• About
    • Login
    View Item 
    •   Institutional Repository Home
    • School of Engineering
    • Biomedical Engineering
    • Collaborative Research
    • View Item
    •   Institutional Repository Home
    • School of Engineering
    • Biomedical Engineering
    • Collaborative Research
    • View Item
    JavaScript is disabled for your browser. Some features of this site may not work without it.

    Browse

    All of Institutional RepositoryCommunities & CollectionsBy Issue DateAuthorsTitlesSubjectsDepartmentThis CollectionBy Issue DateAuthorsTitlesSubjectsDepartment

    My Account

    LoginRegister

    Effects of Prolonged Head-Down Bed Rest on Cardiac and Vascular Baroreceptor Modulation and Orthostatic Tolerance in Healthy Individuals

    Barbic, Franca
    Heusser, Karsten
    Minonzio, Maura
    Shiffer, Dana
    Cairo, Beatrice
    Tank, Jens
    Jordan, Jens
    Diedrich, Andre
    Gauger, Peter
    Zamuner, Roberto Antonio
    Porta, Alberto
    Furlan, Raffaello
    : http://hdl.handle.net/1803/10006
    : 2019-08-23

    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 degrees 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 degrees 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% x 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 (alpha index: 3.4 +/- 0.7 ms/mmHg; BRSSEQ 4.0 +/- 1.0) than before (alpha 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% x 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.
    Show full item record

    Files in this item

    Thumbnail
    Name:
    Effects of Prolonged Head-Down ...
    Size:
    317.3Kb
    Format:
    PDF
    View/Open

    This item appears in the following collection(s):

    • Collaborative Research

    Connect with Vanderbilt Libraries

    Your Vanderbilt

    • Alumni
    • Current Students
    • Faculty & Staff
    • International Students
    • Media
    • Parents & Family
    • Prospective Students
    • Researchers
    • Sports Fans
    • Visitors & Neighbors

    Support the Jean and Alexander Heard Libraries

    Support the Library...Give Now

    Gifts to the Libraries support the learning and research needs of the entire Vanderbilt community. Learn more about giving to the Libraries.

    Become a Friend of the Libraries

    Quick Links

    • Hours
    • About
    • Employment
    • Staff Directory
    • Accessibility Services
    • Contact
    • Vanderbilt Home
    • Privacy Policy