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Effects of Prolonged Head-Down Bed Rest on Cardiac and Vascular Baroreceptor Modulation and Orthostatic Tolerance in Healthy Individuals.
Front Physiol 2019; 10:1061FP

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.

Authors+Show Affiliations

Humanitas Clinical and Research Center, Department of Internal Medicine, Istituto di Ricovero e Cura a Carattere Scientifico (IRCCS), Humanitas University, Rozzano, Italy.German Aerospace Center (DLR), Institute of Aerospace Medicine, Cologne, Germany.Humanitas Clinical and Research Center, Department of Internal Medicine, Istituto di Ricovero e Cura a Carattere Scientifico (IRCCS), Humanitas University, Rozzano, Italy.Humanitas Clinical and Research Center, Department of Internal Medicine, Istituto di Ricovero e Cura a Carattere Scientifico (IRCCS), Humanitas University, Rozzano, Italy.Department of Biomedical Sciences for Health, University of Milan, Milan, Italy.German Aerospace Center (DLR), Institute of Aerospace Medicine, Cologne, Germany.German Aerospace Center (DLR), Institute of Aerospace Medicine, Cologne, Germany.Autonomic Dysfunction Center, Clinical Research Center (CRC), Department of Medicine, Vanderbilt University, Nashville, TN, United States.German Aerospace Center (DLR), Institute of Aerospace Medicine, Cologne, Germany.Departamento de Kinesiología, Universidad Católica del Maule, Talca, Chile.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.Humanitas Clinical and Research Center, Department of Internal Medicine, Istituto di Ricovero e Cura a Carattere Scientifico (IRCCS), Humanitas University, Rozzano, Italy.

Pub Type(s)

Journal Article

Language

eng

PubMed ID

31507438

Citation

Barbic, Franca, et al. "Effects of Prolonged Head-Down Bed Rest On Cardiac and Vascular Baroreceptor Modulation and Orthostatic Tolerance in Healthy Individuals." Frontiers in Physiology, vol. 10, 2019, p. 1061.
Barbic F, Heusser K, Minonzio M, et al. Effects of Prolonged Head-Down Bed Rest on Cardiac and Vascular Baroreceptor Modulation and Orthostatic Tolerance in Healthy Individuals. Front Physiol. 2019;10:1061.
Barbic, F., Heusser, K., Minonzio, M., Shiffer, D., Cairo, B., Tank, J., ... 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, p. 1061. doi:10.3389/fphys.2019.01061.
Barbic F, et al. Effects of Prolonged Head-Down Bed Rest On Cardiac and Vascular Baroreceptor Modulation and Orthostatic Tolerance in Healthy Individuals. Front Physiol. 2019;10:1061. PubMed PMID: 31507438.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Effects of Prolonged Head-Down Bed Rest on Cardiac and Vascular Baroreceptor Modulation and Orthostatic Tolerance in Healthy Individuals. AU - Barbic,Franca, AU - Heusser,Karsten, AU - Minonzio,Maura, AU - Shiffer,Dana, AU - Cairo,Beatrice, AU - Tank,Jens, AU - Jordan,Jens, AU - Diedrich,André, AU - Gauger,Peter, AU - Zamuner,Roberto Antonio, AU - Porta,Alberto, AU - Furlan,Raffaello, Y1 - 2019/08/23/ PY - 2019/01/21/received PY - 2019/08/02/accepted PY - 2019/9/12/entrez PY - 2019/9/12/pubmed PY - 2019/9/12/medline KW - baroreflex sensitivity KW - bed rest KW - muscle sympathetic nerve activity KW - orthostatic intolerance KW - spectrum analysis SP - 1061 EP - 1061 JF - Frontiers in physiology JO - Front Physiol VL - 10 N2 - 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. SN - 1664-042X UR - https://www.unboundmedicine.com/medline/citation/31507438/Effects_of_Prolonged_Head-Down_Bed_Rest_on_Cardiac_and_Vascular_Baroreceptor_Modulation_and_Orthostatic_Tolerance_in_Healthy_Individuals L2 - https://doi.org/10.3389/fphys.2019.01061 DB - PRIME DP - Unbound Medicine ER -