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Mastrandrea CJ, Hedge ET, Hughson RL. The Detrimental Effects of Bedrest: Premature Cardiovascular Aging and Dysfunction. Can J Cardiol 2024; 40:1468-1482. [PMID: 38759726 DOI: 10.1016/j.cjca.2024.05.009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2024] [Revised: 05/08/2024] [Accepted: 05/09/2024] [Indexed: 05/19/2024] Open
Abstract
Bedrest as an experimental paradigm or as an in-patient stay for medical reasons has negative consequences for cardiovascular health. The effects of severe inactivity parallel many of the changes experienced with natural aging but over a much shorter duration. Cardiac function is reduced, arteries stiffen, neural reflex responses are impaired, and metabolic and oxidative stress responses impose burden on the heart and vascular systems. The effect of these changes is revealed in studies of integrative function. Aerobic fitness progressively deteriorates with bedrest and tolerance of upright posture is rapidly impaired. In this review we consider the similarities of aging and bedrest-induced cardiovascular deconditioning. We concur with many recent clinical recommendations that early and regular mobility with upright posture will reduce likelihood of hospital-associated disability related to bedrest.
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Affiliation(s)
- Carmelo J Mastrandrea
- Schlegel-UW Research Institute for Aging, Waterloo, Ontario, Canada; Department of Kinesiology and Health Sciences, University of Waterloo, Waterloo, Ontario, Canada
| | - Eric T Hedge
- Schlegel-UW Research Institute for Aging, Waterloo, Ontario, Canada; Department of Kinesiology and Health Sciences, University of Waterloo, Waterloo, Ontario, Canada
| | - Richard L Hughson
- Schlegel-UW Research Institute for Aging, Waterloo, Ontario, Canada.
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2
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Mastrandrea CJ, Hedge ET, Robertson AD, Heckman GA, Ho J, Granados Unger F, Hughson RL. High-intensity exercise does not protect against orthostatic intolerance following bedrest in 55- to 65-yr-old men and women. Am J Physiol Regul Integr Comp Physiol 2023; 325:R107-R119. [PMID: 37184226 DOI: 10.1152/ajpregu.00315.2022] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2022] [Revised: 04/20/2023] [Accepted: 05/09/2023] [Indexed: 05/16/2023]
Abstract
Prolonged bedrest provokes orthostatic hypotension and intolerance of upright posture. Limited data are available on the cardiovascular responses of older adults to head-up tilt following bedrest, with no studies examining the potential benefits of exercise to mitigate intolerance in this age group. This randomized controlled trial of head-down bedrest (HDBR) in 55- to 65-yr-old men and women investigated if exercise could avert post-HDBR orthostatic intolerance. Twenty-two healthy older adults (11 female) underwent a strict 14-day HDBR and were assigned to either an exercise (EX) or control (CON) group. The exercise intervention included high-intensity, aerobic, and resistance exercises. Head-up tilt-testing to a maximum of 15 minutes was performed at baseline (Pre-Bedrest) and immediately after HDBR (R1), as well as 6 days (R6) and 4 weeks (R4wk) later. At Pre-Bedrest, three participants did not complete the full 15 minutes of tilt. At R1, 18 did not finish, with no difference in tilt end time between CON (422 ± 287 s) and EX (409 ± 346 s). No differences between CON and EX were observed at R6 or R4wk. At R1, just 1 participant self-terminated the test with symptoms, while 12 others reported symptoms only after physiological test termination criteria were reached. Finishers on R1 protected arterial pressure with higher total peripheral resistance relative to Pre-Bedrest. Cerebral blood velocity decreased linearly with reductions in arterial pressure, end-tidal CO2, and cardiac output. High-intensity interval exercise did not benefit post-HDBR orthostatic tolerance in older adults. Multiple factors were associated with the reduction in cerebral blood velocity leading to intolerance.
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Affiliation(s)
| | - Eric T Hedge
- Schlegel-UW Research Institute for Aging, Waterloo, Ontario, Canada
- Department of Kinesiology and Health Studies, University of Waterloo, Waterloo, Ontario, Canada
| | - Andrew D Robertson
- Schlegel-UW Research Institute for Aging, Waterloo, Ontario, Canada
- Department of Kinesiology and Health Studies, University of Waterloo, Waterloo, Ontario, Canada
| | - George A Heckman
- Schlegel-UW Research Institute for Aging, Waterloo, Ontario, Canada
| | - Joanne Ho
- Schlegel-UW Research Institute for Aging, Waterloo, Ontario, Canada
| | - Federico Granados Unger
- Department of Kinesiology and Health Studies, University of Waterloo, Waterloo, Ontario, Canada
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3
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Rabineau J, Issertine M, Hoffmann F, Gerlach D, Caiani EG, Haut B, van de Borne P, Tank J, Migeotte PF. Cardiovascular deconditioning and impact of artificial gravity during 60-day head-down bed rest—Insights from 4D flow cardiac MRI. Front Physiol 2022; 13:944587. [PMID: 36277205 PMCID: PMC9586290 DOI: 10.3389/fphys.2022.944587] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2022] [Accepted: 09/13/2022] [Indexed: 12/03/2022] Open
Abstract
Microgravity has deleterious effects on the cardiovascular system. We evaluated some parameters of blood flow and vascular stiffness during 60 days of simulated microgravity in head-down tilt (HDT) bed rest. We also tested the hypothesis that daily exposure to 30 min of artificial gravity (1 g) would mitigate these adaptations. 24 healthy subjects (8 women) were evenly distributed in three groups: continuous artificial gravity, intermittent artificial gravity, or control. 4D flow cardiac MRI was acquired in horizontal position before (−9 days), during (5, 21, and 56 days), and after (+4 days) the HDT period. The false discovery rate was set at 0.05. The results are presented as median (first quartile; third quartile). No group or group × time differences were observed so the groups were combined. At the end of the HDT phase, we reported a decrease in the stroke volume allocated to the lower body (−30% [−35%; −22%]) and the upper body (−20% [−30%; +11%]), but in different proportions, reflected by an increased share of blood flow towards the upper body. The aortic pulse wave velocity increased (+16% [+9%; +25%]), and so did other markers of arterial stiffness (CAVI; CAVI0). In males, the time-averaged wall shear stress decreased (−13% [−17%; −5%]) and the relative residence time increased (+14% [+5%; +21%]), while these changes were not observed among females. Most of these parameters tended to or returned to baseline after 4 days of recovery. The effects of the artificial gravity countermeasure were not visible. We recommend increasing the load factor, the time of exposure, or combining it with physical exercise. The changes in blood flow confirmed the different adaptations occurring in the upper and lower body, with a larger share of blood volume dedicated to the upper body during (simulated) microgravity. The aorta appeared stiffer during the HDT phase, however all the changes remained subclinical and probably the sole consequence of reversible functional changes caused by reduced blood flow. Interestingly, some wall shear stress markers were more stable in females than in males. No permanent cardiovascular adaptations following 60 days of HDT bed rest were observed.
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Affiliation(s)
- Jeremy Rabineau
- LPHYS, Département de Cardiologie, Université Libre de Bruxelles, Brussels, Belgium
- TIPs, École Polytechnique de Bruxelles, Université Libre de Bruxelles, Brussels, Belgium
- *Correspondence: Jeremy Rabineau,
| | - Margot Issertine
- LPHYS, Département de Cardiologie, Université Libre de Bruxelles, Brussels, Belgium
| | - Fabian Hoffmann
- Institute of Aerospace Medicine, German Aerospace Center (DLR), Cologne, Germany
| | - Darius Gerlach
- Institute of Aerospace Medicine, German Aerospace Center (DLR), Cologne, Germany
| | - Enrico G. Caiani
- Electronic, Information and Biomedical Engineering Department, Politecnico di Milano, Milan, Italy
| | - Benoit Haut
- TIPs, École Polytechnique de Bruxelles, Université Libre de Bruxelles, Brussels, Belgium
| | | | - Jens Tank
- Institute of Aerospace Medicine, German Aerospace Center (DLR), Cologne, Germany
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Hedge ET, Patterson CA, Mastrandrea CJ, Sonjak V, Hajj-Boutros G, Faust A, Morais JA, Hughson RL. Implementation of exercise countermeasures during spaceflight and microgravity analogue studies: Developing countermeasure protocols for bedrest in older adults (BROA). Front Physiol 2022; 13:928313. [PMID: 36017336 PMCID: PMC9395735 DOI: 10.3389/fphys.2022.928313] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2022] [Accepted: 06/27/2022] [Indexed: 12/18/2022] Open
Abstract
Significant progress has been made in the development of countermeasures to attenuate the negative consequences of prolonged exposure to microgravity on astronauts’ bodies. Deconditioning of several organ systems during flight includes losses to cardiorespiratory fitness, muscle mass, bone density and strength. Similar deconditioning also occurs during prolonged bedrest; any protracted time immobile or inactive, especially for unwell older adults (e.g., confined to hospital beds), can lead to similar detrimental health consequences. Due to limitations in physiological research in space, the six-degree head-down tilt bedrest protocol was developed as ground-based analogue to spaceflight. A variety of exercise countermeasures have been tested as interventions to limit detrimental changes and physiological deconditioning of the musculoskeletal and cardiovascular systems. The Canadian Institutes of Health Research and the Canadian Space Agency recently provided funding for research focused on Understanding the Health Impact of Inactivity to study the efficacy of exercise countermeasures in a 14-day randomized clinical trial of six-degree head-down tilt bedrest study in older adults aged 55–65 years old (BROA). Here we will describe the development of a multi-modality countermeasure protocol for the BROA campaign that includes upper- and lower-body resistance exercise and head-down tilt cycle ergometry (high-intensity interval and continuous aerobic exercise training). We provide reasoning for the choice of these modalities following review of the latest available information on exercise as a countermeasure for inactivity and spaceflight-related deconditioning. In summary, this paper sets out to review up-to-date exercise countermeasure research from spaceflight and head-down bedrest studies, whilst providing support for the proposed research countermeasure protocols developed for the bedrest study in older adults.
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Affiliation(s)
- Eric T. Hedge
- Schlegel-University of Waterloo Research Institute for Aging, Waterloo, ON, Canada
- Department of Kinesiology and Health Sciences, University of Waterloo, Waterloo, ON, Canada
| | | | | | - Vita Sonjak
- Research Institute of McGill University Health Centre, McGill University, Montréal, QC, Canada
| | - Guy Hajj-Boutros
- Research Institute of McGill University Health Centre, McGill University, Montréal, QC, Canada
| | - Andréa Faust
- Research Institute of McGill University Health Centre, McGill University, Montréal, QC, Canada
| | - José A. Morais
- Research Institute of McGill University Health Centre, McGill University, Montréal, QC, Canada
- Division of Geriatric Medicine, McGill University Health Centre, McGill University, Montréal, QC, Canada
| | - Richard L. Hughson
- Schlegel-University of Waterloo Research Institute for Aging, Waterloo, ON, Canada
- *Correspondence: Richard L. Hughson,
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5
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Moore JP, Simpson LL, Drinkhill MJ. Differential contributions of cardiac, coronary and pulmonary artery vagal mechanoreceptors to reflex control of the circulation. J Physiol 2022; 600:4069-4087. [PMID: 35903901 PMCID: PMC9544715 DOI: 10.1113/jp282305] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2021] [Accepted: 07/19/2022] [Indexed: 11/25/2022] Open
Abstract
Distinct populations of stretch‐sensitive mechanoreceptors attached to myelinated vagal afferents are found in the heart and adjoining coronary and pulmonary circulations. Receptors at atrio‐venous junctions appear to be involved in control of intravascular volume. These atrial receptors influence sympathetic control of the heart and kidney, but contribute little to reflex control of systemic vascular resistance. Baroreceptors at the origins of the coronary circulation elicit reflex vasodilatation, like feedback control from systemic arterial baroreceptors, as well as having characteristics that could contribute to regulation of mean pressure. In contrast, feedback from baroreceptors in the pulmonary artery and bifurcation is excitatory and elicits a pressor response. Elevation of pulmonary arterial pressure resets the vasomotor limb of the systemic arterial baroreflex, which could be relevant for control of sympathetic vasoconstrictor outflow during exercise and other states associated with elevated pulmonary arterial pressure. Ventricular receptors, situated mainly in the inferior posterior wall of the left ventricle, and attached to unmyelinated vagal afferents, are relatively inactive under basal conditions. However, a change to the biochemical environment of cardiac tissue surrounding these receptors elicits a depressor response. Some ventricular receptors respond, modestly, to mechanical distortion. Probably, ventricular receptors contribute little to tonic feedback control; however, reflex bradycardia and hypotension in response to chemical activation may decrease the work of the heart during myocardial ischaemia. Overall, greater awareness of heterogeneous reflex effects originating from cardiac, coronary and pulmonary artery mechanoreceptors is required for a better understanding of integrated neural control of circulatory function and arterial blood pressure.
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Affiliation(s)
| | | | - Mark J Drinkhill
- Leeds Institute for Cardiovascular and Metabolic Medicine, Leeds, UK
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Amekran Y, Damoun N, El Hangouche AJ. Postural orthostatic tachycardia syndrome and post-acute COVID-19. Glob Cardiol Sci Pract 2022; 2022:e202213. [PMID: 36339677 PMCID: PMC9629292 DOI: 10.21542/gcsp.2022.13] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2022] [Accepted: 06/11/2022] [Indexed: 11/05/2022] Open
Abstract
While the acute illness of COVID-19 was the initial focus of concern, there are increasing reports of patients with chronic symptoms, known as long-COVID. Dysautonomia may be a possible post-acute neurological complication explaining the persistent symptoms observed in long COVID. Postural tachycardia syndrome (POTS), a form of dysautonomia characterized by sustained tachycardia and orthostatic intolerance, has been increasingly reported in patients after SARS-CoV-2 infection. In this context, this review aimed to report and discuss the available literature pertaining to post COVID-19 POTS.
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Affiliation(s)
- Youssra Amekran
- Department of Physiology, Faculty of Medicine and Pharmacy of Tangier, Abdelmalek Essaadi University, Tangier, Morocco
| | - Narjisse Damoun
- Department of Physiology, Faculty of Medicine and Pharmacy of Tangier, Abdelmalek Essaadi University, Tangier, Morocco
| | - Abdelkader Jalil El Hangouche
- Department of Physiology, Faculty of Medicine and Pharmacy of Tangier, Abdelmalek Essaadi University, Tangier, Morocco
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7
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Rocha EA, Mehta N, Távora-Mehta MZP, Roncari CF, Cidrão AADL, Elias Neto J. Dysautonomia: A Forgotten Condition - Part II. Arq Bras Cardiol 2021; 116:981-998. [PMID: 34008826 PMCID: PMC8121459 DOI: 10.36660/abc.20200422] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2020] [Accepted: 11/04/2020] [Indexed: 12/15/2022] Open
Affiliation(s)
- Eduardo Arrais Rocha
- Hospital Universitário Walter Cantídio da Universidade Federal do Ceará (UFC) - Programa de Pós-graduação em Ciências Cardiovasculares da Faculdade de Medicina da UFC, Fortaleza, CE - Brasil
| | - Niraj Mehta
- Universidade Federal do Paraná, Curitiba, PR - Brasil.,Clínica de Eletrofisiologia do Paraná, Curitiba, PR - Brasil
| | | | - Camila Ferreira Roncari
- Departamento de Fisiologia e Farmacologia - Faculdade de Medicina da Universidade Federal do Ceará (UFC), Fortaleza, CE - Brasil
| | - Alan Alves de Lima Cidrão
- Programa de Pós-graduação em Ciências Cardiovasculares da Faculdade de Medicina da UFC, Fortaleza, CE - Brasil
| | - Jorge Elias Neto
- Serviço de Eletrofisiologia do Vitória Apart Hospital, Vitória, ES - Brasil
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8
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Hardin EA, Stoller D, Lawley J, Howden EJ, Hieda M, Pawelczyk J, Jarvis S, Prisk K, Sarma S, Levine BD. Noninvasive Assessment of Cardiac Output: Accuracy and Precision of the Closed-Circuit Acetylene Rebreathing Technique for Cardiac Output Measurement. J Am Heart Assoc 2020; 9:e015794. [PMID: 32851906 PMCID: PMC7660774 DOI: 10.1161/jaha.120.015794] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Background Accurate assessment of cardiac output is critical to the diagnosis and management of various cardiac disease states; however, clinical standards of direct Fick and thermodilution are invasive. Noninvasive alternatives, such as closed‐circuit acetylene (C2H2) rebreathing, warrant validation. Methods and Results We analyzed 10 clinical studies and all available cardiopulmonary stress tests performed in our laboratory that included a rebreathing method and direct Fick or thermodilution. Studies included healthy individuals and patients with clinical disease. Simultaneous cardiac output measurements were obtained under normovolemic, hypovolemic, and hypervolemic conditions, along with submaximal and maximal exercise. A total of 3198 measurements in 519 patients were analyzed (mean age, 59 years; 48% women). The C2H2 method was more precise than thermodilution in healthy individuals with half the typical error (TE; 0.34 L/min [r=0.92] and coefficient of variation, 7.2%) versus thermodilution (TE=0.67 [r=0.70] and coefficient of variation, 13.2%). In healthy individuals during supine rest and upright exercise, C2H2 correlated well with thermodilution (supine: r=0.84, TE=1.02; exercise: r=0.82, TE=2.36). In patients with clinical disease during supine rest, C2H2 correlated with thermodilution (r=0.85, TE=1.43). C2H2 was similar to thermodilution and nitrous oxide (N2O) rebreathing technique compared with Fick in healthy adults (C2H2 rest: r=0.85, TE=0.84; C2H2 exercise: r=0.87, TE=2.39; thermodilution rest: r=0.72, TE=1.11; thermodilution exercise: r=0.73, TE=2.87; N2O rest: r=0.82, TE=0.94; N2O exercise: r=0.84, TE=2.18). The accuracy of the C2H2 and N2O methods was excellent (r=0.99, TE=0.58). Conclusions The C2H2 rebreathing method is more precise than, and as accurate as, the thermodilution method in a variety of patients, with accuracy similar to an N2O rebreathing method approved by the US Food and Drug Administration.
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Affiliation(s)
- E Ashley Hardin
- Division of Cardiology Department of Internal Medicine University of Texas Southwestern Medical Center Dallas TX.,Institute for Exercise and Environmental Medicine Texas Health Presbyterian Hospital Dallas TX
| | - Douglas Stoller
- Division of Cardiology Department of Internal Medicine University of Texas Southwestern Medical Center Dallas TX.,Institute for Exercise and Environmental Medicine Texas Health Presbyterian Hospital Dallas TX
| | - Justin Lawley
- Division of Cardiology Department of Internal Medicine University of Texas Southwestern Medical Center Dallas TX.,Institute for Exercise and Environmental Medicine Texas Health Presbyterian Hospital Dallas TX
| | - Erin J Howden
- Division of Cardiology Department of Internal Medicine University of Texas Southwestern Medical Center Dallas TX.,Institute for Exercise and Environmental Medicine Texas Health Presbyterian Hospital Dallas TX
| | - Michinari Hieda
- Division of Cardiology Department of Internal Medicine University of Texas Southwestern Medical Center Dallas TX.,Institute for Exercise and Environmental Medicine Texas Health Presbyterian Hospital Dallas TX
| | - James Pawelczyk
- Department of Physiology Pennsylvania State University University Park and Hershey PA
| | - Sara Jarvis
- Department of Biological Sciences Northern Arizona University Flagstaff AZ
| | - Kim Prisk
- Department of Medicine University of California at San Diego La Jolla CA
| | - Satyam Sarma
- Division of Cardiology Department of Internal Medicine University of Texas Southwestern Medical Center Dallas TX.,Institute for Exercise and Environmental Medicine Texas Health Presbyterian Hospital Dallas TX
| | - Benjamin D Levine
- Division of Cardiology Department of Internal Medicine University of Texas Southwestern Medical Center Dallas TX.,Institute for Exercise and Environmental Medicine Texas Health Presbyterian Hospital Dallas TX
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Navasiolava N, Yuan M, Murphy R, Robin A, Coupé M, Wang L, Alameddine A, Gauquelin-Koch G, Gharib C, Li Y, Custaud MA. Vascular and Microvascular Dysfunction Induced by Microgravity and Its Analogs in Humans: Mechanisms and Countermeasures. Front Physiol 2020; 11:952. [PMID: 32973543 PMCID: PMC7468431 DOI: 10.3389/fphys.2020.00952] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2020] [Accepted: 07/14/2020] [Indexed: 12/19/2022] Open
Abstract
Weightlessness and physical inactivity have deleterious cardiovascular effects. The space environment and its ground-based models offer conditions to study the cardiovascular effects of physical inactivity in the absence of other vascular risk factors, particularly at the macro- and microcirculatory levels. However, the mechanisms involved in vascular dysfunction and remodeling are not sufficiently studied in the context of weightlessness and its analogs including models of physical inactivity. Here, we summarize vascular and microvascular changes induced by space flight and observed in models of microgravity and physical inactivity and review the effects of prophylactic strategies (i.e., countermeasures) on vascular and microvascular function. We discuss physical (e.g., exercise, vibration, lower body negative pressure, and artificial gravity) and nutritional/pharmacological (e.g., caloric restriction, resveratrol, and other vegetal extracts) countermeasures. Currently, exercise countermeasure appears to be the most effective to protect vascular function. Although pharmacological countermeasures are not currently considered to fight vascular changes due to microgravity, nutritional countermeasures are very promising. Dietary supplements/natural health products, especially plant extracts, should be extensively studied. The best prophylactic strategy is likely a combination of countermeasures that are effective not only at the cardiovascular level but also for the organism as a whole, but this strategy remains to be determined.
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Affiliation(s)
| | - Ming Yuan
- State Key Laboratory of Space Medicine Fundamentals and Application, China Astronaut Research and Training Center (ACC), Beijing, China
| | - Ronan Murphy
- School of Health and Human Performance, Faculty of Science & Health, Dublin City University, Dublin, Ireland
| | - Adrien Robin
- Clinical Research Center, CHU d'Angers, Angers, France.,Mitovasc, UMR INSERM 1083-CNRS 6015, Université d'Angers, Angers, France
| | - Mickael Coupé
- Mitovasc, UMR INSERM 1083-CNRS 6015, Université d'Angers, Angers, France
| | - Linjie Wang
- State Key Laboratory of Space Medicine Fundamentals and Application, China Astronaut Research and Training Center (ACC), Beijing, China
| | - Asmaa Alameddine
- Mitovasc, UMR INSERM 1083-CNRS 6015, Université d'Angers, Angers, France
| | | | - Claude Gharib
- Institut NeuroMyoGène, Faculté de Médecine Lyon-Est, Université de Lyon, Lyon, France
| | - Yinghui Li
- State Key Laboratory of Space Medicine Fundamentals and Application, China Astronaut Research and Training Center (ACC), Beijing, China
| | - Marc-Antoine Custaud
- Clinical Research Center, CHU d'Angers, Angers, France.,Mitovasc, UMR INSERM 1083-CNRS 6015, Université d'Angers, Angers, France
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10
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Simpson LL, Meah VL, Steele A, Thapamagar S, Gasho C, Anholm JD, Drane AL, Dawkins TG, Busch SA, Oliver SJ, Lawley JS, Tymko MM, Ainslie PN, Steinback CD, Stembridge M, Moore JP. Evidence for a physiological role of pulmonary arterial baroreceptors in sympathetic neural activation in healthy humans. J Physiol 2020; 598:955-965. [PMID: 31977069 DOI: 10.1113/jp278731] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2019] [Accepted: 01/20/2020] [Indexed: 12/11/2022] Open
Abstract
KEY POINTS In an anaesthetised animal model, independent stimulation of baroreceptors in the pulmonary artery elicits reflex sympathoexcitation. In humans, pulmonary arterial pressure is positively related to basal muscle sympathetic nerve activity (MSNA) under conditions where elevated pulmonary pressure is evident (e.g. high altitude); however, a causal link is not established. Using a novel experimental approach, we demonstrate that reducing pulmonary arterial pressure lowers basal MSNA in healthy humans. This response is distinct from the negative feedback reflex mediated by aortic and carotid sinus baroreceptors when systemic arterial pressure is lowered. Afferent input from pulmonary arterial baroreceptors may contribute to sympathetic neural activation in healthy lowland natives exposed to high altitude. ABSTRACT In animal models, distension of baroreceptors located in the pulmonary artery induces a reflex increase in sympathetic outflow; however, this has not been examined in humans. Therefore, we investigated whether reductions in pulmonary arterial pressure influenced sympathetic outflow and baroreflex control of muscle sympathetic nerve activity (MSNA). Healthy lowlanders (n = 13; 5 females) were studied 4-8 days following arrival at high altitude (4383 m; Cerro de Pasco, Peru), a setting that increases both pulmonary arterial pressure and sympathetic outflow. MSNA (microneurography) and blood pressure (BP; photoplethysmography) were measured continuously during ambient air breathing (Amb) and a 6 min inhalation of the vasodilator nitric oxide (iNO; 40 ppm in 21% O2 ), to selectively lower pulmonary arterial pressure. A modified Oxford test was performed under both conditions. Pulmonary artery systolic pressure (PASP) was determined using Doppler echocardiography. iNO reduced PASP (24 ± 3 vs. 32 ± 5 mmHg; P < 0.001) compared to Amb, with a similar reduction in MSNA total activity (1369 ± 576 to 994 ± 474 a.u min-1 ; P = 0.01). iNO also reduced the MSNA operating point (burst incidence; 39 ± 16 to 33 ± 17 bursts·100 Hb-1 ; P = 0.01) and diastolic operating pressure (82 ± 8 to 80 ± 8 mmHg; P < 0.001) compared to Amb, without changing heart rate (P = 0.6) or vascular-sympathetic baroreflex gain (P = 0.85). In conclusion, unloading of pulmonary arterial baroreceptors reduced basal sympathetic outflow to the skeletal muscle vasculature and reset vascular-sympathetic baroreflex control of MSNA downward and leftward in healthy humans at high altitude. These data suggest the existence of a lesser-known reflex input involved in sympathetic activation in humans.
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Affiliation(s)
- Lydia L Simpson
- Extremes Research Group, School of Sport, Health and Exercise Sciences, Bangor University, Wales, UK
| | - Victoria L Meah
- Neurovascular Health Laboratory, Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Canada
| | - Andrew Steele
- Neurovascular Health Laboratory, Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Canada
| | - Suman Thapamagar
- Division of Pulmonary and Critical Care, School of Medicine, Loma Linda University, Loma Linda, CA, USA
| | - Christopher Gasho
- Division of Pulmonary and Critical Care, School of Medicine, Loma Linda University, Loma Linda, CA, USA
| | - James D Anholm
- Division of Pulmonary and Critical Care, School of Medicine, Loma Linda University, Loma Linda, CA, USA
| | - Aimee L Drane
- Cardiff School of Sport and Health Sciences, Cardiff Metropolitan University, Wales, UK
| | - Tony G Dawkins
- Cardiff School of Sport and Health Sciences, Cardiff Metropolitan University, Wales, UK
| | - Stephen A Busch
- Neurovascular Health Laboratory, Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Canada
| | - Samuel J Oliver
- Extremes Research Group, School of Sport, Health and Exercise Sciences, Bangor University, Wales, UK
| | - Justin S Lawley
- Department of Sport Science, Division of Physiology, University of Innsbruck, Austria
| | - Michael M Tymko
- Centre for Heart, Lung, and Vascular Health, University of British Columbia Okanagan, Kelowna, Canada
| | - Phillip N Ainslie
- Centre for Heart, Lung, and Vascular Health, University of British Columbia Okanagan, Kelowna, Canada
| | - Craig D Steinback
- Neurovascular Health Laboratory, Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Canada
| | - Mike Stembridge
- Cardiff School of Sport and Health Sciences, Cardiff Metropolitan University, Wales, UK
| | - Jonathan P Moore
- Extremes Research Group, School of Sport, Health and Exercise Sciences, Bangor University, Wales, UK
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Barbic F, Heusser K, Minonzio M, Shiffer D, Cairo B, Tank J, Jordan J, Diedrich A, Gauger P, Zamuner RA, Porta A, Furlan R. Effects of Prolonged Head-Down Bed Rest on Cardiac and Vascular Baroreceptor Modulation and Orthostatic Tolerance in Healthy Individuals. Front Physiol 2019; 10:1061. [PMID: 31507438 PMCID: PMC6716544 DOI: 10.3389/fphys.2019.01061] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2019] [Accepted: 08/02/2019] [Indexed: 11/13/2022] Open
Abstract
Orthostatic intolerance commonly occurs after prolonged bed rest, thus increasing the risk of syncope and falls. Baroreflex-mediated adjustments of heart rate and sympathetic vasomotor activity (muscle sympathetic nerve activity – MSNA) are crucial for orthostatic tolerance. We hypothesized that prolonged bed rest deconditioning alters overall baroreceptor functioning, thereby reducing orthostatic tolerance in healthy volunteers. As part of the European Space Agency Medium-term Bed Rest protocol, 10 volunteers were studied before and after 21 days of −6° head down bed rest (HDBR). In both conditions, subjects underwent ECG, beat-by-beat blood pressure, respiratory activity, and MSNA recordings while supine (REST) and during a 15-min 80° head-up tilt (TILT) followed by a 3-min −10 mmHg stepwise increase of lower body negative pressure to pre-syncope. Cardiac baroreflex sensitivity (cBRS) was obtained in the time (sequence method) and frequency domain (spectrum and cross-spectrum analyses of RR interval and systolic arterial pressure – SAP, variability). Baroreceptor modulation of sympathetic discharge activity to the vessels (sBRS) was estimated by the slope of the regression line between the percentage of MSNA burst occurrence and diastolic arterial pressure. Orthostatic tolerance significantly decreased after HDBR (12 ± 0.6 min) compared to before (21 ± 0.6 min). While supine, heart rate, SAP, and cBRS were unchanged before and after HDBR, sBRS gain was slightly depressed after than before HDBR (sBRS: −6.0 ± 1.1 versus −2.9 ± 1.5 burst% × mmHg−1, respectively). During TILT, HR was higher after than before HDBR (116 ± 4 b/min versus 100 ± 4 b/min, respectively), SAP was unmodified in both conditions, and cBRS indexes were lower after HDBR (α index: 3.4 ± 0.7 ms/mmHg; BRSSEQ 4.0 ± 1.0) than before (α index: 6.4 ± 1.0 ms/mmHg; BRSSEQ 6.8 ± 1.2). sBRS gain was significantly more depressed after HDBR than before (sBRS: −2.3 ± 0.7 versus −4.4 ± 0.4 burst% × mmHg−1, respectively). Our findings suggest that baroreflex-mediated adjustments in heart rate and MSNA are impaired after prolonged bed rest. The mechanism likely contributes to the decrease in orthostatic tolerance.
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Affiliation(s)
- Franca Barbic
- Humanitas Clinical and Research Center, Department of Internal Medicine, Istituto di Ricovero e Cura a Carattere Scientifico (IRCCS), Humanitas University, Rozzano, Italy
| | - Karsten Heusser
- German Aerospace Center (DLR), Institute of Aerospace Medicine, Cologne, Germany
| | - Maura Minonzio
- Humanitas Clinical and Research Center, Department of Internal Medicine, Istituto di Ricovero e Cura a Carattere Scientifico (IRCCS), Humanitas University, Rozzano, Italy
| | - Dana Shiffer
- Humanitas Clinical and Research Center, Department of Internal Medicine, Istituto di Ricovero e Cura a Carattere Scientifico (IRCCS), Humanitas University, Rozzano, Italy
| | - Beatrice Cairo
- Department of Biomedical Sciences for Health, University of Milan, Milan, Italy
| | - Jens Tank
- German Aerospace Center (DLR), Institute of Aerospace Medicine, Cologne, Germany
| | - Jens Jordan
- German Aerospace Center (DLR), Institute of Aerospace Medicine, Cologne, Germany
| | - André Diedrich
- Autonomic Dysfunction Center, Clinical Research Center (CRC), Department of Medicine, Vanderbilt University, Nashville, TN, United States
| | - Peter Gauger
- German Aerospace Center (DLR), Institute of Aerospace Medicine, Cologne, Germany
| | | | - Alberto Porta
- Department of Biomedical Sciences for Health, University of Milan, Milan, Italy.,Department of Cardiothoracic, Vascular Anesthesia and Intensive Care, Istituto di Ricovero e Cura a Carattere Scientifico (IRCCS) Policlinico di San Donato, San Donato Milanese, Italy
| | - Raffaello Furlan
- Humanitas Clinical and Research Center, Department of Internal Medicine, Istituto di Ricovero e Cura a Carattere Scientifico (IRCCS), Humanitas University, Rozzano, Italy
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Bryarly M, Phillips LT, Fu Q, Vernino S, Levine BD. Postural Orthostatic Tachycardia Syndrome. J Am Coll Cardiol 2019; 73:1207-1228. [DOI: 10.1016/j.jacc.2018.11.059] [Citation(s) in RCA: 93] [Impact Index Per Article: 18.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/21/2017] [Revised: 11/01/2018] [Accepted: 11/05/2018] [Indexed: 12/26/2022]
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Cutsforth-Gregory JK, Sandroni P. Clinical neurophysiology of postural tachycardia syndrome. HANDBOOK OF CLINICAL NEUROLOGY 2019; 161:429-445. [PMID: 31307619 DOI: 10.1016/b978-0-444-64142-7.00066-7] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Postural tachycardia syndrome (POTS) is one of several disorders of orthostatic intolerance (OI). It is defined by the development of symptoms of cerebral hypoperfusion or sympathetic activation and a sustained heart rate increment of 30 beats/min or more (40 beats/min for teenagers) within 10min of standing or head-up tilt in the absence of orthostatic hypotension; the standing heart rate is often 120 beats/min or higher. POTS is approximately five times more common in women than men. This heterogeneous syndrome is caused by several pathophysiologic mechanisms (limited autonomic neuropathy, hyperadrenergic state, hypovolemia, venous pooling, deconditioning), which are not mutually exclusive. Anxiety and somatic hypervigilance play significant roles in POTS. Common comorbidities include visceral pain and dysmotility, chronic fatigue and fibromyalgia, migraine, joint hypermobility, mitral valve prolapse, and inappropriate sinus tachycardia. Patients with suspected POTS should undergo comprehensive cardiac and neurologic examinations and autonomic and laboratory tests to determine the most likely pathophysiologic basis of OI. The objectives of POTS management are to (1) increase the time that patients can stand, perform daily activities, and exercise and (2) avoid syncope. Management involves nonpharmacologic (fluid and salt loading, physical countermaneuvers, compression garments, exercise training) and pharmacologic (β-blockers, pyridostigmine, fludrocortisone, midodrine) approaches.
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Affiliation(s)
| | - Paola Sandroni
- Department of Neurology, Mayo Clinic, Rochester, MN, United States.
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Klassen SA, De Abreu S, Greaves DK, Kimmerly DS, Arbeille P, Denise P, Hughson RL, Normand H, Shoemaker JK. Long-duration bed rest modifies sympathetic neural recruitment strategies in male and female participants. J Appl Physiol (1985) 2018; 124:769-779. [PMID: 29212669 PMCID: PMC5899270 DOI: 10.1152/japplphysiol.00640.2017] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2017] [Revised: 11/09/2017] [Accepted: 12/04/2017] [Indexed: 01/07/2023] Open
Abstract
To understand the impact of physical deconditioning with head-down tilt bed rest (HDBR) on the malleability of sympathetic discharge patterns, we studied 1) baseline integrated muscle sympathetic nerve activity (MSNA; microneurography) from 13 female participants in the WISE-2005 60-day HDBR study (retrospective analysis), 2) integrated MSNA and multiunit action potential (AP) analysis in 13 male participants performed on data collected at baseline and during physiological stress imposed by end-inspiratory apnea in a new 60-day HDBR study, and 3) a repeatability study (control; n = 6, retrospective analysis, 4 wk between tests). Neither baseline integrated burst frequency nor incidence were altered with HDBR (both P > 0.35). However, baseline integrated burst latency increased in both HDBR studies (male: 1.35 ± 0.02 to 1.39 ± 0.02 s, P < 0.01; female: 1.23 ± 0.02 to 1.29 ± 0.02 s, P < 0.01), whereas controls exhibited no change across two visits (1.25 ± 0.02 to 1.25 ± 0.02 s, group-by-time interaction, P = 0.02). With the exception of increased AP latency ( P = 0.03), male baseline AP data did not change with HDBR (all P > 0.19). The change in AP frequency on going from baseline to apnea (∆94 ± 25 to ∆317 ± 55 AP/min, P < 0.01) and the number of active sympathetic clusters per burst (∆0 ± 0.2 to ∆1 ± 0.2 clusters/burst, P = 0.02) were greater post- compared with pre-HDBR. The change in total clusters with apnea was ∆0 ± 0.5 clusters pre- and ∆2 ± 0.7 clusters post-HDBR ( P = 0.07). These data indicate that 60-day HDBR modified discharge characteristics in baseline burst latency and sympathetic neural recruitment during apneic stress. NEW & NOTEWORTHY Long-duration bed rest did not modify baseline sympathetic burst frequency in male and female participants, but examination of additional features of the multiunit signal provided novel evidence to suggest augmented synaptic delays or processing times at baseline for all sympathetic action potentials. Furthermore, long-duration bed rest increased reflex-sympathetic arousal to apneic stress in male participants primarily by mechanisms involving an augmented firing rate of action potential clusters active at baseline.
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Affiliation(s)
- Stephen A Klassen
- Neurovascular Research Laboratory, School of Kinesiology, University of Western Ontario , London, Ontario , Canada
| | | | - Danielle K Greaves
- Schlegel-University of Waterloo Research Institute for Aging , Waterloo, Ontario , Canada
| | - Derek S Kimmerly
- Division of Kinesiology, School of Health and Human Performance, Dalhousie University , Halifax, Nova Scotia , Canada
| | - Philippe Arbeille
- UMPS-CERCOM, School of Medicine, University of Tours , Tours , France
| | - Pierre Denise
- Normandie Université, Unicaen, INSERM, Caen , France
| | - Richard L Hughson
- Schlegel-University of Waterloo Research Institute for Aging , Waterloo, Ontario , Canada
| | - Hervé Normand
- Normandie Université, Unicaen, INSERM, Caen , France
| | - J Kevin Shoemaker
- Neurovascular Research Laboratory, School of Kinesiology, University of Western Ontario , London, Ontario , Canada
- Department of Physiology and Pharmacology, University of Western Ontario , London, Ontario , Canada
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Pertab JL, Merkley TL, Cramond AJ, Cramond K, Paxton H, Wu T. Concussion and the autonomic nervous system: An introduction to the field and the results of a systematic review. NeuroRehabilitation 2018; 42:397-427. [PMID: 29660949 PMCID: PMC6027940 DOI: 10.3233/nre-172298] [Citation(s) in RCA: 69] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
BACKGROUND Recent evidence suggests that autonomic nervous dysfunction may be one of many potential factors contributing to persisting post-concussion symptoms. OBJECTIVE This is the first systematic review to explore the impact of concussion on multiple aspects of autonomic nervous system functioning. METHODS The methods employed are in compliance with the American Academy of Neurology (AAN) and PRISMA standards. Embase, MEDLINE, PsychINFO, and Science Citation Index literature searches were performed using relevant indexing terms for articles published prior to the end of December 2016. Data extraction was performed by two independent groups, including study quality indicators to determine potential risk for bias according to the 4-tiered classification scheme of the AAN. RESULTS Thirty-six articles qualified for inclusion in the analysis. Only three studies (one Class II and two Class IV) did not identify anomalies in measures of ANS functioning in concussed populations. CONCLUSIONS The evidence supports the conclusion that it is likely that concussion causes autonomic nervous system anomalies. An awareness of this relationship increases our understanding of the physical impact of concussion, partially explains the overlap of concussion symptoms with other medical conditions, presents opportunities for further research, and has the potential to powerfully inform treatment decisions.
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Affiliation(s)
- Jon L. Pertab
- Neurosciences Institute, Intermountain Healthcare, Murray, UT, USA
| | - Tricia L. Merkley
- Department of Clinical Neuropsychology, Barrow Neurological Institute, Phoenix, AZ, USA
| | | | - Kelly Cramond
- Summit Neuropsychology, Reno, NV, USA
- VA Sierra Nevada Healthcare System, Reno, NV, USA
| | - Holly Paxton
- Hauenstein Neurosciences of Mercy Health and Department of Translational Science and Molecular Medicine, Michigan State University, MI, USA
| | - Trevor Wu
- Hauenstein Neurosciences of Mercy Health and Department of Translational Science and Molecular Medicine, Michigan State University, MI, USA
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Bostock EL, Morse CI, Winwood K, McEwan IM, Onambélé GL. Omega-3 Fatty Acids and Vitamin D in Immobilisation: Part B- Modulation of Muscle Functional, Vascular and Activation Profiles. J Nutr Health Aging 2017; 21:59-66. [PMID: 27999851 PMCID: PMC5306256 DOI: 10.1007/s12603-016-0711-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2015] [Accepted: 09/29/2015] [Indexed: 01/20/2023]
Abstract
OBJECTIVES This study set out to determine whether two potential protein-sparing modulators (eicosapentaenoic acid and vitamin D) would modulate the anticipated muscle functional and related blood vessels function deleterious effects of immobilisation. DESIGN The study used a randomised, double-blind, placebo-controlled design. SETTING The study took part in a laboratory setting. PARTICIPANTS Twenty-four male and female healthy participants, aged 23.0±5.8 years. INTERVENTION The non-dominant arm was immobilised in a sling for a period of nine waking hours a day over two continuous weeks. Participants were randomly assigned to one of three groups: placebo (n=8, Lecithin, 2400 mg daily), omega-3 (ω-3) fatty acids (n=8, eicosapentaenoic acid (EPA); 1770 mg, and docosahexaenoic acid (DHA); 390 mg, daily) or vitamin D (n=8, 1,000 IU daily). MEASUREMENTS Isometric and isokinetic torque, antagonist muscle co-contraction (activation profile), muscle fatigability indices, and arterial resting blood flow were measured before, at the end of the immobilisation period, and two weeks after re-mobilisation. RESULTS Muscle elbow flexion and extension isometric and isokinetic torque decreased significantly with limb immobilisation in the placebo group (P<0.05). Despite no significant effect of supplementation, ω-3 and vitamin D supplementation showed trends (P>0.05) towards attenuating the decreases observed in the placebo group. There was no significant change in muscle fatigue parameters or co-contraction values with immobilisation and no effect of supplementation group (P>0.05). Similarly, this immobilisation model had no impact on the assessed blood flow characteristics. All parameters had returned to baseline values at the re-mobilisation phase of the study. CONCLUSION Overall, at the current doses, neither ω-3 nor vitamin D supplementation significantly attenuated declines in torque associated with immobilisation. It would appear that muscle function (described here in Part B) might not be as useful a marker of the effectiveness of a supplement against the impact of immobilisation compared to tissue composition changes (described in Part A).
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Affiliation(s)
- E L Bostock
- Gladys Onambele-Pearson, Health, Exercise and Active Living Research Centre, Department of Exercise and Sport Science, Manchester Metropolitan University, Crewe Green Road, Crewe, CW1 5DU, United Kingdom. Tel: +44 (0) 161 247 5594;
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18
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Eckberg DL, Diedrich A, Cooke WH, Biaggioni I, Buckey JC, Pawelczyk JA, Ertl AC, Cox JF, Kuusela TA, Tahvanainen KUO, Mano T, Iwase S, Baisch FJ, Levine BD, Adams-Huet B, Robertson D, Blomqvist CG. Respiratory modulation of human autonomic function: long-term neuroplasticity in space. J Physiol 2016; 594:5629-46. [PMID: 27029027 DOI: 10.1113/jp271656] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2015] [Accepted: 03/14/2016] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS We studied healthy astronauts before, during and after the Neurolab Space Shuttle mission with controlled breathing and apnoea, to identify autonomic changes that might contribute to postflight orthostatic intolerance. Measurements included the electrocardiogram, finger photoplethysmographic arterial pressure, respiratory carbon dioxide levels, tidal volume and peroneal nerve muscle sympathetic activity. Arterial pressure fell and then rose in space, and drifted back to preflight levels after return to Earth. Vagal metrics changed in opposite directions: vagal baroreflex gain and two indices of vagal fluctuations rose and then fell in space, and descended to preflight levels upon return to Earth. Sympathetic burst frequencies (but not areas) were greater than preflight in space and on landing day, and astronauts' abilities to modulate both burst areas and frequencies during apnoea were sharply diminished. Spaceflight triggers long-term neuroplastic changes reflected by reciptocal sympathetic and vagal motoneurone responsiveness to breathing changes. ABSTRACT We studied six healthy astronauts five times, on Earth, in space on the first and 12th or 13th day of the 16 day Neurolab Space Shuttle mission, on landing day, and 5-6 days later. Astronauts followed a fixed protocol comprising controlled and random frequency breathing and apnoea, conceived to perturb their autonomic function and identify changes, if any, provoked by microgravity exposure. We recorded the electrocardiogram, finger photoplethysmographic arterial pressure, tidal carbon dioxide concentrations and volumes, and peroneal nerve muscle sympathetic activity on Earth (in the supine position) and in space. (Sympathetic nerve recordings were made during three sessions: preflight, late mission and landing day.) Arterial pressure changed systematically from preflight levels: pressure fell during early microgravity exposure, rose as microgravity exposure continued, and drifted back to preflight levels after return to Earth. Vagal metrics changed in opposite directions: vagal baroreflex gain and two indices of vagal fluctuations (root mean square of successive normal R-R intervals; and proportion of successive normal R-R intervals greater than 50 ms, divided by the total number of normal R-R intervals) rose significantly during early microgravity exposure, fell as microgravity exposure continued, and descended to preflight levels upon return to Earth. Sympathetic mechanisms also changed. Burst frequencies (but not areas) during fixed frequency breathing were greater than preflight in space and on landing day, but their control during apnoea was sharply altered: astronauts increased their burst frequencies from already high levels, but they could not modulate either burst areas or frequencies appropriately. Space travel provokes long-lasting sympathetic and vagal neuroplastic changes in healthy humans.
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Affiliation(s)
- Dwain L Eckberg
- Departments of Medicine and Physiology, Hunter Holmes McGuire Department of Veterans Affairs Medical Center, Virginia Commonwealth University School of Medicine, Richmond, VA, USA.
| | - André Diedrich
- Department of Medicine, Division of Clinical Pharmacology, Autonomic Dysfunction Center, Vanderbilt University School of Medicine, Vanderbilt University, Nashville, TN, USA
| | - William H Cooke
- Department of Kinesiology, Health, and Nutrition, University of Texas at San Antonio, San Antonio, TX, USA
| | - Italo Biaggioni
- Department of Medicine, Division of Clinical Pharmacology, Autonomic Dysfunction Center, Vanderbilt University School of Medicine, Vanderbilt University, Nashville, TN, USA
| | - Jay C Buckey
- Dartmouth Hitchcock Medical Centre, Lebanon, NH, USA
| | - James A Pawelczyk
- Department of Physiology, Pennsylvania State University, University Park and Hershey, PA, USA
| | - Andrew C Ertl
- Department of Medicine, Division of Clinical Pharmacology, Autonomic Dysfunction Center, Vanderbilt University School of Medicine, Vanderbilt University, Nashville, TN, USA
| | - James F Cox
- Departments of Medicine and Physiology, Hunter Holmes McGuire Department of Veterans Affairs Medical Center, Virginia Commonwealth University School of Medicine, Richmond, VA, USA
| | - Tom A Kuusela
- Department of Physics, Turku University, Turku, Finland
| | - Kari U O Tahvanainen
- Department of Clinical Physiology and Nuclear Medicine, South Karelia Central Hospital, Lappeenranta, Finland
| | - Tadaaki Mano
- Gifu University of Medical Science, 795-1 Nagamine Ichihiraga, Seki, Gifu, 501-3892, Japan
| | - Satoshi Iwase
- Department of Physiology, Aichi Medical University, Aichi, Japan
| | | | - Benjamin D Levine
- Department of Medicine, University of Texas Southwestern Medical Centre at Dallas, Dallas, TX, USA.,Institute for Exercise and Environmental Medicine, Texas Health Presbyterian, Hospital, Dallas, TX, USA
| | | | - David Robertson
- Department of Medicine, Division of Clinical Pharmacology, Autonomic Dysfunction Center, Vanderbilt University School of Medicine, Vanderbilt University, Nashville, TN, USA
| | - C Gunnar Blomqvist
- Department of Medicine, University of Texas Southwestern Medical Centre at Dallas, Dallas, TX, USA
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Florian JP, Baisch FJ, Heer M, Pawelczyk JA. Caloric restriction diminishes the pressor response to static exercise. EXTREME PHYSIOLOGY & MEDICINE 2016; 5:2. [PMID: 26793301 PMCID: PMC4719559 DOI: 10.1186/s13728-016-0043-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/25/2015] [Accepted: 01/05/2016] [Indexed: 11/10/2022]
Abstract
BACKGROUND Astronauts in space consume fewer calories and return to earth predisposed to orthostatic intolerance. The role that caloric deficit plays in the modulation of autonomic control of the cardiovascular system is unknown. Therefore, the purpose of this study was to determine the effects of 6° head-down bedrest (an analog of spaceflight) with a hypocaloric diet (25 % caloric restriction) (CR) on autonomic neural control during static handgrip (HG) and cold pressor (CP) tests. Nine healthy young men participated in a randomized crossover bedrest (BR) study, consisting of four, two-week interventions (hypocaloric ambulatory, hypocaloric bedrest, normocaloric ambulatory, and normocaloric bedrest), each separated by 5 months. Heart rate (HR), arterial pressure, and muscle sympathetic nerve activity (MSNA) were recorded before, during, and after HG (40 % of maximum voluntary contraction to fatigue), post-exercise muscle ischemia (forearm occlusion), and CP. Bedrest and nutritional combinations were compared using two-way ANOVA with repeated measures. RESULTS HR, MSNA, and the change in systolic blood pressure during HG were attenuated with caloric restriction, but post-intervention responses for all groups were similar during post-exercise muscle ischemia. CR was associated with a higher diastolic blood pressure during CP; however, HR was directionally opposite (i.e., increase with BR, decrease with CR). CONCLUSIONS In summary 14-day caloric/fat restriction attenuated MSNA and pressor responses during isometric exercise to fatigue but not to post-exercise muscle ischemia. This indicates that the integrity of the metaboreflex is maintained whereas the influence of the mechanoreflex and/or central command may be reduced.
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Affiliation(s)
- John P Florian
- Navy Experimental Diving Unit, 321 Bullfinch Rd., Panama City, FL 32407 USA
| | | | - Martina Heer
- DLR-Institute of Aerospace Medicine, Cologne, Germany
| | - James A Pawelczyk
- Noll Laboratory, Department of Kinesiology, The Pennsylvania State University, University Park, PA 16802 USA
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Caloric restriction decreases orthostatic tolerance independently from 6° head-down bedrest. PLoS One 2015; 10:e0118812. [PMID: 25915488 PMCID: PMC4411149 DOI: 10.1371/journal.pone.0118812] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2013] [Accepted: 01/09/2015] [Indexed: 11/19/2022] Open
Abstract
Astronauts consume fewer calories during spaceflight and return to earth with an increased risk of orthostatic intolerance. Whether a caloric deficiency modifies orthostatic responses is not understood. Thus, we determined the effects of a hypocaloric diet (25% caloric restriction) during 6° head down bedrest (an analog of spaceflight) on autonomic neural control during lower body negative pressure (LBNP). Nine healthy young men completed a randomized crossover bedrest study, consisting of four (2 weeks each) interventions (normocaloric bedrest, normocaloric ambulatory, hypocaloric bedrest, hypocaloric ambulatory), each separated by 5 months. Muscle sympathetic nerve activity (MSNA) was recorded at baseline following normocaloric and hypocaloric interventions. Heart rate (HR) and arterial pressure were recorded before, during, and after 3 consecutive stages (7 min each) of LBNP (-15, -30, -45 mmHg). Caloric and posture effects during LBNP were compared using two-way ANOVA with repeated measures. There was a strong trend toward reduced basal MSNA following caloric restriction alone (normcaloric vs. hypocaloric: 22±3 vs. 14±4 burst/min, p = 0.06). Compared to the normocaloric ambulatory, both bedrest and caloric restriction were associated with lower systolic blood pressure during LBNP (p<0.01); however, HR responses were directionally opposite (i.e., increase with bedrest, decrease with caloric restriction). Survival analysis revealed a significant reduction in orthostatic tolerance following caloric restriction (normocaloric finishers: 12/16; hypocaloric finishers: 6/16; χ2, p = 0.03). Caloric restriction modifies autonomic responses to LBNP, which may decrease orthostatic tolerance after spaceflight.
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Hughson RL, Shoemaker JK. Autonomic responses to exercise: Deconditioning/inactivity. Auton Neurosci 2015; 188:32-5. [DOI: 10.1016/j.autneu.2014.10.012] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2014] [Accepted: 10/13/2014] [Indexed: 12/29/2022]
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Florian JP, Simmons EE, Chon KH, Faes L, Shykoff BE. Cardiovascular and autonomic responses to physiological stressors before and after six hours of water immersion. J Appl Physiol (1985) 2013; 115:1275-89. [PMID: 23950166 DOI: 10.1152/japplphysiol.00466.2013] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The physiological responses to water immersion (WI) are known; however, the responses to stress following WI are poorly characterized. Ten healthy men were exposed to three physiological stressors before and after a 6-h resting WI (32-33°C): 1) a 2-min cold pressor test, 2) a static handgrip test to fatigue at 40% of maximum strength followed by postexercise muscle ischemia in the exercising forearm, and 3) a 15-min 70° head-up-tilt (HUT) test. Heart rate (HR), systolic and diastolic blood pressure (SBP and DBP), cardiac output (Q), limb blood flow (BF), stroke volume (SV), systemic and calf or forearm vascular resistance (SVR and CVR or FVR), baroreflex sensitivity (BRS), and HR variability (HRV) frequency-domain variables [low-frequency (LF), high-frequency (HF), and normalized (n)] were measured. Cold pressor test showed lower HR, SBP, SV, Q, calf BF, LFnHRV, and LF/HFHRV and higher CVR and HFnHRV after than before WI (P < 0.05). Handgrip test showed no effect of WI on maximum strength and endurance and lower HR, SBP, SV, Q, and calf BF and higher SVR and CVR after than before WI (P < 0.05). During postexercise muscle ischemia, HFnHRV increased from baseline after WI only, and LFnHRV was lower after than before WI (P < 0.05). HUT test showed lower SBP, DBP, SV, forearm BF, and BRS and higher HR, FVR, LF/HFHRV, and LFnHRV after than before WI (P < 0.05). The changes suggest differential activation/depression during cold pressor and handgrip (reduced sympathetic/elevated parasympathetic) and HUT (elevated sympathetic/reduced parasympathetic) following 6 h of WI.
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Adami A, Pizzinelli P, Bringard A, Capelli C, Malacarne M, Lucini D, Simunič B, Pišot R, Ferretti G. Cardiovascular re-adjustments and baroreflex response during clinical reambulation procedure at the end of 35-day bed rest in humans. Appl Physiol Nutr Metab 2013; 38:673-80. [DOI: 10.1139/apnm-2012-0396] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
During the reambulation procedure after 35-day head-down tilt bed rest (HDTBR) for 9 men, we recorded for the first time heart rate (HR; with electrocardiogram) and arterial pressure profiles (fingertip plethysmography) for 5 min in HDTBR and horizontal (SUP) positions, followed by 12 min in standing position, during which 4 subjects fainted (intolerant, INT) and were laid horizontal again (Recovery). We computed: mean arterial pressure (P¯; pressure profiles integral mean), stroke volume (SV; obtained with Modelflow method), and cardiac output (Q̇; SV × HR). All cardiovascular data remained stable in HDTBR and SUP for both groups (EXP). Taking the upright posture, EXP showed a decrease in SV and an increase in HR, becoming significantly different from SUP within 1 min. Further evolution of these parameters kept Q̇ stable in both groups until the second minute of standing. Afterward, in INT, P̄ precipitated without further HR increases: SV stopped being corrected and Q̇ reached 2.9 ± 0.4 L·min−1 at the last 15 s of standing. Sudden drop in P̄ allowed identification of a low-pressure threshold in INT (70.7 ± 12.9 mm Hg), after which syncope occurred within 80 s. During Recovery, baroreflex curves showed a flat phase (P̄ increase, HR stable), followed by a steep phase (P̄ increased, HR decreased, starting when P̄ was 84.5 ± 12.5 mm Hg and Q̇ was 9.6 ± 1.5 L·min−1). INT, in contrast with tolerant subjects, did not sustain standing because HR was unable to correct for the P̄ drop. These results indicate a major role for impaired arterial baroreflexes in the onset of orthostatic intolerance.
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Affiliation(s)
- Alessandra Adami
- Département de Neuroscience Fondamentales, Centre Médical Universitaire, Université de Genève, 1 Rue Michel Servet, CH-1211 Genève 4, Switzerland
| | - Paolo Pizzinelli
- Dipartimento di Scienze Cliniche, Ospedale L. Sacco, Università di Milano, via GB. Grassi 74, Milano, Italia
| | - Aurélien Bringard
- Département de Neuroscience Fondamentales, Centre Médical Universitaire, Université de Genève, 1 Rue Michel Servet, CH-1211 Genève 4, Switzerland
| | - Carlo Capelli
- Dipartimento di Scienze Neurologiche, Neuropsicologiche, Morfologiche e Motorie, Facoltà di Scienze Motorie, Università di Verona, via F. Casorati, 54, 37100 Verona, Italia
| | - Mara Malacarne
- Dipartimento di Scienze Cliniche, Ospedale L. Sacco, Università di Milano, via GB. Grassi 74, Milano, Italia
| | - Daniela Lucini
- Dipartimento di Scienze Cliniche, Ospedale L. Sacco, Università di Milano, via GB. Grassi 74, Milano, Italia
| | - Boštjan Simunič
- Institute of Kinesiology Research, Science and Research Center, University of Primorska, Koper, Garibaldijeva street 1, 6000 Koper, Slovenia
| | - Rado Pišot
- Institute of Kinesiology Research, Science and Research Center, University of Primorska, Koper, Garibaldijeva street 1, 6000 Koper, Slovenia
| | - Guido Ferretti
- Département de Neuroscience Fondamentales, Centre Médical Universitaire, Université de Genève, 1 Rue Michel Servet, CH-1211 Genève 4, Switzerland
- Dipartimento di Scienze Biomediche e Biotecnologie, Facoltà di Medicina, Università di Brescia, Viale Europa 11, 25123 Brescia, Italia
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Arzeno NM, Stenger MB, Lee SMC, Ploutz-Snyder R, Platts SH. Sex differences in blood pressure control during 6° head-down tilt bed rest. Am J Physiol Heart Circ Physiol 2013; 304:H1114-23. [PMID: 23396455 DOI: 10.1152/ajpheart.00391.2012] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Spaceflight-induced orthostatic intolerance has been studied for decades. Although ∼22% of the astronaut corps are women, most mechanistic studies use mostly male subjects, despite known sex differences in autonomic control and postflight orthostatic intolerance. We studied adrenergic, baroreflex, and autonomic indexes during continuous infusions of vasoactive drugs in men and women during a 60-day head-down bed rest. Volunteers were tested before bed rest (20 men and 10 women) and around day 30 (20 men and 10 women) and day 60 (16 men and 8 women) of bed rest. Three increasing doses of phenylephrine (PE) and sodium nitroprusside were infused for 10 min after an infusion of normal saline. A 20-min rest period separated the phenylephrine and sodium nitroprusside infusions. Autonomic activity was approximated by spectral indexes of heart rate and blood pressure variability, and baroreflex sensitivity was measured by the spontaneous baroreflex slope. Parasympathetic modulation and baroreflex sensitivity decreased with bed rest, with women experiencing a larger decrease in baroreflex sensitivity by day 30 than men. The sympathetic activation of men and parasympathetic responsiveness of women in blood pressure control during physiological stress were preserved throughout bed rest. During PE infusions, women experienced saturation of the R-R interval at high frequency, whereas men did not, revealing a sex difference in the parabolic relationship between high-frequency R-R interval, a measurement of respiratory sinus arrhythmia, and R-R interval. These sex differences in blood pressure control during simulated microgravity reveal the need to study sex differences in long-duration spaceflight to ensure the health and safety of the entire astronaut corps.
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Affiliation(s)
- Natalia M Arzeno
- Wyle Science, Technology and Engineering Group, Houston, Texas, USA
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Benarroch EE. Postural tachycardia syndrome: a heterogeneous and multifactorial disorder. Mayo Clin Proc 2012; 87:1214-25. [PMID: 23122672 PMCID: PMC3547546 DOI: 10.1016/j.mayocp.2012.08.013] [Citation(s) in RCA: 241] [Impact Index Per Article: 20.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/02/2012] [Revised: 08/28/2012] [Accepted: 08/28/2012] [Indexed: 02/07/2023]
Abstract
Postural tachycardia syndrome (POTS) is defined by a heart rate increment of 30 beats/min or more within 10 minutes of standing or head-up tilt in the absence of orthostatic hypotension; the standing heart rate is often 120 beats/min or higher. POTS manifests with symptoms of cerebral hypoperfusion and excessive sympathoexcitation. The pathophysiology of POTS is heterogeneous and includes impaired sympathetically mediated vasoconstriction, excessive sympathetic drive, volume dysregulation, and deconditioning. POTS is frequently included in the differential diagnosis of chronic unexplained symptoms, such as inappropriate sinus tachycardia, chronic fatigue, chronic dizziness, or unexplained spells in otherwise healthy young individuals. Many patients with POTS also report symptoms not attributable to orthostatic intolerance, including those of functional gastrointestinal or bladder disorders, chronic headache, fibromyalgia, and sleep disturbances. In many of these cases, cognitive and behavioral factors, somatic hypervigilance associated with anxiety, depression, and behavioral amplification contribute to symptom chronicity. The aims of evaluation in patients with POTS are to exclude cardiac causes of inappropriate tachycardia; elucidate, if possible, the most likely pathophysiologic basis of postural intolerance; assess for the presence of treatable autonomic neuropathies; exclude endocrine causes of a hyperadrenergic state; evaluate for cardiovascular deconditioning; and determine the contribution of emotional and behavioral factors to the patient's symptoms. Management of POTS includes avoidance of precipitating factors, volume expansion, physical countermaneuvers, exercise training, pharmacotherapy (fludrocortisone, midodrine, β-blockers, and/or pyridostigmine), and behavioral-cognitive therapy. A literature search of PubMed for articles published from January 1, 1990, to June 15, 2012, was performed using the following terms (or combination of terms): POTS; postural tachycardia syndrome, orthostatic; orthostatic; syncope; sympathetic; baroreceptors; vestibulosympathetic; hypovolemia; visceral pain; chronic fatigue; deconditioning; headache; Chiari malformation; Ehlers-Danlos; emotion; amygdala; insula; anterior cingulate; periaqueductal gray; fludrocortisone; midodrine; propranolol; β-adrenergic; and pyridostigmine. Studies were limited to those published in English. Other articles were identified from bibliographies of the retrieved articles.
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Shoemaker JK, Usselman CW, Rothwell A, Wong SW. Altered cortical activation patterns associated with baroreflex unloading following 24 h of physical deconditioning. Exp Physiol 2012; 97:1249-62. [DOI: 10.1113/expphysiol.2012.065557] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
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Aletti F, Ferrario M, Xu D, Greaves DK, Shoemaker JK, Arbeille P, Baselli G, Hughson RL. Short-term variability of blood pressure: effects of lower-body negative pressure and long-duration bed rest. Am J Physiol Regul Integr Comp Physiol 2012; 303:R77-85. [DOI: 10.1152/ajpregu.00050.2012] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Mild lower-body negative pressure (LBNP) has been utilized to selectively unload cardiopulmonary baroreceptors, but there is evidence that arterial baroreceptors can be transiently unloaded after the onset of mild LBNP. In this paper, a black box mathematical model for the prediction of diastolic blood pressure (DBP) variability from multiple inputs (systolic blood pressure, R-R interval duration, and central venous pressure) was applied to interpret the dynamics of blood pressure maintenance under the challenge of LBNP and in long-duration, head-down bed rest (HDBR). Hemodynamic recordings from seven participants in the WISE (Women's International Space Simulation for Exploration) Study collected during an experiment of incremental LBNP (−10 mmHg, −20 mmHg, −30 mmHg) were analyzed before and on day 50 of a 60-day-long HDBR campaign. Autoregressive spectral analysis focused on low-frequency (LF, ∼0.1 Hz) oscillations of DBP, which are related to fluctuations in vascular resistance due to sympathetic and baroreflex regulation of vasomotor tone. The arterial baroreflex-related component explained 49 ± 13% of LF variability of DBP in spontaneous conditions, and 89 ± 9% ( P < 0.05) on day 50 of HDBR, while the cardiopulmonary baroreflex component explained 17 ± 9% and 12 ± 4%, respectively. The arterial baroreflex-related variability was significantly increased in bed rest also for LBNP equal to −20 and −30 mmHg. The proposed technique provided a model interpretation of the proportional effect of arterial baroreflex vs. cardiopulmonary baroreflex-mediated components of blood pressure control and showed that arterial baroreflex was the main player in the mediation of DBP variability. Data during bed rest suggested that cardiopulmonary baroreflex-related effects are blunted and that blood pressure maintenance in the presence of an orthostatic stimulus relies mostly on arterial control.
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Affiliation(s)
- Federico Aletti
- Dipartimento di Bioingegneria, Politecnico di Milano, Milan, Italy
| | - Manuela Ferrario
- Dipartimento di Bioingegneria, Politecnico di Milano, Milan, Italy
| | - Da Xu
- Faculty of Applied Health Sciences, University of Waterloo, Waterloo, Ontario, Canada
| | - Danielle K. Greaves
- Faculty of Applied Health Sciences, University of Waterloo, Waterloo, Ontario, Canada
| | - J. Kevin Shoemaker
- School of Kinesiology, University of Western Ontario, London, Ontario, Canada; and
| | - Philippe Arbeille
- Unité Médecine et Physiologie Spatiale CEntre de Recherche COeur et Maladies vasculaires, University Hospital Trousseau, Tours, France
| | - Giuseppe Baselli
- Dipartimento di Bioingegneria, Politecnico di Milano, Milan, Italy
| | - Richard L. Hughson
- Faculty of Applied Health Sciences, University of Waterloo, Waterloo, Ontario, Canada
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Dyckman DJ, Sauder CL, Ray CA. Effects of short-term and prolonged bed rest on the vestibulosympathetic reflex. Am J Physiol Heart Circ Physiol 2011; 302:H368-74. [PMID: 22021328 DOI: 10.1152/ajpheart.00193.2011] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The mechanism(s) for post-bed rest (BR) orthostatic intolerance is equivocal. The vestibulosympathetic reflex contributes to postural blood pressure regulation. It was hypothesized that muscle sympathetic nerve responses to otolith stimulation would be attenuated by prolonged head-down BR. Arterial blood pressure, heart rate, muscle sympathetic nerve activity (MSNA), and peripheral vascular conductance were measured during head-down rotation (HDR; otolith organ stimulation) in the prone posture before and after short-duration (24 h; n = 22) and prolonged (36 ± 1 day; n = 8) BR. Head-up tilt at 80° was performed to assess orthostatic tolerance. After short-duration BR, MSNA responses to HDR were preserved (Δ5 ± 1 bursts/min, Δ53 ± 13% burst frequency, Δ65 ± 13% total activity; P < 0.001). After prolonged BR, MSNA responses to HDR were attenuated ∼50%. MSNA increased by Δ8 ± 2 vs. Δ3 ± 2 bursts/min and Δ83 ± 12 vs. Δ34 ± 22% total activity during HDR before and after prolonged BR, respectively. Moreover, these results were observed in three subjects tested again after 75 ± 1 days of BR. This reduction in MSNA responses to otolith organ stimulation at 5 wk occurred with reductions in head-up tilt duration. These results indicate that prolonged BR (∼5 wk) unlike short-term BR (24 h) attenuates the vestibulosympathetic reflex and possibly contributes to orthostatic intolerance following BR in humans. These results suggest a novel mechanism in the development of orthostatic intolerance in humans.
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Affiliation(s)
- Damian J Dyckman
- Penn State Heart and Vascular Institute, Department of Cellular and Molecular Physiology, General Clinical Research Center, Pennsylvania State University College of Medicine, Hershey, 17033-2390, USA
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Thijssen DHJ, Green DJ, Hopman MTE. Blood vessel remodeling and physical inactivity in humans. J Appl Physiol (1985) 2011; 111:1836-45. [PMID: 21737819 DOI: 10.1152/japplphysiol.00394.2011] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Physical inactivity is associated with an increase in cardiovascular risk that cannot be fully explained by traditional or novel risk factors. Inactivity is also associated with changes in hemodynamic stimuli, which exert direct effects on the vasculature leading to remodeling and a proatherogenic phenotype. In this review, we synthesize and summarize in vivo evidence relating to the impact of local and systemic models of physical inactivity on conduit arteries, resistance vessels, and the microcirculation in humans. Taken together, the literature suggests that a rapid inward structural remodeling of vessels occurs in response to physical inactivity. The magnitude of this response is dependent on the "dose" of inactivity. Moreover, changes in vascular function are found at resistance and microvessel levels in humans. In conduit arteries, a strong interaction between vascular function and structure is present, which results in conflicting data regarding the impact of inactivity on conduit artery function. While much of the cardioprotective effect of exercise is related to the nitric oxide pathway, deconditioning may primarily be associated with activation of vasoconstrictor pathways. The effects of deconditioning on the vasculature are therefore not simply the opposite of those in response to exercise training. Given the importance of sedentary behavior, future studies should provide further insight into the impact of inactivity on the vasculature and other (novel) markers of vascular health. Moreover, studies should examine the role of (hemodynamic) stimuli that underlie the characteristic vascular adaptations during deconditioning. Our review concludes with some suggestions for future research directions.
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Affiliation(s)
- Dick H J Thijssen
- Research Institute for Sport and Exercise Science, Liverpool John Moores University, Liverpool, United Kingdom.
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Artificial gravity with ergometric exercise as a countermeasure against cardiovascular deconditioning during 4 days of head-down bed rest in humans. Eur J Appl Physiol 2011; 111:2315-25. [DOI: 10.1007/s00421-011-1866-7] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2010] [Accepted: 02/03/2011] [Indexed: 10/18/2022]
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31
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Thijssen DHJ, Maiorana AJ, O’Driscoll G, Cable NT, Hopman MTE, Green DJ. Impact of inactivity and exercise on the vasculature in humans. Eur J Appl Physiol 2010; 108:845-75. [PMID: 19943061 PMCID: PMC2829129 DOI: 10.1007/s00421-009-1260-x] [Citation(s) in RCA: 209] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/17/2009] [Indexed: 12/12/2022]
Abstract
The effects of inactivity and exercise training on established and novel cardiovascular risk factors are relatively modest and do not account for the impact of inactivity and exercise on vascular risk. We examine evidence that inactivity and exercise have direct effects on both vasculature function and structure in humans. Physical deconditioning is associated with enhanced vasoconstrictor tone and has profound and rapid effects on arterial remodelling in both large and smaller arteries. Evidence for an effect of deconditioning on vasodilator function is less consistent. Studies of the impact of exercise training suggest that both functional and structural remodelling adaptations occur and that the magnitude and time-course of these changes depends upon training duration and intensity and the vessel beds involved. Inactivity and exercise have direct "vascular deconditioning and conditioning" effects which likely modify cardiovascular risk.
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Affiliation(s)
- Dick H. J. Thijssen
- Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Henry Cotton Campus, 15–21 Webster Street, Liverpool, L3 2ET UK
- Department of Physiology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands
| | - Andrew J. Maiorana
- Advanced Heart Failure and Cardiac Transplant Service, Royal Perth Hospital, Perth, Australia
- School of Physiotherapy, Curtin University of Technology, Perth, Australia
| | - Gerry O’Driscoll
- Advanced Heart Failure and Cardiac Transplant Service, Royal Perth Hospital, Perth, Australia
- School of Medicine, University of Notre Dame, Fremantle, Australia
| | - Nigel T. Cable
- Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Henry Cotton Campus, 15–21 Webster Street, Liverpool, L3 2ET UK
| | - Maria T. E. Hopman
- Department of Physiology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands
| | - Daniel J. Green
- Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Henry Cotton Campus, 15–21 Webster Street, Liverpool, L3 2ET UK
- School of Sport Science, Exercise and Health, The University of Western Australia, Perth, Australia
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32
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Eckberg DL, Halliwill JR, Beightol LA, Brown TE, Taylor JA, Goble R. Human vagal baroreflex mechanisms in space. J Physiol 2010; 588:1129-38. [PMID: 20156846 DOI: 10.1113/jphysiol.2009.186650] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Although astronauts' cardiovascular function is normal while they are in space, many have altered haemodynamic responses to standing after they return to Earth, including inordinate tachycardia, orthostatic hypotension, and uncommonly, syncope. Simulated microgravity impairs vagal baroreceptor-cardiac reflex function and causes orthostatic hypotension. Actual microgravity, however, has been shown to either increase, or not change vagal baroreflex gain. In this study, we tested the null hypothesis that spaceflight does not impair human baroreflex mechanisms. We studied 11 American and two German astronauts before, during (flight days 2-8), and after two, 9- and 10-day space shuttle missions, with graded neck pressure and suction, to elicit sigmoid, vagally mediated carotid baroreflex R-R interval responses. Baseline systolic pressures tended to be higher in space than on Earth (P = 0.015, repeated measures analysis of variance), and baseline R-R intervals tended to be lower (P = 0.049). Baroreceptor-cardiac reflex relations were displaced downward on the R-R interval axis in space. The average range of R-R interval responses to neck pressure changes declined from preflight levels by 37% on flight day 8 (P = 0.051), maximum R-R intervals declined by 14% (P = 0.003), and vagal baroreflex gain by 9% (P = 0.009). These measures returned to preflight levels by 7-10 days after astronauts returned to Earth. This study documents significant increases of arterial pressure and impairment of vagal baroreflex function in space. These results and results published earlier indicate that microgravity exposure augments sympathetic, and diminishes vagal cardiovascular influences.
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Affiliation(s)
- Dwain L Eckberg
- Department of Medicine, Hunter Holmes McGuire Department of Veterans Affairs Medical Center and Medical College of Virginia at Virginia Commonwealth University, Richmond, VA, USA.
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A definition of normovolaemia and consequences for cardiovascular control during orthostatic and environmental stress. Eur J Appl Physiol 2010; 109:141-57. [PMID: 20052592 PMCID: PMC2861179 DOI: 10.1007/s00421-009-1346-5] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/22/2009] [Indexed: 11/20/2022]
Abstract
The Frank–Starling mechanism describes the relationship between stroke volume and preload to the heart, or the volume of blood that is available to the heart—the central blood volume. Understanding the role of the central blood volume for cardiovascular control has been complicated by the fact that a given central blood volume may be associated with markedly different central vascular pressures. The central blood volume varies with posture and, consequently, stroke volume and cardiac output (\documentclass[12pt]{minimal}
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\begin{document}$$ \dot{Q} $$\end{document}) are affected, but with the increased central blood volume during head-down tilt, stroke volume and \documentclass[12pt]{minimal}
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\begin{document}$$ \dot{Q} $$\end{document} do not increase further indicating that in the supine resting position the heart operates on the plateau of the Frank–Starling curve which, therefore, may be taken as a functional definition of normovolaemia. Since the capacity of the vascular system surpasses the blood volume, orthostatic and environmental stress including bed rest/microgravity, exercise and training, thermal loading, illness, and trauma/haemorrhage is likely to restrict venous return and \documentclass[12pt]{minimal}
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\begin{document}$$ \dot{Q} $$\end{document}. Consequently the cardiovascular responses are determined primarily by their effect on the central blood volume. Thus during environmental stress, flow redistribution becomes dependent on sympathetic activation affecting not only skin and splanchnic blood flow, but also flow to skeletal muscles and the brain. This review addresses the hypothesis that deviations from normovolaemia significantly influence these cardiovascular responses.
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Fu Q, Shibata S, Hastings JL, Prasad A, Palmer MD, Levine BD. Evidence for unloading arterial baroreceptors during low levels of lower body negative pressure in humans. Am J Physiol Heart Circ Physiol 2008; 296:H480-8. [PMID: 19074678 DOI: 10.1152/ajpheart.00184.2008] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Low levels (i.e., </=20 mmHg) of lower body negative pressure (LBNP) have been utilized to unload "selectively" cardiopulmonary baroreceptors in humans, since steady-state mean arterial pressure and heart rate (HR) have been found unchanged at such levels. However, transient reductions in blood pressure (BP), followed by reflex compensation, may occur without detection, which could unload arterial baroreceptors. The purposes of this study were to test the hypothesis that the arterial baroreflex is engaged even during low levels of LBNP and to determine the time course of changes in hemodynamics. Fourteen healthy individuals (age range 20-54 yr) were studied. BP (Portapres and Suntech), HR (ECG), pulmonary capillary wedge pressure (PCWP) or pulmonary artery diastolic pressure (PDP) and right atrial pressure (RAP) (Swan-Ganz catheter) and hemodynamics (Modelflow) were recorded continuously at baseline and -15- and -30-mmHg LBNP for 6 min each. Application of -15-mmHg LBNP resulted in rapid and sustained falls in RAP and PCWP or PDP, progressive decreases in cardiac output and stroke volume, followed subsequently by transient reductions in both systolic and diastolic BP, which were then restored through the arterial baroreflex feedback mechanism after approximately 15 heartbeats. Additional studies were performed in five subjects using even lower levels of LBNP, and this transient reduction in BP was observed in three at -5- and in all at -10-mmHg LBNP. The delay for left ventricular stroke volume to fall at -15-mmHg LBNP was about 10 cardiac cycles. An increase in systemic vascular resistance was detectable after 20 heartbeats during -15-mmHg LBNP. Steady-state BP and HR remained unchanged during mild LBNP. However, BP decreased, while HR increased, at -30-mmHg LBNP. These results suggest that arterial baroreceptors are consistently unloaded during low levels (i.e., -10 and -15 mmHg) of LBNP in humans. Thus "selective" unloading of cardiopulmonary baroreceptors cannot be presumed to occur during these levels of mild LBNP.
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Affiliation(s)
- Qi Fu
- Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, Dallas, Texas, USA
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35
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Capelli C, Antonutto G, Cautero M, Tam E, Ferretti G. Metabolic and cardiovascular responses during sub-maximal exercise in humans after 14 days of head-down tilt bed rest and inactivity. Eur J Appl Physiol 2008; 104:909-18. [DOI: 10.1007/s00421-008-0848-x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/25/2008] [Indexed: 11/28/2022]
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Fischer D, Arbeille P, Shoemaker JK, O'Leary DD, Hughson RL. Altered hormonal regulation and blood flow distribution with cardiovascular deconditioning after short-duration head down bed rest. J Appl Physiol (1985) 2007; 103:2018-25. [PMID: 17872408 DOI: 10.1152/japplphysiol.00121.2007] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
This study tested the hypothesis that cardiovascular and hormonal responses to lower body negative pressure (LBNP) would be altered by 4-h head down bed rest (HDBR) in 11 healthy young men. In post-HDBR testing, three subjects failed to finish the protocol due to presyncopal symptoms, heart rate was increased during LBNP compared with pre-HDBR, mean arterial blood pressure was elevated at 0, −10, and −20 mmHg and reduced at −40 mmHg, central venous pressure (CVP) and cardiac stroke volume were reduced at all levels of LBNP. Plasma concentrations of renin, angiotensin II, and aldosterone were significantly lower after HDBR. Renin and angiotensin II increased in response to LBNP only post-HDBR. There was no effect of HDBR or LBNP on norepinephrine while epinephrine tended to increase at −40 mmHg post-HDBR ( P = 0.07). Total blood volume was not significantly reduced. Splanchnic blood flow taken from ultrasound measurement of the portal vein was higher at each level of LBNP post-compared with pre-HDBR. The gain of the cardiopulmonary baroreflex relating changes in total peripheral resistance to CVP was increased after HDBR, but splanchnic vascular resistance was actually reduced. These results are consistent with our hypothesis and suggest that cardiovascular instability following only 4-h HDBR might be related to altered hormonal and/or neural control of regional vascular resistance. Impaired ability to distribute blood away from the splanchnic region was associated with reduced stroke volume, elevated heart rate, and the inability to protect mean arterial pressure.
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Affiliation(s)
- D Fischer
- Faculty of Applied Health Sciences, University of Waterloo, Waterloo, ON, Canada
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Pavy-Le Traon A, Heer M, Narici MV, Rittweger J, Vernikos J. From space to Earth: advances in human physiology from 20 years of bed rest studies (1986-2006). Eur J Appl Physiol 2007; 101:143-94. [PMID: 17661073 DOI: 10.1007/s00421-007-0474-z] [Citation(s) in RCA: 375] [Impact Index Per Article: 22.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/13/2007] [Indexed: 01/11/2023]
Abstract
Bed rest studies of the past 20 years are reviewed. Head-down bed rest (HDBR) has proved its usefulness as a reliable simulation model for the most physiological effects of spaceflight. As well as continuing to search for better understanding of the physiological changes induced, these studies focused mostly on identifying effective countermeasures with encouraging but limited success. HDBR is characterised by immobilization, inactivity, confinement and elimination of Gz gravitational stimuli, such as posture change and direction, which affect body sensors and responses. These induce upward fluid shift, unloading the body's upright weight, absence of work against gravity, reduced energy requirements and reduction in overall sensory stimulation. The upward fluid shift by acting on central volume receptors induces a 10-15% reduction in plasma volume which leads to a now well-documented set of cardiovascular changes including changes in cardiac performance and baroreflex sensitivity that are identical to those in space. Calcium excretion is increased from the beginning of bed rest leading to a sustained negative calcium balance. Calcium absorption is reduced. Body weight, muscle mass, muscle strength is reduced, as is the resistance of muscle to insulin. Bone density, stiffness of bones of the lower limbs and spinal cord and bone architecture are altered. Circadian rhythms may shift and are dampened. Ways to improve the process of evaluating countermeasures--exercise (aerobic, resistive, vibration), nutritional and pharmacological--are proposed. Artificial gravity requires systematic evaluation. This review points to clinical applications of BR research revealing the crucial role of gravity to health.
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Affiliation(s)
- A Pavy-Le Traon
- Service D'explorations Fonctionnelles Respiratoires Et d'analyses Physiologiques, Hopital La Cavale Blanche, University Hospital of Brest, 29609, Brest Cedex, France.
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Abstract
Body fluid regulation is affected by gravity. The primary mechanisms of the etiology of hypovolemia found in simulation studies on earth and after space flight are different. The increased diuresis after increase of central blood volume postulated by Henry Gauer could not be found. Based on recent findings, new hypotheses about fluid volume regulation during space flight have emerged. The reduced blood volume in space is the result of 1) a negative balance of decreased fluid intake and smaller reduction of urine output; 2) fast fluid shifts from the intravascular to interstitial space as the result of lower transmural pressure after reduced compression of all tissue by gravitational forces especially of the thorax cage; and 3) fluid shifts from intravascular to muscle interstitial space because of less muscle tone required to maintain body posture. Additionally, loss of erythrocytes reduces blood volume. The attenuated diuresis during space flight can be explained by increased retention after stress-mediated sympathetic activation during initial phase of space flight, stimulation caused by reduced red cell mass, and activation after fast blood volume contraction. Additionally, the relation between plasma osmolarity and vasopressin release might be disturbed in microgravity.
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Affiliation(s)
- André Diedrich
- Center for Space Medicine and Physiology, Vanderbilt University School of Medicine, Division of Clinical Pharmacology, Department of Medicine, Autonomic Dysfunction Center, Nashville, Tennessee 37232-2195, USA.
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Jarvis SS, Levine BD, Prisk GK, Shykoff BE, Elliott AR, Rosow E, Blomqvist CG, Pawelczyk JA. Simultaneous determination of the accuracy and precision of closed-circuit cardiac output rebreathing techniques. J Appl Physiol (1985) 2007; 103:867-74. [PMID: 17556490 DOI: 10.1152/japplphysiol.01106.2006] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Foreign and soluble gas rebreathing methods are attractive for determining cardiac output (Q(c)) because they incur less risk than traditional invasive methods such as direct Fick and thermodilution. We compared simultaneously obtained Q(c) measurements during rest and exercise to assess the accuracy and precision of several rebreathing methods. Q(c) measurements were obtained during rest (supine and standing) and stationary cycling (submaximal and maximal) in 13 men and 1 woman (age: 24 +/- 7 yr; height: 178 +/- 5 cm; weight: 78 +/- 13 kg; Vo(2max): 45.1 +/- 9.4 ml.kg(-1).min(-1); mean +/- SD) using one-N(2)O, four-C(2)H(2), one-CO(2) (single-step) rebreathing technique, and two criterion methods (direct Fick and thermodilution). CO(2) rebreathing overestimated Q(c) compared with the criterion methods (supine: 8.1 +/- 2.0 vs. 6.4 +/- 1.6 and 7.2 +/- 1.2 l/min, respectively; maximal exercise: 27.0 +/- 6.0 vs. 24.0 +/- 3.9 and 23.3 +/- 3.8 l/min). C(2)H(2) and N(2)O rebreathing techniques tended to underestimate Q(c) (range: 6.6-7.3 l/min for supine rest; range: 16.0-19.1 l/min for maximal exercise). Bartlett's test indicated variance heterogeneity among the methods (P < 0.05), where CO(2) rebreathing consistently demonstrated larger variance. At rest, most means from the noninvasive techniques were +/-10% of direct Fick and thermodilution. During exercise, all methods fell outside the +/-10% range, except for CO(2) rebreathing. Thus the CO(2) rebreathing method was accurate over a wider range (rest through maximal exercise), but was less precise. We conclude that foreign gas rebreathing can provide reasonable Q(c) estimates with fewer repeat trials during resting conditions. During exercise, these methods remain precise but tend to underestimate Q(c). Single-step CO(2) rebreathing may be successfully employed over a wider range but with more measurements needed to overcome the larger variability.
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Affiliation(s)
- S S Jarvis
- Department of Kinesiology, Pennsylvania State University, University Park, Pennsylvania 16802, USA
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Iwasaki KI, Levine BD, Zhang R, Zuckerman JH, Pawelczyk JA, Diedrich A, Ertl AC, Cox JF, Cooke WH, Giller CA, Ray CA, Lane LD, Buckey JC, Baisch FJ, Eckberg DL, Robertson D, Biaggioni I, Blomqvist CG. Human cerebral autoregulation before, during and after spaceflight. J Physiol 2006; 579:799-810. [PMID: 17185344 PMCID: PMC2151354 DOI: 10.1113/jphysiol.2006.119636] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Exposure to microgravity alters the distribution of body fluids and the degree of distension of cranial blood vessels, and these changes in turn may provoke structural remodelling and altered cerebral autoregulation. Impaired cerebral autoregulation has been documented following weightlessness simulated by head-down bed rest in humans, and is proposed as a mechanism responsible for postspaceflight orthostatic intolerance. In this study, we tested the hypothesis that spaceflight impairs cerebral autoregulation. We studied six astronauts approximately 72 and 23 days before, after 1 and 2 weeks in space (n = 4), on landing day, and 1 day after the 16 day Neurolab space shuttle mission. Beat-by-beat changes of photoplethysmographic mean arterial pressure and transcranial Doppler middle cerebral artery blood flow velocity were measured during 5 min of spontaneous breathing, 30 mmHg lower body suction to simulate standing in space, and 10 min of 60 deg passive upright tilt on Earth. Dynamic cerebral autoregulation was quantified by analysis of the transfer function between spontaneous changes of mean arterial pressure and cerebral artery blood flow velocity, in the very low- (0.02-0.07 Hz), low- (0.07-0.20 Hz) and high-frequency (0.20-0.35 Hz) ranges. Resting middle cerebral artery blood flow velocity did not change significantly from preflight values during or after spaceflight. Reductions of cerebral blood flow velocity during lower body suction were significant before spaceflight (P < 0.05, repeated measures ANOVA), but not during or after spaceflight. Absolute and percentage reductions of mean (+/- s.e.m.) cerebral blood flow velocity after 10 min upright tilt were smaller after than before spaceflight (absolute, -4 +/- 3 cm s(-1) after versus -14 +/- 3 cm s(-1) before, P = 0.001; and percentage, -8.0 +/- 4.8% after versus -24.8 +/- 4.4% before, P < 0.05), consistent with improved rather than impaired cerebral blood flow regulation. Low-frequency gain decreased significantly (P < 0.05) by 26, 23 and 27% after 1 and 2 weeks in space and on landing day, respectively, compared with preflight values, which is also consistent with improved autoregulation. We conclude that human cerebral autoregulation is preserved, and possibly even improved, by short-duration spaceflight.
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Affiliation(s)
- Ken-ichi Iwasaki
- Institute for Exercise and Environmental Medicine, 7232 Greenville Avenue, Suite 435, Dallas, TX 75231, USA
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Parker BA, Smithmyer SL, Jarvis SS, Ridout SJ, Pawelczyk JA, Proctor DN. Evidence for reduced sympatholysis in leg resistance vasculature of healthy older women. Am J Physiol Heart Circ Physiol 2006; 292:H1148-56. [PMID: 17071730 DOI: 10.1152/ajpheart.00729.2006] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Inhibition of a sympathetic stimulus (i.e., sympatholysis) during forearm exercise is reduced with age in women. This age-related alteration has not been characterized in the lower extremity vasculature of women, and the potential for blunting of the conduit artery dilatory response to a sudden increase in shear stress [flow-mediated dilation (FMD)] has not been examined in older adults of either sex. In the present study, we assessed popliteal artery diameter and velocity (Doppler ultrasound) in 16 young (23 +/- 1 yr) and 14 older (69 +/- 1 yr) women after 5 min of distal calf occlusion (FMD), 3 min of hand immersion in ice water [cold pressor test (CPT)], and 5 min of distal calf occlusion combined with hand immersion in ice water (FMD+CPT). Peak popliteal conductance after 5-min ischemia was not significantly different in young vs. older women. During the combined stimulus (FMD+CPT), the magnitude of vasoconstriction in the calf (reduction in peak popliteal artery conductance) was similar (5-8%), despite reduced resting adrenergic sensitivity to CPT [young (Y): -27.3 +/- 3.8%; older (O): -15.8 +/- 2.2%; P < 0.05] and blunted muscle sympathetic nerve activity responses to CPT (Y: 12.7 +/- 3.6 bursts/min; O: 7.8 +/- 2.5 bursts/min; P < 0.05) in older women. Popliteal FMD, normalized to the shear stimulus, was attenuated by 60-70% in older women. Peak popliteal diameter, measured during the combined stimulus (FMD+CPT), was blunted in young but not in older women (Y FMD: 5.5 +/- 0.1 mm; Y FMD+CPT: 5.4 +/- 0.1 mm; P = 0.03; O FMD: 5.8 +/- 0.2 mm; O FMD+CPT: 5.8 +/- 0.2 mm). These results confirm previous findings of diminished reactivity in the conduit arteries of older humans and provide the first evidence of reduced sympatholysis in the leg resistance vasculature of older women.
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Affiliation(s)
- Beth A Parker
- Department of Kinesiology, Pennsylvania State University, 105 Noll Laboratory, University Park, PA 16802-6900, USA
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Mueller PJ, Sullivan MJ, Grindstaff RR, Cunningham JT, Hasser EM. Regulation of plasma vasopressin and renin activity in conscious hindlimb-unloaded rats. Am J Physiol Regul Integr Comp Physiol 2006; 291:R46-52. [PMID: 16469838 DOI: 10.1152/ajpregu.00622.2005] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cardiovascular deconditioning occurs in astronauts after spaceflight or in individuals subjected to bed rest. It is characterized by an increased incidence of orthostatic intolerance. The mechanisms responsible for orthostatic intolerance are likely multifactorial and may include hypovolemia, autonomic dysfunction, and vascular and cardiac alterations. The arterial baroreflex is an important compensatory mechanism in the response to an orthostatic stress. In a previous study, we demonstrated that arterial baroreflex mediated sympathoexcitation was blunted in hindlimb-unloaded (HU) rats, a model of cardiovascular deconditioning. The arterial baroreflex also contributes to the regulation of vasoactive hormones including vasopressin and angiotensin II. In the present study, we tested the hypothesis that the neurohumoral response to hypotension is also attenuated in rats after 14 days of hindlimb unloading. To test this hypothesis, the vasodilator diazoxide (15 or 25 mg/kg) or saline (0.9%) was administered to produce hypotension or control conditions, respectively, in conscious HU and control rats. Plasma samples were collected and assayed for vasopressin and plasma renin activity (PRA). Diazoxide (25 mg/kg) produced significant increases in vasopressin and PRA compared with saline controls. HU rats exhibited significantly higher levels of vasopressin at rest and the increase in vasopressin levels during hypotension was enhanced by hindlimb unloading. Neither resting nor hypotension-induced PRA was altered by hindlimb unloading. These data suggest that although baroreflex-mediated sympathoexcitation is blunted by hindlimb unloading, hypotension-induced vasopressin release is enhanced and hypotension-induced PRA is unaffected. Increased circulating vasopressin may serve to compensate for blunted baroreflex regulation of sympathetic nervous activity produced by hindlimb unloading or may actually contribute to it.
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Affiliation(s)
- Patrick J Mueller
- Department of Biomedical Sciences, University of Missouri-Columbia, Columbia, Missouri 65211-3300, USA.
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Farquhar WB, Wenner MM, Delaney EP, Prettyman AV, Stillabower ME. Sympathetic neural responses to increased osmolality in humans. Am J Physiol Heart Circ Physiol 2006; 291:H2181-6. [PMID: 16766644 DOI: 10.1152/ajpheart.00191.2006] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The purpose of this study was to examine the relationship between osmolality and efferent sympathetic outflow in humans. We hypothesized that increased plasma osmolality would be associated with increases in directly measured sympathetic outflow. Muscle sympathetic outflow was successfully recorded in eight healthy subjects during a 60-min intravenous hypertonic saline infusion (HSI; 3% NaCl) on one day and during a 60-min intravenous isotonic saline (ISO) infusion (0.9% NaCl) on a different day. The HSI provides an osmotic and volume stimulus, whereas the ISO infusion provides a volume-only stimulus. Muscle sympathetic nerve activity was quantified using the technique of peroneal microneurography. Plasma osmolality increased during the HSI but not during the ISO infusion (ANOVA, P < 0.05). Sympathetic outflow differed between the trials (ANOVA, P < 0.05); during the HSI burst, frequency initially increased from 14.6 +/- 2.5 to 18.1 +/- 1.9 bursts/min; during the ISO infusion, burst frequency initially declined from 14.7 +/- 2.5 to 12.0 +/- 2.1 bursts/min. Plasma norepinephrine concentration was greater at the end of the HSI compared with the end of the ISO infusion (HSI: 297 +/- 64 vs. ISO: 202 +/- 49 pg/ml; ANOVA, P < 0.05). We conclude that HSI-induced increases in plasma osmolality are associated with increases in sympathetic activity in humans.
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Affiliation(s)
- William B Farquhar
- Department of Health, Nutrition, and Excercise Science, University of Delaware, USA.
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de Groot PC, Bleeker MW, van Kuppevelt DH, van der Woude LH, Hopman MT. Rapid and extensive arterial adaptations after spinal cord injury. Arch Phys Med Rehabil 2006; 87:688-96. [PMID: 16635632 DOI: 10.1016/j.apmr.2006.01.022] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2005] [Accepted: 01/27/2006] [Indexed: 11/20/2022]
Abstract
OBJECTIVE To assess the time course of adaptations in leg vascular dimension and function within the first 6 weeks after a spinal cord injury (SCI). DESIGN Longitudinal study design. SETTING University medical center and rehabilitation clinic. PARTICIPANTS Six men were studied serially at 1, 2, 3, 4, and 6 weeks after SCI. INTERVENTIONS Not applicable. MAIN OUTCOME MEASURES Diameter, blood flow, and shear rate levels of the common femoral artery (CFA), superficial femoral artery (SFA), brachial artery, and carotid artery were measured with echo Doppler ultrasound (diameter, blood flow, shear rate). Endothelial function in the SFA was measured with flow-mediated dilation (FMD). In addition, leg volume and blood pressure measurements were performed. RESULTS Femoral artery diameter (CFA, 25%; SFA, 16%; P<.01) and leg volume (22%, P<.01) decreased simultaneously, and these reductions were largely accomplished within 3 weeks postinjury. Significant increases were observed for basal shear rate levels (64% increase at week 3; 117% increase at week 6; P<.01), absolute FMD responses (8% increase at week 3, 23% increase at week 6; P<.05) and relative FMD responses (26% increase at week 3, 44% increase at week 6; P<.001). CONCLUSIONS Our findings show a rapid onset of adaptations in arterial dimension and function to extreme inactivity in humans. Vascular adaptations include extensive reductions in femoral diameter and leg volume, as well as increased basal shear rate levels and FMD responses, which all appear to be largely accomplished within 3 weeks after an SCI.
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Affiliation(s)
- Patricia C de Groot
- Department of Physiology, Radboud University Nijmegen Medical Centre, Nijmegen, the Netherlands
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Pancheva MV, Panchev VS, Suvandjieva AV. Lower body negative pressure vs. lower body positive pressure to prevent cardiac atrophy after bed rest and spaceflight. What caused the controversy? J Appl Physiol (1985) 2006; 100:1090; author reply 1091-2. [PMID: 16467397 DOI: 10.1152/japplphysiol.00950.2005] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Cardiac muscle adapts well to changes in loading conditions. For example, left ventricular (LV) hypertrophy may be induced physiologically (via exercise training) or pathologically (via hypertension or valvular heart disease). If hypertension is treated, LV hypertrophy regresses, suggesting a sensitivity to LV work. However, whether physical inactivity in nonathletic populations causes adaptive changes in LV mass or even frank atrophy is not clear. We exposed previously sedentary men to 6 ( n = 5) and 12 ( n = 3) wk of horizontal bed rest. LV and right ventricular (RV) mass and end-diastolic volume were measured using cine magnetic resonance imaging (MRI) at 2, 6, and 12 wk of bed rest; five healthy men were also studied before and after at least 6 wk of routine daily activities as controls. In addition, four astronauts were exposed to the complete elimination of hydrostatic gradients during a spaceflight of 10 days. During bed rest, LV mass decreased by 8.0 ± 2.2% ( P = 0.005) after 6 wk with an additional atrophy of 7.6 ± 2.3% in the subjects who remained in bed for 12 wk; there was no change in LV mass for the control subjects (153.0 ± 12.2 vs. 153.4 ± 12.1 g, P = 0.81). Mean wall thickness decreased (4 ± 2.5%, P = 0.01) after 6 wk of bed rest associated with the decrease in LV mass, suggesting a physiological remodeling with respect to altered load. LV end-diastolic volume decreased by 14 ± 1.7% ( P = 0.002) after 2 wk of bed rest and changed minimally thereafter. After 6 wk of bed rest, RV free wall mass decreased by 10 ± 2.7% ( P = 0.06) and RV end-diastolic volume by 16 ± 7.9% ( P = 0.06). After spaceflight, LV mass decreased by 12 ± 6.9% ( P = 0.07). In conclusion, cardiac atrophy occurs during prolonged (6 wk) horizontal bed rest and may also occur after short-term spaceflight. We suggest that cardiac atrophy is due to a physiological adaptation to reduced myocardial load and work in real or simulated microgravity and demonstrates the plasticity of cardiac muscle under different loading conditions.
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46
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Hesse C, Siedler H, Luntz SP, Arendt BM, Goerlich R, Fricker R, Heer M, Haefeli WE. Modulation of endothelial and smooth muscle function by bed rest and hypoenergetic, low-fat nutrition. J Appl Physiol (1985) 2005; 99:2196-203. [PMID: 16099888 DOI: 10.1152/japplphysiol.00888.2005] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Prolonged microgravity alters the regulation of the peripheral vasculature. The influence of reduced food intake, as often observed in astronauts, on vascular function is unclear. In a randomized, four-phase, crossover study, the effect of simulated microgravity (13 days of bed rest), energetic restriction (-25%, fat reduced), and their combination on endothelium-dependent and -independent vasodilation was compared with ambulatory control conditions. Using venous occlusion plethysmography, cumulative intra-arterial dose-response curves to endothelium-dependent (acetylcholine) and -independent (sodium nitroprusside) vasodilators were constructed in 10 healthy male volunteers before and on day 13 of each of the four intervention periods. Bed rest combined with normoenergetic nutrition impaired the dose-response to acetylcholine (ANOVA, P = 0.004) but not to sodium nitroprusside, whereas hypoenergetic diet under ambulatory conditions improved responses to acetylcholine (P = 0.044) and sodium nitroprusside (P < 0.001). When bed rest was combined with hypoenergetic diet, acetylcholine responses did not change. Similarly, under control conditions, no change was observed. Individual changes in the total cholesterol-to-HDL ratio were correlated with changes in endothelial and vascular smooth muscle relaxation. In conclusion, short-term bed rest impairs endothelium-dependent arterial relaxation in humans. A hypoenergetic, low-fat diet modulates serum lipids, improves endothelium-dependent and -independent relaxation, and may antagonize the unfavorable effects of simulated microgravity on endothelial function.
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Affiliation(s)
- Christiane Hesse
- Dept. of Internal Medicine VI, Clinical Pharmacology and Pharmacoepidemiology, University of Heidelberg, Germany
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Arbeille PP, Besnard SS, Kerbeci PP, Mohty DM. Portal vein cross-sectional area and flow and orthostatic tolerance: a 90-day bed rest study. J Appl Physiol (1985) 2005; 99:1853-7. [PMID: 16227458 DOI: 10.1152/japplphysiol.00331.2005] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The objective of this study was to evaluate the changes in the portal vein cross-sectional area (PV CSA) and flow during a stand test associated with orthostatic intolerance. Eighteen subjects underwent a 90-day head-down tilt (HDT) bed rest at 6°: 9 controls (Con) and 9 with flywheel exercise countermeasures (CM). At post-HDT, nine subjects (5 CM, 4 Con) were tolerant, and nine were intolerant. The PV CSA was measured by echography. We found that at HDT day 85, the PV CSA at rest had increased less in the CM subjects than in the Con (+12 vs. +27% from pre-HDT supine; P < 0.05), whereas it increased similarly in tolerant and intolerant subjects (23 and 16%, respectively). Two days after the HDT, there was a decrease in the PV CSA supine compared with the pre-HDT PV CSA supine that was similar for all groups (Con: −11%, CM: −21%; tolerant: −10%, intolerant: −16%; P < 0.05). The PV CSA decreased significantly less from supine to standing in the Con than in the CM group (−2 vs. −10% compared with the pre-HDT stand test; P < 0.05). The PV CSA also decreased significantly from supine to standing compared with the pre-HDT stand test in the tolerant group but not in the intolerant group (−20 vs. +2%; P < 0.05). From these findings, we conclude the following. 1) Because the portal vein is the only output from the splanchnic vascular area, we suggest that the lower reduction in the PV CSA and flow associated with orthostatic intolerance was related to a lower splanchnic arterial vasoconstriction. 2) The flywheel exercise CM helped to reduce the distention of the splanchnic network at rest and to maintain partially the splanchnic vasoconstriction, but it did not reduce the orthostatic intolerance.
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Affiliation(s)
- Philippe P Arbeille
- Unité Médecine et Physiologie Spatiale, Departement de Médecine Nucléaire et Ultrasons, Centres Hospitaliers Universitaires Trousseau, 37044 Tours, France.
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Foley CM, Mueller PJ, Hasser EM, Heesch CM. Hindlimb unloading and female gender attenuate baroreflex-mediated sympathoexcitation. Am J Physiol Regul Integr Comp Physiol 2005; 289:R1440-7. [PMID: 16051718 DOI: 10.1152/ajpregu.00356.2005] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Exposure to a period of microgravity or bed rest produces several physiological adaptations. These changes, which include an increased incidence of orthostatic intolerance, have an impact when people return to a 1G environment or resume an upright posture. Compared with males, females appear more susceptible to orthostatic intolerance after exposure to real or simulated microgravity. Decreased arterial baroreflex compensation may contribute to orthostatic intolerance. We hypothesized that female rats would exhibit a greater reduction in arterial baroreflex function after hindlimb unloading (HU) compared with male rats. Mean arterial pressure (MAP), heart rate (HR), and renal sympathetic nerve activity (RSNA) were recorded in conscious animals after 13–15 days of HU. Baseline HR was elevated in female rats, and HU increased HR in both genders. Consistent with previous results in males, baroreflex-mediated activation of RSNA was blunted by HU in both genders. Maximum RSNA in response to decreases in MAP was reduced by HU (male control 513 ± 42%, n = 11; male HU 346 ± 38%, n = 13; female control 359 ± 44%, n = 10; female HU 260 ± 43%, n = 10). Maximum baroreflex increase in RSNA was lower in females compared with males in both control and HU rats. Both female gender and HU attenuated baroreflex-mediated increases in sympathetic activity. The combined effects of HU and gender resulted in reduced baroreflex sympathetic reserve in females compared with males and could contribute to the greater incidence of orthostatic intolerance in females after exposure to spaceflight or bed rest.
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Affiliation(s)
- C Michael Foley
- Department of Biomedical Sciences, Dalton Cardiovascular Research Center, University of Missouri-Columbia, 134 Research Park Drive, Columbia, Missouri 65211, USA.
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Christensen NJ, Heer M, Ivanova K, Norsk P. Sympathetic nervous activity decreases during head-down bed rest but not during microgravity. J Appl Physiol (1985) 2005; 99:1552-7. [PMID: 15961614 DOI: 10.1152/japplphysiol.00017.2005] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We tested the hypothesis that sympathoadrenal activity in humans is low during spaceflight and that this effect can be simulated by head-down bed rest (HDBR). Platelet norepinephrine and epinephrine were measured as indexes of long-term changes in sympathoadrenal activity. Ten normal healthy subjects were studied before and during HDBR of 2-wk duration, as well as during an ambulatory study period of a similar length. Platelet norepinephrine concentrations (half-life = 2 days) were studied in five cosmonauts, 2 wk before launch, within 12 h after landing after 11–12 days of flight, and at least 2 wk after return to Earth. Because of the long half-life of platelet norepinephrine, data obtained early after landing would still reflect the microgravity state. Platelet norepinephrine decreased markedly during HDBR ( P < 0.001), whereas there were no significant changes when subjects were ambulatory. Platelet epinephrine did not change during HDBR. During microgravity, platelet norepinephrine and epinephrine increased in four of the five cosmonauts. Platelet norepinephrine concentrations expressed in percentage of preflight and pre-HDBR values, respectively, were significantly different during microgravity compared with HDBR [153 ± 28% (mean ± SE) vs. 60 ± 6%, P < 0.004]. Corresponding values for platelet epinephrine were also significant (293 ± 85 vs. 90 ± 12%, P < 0.01). The mechanism of the platelet norepinephrine and epinephrine response during spaceflight flight is most likely related to the concomitant decrease in plasma volume. HDBR cannot be applied to simulate changes in sympathoadrenal activity during microgravity.
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Affiliation(s)
- Niels J Christensen
- Department of Endocrinology, Herlev University Hospital, University of Copenhagen, Denmark.
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Bleeker MWP, De Groot PCE, Rongen GA, Rittweger J, Felsenberg D, Smits P, Hopman MTE. Vascular adaptation to deconditioning and the effect of an exercise countermeasure: results of the Berlin Bed Rest study. J Appl Physiol (1985) 2005; 99:1293-300. [PMID: 15932956 DOI: 10.1152/japplphysiol.00118.2005] [Citation(s) in RCA: 107] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Deconditioning is a risk factor for cardiovascular disease. The physiology of vascular adaptation to deconditioning has not been elucidated. The purpose of the present study was to assess the effects of bed rest deconditioning on vascular dimension and function of leg conduit arteries. In addition, the effectiveness of resistive vibration exercise as a countermeasure for vascular deconditioning during bed rest was evaluated. Sixteen healthy men were randomly assigned to bed rest (BR-Ctrl) or to bed rest with resistive vibration exercise (BR-RVE). Before and after 25 and 52 days of strict horizontal bed rest, arterial diameter, blood flow, flow-mediated dilatation (FMD), and nitroglycerin-mediated dilatation were measured by echo Doppler ultrasound. In the BR-Ctrl group, the diameter of the common femoral artery decreased by 13 ± 3% after 25 and 17 ± 1% after 52 days of bed rest ( P < 0.001). In the BR-RVE group this decrease in diameter was significantly attenuated (5 ± 2% after 25 days and 6 ± 2% after 52 days, P < 0.01 vs. BR-Ctrl). Baseline blood flow did not change after bed rest in either group. After 52 days of bed rest, FMD and nitroglycerin-mediated dilatation of the superficial femoral artery were increased in both groups, possibly by increased nitric oxide sensitivity. In conclusion, bed rest deconditioning is accompanied by a reduction in the diameter of the conduit arteries and by an increased reactivity to nitric oxide. Resistive vibration exercise effectively attenuates the diameter decrease of leg conduit arteries after bed rest.
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Affiliation(s)
- Michiel W P Bleeker
- Department of Physiology, Radboud University Nijmegen Medical Centre, The Netherlands
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