Effects of Prolonged Head-Down Bed Rest on Cardiac and Vascular Baroreceptor Modulation and Orthostatic Tolerance in Healthy Individuals.
baroreflex sensitivity
bed rest
muscle sympathetic nerve activity
orthostatic intolerance
spectrum analysis
Journal
Frontiers in physiology
ISSN: 1664-042X
Titre abrégé: Front Physiol
Pays: Switzerland
ID NLM: 101549006
Informations de publication
Date de publication:
2019
2019
Historique:
received:
21
01
2019
accepted:
02
08
2019
entrez:
12
9
2019
pubmed:
12
9
2019
medline:
12
9
2019
Statut:
epublish
Résumé
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
Identifiants
pubmed: 31507438
doi: 10.3389/fphys.2019.01061
pmc: PMC6716544
doi:
Types de publication
Journal Article
Langues
eng
Pagination
1061Subventions
Organisme : NHLBI NIH HHS
ID : P01 HL056693
Pays : United States
Organisme : NHLBI NIH HHS
ID : R01 HL142583
Pays : United States
Organisme : NHLBI NIH HHS
ID : R56 HL142583
Pays : United States
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