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Persistent Exertional Intolerance after COVID-19: Insights from Invasive Cardiopulmonary Exercise Testing. Chest 2021; 161:54-63. [PMID: 34389297 PMCID: PMC8354807 DOI: 10.1016/j.chest.2021.08.010] [Citation(s) in RCA: 174] [Impact Index Per Article: 58.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2021] [Revised: 08/02/2021] [Accepted: 08/04/2021] [Indexed: 11/23/2022] Open
Abstract
BACKGROUND Some Coronavirus disease 2019 (COVID-19) patients who have recovered from their acute infection after experiencing only mild symptoms continue to exhibit persistent exertional limitation that is often unexplained by conventional investigative studies. RESEARCH QUESTION What is the patho-physiological mechanism of exercise intolerance that underlies the post-COVID-19 long haul syndrome following COVID-19 in patients without cardio-pulmonary disease? STUDY DESIGN AND METHODS This study examined the systemic and pulmonary hemodynamics, ventilation, and gas exchange in 10 post-COVID-19 patients without cardio-pulmonary disease during invasive cardiopulmonary exercise testing (iCPET) and compared the results to 10 age- and sex matched controls. These data were then used to define potential reasons for exertional limitation in the post-COVID-19 cohort. RESULTS Post-COVID-19 patients exhibited markedly reduced peak exercise aerobic capacity (VO2) compared to controls (70±11%predicted vs. 131±45%predicted; p<0.0001). This reduction in peak VO2 was associated with impaired systemic oxygen extraction (i.e., narrow CaVO2/CaO2) compared to controls (0.49±0.1 vs. 0.78±0.1, p<0.0001) despite a preserved peak cardiac index (7.8±3.1 vs. 8.4±2.3 L/min, p>0.05). Additionally, post-COVID-19 patients demonstrated greater ventilatory inefficiency (i.e., abnormal VE/VCO2 slope: 35±5 vs. 27±5, p=0.01) compared to controls without an increase in dead space ventilation. INTERPRETATION Post-COVID-19 patients without cardiopulmonary disease demonstrate a marked reduction in peak VO2 from a peripheral rather than a central cardiac limit along with an exaggerated hyper-ventilatory response during exercise.
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Lalande S, Cross TJ, Keller-Ross ML, Morris NR, Johnson BD, Taylor BJ. Exercise Intolerance in Heart Failure: Central Role for the Pulmonary System. Exerc Sport Sci Rev 2020; 48:11-19. [PMID: 31453845 DOI: 10.1249/jes.0000000000000208] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
We propose that abnormalities of the pulmonary system contribute significantly to the exertional dyspnea and exercise intolerance observed in patients with chronic heart failure. Interventions designed to address the deleterious pulmonary manifestations of heart failure may, therefore, yield promising improvements in exercise tolerance in this population.
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Affiliation(s)
- Sophie Lalande
- Department of Kinesiology and Heath Education, The University of Texas at Austin, Austin, TX
| | | | - Manda L Keller-Ross
- Divisions of Physical Therapy and Rehabilitation Sciences, Department of Rehabilitation Medicine, Medical School, University of Minnesota, Minneapolis, MN
| | - Norman R Morris
- School of Physiotherapy and Exercise Science, Griffith University, Queensland, Australia
| | - Bruce D Johnson
- Department of Cardiovascular Diseases, Mayo Clinic, Rochester, MN
| | - Bryan J Taylor
- School of Biomedical Sciences, Faculty of Biological Sciences, University of Leeds, Leeds, UK
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Shevtsova NA, Marchenko V, Bezdudnaya T. Modulation of Respiratory System by Limb Muscle Afferents in Intact and Injured Spinal Cord. Front Neurosci 2019; 13:289. [PMID: 30971888 PMCID: PMC6443963 DOI: 10.3389/fnins.2019.00289] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2018] [Accepted: 03/11/2019] [Indexed: 12/20/2022] Open
Abstract
Breathing constantly adapts to environmental, metabolic or behavioral changes by responding to different sensory information, including afferent feedback from muscles. Importantly, not just respiratory muscle feedback influences respiratory activity. Afferent sensory information from rhythmically moving limbs has also been shown to play an essential role in the breathing. The present review will discuss the neuronal mechanisms of respiratory modulation by activation of peripheral muscles that usually occurs during locomotion or exercise. An understanding of these mechanisms and finding the most effective approaches to regulate respiratory motor output by stimulation of limb muscles could be extremely beneficial for people with respiratory dysfunctions. Specific attention in the present review is given to the muscle stimulation to treat respiratory deficits following cervical spinal cord injury.
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Affiliation(s)
- Natalia A Shevtsova
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA, United States
| | - Vitaliy Marchenko
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA, United States
| | - Tatiana Bezdudnaya
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA, United States
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Keller-Ross ML, Sarkinen AL, Cross T, Johnson BD, Olson TP. Ventilation Increases with Lower Extremity Venous Occlusion in Young Adults. Med Sci Sports Exerc 2017; 48:377-83. [PMID: 26484951 DOI: 10.1249/mss.0000000000000797] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
INTRODUCTION Venous distention via subsystolic occlusion of the lower limbs may augment ventilation via stimulation of group III/IV afferent neurons. PURPOSE The purpose of this study was to examine the ventilatory response to graded lower extremity venous occlusion during exercise in healthy adults. METHODS Nineteen adults (9 men, 25 ± 5 yr) completed two visits. Visit 1 included a maximal cycle ergometry exercise test. Visit 2 included a 30% peak workload cycle exercise with randomized inflations of bilateral thigh pressure tourniquets to 20, 40, 60, 80, and 100 mm Hg for 2 min each, separated by 2 min of deflation. Three minutes of cycling occurred before cuffing (control [CTL]). Expired minute ventilation (V˙E), whole body gas exchange, rating of perceived exertion, and dyspnea were measured during each session. RESULTS V˙E increased significantly from the control condition (exercise only, CTL) to each occlusion pressure (P < 0.05) with the greatest increase at 100 mm Hg (CTL to 100 mm Hg: 31.5 ± 6.6 to 40.1 ± 10.7 L·min). Respiratory rate (RR) increased as well (CTL to 100 mm Hg: 24.8 ± 6.0 to 30.9 ± 11.5 breaths per minute, P < 0.05, condition effect) with no change in tidal volume (P > 0.05). Tidal volume to inspiratory time (VT/TI) increased significantly from the CTL condition to each occlusion pressure (CTL to 100 mm Hg: 1.5 ± 0.3 to 1.8 ± 0.4 L·min, P < 0.05, all pressures). Dyspnea and RPE increased with all occlusion pressures from CTL exercise (P < 0.05, all pressures). CONCLUSIONS Our findings suggest that mild-to-moderate venous occlusion of the lower extremity evokes a tachypneic breathing pattern which, in turn, augments V˙E and perceived breathing effort during exercise.
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Affiliation(s)
- Manda L Keller-Ross
- 1Program in Physical Therapy, University of Minnesota, Minneapolis, MN; and 2Internal Medicine, Mayo Clinic College of Medicine, Rochester, MN
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Leal AK, Yamauchi K, Kim J, Ruiz-Velasco V, Kaufman MP. Peripheral δ-opioid receptors attenuate the exercise pressor reflex. Am J Physiol Heart Circ Physiol 2013; 305:H1246-55. [PMID: 23934854 DOI: 10.1152/ajpheart.00116.2013] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In rats with ligated femoral arteries, the exercise pressor reflex is exaggerated, an effect that is attenuated by stimulation of peripheral μ-opioid receptors on group IV metabosensitive afferents. In contrast, δ-opioid receptors are expressed mostly on group III mechanosensitive afferents, a finding that prompted us to determine whether stimulation of these opioid receptors could also attenuate the exaggerated exercise pressor reflex in "ligated" rats. We found femoral arterial injection of [D-Pen2,D-Pen5]enkephalin (DPDPE; 1.0 μg), a δ-opioid agonist, significantly attenuated the pressor and cardioaccelerator components of the exercise pressor reflex evoked by hindlimb muscle contraction in both rats with ligated and patent femoral arteries. DPDPE significantly decreased the pressor responses to muscle mechanoreflex activation, evoked by tendon stretch, in ligated rats only. DPDPE (1.0 μg) had no effect in either group on the pressor and cardioaccelerator responses to capsaicin (0.2 μg), which primarily stimulates group IV afferents. DPDPE (1.0 μg) had no effect on the pressor and cardioaccelerator responses to lactic acid (24 mM), which stimulates group III and IV afferents, in rats with patent femoral arteries but significantly decreased the pressor response in ligated rats. Western blots revealed the amount of protein comprising the δ-opioid receptor was greater in dorsal root ganglia innervating hindlimbs with ligated femoral arteries than in dorsal root ganglia innervating hindlimbs with patent femoral arteries. Our findings support the hypothesis that stimulation of δ-opioid receptors on group III afferents attenuated the exercise pressor reflex.
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Affiliation(s)
- Anna K Leal
- Heart and Vascular Institute, Penn State College of Medicine, Hershey, Pennsylvania; and
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Dampney RAL, Horiuchi J. Functional organisation of central cardiovascular pathways: studies using c-fos gene expression. Prog Neurobiol 2003; 71:359-84. [PMID: 14757116 DOI: 10.1016/j.pneurobio.2003.11.001] [Citation(s) in RCA: 124] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Until about 10 years ago, knowledge of the functional organisation of the central pathways that subserve cardiovascular responses to homeostatic challenges and other stressors was based almost entirely on studies in anaesthetised animals. More recently, however, many studies have used the method of the expression of immediate early genes, particularly the c-fos gene, to identify populations of central neurons that are activated by such challenges in conscious animals. In this review we first consider the advantages and limitations of this method. Then, we discuss how the application of the method of immediate early gene expression, when used alone or in combination with other methods, has contributed to our understanding of the central mechanisms that regulate the autonomic and neuroendocrine response to various cardiovascular challenges (e.g., hypotension, hypoxia, hypovolemia, and other stressors) as they operate in the conscious state. In general, the results of studies of central cardiovascular pathways using immediate early gene expression are consistent with previous studies in anaesthetised animals, but in addition have revealed other previously unrecognised pathways that also contribute to cardiovascular regulation. Finally, we briefly consider recent evidence indicating that immediate early gene expression can modify the functional properties of central cardiovascular neurons, and the possible significance of this in producing long-term changes in the regulation of the cardiovascular system both in normal and pathological conditions.
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Affiliation(s)
- R A L Dampney
- Department of Physiology and Institute for Biomedical Research, University of Sydney, Sydney, NSW 2006, Australia.
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Smith SA, Mitchell JH, Garry MG. Electrically induced static exercise elicits a pressor response in the decerebrate rat. J Physiol 2001; 537:961-70. [PMID: 11744768 PMCID: PMC2278979 DOI: 10.1111/j.1469-7793.2001.00961.x] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
1. The purpose of this investigation was to determine if activation of the exercise pressor reflex in the decerebrate rat induced circulatory responses comparable to those reported in large mammalian species. 2. To activate both mechanically and metabolically sensitive afferent fibres, static hindlimb contractions were induced by stimulating the cut ends of L4 and L5 spinal ventral roots in Sprague-Dawley rats (300-400 g). To selectively stimulate mechanically sensitive receptors, hindlimb muscles were passively stretched. 3. In intact halothane-anaesthetized animals (n = 10), static contraction and passive stretch induced a decrease in mean arterial pressure (Delta MAP = -17 +/- 3 and -8 +/- 1 mmHg for contraction and stretch, respectively) and heart rate (HR). In contrast, MAP increased 23 +/- 2 mmHg during contraction and 19 +/- 3 mmHg during stretch in decerebrate rats (n = 10). These pressor responses were accompanied by a significant tachycardia. In decerebrate animals, the reintroduction of halothane attenuated the increase in MAP and HR caused by both contraction and stretch. 4. In both anaesthetized and decerebrate rats, sectioning the spinal dorsal roots innervating the activated skeletal muscle eliminated responses to contraction and stretch. This finding indicated that an intramuscular neural reflex mediated the response to each stimulus. 5. The results demonstrate that a decerebrate preparation in the rat is a reliable model for the study of the exercise pressor reflex. Development of the model would enable the study of this reflex in a variety of pathological conditions and allow investigation of the mechanisms controlling cardiovascular responses to exercise in health and disease.
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Affiliation(s)
- S A Smith
- Harry S. Moss Heart Center, Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX 75390-9174, USA.
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Reidman DA, Maher TJ, Chaiyakul P, Ally A. Modulation of extracellular glutamate and pressor response to muscle contraction during NMDA-receptor blockade in the rostral ventrolateral medulla. Neurosci Res 2000; 36:147-56. [PMID: 10711812 DOI: 10.1016/s0168-0102(99)00118-2] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Recently our laboratory demonstrated increases in extracellular glutamate concentrations within the rostral ventrolateral medulla (RVLM) during static muscle contraction (Caringi, D.C., Maher, T., Chaiyakul, P., Asmundsson, G., Ishide, T., Ally, A. Pflügers Arch. Eur. J. Physiol., 435:465-471, 1998). In this study, we determined effects of microdialyzing D(-)2-amino-7-phosphonohepatanoic acid (AP-7), an NMDA-receptor antagonist, into the RVLM on changes in mean arterial pressure (MAP), heart rate (HR), and extracellular glutamate levels during muscle contraction in anesthetized rats. Bilateral placements of microdialysis probes into the RVLM were verified by perfusing L-glutamate and obtaining a pressor response. Muscle contraction for 2 min, increased MAP and HR by 22+/-4 mmHg and 28+/-5 bpm, respectively. Extracellular glutamate as determined by microdialysis increased from 0.8+/-0.2 to 6.3+/-1.2 ng/5 microl. Microdialysis of AP-7 (1.0 microM) for 30 min inhibited contraction-evoked MAP and HR responses (10+/-3 mmHg and 13+/-3 bpm) and attenuated increases in glutamate during muscle contraction. Developed tensions did not differ during contractions before and after AP-7. Results demonstrate that NMDA-receptor blockade in the RVLM inhibits cardiovascular responses during static muscle contraction via a reduction in extracellular glutamate levels.
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Affiliation(s)
- D A Reidman
- Department of Physiology, University of New England, College of Osteopathic Medicine, Biddeford, ME 04005, USA
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Williams CA, Loyd SD, Hampton TA, Hoover DB. Expression of c-fos-like immunoreactivity in the feline brainstem in response to isometric muscle contraction and baroreceptor reflex changes in arterial pressure. Brain Res 2000; 852:424-35. [PMID: 10678770 DOI: 10.1016/s0006-8993(99)02217-9] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
This study compared whether activation of muscle ergoreceptor afferents caused by isometric muscle contraction, activation of baroreceptor afferents induced by i.v. infusion of phenylephrine, or baroreceptor afferent inactivation, caused by carotid artery occlusion, elicit similar patterns of c-Fos induction in brainstem areas. Adult cats were anesthetized with alpha-chloralose, and in each case, the experimental intervention caused an increase in the arterial blood pressure. There were two sets of control experiments: in both, animals underwent the same surgical procedures but then either remained at rest for the entire study, or the tibial nerve was stimulated, as in the contraction group, following muscle paralysis with tubocurarine. Following the procedures, animals rested for 90 min to allow neuronal expression of c-Fos. Control cats showed very little c-Fos immunoreactivity (c-Fos-ir) in the brainstem. Muscle contraction induced c-Fos-ir expression mainly in the nucleus tractus solitarius, lateral reticular nucleus, lateral tegmental field, vestibular nucleus, subretrofacial nucleus, spinal trigeminal tract and in a lateral region of the periaqueductal grey (P 0.5-1.0). The majority of the c-Fos-ir was found in brainstem areas contralateral to the contracted muscle. In addition, muscle contraction induced c-Fos-ir in the dorsal horns of spinal segments L6-S1 on the ipsilateral side of the spinal cord. Phenylephrine infusion caused c-Fos-ir expression in the nucleus tractus solitarius, spinal trigeminal tract, solitary tract, and dorsal motor nucleus of the vagus. No c-Fos-ir was apparent in the periaqueductal grey. Carotid occlusions induced c-Fos-ir expression in the area postrema, nucleus tractus solitarius, solitary tract, and spinal trigeminal tract. Expression was bilateral. Areas that exhibited c-Fos-ir correspond to sites previously reported to release various neuropeptides in response to muscle contraction or carotid occlusions. These results indicate that the exercise pressor reflex and baroreflex activate similar, but not completely identical, sites in the brainstem.
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Affiliation(s)
- C A Williams
- Department of Physiology, The James H. Quillen College of Medicine, East Tennessee State University, Johnson City 37614-0576, USA.
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Lillaney R, Maher TJ, Chaiyakul P, Ally A. Changes in extracellular glutamate and pressor response during muscle contraction following AMPA-receptor blockade in the RVLM and CVLM. Brain Res 1999; 844:164-73. [PMID: 10536273 DOI: 10.1016/s0006-8993(99)01920-4] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
We examined whether modulation of cardiovascular responses by administering 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, an AMPA-receptor antagonist) into the rostral (RVLM) or caudal (CVLM) ventrolateral medulla are mediated via changes in extracellular levels of glutamate. Microdialysis probes were inserted bilaterally into the RVLM or the CVLM. For the RVLM experiments (n=8), muscle contraction for 2 min increased mean arterial pressure (MAP) and heart rate (HR) by 18+/-3 mmHg and 24+/-5 bpm, respectively. Extracellular glutamate concentrations increased from 1.5+/-0.3 to 4.3+/-0.9 ng/5 microl during the contraction. Microdialysis of CNQX (1.0 microM) for 30 min into the RVLM attenuated the increases in MAP, HR, and glutamate concentration in response to a muscle contraction (8+/-2 mmHg, 11+/-3 bpm, and 2.2+/-0.7 ng/5 microl, respectively). Developed tensions did not change during contractions before and after CNQX. Microdialysis of CNQX into the CVLM (n=8) potentiated the contraction-evoked responses in MAP (19+/-3 vs. 34+/-3 mmHg) and HR (25+/-4 vs. 49+/-5 bpm) without a change in developed tension. Following CNQX perfusion into the CVLM, the levels of extracellular glutamate in the CVLM were also augmented during the contraction. Results suggests that AMPA-receptors within the RVLM and CVLM differentially modulate cardiovascular responses during static muscle contraction via increasing and decreasing, respectively, extracellular glutamate concentrations.
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Affiliation(s)
- R Lillaney
- Department of Physiology, College of Osteopathic Medicine, University of New England, Biddeford, ME 04055, USA
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Ally A. Ventrolateral medullary control of cardiovascular activity during muscle contraction. Neurosci Biobehav Rev 1998; 23:65-86. [PMID: 9861613 DOI: 10.1016/s0149-7634(97)00069-9] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
An overview of the role of ventrolateral medulla (VLM) in regulation of cardiovascular activity is presented. A summary of VLM anatomy and its functional relation to other areas in the central nervous system is described. Over the past few years, various studies have investigated the VLM and its involvement in cardiovascular regulation during static muscle contraction, a type of static exercise as seen, for example, during knee extension or hand-grip exercise. Understanding the neural mechanisms that are responsible for regulation of cardiovascular activity during static muscle contraction is of particular interest since it helps understand circulatory adjustments in response to an increase in physical activity. This review surveys the role of several receptors and neurotransmitters in the VLM that are associated with changes in mean arterial pressure and heart rate during static muscle contraction in anesthetized animals. Possible mechanisms in the VLM that modulate cardiovascular changes during static muscle contraction are summarized and discussed. Localized administration of an excitatory amino-acid antagonist into the rostral portion of the VLM (RVLM) attenuates increases in blood pressure and heart rate during static muscle contraction, whereas its administration into the caudal part of the VLM (CVLM) augments these responses. Opioid or 5-HT1A receptor stimulation in the RVLM, but not in the CVLM, attenuates cardiovascular responses to muscle contraction. Furthermore, intravenous, intracerebroventricular or intracisternal injection of an alpha 2-adrenoceptor agonist or a cholinesterase inhibitor attenuates increases in blood pressure and heart rate during static muscle contraction. Finally, the possible involvement of endogenous neurotransmitters in the RVLM and the CVLM associated with cardiovascular responses during static muscle contraction is discussed. An overview of the role of the VLM in the overall cardiovascular control network in the brain is presented and critically reviewed.
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Affiliation(s)
- A Ally
- Department of Pharmacology, University of New England, College of Osteopathic Medicine, Biddeford, ME 04005, USA.
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Li J, Potts JT, Mitchell JH. Effect of barodenervation on c-Fos expression in the medulla induced by static muscle contraction in cats. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 274:H901-8. [PMID: 9530202 DOI: 10.1152/ajpheart.1998.274.3.h901] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
A previous study has shown increased Fos-like immunoreactivity (FLI), a marker of neural activation, in the nucleus of the solitary tract (NTS) and the ventrolateral medulla (VLM) after static muscle contraction elicited by electrical stimulation of L7 and S1 ventral roots of the spinal cord in anesthetized, baroreceptor-intact cats. Because the electrically induced static muscle contraction reflexly increased arterial blood pressure, the concomitant activation of the arterial baroreceptor reflex during static muscle contraction may have resulted in some of the FLI labeling that was observed in the medulla. The purpose of this study was to determine regions in the medulla that are activated by muscle contraction in the absence of arterial baroreceptor input. Electrical stimulation of L7 and S1 ventral roots of the spinal cord was used to elicit static muscle contraction, and FLI in the medulla was determined in barointact and barodenervated cats. In barointact contraction cats, FLI was observed in the lateral reticular nucleus (LRN), NTS, lateral tegmental field (FTL), subretrofacial nucleus (SRF), and A1 region of the medulla. In barodenervated contraction cats, FLI increased in the same regions; however, the number of FLI-labeled cells in the NTS, FTL, and A1 region was significantly less than in barointact contraction animals. No significant difference in the number of FLI-labeled cells was found in the LRN and SRF between the two groups. These results clearly demonstrate that cardiovascular regions in the medulla are activated by input from afferent activity originating in skeletal muscle independently of concomitant arterial baroreceptor reflex activation.
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Affiliation(s)
- J Li
- Moss Heart Center, Dallas, Texas 75235-9034, USA
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Wilson LB, Hand GA. The pressor reflex evoked by static contraction: neurochemistry at the site of the first synapse. BRAIN RESEARCH. BRAIN RESEARCH REVIEWS 1997; 23:196-209. [PMID: 9164670 DOI: 10.1016/s0165-0173(96)00019-7] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Stimulation of somatic sensory neurons activates the sympathetic nervous system, in turn enhancing cardiovascular function. This has been repeatedly demonstrated when afferent fibers arising from skeletal muscle serve as the sensory neurons. Over the past several years, studies have been performed examining the central nervous system (CNS) mechanisms that cause the reflex increases in arterial blood pressure and heart rate when skeletal muscle contracts. These studies have provided insights into how the CNS alters cardiovascular function, and have helped to enhance our understanding of central sensory transduction processes. Using a variety of techniques, several sites have been identified within the brain and spinal cord that are responsible for producing the reflex pressor response to static contraction. However, the purpose of this manuscript is to review the recent developments concerning only one CNS site: the dorsal horn of the spinal cord. This region serves as the first synapse for afferent fibers from skeletal muscle. The release of neurotransmitters, and possibly neuromodulators, into this region initiates the CNS component of this reflex. In addition, the magnitude of the reflex cardiovascular changes can be modulated at this site. The studies described in this review suggest that the dorsal horn of the spinal cord serves as an important site of integration for sensory signals that influence the cardiovascular system.
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Affiliation(s)
- L B Wilson
- Department of Physiology, University of South Alabama College of Medicine, Mobile 36688-0002, USA.
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Sothmann M, Kastello GK. Simulated weightlessness to induce chronic hypoactivity of brain norepinephrine for exercise and stress studies. Med Sci Sports Exerc 1997; 29:39-44. [PMID: 9000154 DOI: 10.1097/00005768-199701000-00007] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Although research on the relationship between exercise training and physiological stress reactivity is increasing, we know little about the involvement of brain neurochemistry. Moreover, the few studies that have been performed have concentrated on animals with normally functioning neurochemistry exposed to an acute stressor. Biomedical research is drawing an association between hypoactivation of the physiological stress response and certain medical conditions. As such, there is a need for an animal model that manifests a chronic hypoactivity of the stress system. In this report we describe the results from studies on norepinephrine changes with actual and simulated weightlessness in animals and humans. There is consistent evidence with rats that 14 d of simulated weightlessness produces reduced norepinephrine turnover in selected brainstem nuclei and peripheral tissue mediating the physiological stress response. Little is known about other brain regions, particularly the hypothlamus. These preliminary data suggest that simulated weightlessness is one method by which a chronic hypoactivity of norepinephrine biosynthesis or release might be induced to study exercise training as an intervention.
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Affiliation(s)
- M Sothmann
- School of Allied Health Sciences, Indiana University School of Medicine, Indianapolis 46202-5119, USA.
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