascular Research Center, University of Iowa , Iowa City, Iowa
| | - Gary L Pierce
- Department of Health and Human Physiology, University of Iowa , Iowa City, Iowa.,Abboud Cardiovascular Research Center, University of Iowa , Iowa City, Iowa.,Fraternal Order of Eagles Diabetes Research Center, University of Iowa , Iowa City, Iowa
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23
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Limberg JK, Ott EP, Holbein WW, Baker SE, Curry TB, Nicholson WT, Joyner MJ, Shoemaker JK. Pharmacological assessment of the contribution of the arterial baroreflex to sympathetic discharge patterns in healthy humans. J Neurophysiol 2018; 119:2166-2175. [PMID: 29488839 DOI: 10.1152/jn.00935.2017] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
To study how changes in baroreceptor afferent activity affect patterns of sympathetic neural activation, we manipulated arterial blood pressure with intravenous nitroprusside (NTP) and phenylephrine (PE) and measured action potential (AP) patterns with wavelet-based methodology. We hypothesized that 1) baroreflex unloading (NTP) would increase firing of low-threshold axons and recruitment of latent axons and 2) baroreflex loading (PE) would decrease firing of low-threshold axons. Heart rate (HR, ECG), arterial blood pressure (BP, brachial catheter), and muscle sympathetic nerve activity (MSNA, microneurography of peroneal nerve) were measured at baseline and during steady-state systemic, intravenous NTP (0.5-1.2 µg·kg-1·min-1, n = 13) or PE (0.2-1.0 µg·kg-1·min-1, n = 9) infusion. BP decreased and HR and integrated MSNA increased with NTP ( P < 0.01). AP incidence (326 ± 66 to 579 ± 129 APs/100 heartbeats) and AP content per integrated burst (8 ± 1 to 11 ± 2 APs/burst) increased with NTP ( P < 0.05). The firing probability of low-threshold axons increased with NTP, and recruitment of high-threshold axons was observed (22 ± 3 to 24 ± 3 max cluster number, 9 ± 1 to 11 ± 1 clusters/burst; P < 0.05). BP increased and HR and integrated MSNA decreased with PE ( P < 0.05). PE decreased AP incidence (406 ± 128 to 166 ± 42 APs/100 heartbeats) and resulted in fewer unique clusters (15 ± 2 to 9 ± 1 max cluster number, P < 0.05); components of an integrated burst (APs or clusters per burst) were not altered ( P > 0.05). These data support a hierarchical pattern of sympathetic neural activation during manipulation of baroreceptor afferent activity, with rate coding of active neurons playing the predominant role and recruitment/derecruitment of higher-threshold units occurring with steady-state hypotensive stress. NEW & NOTEWORTHY To study how changes in baroreceptor afferent activity affect patterns of sympathetic neural activation, we manipulated arterial blood pressure with intravenous nitroprusside and phenylephrine and measured sympathetic outflow with wavelet-based methodology. Baroreflex unloading increased sympathetic activity by increasing firing probability of low-threshold axons (rate coding) and recruiting new populations of high-threshold axons. Baroreflex loading decreased sympathetic activity by decreasing the firing probability of larger axons (derecruitment); however, the components of an integrated burst were unaffected.
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Affiliation(s)
- Jacqueline K Limberg
- Department of Nutrition and Exercise Physiology, University of Missouri , Columbia, Missouri.,Department of Anesthesiology and Perioperative Medicine, Mayo Clinic , Rochester, Minnesota
| | - Elizabeth P Ott
- Department of Nutrition and Exercise Physiology, University of Missouri , Columbia, Missouri
| | - Walter W Holbein
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic , Rochester, Minnesota
| | - Sarah E Baker
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic , Rochester, Minnesota
| | - Timothy B Curry
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic , Rochester, Minnesota
| | - Wayne T Nicholson
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic , Rochester, Minnesota
| | - Michael J Joyner
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic , Rochester, Minnesota
| | - J Kevin Shoemaker
- School of Kinesiology, University of Western Ontario , London, Ontario , Canada
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24
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Shoemaker JK, Klassen SA, Badrov MB, Fadel PJ. Fifty years of microneurography: learning the language of the peripheral sympathetic nervous system in humans. J Neurophysiol 2018; 119:1731-1744. [PMID: 29412776 DOI: 10.1152/jn.00841.2017] [Citation(s) in RCA: 45] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
As a primary component of homeostasis, the sympathetic nervous system enables rapid adjustments to stress through its ability to communicate messages among organs and cause targeted and graded end organ responses. Key in this communication model is the pattern of neural signals emanating from the central to peripheral components of the sympathetic nervous system. But what is the communication strategy employed in peripheral sympathetic nerve activity (SNA)? Can we develop and interpret the system of coding in SNA that improves our understanding of the neural control of the circulation? In 1968, Hagbarth and Vallbo (Hagbarth KE, Vallbo AB. Acta Physiol Scand 74: 96-108, 1968) reported the first use of microneurographic methods to record sympathetic discharges in peripheral nerves of conscious humans, allowing quantification of SNA at rest and sympathetic responsiveness to physiological stressors in health and disease. This technique also has enabled a growing investigation into the coding patterns within, and cardiovascular outcomes associated with, postganglionic SNA. This review outlines how results obtained by microneurographic means have improved our understanding of SNA outflow patterns at the action potential level, focusing on SNA directed toward skeletal muscle in conscious humans.
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Affiliation(s)
- J Kevin Shoemaker
- School of Kinesiology, University of Western Ontario , London, Ontario , Canada
| | - Stephen A Klassen
- School of Kinesiology, University of Western Ontario , London, Ontario , Canada
| | - Mark B Badrov
- School of Kinesiology, University of Western Ontario , London, Ontario , Canada
| | - Paul J Fadel
- Department of Kinesiology, University of Texas at Arlington , Arlington, Texas
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25
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Esler M, Lambert G, Schlaich M, Dixon J, Sari CI, Lambert E. Obesity Paradox in Hypertension: Is This Because Sympathetic Activation in Obesity-Hypertension Takes a Benign Form? Hypertension 2017; 71:22-33. [PMID: 29158358 DOI: 10.1161/hypertensionaha.117.09790] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Murray Esler
- From the Baker Heart and Diabetes Institute, Melbourne, Australia (M.E., J.D., C.I.S.); Swinburne University of Technology, Melbourne, Australia (G.L., E.L.); and School of Medicine, Royal Perth Hospital Unit, Faculty of Medicine, Dentistry and Health Sciences, University of Western Australia, Perth (M.S.).
| | - Gavin Lambert
- From the Baker Heart and Diabetes Institute, Melbourne, Australia (M.E., J.D., C.I.S.); Swinburne University of Technology, Melbourne, Australia (G.L., E.L.); and School of Medicine, Royal Perth Hospital Unit, Faculty of Medicine, Dentistry and Health Sciences, University of Western Australia, Perth (M.S.)
| | - Markus Schlaich
- From the Baker Heart and Diabetes Institute, Melbourne, Australia (M.E., J.D., C.I.S.); Swinburne University of Technology, Melbourne, Australia (G.L., E.L.); and School of Medicine, Royal Perth Hospital Unit, Faculty of Medicine, Dentistry and Health Sciences, University of Western Australia, Perth (M.S.)
| | - John Dixon
- From the Baker Heart and Diabetes Institute, Melbourne, Australia (M.E., J.D., C.I.S.); Swinburne University of Technology, Melbourne, Australia (G.L., E.L.); and School of Medicine, Royal Perth Hospital Unit, Faculty of Medicine, Dentistry and Health Sciences, University of Western Australia, Perth (M.S.)
| | - Carolina Ika Sari
- From the Baker Heart and Diabetes Institute, Melbourne, Australia (M.E., J.D., C.I.S.); Swinburne University of Technology, Melbourne, Australia (G.L., E.L.); and School of Medicine, Royal Perth Hospital Unit, Faculty of Medicine, Dentistry and Health Sciences, University of Western Australia, Perth (M.S.)
| | - Elisabeth Lambert
- From the Baker Heart and Diabetes Institute, Melbourne, Australia (M.E., J.D., C.I.S.); Swinburne University of Technology, Melbourne, Australia (G.L., E.L.); and School of Medicine, Royal Perth Hospital Unit, Faculty of Medicine, Dentistry and Health Sciences, University of Western Australia, Perth (M.S.)
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26
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Macefield VG, Wallin BG. Physiological and pathophysiological firing properties of single postganglionic sympathetic neurons in humans. J Neurophysiol 2017; 119:944-956. [PMID: 29142091 DOI: 10.1152/jn.00004.2017] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
It has long been known from microneurographic recordings in human subjects that the activity of postganglionic sympathetic axons occurs as spontaneous bursts, with muscle sympathetic nerve activity (MSNA) exhibiting strong cardiac rhythmicity via the baroreflex and skin sympathetic nerve activity showing much weaker cardiac modulation. Here we review the firing properties of single sympathetic neurons, obtained using highly selective microelectrodes. Individual vasoconstrictor neurons supplying muscle or skin, or sudomotor neurons supplying sweat glands, always discharge with a low firing probability (~30%) and at very low frequencies (~0.5 Hz). Moreover, they usually fire only once per cardiac interval but can fire greater than four times within a burst. Modeling has shown that this pattern can best be explained by individual neurons being driven by, on average, two preganglionic inputs. Unitary recordings of muscle vasoconstrictor neurons have been made in several pathophysiological states, including heart failure, hypertension, obstructive sleep apnea, bronchiectasis, chronic obstructive pulmonary disease, depression, and panic disorder. The augmented MSNA in each of these diseases features an increase in firing probability and discharge frequency of individual muscle vasoconstrictor neurons above that seen in healthy subjects, yet firing rates rarely exceed 1 Hz. However, unlike patients with heart failure, all patients with respiratory disease or panic disorder, and patients with hyperhidrosis, exhibited an increase in multiple within-burst firing, which emphasizes the different modes by which the sympathetic nervous system grades its output in pathophysiological states of high sympathetic nerve activity.
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Affiliation(s)
- Vaughan G Macefield
- School of Medicine, Western Sydney University , Sydney , Australia.,Neuroscience Research Australia, Sydney , Australia.,Baker Heart and Diabetes Institute , Melbourne , Australia
| | - B Gunnar Wallin
- Department of Clinical Neurophysiology, Institute of Neuroscience and Physiology, Sahlgren Academy at University of Gothenburg , Gothenburg , Sweden
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27
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Shoemaker JK. Recruitment strategies in efferent sympathetic nerve activity. Clin Auton Res 2017; 27:369-378. [DOI: 10.1007/s10286-017-0459-x] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2017] [Accepted: 08/09/2017] [Indexed: 12/13/2022]
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28
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Hart EC, Head GA, Carter JR, Wallin BG, May CN, Hamza SM, Hall JE, Charkoudian N, Osborn JW. Recording sympathetic nerve activity in conscious humans and other mammals: guidelines and the road to standardization. Am J Physiol Heart Circ Physiol 2017; 312:H1031-H1051. [PMID: 28364017 DOI: 10.1152/ajpheart.00703.2016] [Citation(s) in RCA: 112] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/26/2016] [Revised: 03/06/2017] [Accepted: 03/06/2017] [Indexed: 01/03/2023]
Abstract
Over the past several decades, studies of the sympathetic nervous system in humans, sheep, rabbits, rats, and mice have substantially increased mechanistic understanding of cardiovascular function and dysfunction. Recently, interest in sympathetic neural mechanisms contributing to blood pressure control has grown, in part because of the development of devices or surgical procedures that treat hypertension by manipulating sympathetic outflow. Studies in animal models have provided important insights into physiological and pathophysiological mechanisms that are not accessible in human studies. Across species and among laboratories, various approaches have been developed to record, quantify, analyze, and interpret sympathetic nerve activity (SNA). In general, SNA demonstrates "bursting" behavior, where groups of action potentials are synchronized and linked to the cardiac cycle via the arterial baroreflex. In humans, it is common to quantify SNA as bursts per minute or bursts per 100 heart beats. This type of quantification can be done in other species but is only commonly reported in sheep, which have heart rates similar to humans. In rabbits, rats, and mice, SNA is often recorded relative to a maximal level elicited in the laboratory to control for differences in electrode position among animals or on different study days. SNA in humans can also be presented as total activity, where normalization to the largest burst is a common approach. The goal of the present paper is to put together a summary of "best practices" in several of the most common experimental models and to discuss opportunities and challenges relative to the optimal measurement of SNA across species.Listen to this article's corresponding podcast at https://ajpheart.podbean.com/e/guidelines-for-measuring-sympathetic-nerve-activity/.
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Affiliation(s)
- Emma C Hart
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, United Kingdom;
| | - Geoffrey A Head
- Baker IDI Heart and Diabetes Institute, Melbourne, Victoria, Australia
| | | | | | - Clive N May
- Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville, Victoria, Australia
| | | | - John E Hall
- Department of Physiology and Biophysics, Mississippi Center for Obesity Research, University of Mississippi Medical Center, Jackson, Mississippi
| | - Nisha Charkoudian
- United States Army Research Institute of Environmental Medicine, Natick, Massachusetts; and
| | - John W Osborn
- Department of Integrative Biology and Physiology, University of Minnesota Medical School, Minneapolis, Minnesota
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29
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Tomek J, Bub G. Hypertension-induced remodelling: on the interactions of cardiac risk factors. J Physiol 2017; 595:4027-4036. [PMID: 28217927 PMCID: PMC5471416 DOI: 10.1113/jp273043] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2016] [Accepted: 01/25/2017] [Indexed: 12/19/2022] Open
Abstract
Hypertension induces considerable cardiac remodelling, such as hypertrophy, interstitial fibrosis, and abnormal activity of the cardiac sympathetic nervous system, which are established risk factors in several highly dangerous heart diseases, such as ventricular fibrillation and congestive heart failure. All these risk factors and heart diseases are studied extensively in isolation, but to our knowledge, there is no comprehensive review of their interactions. At the same time, there is growing evidence suggesting that such interactions are numerous and that a successful therapy against a particular condition may have unexpectedly weak effects on mortality, as treated patients may die of a different cause exacerbated by the therapy. In this article, we present a multiscale review of the literature focusing on the relationships between the above‐mentioned risk factors and heart diseases, and introduce a framework that gives insight into their possible interactions. We use this framework to demonstrate that conditions such as fibrosis and elevated activity of the sympathetic nervous system may be compensatory, rather than purely pathological, mechanisms in certain contexts. Finally, we show why the described mechanisms are relevant not only in hypertension, but also in the case of healed myocardial infarction.
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Affiliation(s)
- Jakub Tomek
- Department of Physiology Anatomy and Genetics, University of Oxford, Oxford, UK
| | - Gil Bub
- Department of Physiology, McGill University, Canada
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30
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Crotty TP. Ageing is a process where the growth effect of neuronal noradrenaline changes progressively in favour of the flow mediated, neurodegenerative and inflammatory effect of plasma noradrenaline. Med Hypotheses 2016; 93:106-12. [PMID: 27372867 DOI: 10.1016/j.mehy.2016.05.017] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2015] [Revised: 05/13/2016] [Accepted: 05/18/2016] [Indexed: 02/07/2023]
Abstract
The noradrenaline stimulus has two components, one excitor, the other inhibitory. Neuronal noradrenaline is the excitor component and plasma noradrenaline is the inhibitory. The balance of effect between the two, the noradrenergic balance, is the controlled variable of the sympathetic system and determines the effect of noradrenaline. Neuronal noradrenaline stimulates tissues by diffusion from their sympathetic nerve endings, plasma noradrenaline does so by diffusion from their microcirculations. Changes in microcirculatory flow, by altering the flow mediated effect of plasma noradrenaline, are mainly responsible for altering the noradrenergic balance in the peripheral tissues; changes in CSF flow are speculated to be mainly responsible for doing the same in the brain, by altering the balance between synaptic noradrenaline in the brain and nonsynaptic noradrenaline in the subarachnoid CSF. When plasma noradrenaline alters the noradrenergic balance it triggers afferent sympathetic activity that alerts hypothalamic neurons to the event and they restore the balance and tissue homeostasis, within milliseconds, by adjusting the level of efferent sympathetic activity they project back to the affected tissue. Because the restoration is so rapid the effect of plasma noradrenaline is normally unobservable and dismissed as not having occurred. Because the hypothalamus is not involved with the responses of isolated canine lateral saphenous vein segments to noradrenaline, the effects of plasma noradrenaline in that preparation are not countered by reactive efferent activity and, consequently, are readily apparent in it. Quantitatively, they have been found to be a function of microcirculatory flow and noradrenaline concentration and, qualitatively, to be inhibitory, dilator, pro inflammatory and neurodegenerative. In life, due to a progressive increase in plasma noradrenaline concentration and, more so, in microcirculatory flow, the noradrenergic balance moves progressively in favour of the neurodegenerative and inflammatory effects of plasma noradrenaline. These observations are the basis of an hypothesis that ageing is caused by a genetically programmed shift in balance away from the growth and anti-inflammatory effects of neuronal noradrenaline, early in life, towards the neurodegenerative and pro-inflammatory effects of plasma noradrenalin, later in life. Death is believed to occur when plasma noradrenaline has damaged the structure of the sympathetic system so much that it can no longer create the minimum quantity of neurotransmitter needed to maintain the level of noradrenergic balance and homeostasis necessary for life.
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Affiliation(s)
- T P Crotty
- Physiology Dept., University College Cork Medical and Health School, Western Gateway Building, Western Road, Cork, Ireland.
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31
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Hamaoka T, Murai H, Kaneko S, Usui S, Okabe Y, Tokuhisa H, Kato T, Furusho H, Sugiyama Y, Nakatsumi Y, Takata S, Takamura M. Single-Unit Muscle Sympathetic Nerve Activity Reflects Sleep Apnea Severity, Especially in Severe Obstructive Sleep Apnea Patients. Front Physiol 2016; 7:66. [PMID: 26973534 PMCID: PMC4773439 DOI: 10.3389/fphys.2016.00066] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2015] [Accepted: 02/12/2016] [Indexed: 01/19/2023] Open
Abstract
Obstructive sleep apnea syndrome (OSAS) is associated with augmented sympathetic nerve activity, as assessed by multi-unit muscle sympathetic nerve activity (MSNA). However, it is still unclear whether single-unit MSNA is a better reflection of sleep apnea severity according to the apnea-hypopnea index (AHI). One hundred and two OSAS patients underwent full polysomnography and single- and multi-unit MSNA measurements. Univariate and multivariate regression analysis were performed to determine which parameters correlated with OSAS severity, which was defined by the AHI. Single- and multi-unit MSNA were significantly and positively correlated with AHI severity. The AHI was also significantly correlated with multi-unit MSNA burst frequency (r = 0.437, p < 0.0001) and single-unit MSNA spike frequency (r = 0.632, p < 0.0001). Multivariable analysis revealed that SF was correlated most significantly with AHI (T = 7.27, p < 0.0001). The distributions of multiple single-unit spikes per one cardiac interval did not differ between patients with an AHI of <30 and those with and AHI of 30–55 events/h; however, the pattern of each multiple spike firing were significantly higher in patients with an AHI of >55. These results suggest that sympathetic nerve activity is associated with sleep apnea severity. In addition, single-unit MSNA is a more accurate reflection of sleep apnea severity with alternation of the firing pattern, especially in patients with very severe OSAS.
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Affiliation(s)
- Takuto Hamaoka
- Department of Disease Control and Homeostasis, Graduate School of Medical Science, Kanazawa University Kanazawa, Japan
| | - Hisayoshi Murai
- Department of Disease Control and Homeostasis, Graduate School of Medical Science, Kanazawa University Kanazawa, Japan
| | - Shuichi Kaneko
- Department of Disease Control and Homeostasis, Graduate School of Medical Science, Kanazawa University Kanazawa, Japan
| | - Soichiro Usui
- Department of Disease Control and Homeostasis, Graduate School of Medical Science, Kanazawa University Kanazawa, Japan
| | - Yoshitaka Okabe
- Department of Disease Control and Homeostasis, Graduate School of Medical Science, Kanazawa University Kanazawa, Japan
| | - Hideki Tokuhisa
- Department of Disease Control and Homeostasis, Graduate School of Medical Science, Kanazawa University Kanazawa, Japan
| | - Takeshi Kato
- Department of Disease Control and Homeostasis, Graduate School of Medical Science, Kanazawa University Kanazawa, Japan
| | - Hiroshi Furusho
- Department of Disease Control and Homeostasis, Graduate School of Medical Science, Kanazawa University Kanazawa, Japan
| | | | | | | | - Masayuki Takamura
- Department of Disease Control and Homeostasis, Graduate School of Medical Science, Kanazawa University Kanazawa, Japan
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Briant LJB, O'Callaghan EL, Champneys AR, Paton JFR. Respiratory modulated sympathetic activity: a putative mechanism for developing vascular resistance? J Physiol 2015; 593:5341-60. [PMID: 26507780 DOI: 10.1113/jp271253] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2015] [Accepted: 10/23/2015] [Indexed: 12/29/2022] Open
Abstract
KEY POINTS Sympathetic activity exhibits respiratory modulation that is amplified in hypertensive rats. Respiratory modulated sympathetic activity produces greater changes in vascular resistance than tonic stimulation of the same stimulus magnitude in normotensive but not hypertensive rats. Mathematical modelling demonstrates that respiratory modulated sympathetic activity may fail to produce greater vascular resistance changes in hypertensive rats because the system is saturated as a consequence of a dysfunctional noradrenaline reuptake mechanism. Respiratory modulated sympathetic activity is an efficient mechanism to raise vascular resistance promptly, corroborating its involvement in the ontogenesis of hypertension. ABSTRACT Sympathetic nerve activity (SNA) exhibits respiratory modulation. This component of SNA is important - being recruited under cardiorespiratory reflex conditions and elevated in the spontaneously hypertensive (SH) rat - and yet the exact influence of this modulation on vascular tone is not understood, even in normotensive conditions. We constructed a mathematical model of the sympathetic innervation of an arteriole, and used it to test the hypothesis that respiratory modulation of SNA preferentially increases vasoconstriction compared to a frequency-matched tonic pattern. Simulations supported the hypothesis, where respiratory modulated increases in vasoconstriction were mediated by a noradrenergic mechanism. These predictions were tested in vivo in adult Wistar rats. Stimulation of the sympathetic chain (L3) with respiratory modulated bursting patterns, revealed that bursting increases vascular resistance (VR) more than tonic stimulation (57.8 ± 3.3% vs. 44.8 ± 4.2%; P < 0.001; n = 8). The onset of the VR response was also quicker for bursting stimulation (rise time constant = 1.98 ± 0.09 s vs. 2.35 ± 0.20 s; P < 0.01). In adult SH rats (n = 8), the VR response to bursting (44.6 ± 3.9%) was not different to tonic (37.4 ± 3.5%; P = 0.57). Using both mathematical modelling and in vivo techniques, we have shown that VR depends critically on respiratory modulation and revealed that this pattern dependency in Wistar rats is due to a noradrenergic mechanism. This respiratory component may therefore contribute to the ontogenesis of hypertension in the pre-hypertensive SH rat - raising VR and driving vascular remodelling. Why adult SH rats do not exhibit a pattern-dependent response is not known, but further modelling revealed that this may be due to dysfunctional noradrenaline reuptake.
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Affiliation(s)
- Linford J B Briant
- School of Physiology & Pharmacology, Medical Sciences Building, University Walk, University of Bristol, Bristol, BS81TD, UK.,Department of Engineering Mathematics, Merchant Venturers Building, Woodland Road, University of Bristol, Bristol, BS8 1UB, UK
| | - Erin L O'Callaghan
- School of Physiology & Pharmacology, Medical Sciences Building, University Walk, University of Bristol, Bristol, BS81TD, UK
| | - Alan R Champneys
- Department of Engineering Mathematics, Merchant Venturers Building, Woodland Road, University of Bristol, Bristol, BS8 1UB, UK
| | - Julian F R Paton
- School of Physiology & Pharmacology, Medical Sciences Building, University Walk, University of Bristol, Bristol, BS81TD, UK
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El-Hamad F, Lambert E, Abbott D, Baumert M. Relation between QT interval variability and muscle sympathetic nerve activity in normal subjects. Am J Physiol Heart Circ Physiol 2015; 309:H1218-24. [DOI: 10.1152/ajpheart.00230.2015] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/27/2015] [Accepted: 08/12/2015] [Indexed: 01/06/2023]
Abstract
Beat-to-beat variability of the QT interval (QTV) is sought to provide an indirect noninvasive measure of sympathetic nerve activity, but a formal quantification of this relationship has not been provided. In this study we used power contribution analysis to study the relationship between QTV and muscle sympathetic nerve activity (MSNA). ECG and MSNA were recorded in 10 healthy subjects in the supine position and after 40° head-up tilt. Power spectrum analysis was performed using a linear autoregressive model with two external inputs: heart period (RR interval) variability (RRV) and MSNA. Total and low-frequency power of QTV was decomposed into contributions by RRV, MSNA, and sources independent of RRV and MSNA. Results show that the percentage of MSNA power contribution to QT is very small and does not change with tilt. RRV power contribution to QT power is notable and decreases with tilt, while the greatest percentage of QTV is independent of RRV and MSNA in the supine position and after 40° head-up tilt. In conclusion, beat-to-beat QTV in normal subjects does not appear to be significantly affected by the rhythmic modulations in MSNA following low to moderate orthostatic stimulation. Therefore, MSNA oscillations may not represent a useful surrogate for cardiac sympathetic nerve activity at moderate levels of activation, or, alternatively, sympathetic influences on QTV are complex and not quantifiable with linear shift-invariant autoregressive models.
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Affiliation(s)
- Fatima El-Hamad
- School of Electrical and Electronic Engineering, The University of Adelaide, Adelaide, South Australia, Australia; and
| | - Elisabeth Lambert
- Human Neurotransmitter Laboratory, Baker IDI Heart and Diabetes Institute, Melbourne, Victoria, Australia
| | - Derek Abbott
- School of Electrical and Electronic Engineering, The University of Adelaide, Adelaide, South Australia, Australia; and
| | - Mathias Baumert
- School of Electrical and Electronic Engineering, The University of Adelaide, Adelaide, South Australia, Australia; and
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Ghotbi AA, Sander M, Køber L, Philbert BT, Gustafsson F, Hagemann C, Kjær A, Jacobsen PK. Optimal Cardiac Resynchronization Therapy Pacing Rate in Non-Ischemic Heart Failure Patients: A Randomized Crossover Pilot Trial. PLoS One 2015; 10:e0138124. [PMID: 26382243 PMCID: PMC4575161 DOI: 10.1371/journal.pone.0138124] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2015] [Accepted: 08/21/2015] [Indexed: 12/27/2022] Open
Abstract
Background The optimal pacing rate during cardiac resynchronization therapy (CRT) is unknown. Therefore, we investigated the impact of changing basal pacing frequencies on autonomic nerve function, cardiopulmonary exercise capacity and self-perceived quality of life (QoL). Methods Twelve CRT patients with non-ischemic heart failure (NYHA class II–III) were enrolled in a randomized, double-blind, crossover trial, in which the basal pacing rate was set at DDD-60 and DDD-80 for 3 months (DDD-R for 2 patients). At baseline, 3 months and 6 months, we assessed sympathetic nerve activity by microneurography (MSNA), peak oxygen consumption (pVO2), N-terminal pro-brain natriuretic peptide (p-NT-proBNP), echocardiography and QoL. Results DDD-80 pacing for 3 months increased the mean heart rate from 77.3 to 86.1 (p = 0.001) and reduced sympathetic activity compared to DDD-60 (51±14 bursts/100 cardiac cycles vs. 64±14 bursts/100 cardiac cycles, p<0.05). The mean pVO2 increased non-significantly from 15.6±6 mL/min/kg during DDD-60 to 16.7±6 mL/min/kg during DDD-80, and p-NT-proBNP remained unchanged. The QoL score indicated that DDD-60 was better tolerated. Conclusion In CRT patients with non-ischemic heart failure, 3 months of DDD-80 pacing decreased sympathetic outflow (burst incidence only) compared to DDD-60 pacing. However, Qol scores were better during the lower pacing rate. Further and larger scale investigations are indicated. Trial Registration ClinicalTrials.gov NCT02258061
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Affiliation(s)
- Adam Ali Ghotbi
- The Heart Center, Department of Cardiology, Rigshospitalet Copenhagen University Hospital, Copenhagen, Denmark
- Department of Clinical Physiology, Nuclear Medicine & PET, Rigshospitalet Copenhagen University Hospital, Copenhagen, Denmark
- * E-mail:
| | - Mikael Sander
- The Heart Center, Department of Cardiology, Rigshospitalet Copenhagen University Hospital, Copenhagen, Denmark
| | - Lars Køber
- The Heart Center, Department of Cardiology, Rigshospitalet Copenhagen University Hospital, Copenhagen, Denmark
| | - Berit Th. Philbert
- The Heart Center, Department of Cardiology, Rigshospitalet Copenhagen University Hospital, Copenhagen, Denmark
| | - Finn Gustafsson
- The Heart Center, Department of Cardiology, Rigshospitalet Copenhagen University Hospital, Copenhagen, Denmark
| | - Christoffer Hagemann
- Department of Clinical Physiology, Nuclear Medicine & PET, Rigshospitalet Copenhagen University Hospital, Copenhagen, Denmark
| | - Andreas Kjær
- Department of Clinical Physiology, Nuclear Medicine & PET, Rigshospitalet Copenhagen University Hospital, Copenhagen, Denmark
| | - Peter K. Jacobsen
- The Heart Center, Department of Cardiology, Rigshospitalet Copenhagen University Hospital, Copenhagen, Denmark
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Carter JR, Goldstein DS. Sympathoneural and adrenomedullary responses to mental stress. Compr Physiol 2015; 5:119-46. [PMID: 25589266 DOI: 10.1002/cphy.c140030] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
This concept-based review provides historical perspectives and updates about sympathetic noradrenergic and sympathetic adrenergic responses to mental stress. The topic of this review has incited perennial debate, because of disagreements over definitions, controversial inferences, and limited availability of relevant measurement tools. The discussion begins appropriately with Cannon's "homeostasis" and his pioneering work in the area. This is followed by mental stress as a scientific idea and the relatively new notions of allostasis and allostatic load. Experimental models of mental stress in rodents and humans are discussed, with particular attention to ethical constraints in humans. Sections follow on sympathoneural responses to mental stress, reactivity of catecholamine systems, clinical pathophysiologic states, and the cardiovascular reactivity hypothesis. Future advancement of the field will require integrative approaches and coordinated efforts between physiologists and psychologists on this interdisciplinary topic.
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Affiliation(s)
- Jason R Carter
- Department of Kinesiology and Integrative Physiology, Michigan Technological University, Houghton, Michigan Clinical Neurocardiology Section, Clinical Neurosciences Program, Division of Intramural Research, National Institutes of Health, Bethesda, Maryland
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[Position paper on the results of Symplicity HTN-3 trial. Grupo de estudio de la hipertensión arterial resistente]. ARCHIVOS DE CARDIOLOGIA DE MEXICO 2015; 85:154-7. [PMID: 25700579 DOI: 10.1016/j.acmx.2014.11.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2014] [Revised: 11/27/2014] [Accepted: 11/27/2014] [Indexed: 11/23/2022] Open
Abstract
Renal artery denervation has shown to be an effective treatment for resistant hypertension. Symplicity HTN 1 and 2 trials showed in small and uncontrolled groups, significant systolic blood pressure reductions down to 30 mm Hg. Symplicity HTN-3, a double blind, randomized, placebo controlled clinical trial shaded this initial enthusiasm. Surprisingly, their results showed that renal denervation has a similar effect to placebo. Pre-specified subgroup analysis showed that non-black race individuals, younger than 65 years and with normal renal function, had a statistically significant systolic blood pressure decrease. This manuscript critically appraises the Symplicity HTN-3 trial, proposing possible explanations for the results. Also declares our group position and future actions regarding renal denervation.
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Convertino VA. Neurohumoral mechanisms associated with orthostasis: reaffirmation of the significant contribution of the heart rate response. Front Physiol 2014; 5:236. [PMID: 25071585 PMCID: PMC4074989 DOI: 10.3389/fphys.2014.00236] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2014] [Accepted: 06/05/2014] [Indexed: 11/23/2022] Open
Abstract
The inability to compensate for acute central hypovolemia underlies the clinical development of orthostatic hypotension and instability (e.g., syncope). Although neuro-humoral control of both cardiac output and peripheral vascular resistance contributes to hemodynamic stability during orthostasis, a notion has been proposed that the failure of adequate peripheral vascular constriction rather than cardiac responses represents the primary mechanism underlying the development of orthostatic intolerance. This review article provides an opportunity to present compelling evidence captured over the past 30 years in our laboratory to support the concept that neural-mediated tachycardia during orthostasis in healthy individuals represents a critical response to tolerating acute reduction in central blood volume in addition to, and independent of, peripheral vascular constriction. In this review paper, data are presented from experiments using graded lower body negative pressure (LBNP) as a method to induce orthostatic intolerance in two experimental human models: (1) comparison of heart rate and autonomic responses in individuals with relatively high and low tolerance to LBNP; and (2) vagal and sympathetic blockade of cardiac neural control. These experiments revealed that: (1) greater elevations in heart rate are associated with higher orthostatic (LBNP) tolerance; (2) higher orthostatic heart rate is associated with greater sympathetic nerve activity and withdrawal of vagally-mediated cardiac baroreflex response; and (3) non-specific sympathetic blockade causes a pronounced reduction in heart rate and LBNP tolerance. Cardiac parasympathetic withdrawal contributes to protection against development of hypotension during the initial seconds of transition to an orthostatic challenge, while the primary mechanism by which tachycardia defends orthostatic stability in healthy subjects for extended durations is mediated predominantly through sympathetic adrenergic control.
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Affiliation(s)
- Victor A Convertino
- U.S. Army Institute of Surgical Research, Research Division JBSA Fort Sam Houston, TX, USA
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Sympathetic single axonal discharge after spinal cord injury in humans: activity at rest and after bladder stimulation. Spinal Cord 2014; 52:434-8. [PMID: 24663001 DOI: 10.1038/sc.2014.35] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2013] [Revised: 02/24/2014] [Accepted: 02/28/2014] [Indexed: 11/08/2022]
Abstract
STUDY DESIGN Clinical experimental mechanistic study. OBJECTIVES (1) To determine in three spinal cord-injured patients whether individual muscle sympathetic nerve fibres below the level of the spinal lesion display spontaneous activity. (2) To determine in these patients if individual sympathetic vasoconstrictor fibres show a prolonged discharge following a bladder stimulus. SETTING University hospital in Gothenburg, Sweden. METHODS Microneurographic recordings of action potentials from individual muscle nerve sympathetic fibres in a peroneal nerve. Recordings of skin blood flow and electrodermal responses in a foot. RESULTS In all patients, there was sparse ongoing spontaneous impulse traffic in individual sympathetic fibres. Brisk mechanical pressure over the urinary bladder evoked a varying number of action potentials in individual fibres, but the activity was brief and did not continue after the end of the evoked multiunit burst. CONCLUSION Prolonged discharges in individual sympathetic fibres are unlikely to contribute to a long duration of blood pressure increases induced by brief bladder stimuli.
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Millar PJ, Murai H, Morris BL, Floras JS. Microneurographic evidence in healthy middle-aged humans for a sympathoexcitatory reflex activated by atrial pressure. Am J Physiol Heart Circ Physiol 2013; 305:H931-8. [DOI: 10.1152/ajpheart.00375.2013] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Atrial mechanoreceptors, stimulated by increased pressure or volume, elicit in healthy humans a net sympathoinhibitory response. The co-existence of an atrial reflex eliciting muscle sympathoexcitation has been postulated but undetected by conventional multi-unit muscle sympathetic nerve activity (MSNA). We hypothesized that in response to a selective increase in atrial pressure, single-unit MSNA would reveal a subpopulation of efferent sympathetic neurons with firing patterns opposite to the integrated multi-unit MSNA envelope. Multi- and single-unit MSNA recordings were acquired in eight healthy middle-aged subjects (age, 57 ± 8 years; body mass index, 25 ± 2 kg/m2) submitted to selective decreases or increases in atrial pressure by nonhypotensive lower body negative pressure (LBNP; −10 mmHg) or nonhypertensive lower body positive pressure (LBPP; +10 mmHg), respectively. Single-unit MSNA firing responses were classified as anticipated if spike frequency and incidence increased with LBNP or decreased with LBPP and paradoxical if they decreased with LBNP or increased with LBPP. LBNP decreased (3.2 ± 2.8 to 1.4 ± 3.1 mmHg, P < 0.01) and LBPP increased (3.3 ± 2.7 to 4.9 ± 2.8 mmHg, P < 0.01) estimated central venous pressure without affecting stroke volume, systemic pressure, or resistance. Multi-unit MSNA increased with LBNP (31 ± 17 to 38 ± 19 bursts/min, P < 0.01) and diminished with LBPP (33 ± 15 to 28 ± 15 bursts/min, P < 0.01). Of 21 single-units identified, 76% exhibited firing responses to both LBNP and LBPP concordant with multi-unit MSNA, whereas 24% demonstrated discordant or paradoxical responses. The detection of two subpopulations of single-units within the multi-unit MSNA recording, exhibiting opposite firing characteristics, establishes the first evidence in humans for the existence of an excitatory cardiac-muscle sympathetic reflex activated by increasing atrial pressure.
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Affiliation(s)
- Philip J. Millar
- University Health Network and Mount Sinai Hospital Division of Cardiology, University of Toronto, Toronto, Ontario, Canada
| | - Hisayoshi Murai
- University Health Network and Mount Sinai Hospital Division of Cardiology, University of Toronto, Toronto, Ontario, Canada
| | - Beverley L. Morris
- University Health Network and Mount Sinai Hospital Division of Cardiology, University of Toronto, Toronto, Ontario, Canada
| | - John S. Floras
- University Health Network and Mount Sinai Hospital Division of Cardiology, University of Toronto, Toronto, Ontario, Canada
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Millar PJ, O’Donnell E. Alpha males: muscle sympathetic discharge on beat-to-beat forearm vascular conductance. J Physiol 2013; 591:4375-6. [DOI: 10.1113/jphysiol.2013.261743] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
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Shinzawa G, Sato D, Kusunoki M, Karimata T, Sasaki H, Nakamura R, Feng Z, Nishina A, Nakamura T. Characteristics of spike rate of peripheral sympathetic nervous signal in streptozotocin-induced diabetic rats. Auton Neurosci 2013; 179:23-7. [PMID: 23830533 DOI: 10.1016/j.autneu.2013.06.005] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2013] [Revised: 05/27/2013] [Accepted: 06/14/2013] [Indexed: 11/25/2022]
Abstract
Although streptozotocin-administered (STZ) rats were widely used as an experimental diabetic neuropathy model, sympathetic nerve activity (SNA) in STZ rats has not been microneurographically evaluated so far. In the present study, we investigated the multi-unit, compound sympathetic signal from the sciatic nerve of rats 3 weeks after the administration of streptozotocin, and compared the signal with that of normal (control) rats. After obtaining the sympathetic signal, glucose was intravenously administered to make a transient increase in the blood glucose level to cause SNA change. The sympathetic burst rate did not show any statistical difference between groups at steady state. Even after the glucose administration, it changed little in each group. On the other hand, the firing rate of action potentials (AP-rate) in STZ group was significantly lower than that in control group before glucose administration (p<0.05). In addition, AP-rate was increased in control animals after glucose administration, but not in STZ rats. The results suggest a lower sympathetic tone and poorer response to glucose load under high blood glucose and low plasma insulin condition, and that the AP-rate may be useful for the evaluation of microneurographically measured, peripheral sympathetic activity.
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Affiliation(s)
- Go Shinzawa
- Department of Biomedical Information Engineering, Graduate School of Medical Science, Yamagata University, 2-2-2, Iida-nishi, Yamagata 990-9585, Japan
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Hering D, Lambert EA, Marusic P, Walton AS, Krum H, Lambert GW, Esler MD, Schlaich MP. Substantial reduction in single sympathetic nerve firing after renal denervation in patients with resistant hypertension. Hypertension 2012; 61:457-64. [PMID: 23172929 DOI: 10.1161/hypertensionaha.111.00194] [Citation(s) in RCA: 270] [Impact Index Per Article: 22.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Renal denervation (RDN) has been shown to reduce blood pressure (BP) and muscle sympathetic nerve activity (MSNA) in patients with resistant hypertension. The mechanisms underlying sympathetic neural inhibition are unknown. We examined whether RDN differentially influences the sympathetic discharge pattern of vasoconstrictor neurons in patients with resistant hypertension. Standardized office BP, single-unit MSNA, and multi-unit MSNA were obtained at baseline and at 3-month follow-up in 35 patients with resistant hypertension. Twenty-five patients underwent RDN, and 10 patients underwent repeated measurements without RDN (non-RDN). Baseline BP averaged 164/93 mm Hg (RDN) and 164/87 mm Hg (non-RDN) despite use of an average of 4.8 ± 0.4 and 4.4 ± 0.5 antihypertensive drugs, respectively. Mean office BP decreased significantly by -13/-6 mm Hg for systolic BP (P<0.001) and diastolic BP (P<0.05) with RDN but not in non-RDN at 3-month follow-up. RDN moderately decreased multi-unit MSNA (79 ± 3 versus 73 ± 4 bursts/100 heartbeats; P<0.05), whereas all properties of single-unit MSNA including firing rates of individual vasoconstrictor fibers (43 ± 5 versus 27 ± 3 spikes/100 heartbeats; P<0.01), firing probability (30 ± 2 versus 22 ± 2% per heartbeat; P<0.02), and multiple firing incidence of single units within a cardiac cycle (8 ± 1 versus 4 ± 1% per heartbeat; P<0.05) were substantially reduced at follow-up. BP, single-unit MSNA, and multi-unit MSNA remained unaltered in the non-RDN cohort at follow-up. RDN results in the substantial and rapid reduction in firing properties of single sympathetic vasoconstrictor fibers, this being more pronounced than multi-unit MSNA inhibition. Whether the earlier changes in single-unit firing patterns may predict long-term BP response to RDN warrants further exploration.
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Affiliation(s)
- Dagmara Hering
- Neurovascular Hypertension and Kidney Disease Laboratory, Baker IDI Heart and Diabetes Institute, Melbourne, Victoria 8008, Australia
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Lambert EA, Straznicky NE, Lambert GW. A sympathetic view of human obesity. Clin Auton Res 2012; 23:9-14. [DOI: 10.1007/s10286-012-0169-3] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2012] [Accepted: 05/24/2012] [Indexed: 11/30/2022]
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Macefield VG. Firing patterns of muscle vasoconstrictor neurons in respiratory disease. Front Physiol 2012; 3:153. [PMID: 22654767 PMCID: PMC3358712 DOI: 10.3389/fphys.2012.00153] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2012] [Accepted: 05/03/2012] [Indexed: 11/29/2022] Open
Abstract
Because the cardiovascular system and respiration are so intimately coupled, disturbances in respiratory control often lead to disturbances in cardiovascular control. Obstructive Sleep Apnea (OSA), Chronic Obstructive Pulmonary Disease (COPD), and Bronchiectasis (BE) are all associated with a greatly elevated muscle vasoconstrictor drive (muscle sympathetic nerve activity, MSNA). Indeed, the increase in MSNA is comparable to that seen in congestive heart failure (CHF), in which the increase in MSNA compensates for the reduced cardiac output and thereby assists in maintaining blood pressure. However, in OSA – but not COPD or BE – the increase in MSNA can lead to hypertension. Here, the features of the sympathoexcitation in OSA, COPD, and BE are reviewed in terms of the firing properties of post-ganglionic muscle vasoconstrictor neurons. Compared to healthy subjects with low levels of resting MSNA, single-unit recordings revealed that the augmented MSNA seen in OSA, BE, COPD, and CHF were each associated with an increase in firing probability and mean firing rates of individual neurons. However, unlike patients with heart failure, all patients with respiratory disease exhibited an increase in multiple within-burst firing which, it is argued, reflects an increase in central sympathetic drive. Similar patterns to those seen in OSA, COPD, and BE were seen in healthy subjects during an acute increase in muscle vasoconstrictor drive. These observations emphasize the differences by which the sympathetic nervous system grades its output in health and disease, with an increase in firing probability of active neurons and recruitment of additional neurons being the dominant mechanisms.
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Murai H, Takamura M, Kaneko S. Advantage of recording single-unit muscle sympathetic nerve activity in heart failure. Front Physiol 2012; 3:109. [PMID: 22563318 PMCID: PMC3342584 DOI: 10.3389/fphys.2012.00109] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2012] [Accepted: 04/03/2012] [Indexed: 01/08/2023] Open
Abstract
Elevated sympathetic activation is a characteristic feature of heart failure (HF). Excessive sympathetic activation under resting conditions has been shown to increase from the early stages of the disease, and is related to prognosis. Direct recording of multiunit efferent muscle sympathetic nerve activity (MSNA) by microneurography is the best method for quantifying sympathetic nerve activity in humans. To date, this technique has been used to evaluate the actual central sympathetic outflow to the periphery in HF patients at rest and during exercise; however, because the firing occurrence of sympathetic activation is mainly synchronized by pulse pressure, multiunit MSNA, expressed as burst frequency (bursts/min) and burst incidence (bursts/100 heartbeats), may have limitations for the quantification of sympathetic nerve activity. In HF, multiunit MSNA is near the maximum level, and cannot increase further than the heartbeat. Single-unit MSNA analysis in humans is technically demanding, but provides more detailed information regarding central sympathetic firing. Although a great deal is known about the response of multiunit MSNA to stress, little information is available regarding the responses of single-unit MSNA to physiological stress and disease. The purposes of this review are to describe the differences between multiunit and single-unit MSNA during stress and to discuss the advantages of single-unit MSNA recording in improving our understanding the pathology of increased sympathetic activity in HF.
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Affiliation(s)
- Hisayoshi Murai
- Department of Disease Control and Homeostasis, Graduate School of Medical Science, Kanazawa University Kanazawa, Japan
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Lambert E, Hering D, Schlaich M, Lambert G. Advances in sympathetic nerve recording in humans. Front Physiol 2012; 3:11. [PMID: 22347191 PMCID: PMC3273724 DOI: 10.3389/fphys.2012.00011] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2011] [Accepted: 01/17/2012] [Indexed: 01/20/2023] Open
Abstract
In humans, sympathetic activity is commonly assessed by measuring the efferent traffic in the peroneal nerve. The firing activity is the sum of several active neurons, which have the tendency to fire together in a bursting manner. While the estimation of overall sympathetic nervous activity using this multiunit recording approach has advanced our understanding of sympathetic regulation in health and disease no information is gained regarding the underling mechanisms generating the bursts of sympathetic activity. The introduction of single-unit recording has been a major step forward, enabling the examination of specific sympathetic firing patterns in diverse clinical conditions. Disturbances in sympathetic nerve firing, including high firing probabilities, high firing rates or high incidence of multiple firing, or a combination of both may impact on noradrenaline release and effector response, and therefore have clinical implications with regards to the development and progression of target organ damage. Understanding the mechanisms and consequences of specific firing patterns would permit the development of therapeutic strategies targeting these nuances of sympathetic overdrive.
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Affiliation(s)
- Elisabeth Lambert
- Human Neurotransmitters, Baker IDI Heart and Diabetes Institute Melbourne, VIC, Australia
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Ikeda T, Murai H, Kaneko S, Usui S, Kobayashi D, Nakano M, Ikeda K, Takashima SI, Kato T, Okajima M, Furusho H, Takamura M. Augmented single-unit muscle sympathetic nerve activity in heart failure with chronic atrial fibrillation. J Physiol 2011; 590:509-18. [PMID: 22144576 DOI: 10.1113/jphysiol.2011.223842] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Atrial fibrillation (AF) is a common complication in heart failure (HF) patients. However, it remains unclear whether irregular ventricular response patterns induced by AF increase sympathetic nerve activity. We measured resting multi- and single-unit muscle sympathetic nerve activity (MSNA) in 21 age-matched HF patients with chronic AF (n = 11) rhythm or sinus rhythm (SR, n = 10). The multi-unit MSNA, which was expressed as total activity, was similar between HF + AF patients and HF + SR patients. However, the single-unit MSNA in HF + AF patients was significantly greater than that in HF + SR patients (62 ± 9 spikes min(-1) vs. 42 ± 4 spikes min(-1), P < 0.05). Moreover, the incidence of multiple firing of single-unit MSNA within a given burst was augmented in HF + AF patients as compared with HF + SR patients (48 ± 8% vs. 26 ± 3%, P < 0.01). A significant negative relationship was observed between the reduced diastolic pressure induced by a prolonged cardiac interval in AF subjects and single-unit MSNA frequency within one cardiac interval in each HF + AF subject. The firing characteristics of single-unit MSNA were different between HF patients with AF and HF patients with SR; particularly, those with a prolonged long RR interval showed multiple firings of single-unit MSNA. These findings suggest that AF per se leads to the instantaneous augmentation of single-unit MSNA induced by decreased diastolic pressure, which might partially contribute to disease progression in HF patients.
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Affiliation(s)
- Tatsunori Ikeda
- Disease Control and Homeostasis, Graduate School of Medical Science, Kanazawa, University, 13-1 Takara-machi, Kanazawa 920-8641, Japan
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Lambert E, Straznicky NE, Dawood T, Ika-Sari C, Grima M, Esler MD, Schlaich MP, Lambert GW. Change in sympathetic nerve firing pattern associated with dietary weight loss in the metabolic syndrome. Front Physiol 2011; 2:52. [PMID: 21904529 PMCID: PMC3162210 DOI: 10.3389/fphys.2011.00052] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2011] [Accepted: 08/05/2011] [Indexed: 01/20/2023] Open
Abstract
Sympathetic activation in subjects with the metabolic syndrome (MS) plays a role in the pathogenesis of cardiovascular disease development. Diet-induced weight loss decreases sympathetic outflow. However the mechanisms that account for sympathetic inhibition are not known. We sought to provide a detailed description of the sympathetic response to diet by analyzing the firing behavior of single-unit sympathetic nerve fibers. Fourteen subjects (57 ± 2 years, nine men, five females) fulfilling ATP III criteria for the MS underwent a 3-month low calorie diet. Metabolic profile, hemodynamic parameters, and multi-unit and single-unit muscle sympathetic nerve activity (MSNA, microneurography) were assessed prior to and at the end of the diet. Patients’ weight dropped from 96 ± 4 to 88 ± 3 kg (P < 0.001). This was associated with a decrease in systolic and diastolic blood pressure (−12 ± 3 and −5 ± 2 mmHg, P < 0.05), and in heart rate (−7 ± 2 bpm, P < 0.01) and an improvement in all metabolic parameters (fasting glucose: −0.302.1 ± 0.118 mmol/l, total cholesterol: −0.564 ± 0.164 mmol/l, triglycerides: −0.414 ± 0.137 mmol/l, P < 0.05). Multi-unit MSNA decreased from 68 ± 4 to 59 ± 5 bursts/100 heartbeats (P < 0.05). Single-unit MSNA indicated that the firing rate of individual vasoconstrictor fibers decreased from 59 ± 10 to 32 ± 4 spikes/100 heart beats (P < 0.05). The probability of firing decreased from 34 ± 5 to 23 ± 3% of heartbeats (P < 0.05), and the incidence of multiple firing decreased from 14 ± 4 to 6 ± 1% of heartbeats (P < 0.05). Cardiac and sympathetic baroreflex function were significantly improved (cardiac slope: 6.57 ± 0.69 to 9.57 ± 1.20 ms·mmHg−1; sympathetic slope: −3.86 ± 0.34 to −5.05 ± 0.47 bursts/100 heartbeats·mmHg−1, P < 0.05 for both). Hypocaloric diet decreased sympathetic activity and improved hemodynamic and metabolic parameters. The sympathoinhibition associated with weight loss involves marked changes, not only in the rate but also in the firing pattern of active vasoconstrictive fibers.
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Affiliation(s)
- Elisabeth Lambert
- Human Neurotransmitters, Baker IDI Heart and Diabetes Institute Melbourne, VIC, Australia
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