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Effects of prolonged head-down bed rest on cardiac and vascular baroreceptor modulation and orthostatic tolerance in healthy individuals

Barbic, F. and Heusser, K. and Minonzio, M. and Shiffer, D. and Cairo, B. and Tank, J. and Jordan, J. and Diedrich, A. and Gauger, P. and Zamuner, R. and Porta, A. and Furlan, R. (2019) Effects of prolonged head-down bed rest on cardiac and vascular baroreceptor modulation and orthostatic tolerance in healthy individuals. Frontiers in Physiology, 10 (1061). Frontiers Media S.A. DOI: 10.3389/fphys.2019.01061 ISSN 1664-042X

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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.

Item URL in elib:https://elib.dlr.de/129788/
Document Type:Article
Title:Effects of prolonged head-down bed rest on cardiac and vascular baroreceptor modulation and orthostatic tolerance in healthy individuals
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Barbic, F.Department of Internal Medicine, Humanitas Clinical and Research Center, Rozzano (MI), Humanitas University, Rozzano, ItalyUNSPECIFIED
Heusser, K.Institute of Aerospace Medicine, German Aerospace Center, Cologne, GermanyUNSPECIFIED
Minonzio, M.Department of Internal Medicine, Humanitas Clinical and Research Center, Rozzano (MI), Humanitas University, Rozzano, ItalyUNSPECIFIED
Shiffer, D.Department of Internal Medicine, Humanitas Clinical and Research Center, Rozzano (MI), Humanitas University, Rozzano, ItalyUNSPECIFIED
Cairo, B.Department of Biomedical Sciences for Health, University of Milan, ItalyUNSPECIFIED
Tank, J.Institute of Aerospace Medicine, German Aerospace Center (DLR), Cologne, Germany.UNSPECIFIED
Jordan, J.Institute of Aerospace Medicine, German Aerospace Center (DLR), Cologne, Germany.UNSPECIFIED
Diedrich, A.Division of Clinical Pharmacology, Department of Medicine, Autonomic Dysfunction Service, Vanderbilt University, Nashville, TNUNSPECIFIED
Gauger, P.German Aerospace Center (DLR), Institute of Aerospace Medicine, Space Physiology, Cologne, GermanyUNSPECIFIED
Zamuner, R.Departamento de Kinesiología, Universidad Católica del Maule, Talca, ChileUNSPECIFIED
Porta, A.Department of Biomedical Sciences for Health, University of Milan, Italy;Department of Cardiothoracic, Vascular Anesthesia and Intensive Care, IRCCS Policlinico di San Donato, San Donato Milanese, ItalyUNSPECIFIED
Furlan, R.Department of Internal Medicine, Humanitas Clinical and Research Center, Rozzano (MI), Humanitas University, Rozzano, ItalyUNSPECIFIED
Date:23 August 2019
Journal or Publication Title:Frontiers in Physiology
Refereed publication:Yes
Open Access:Yes
Gold Open Access:Yes
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:10
DOI :10.3389/fphys.2019.01061
Publisher:Frontiers Media S.A
ISSN:1664-042X
Status:Published
Keywords:baroreflex sensitivity; bed rest; muscle sympathetic nerve activity; orthostatic intolerance; spectrum analysis
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Research under Space Conditions
DLR - Research area:Raumfahrt
DLR - Program:R FR - Forschung unter Weltraumbedingungen
DLR - Research theme (Project):R - Vorhaben Systemphysiologie
Location: Köln-Porz
Institutes and Institutions:Institute of Aerospace Medicine
Institute of Aerospace Medicine > Cardiovascular Medicine in Aerospace
Institute of Aerospace Medicine > Leitungsbereich ME
Deposited By: Schrage, Larissa
Deposited On:23 Oct 2019 11:00
Last Modified:23 Oct 2019 11:00

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