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Cerebral autoregulation is compromised during simulated fluctuations in gravitational stress

Brown, Clive ; Dütsch, Matthias ; Öhring, Susanne ; Neundörfer, Bernhard ; Hilz, Max

In: European Journal of Applied Physiology, 2004, vol. 91, no. 2-3, p. 279-286

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    Title
    • Cerebral autoregulation is compromised during simulated fluctuations in gravitational stress
    Author
    • Brown, Clive. Autonomic Laboratory, Dept. of Neurology, University of Erlangen-Nuremberg, Germany
    • Dütsch, Matthias. Autonomic Laboratory, Dept. of Neurology, University of Erlangen-Nuremberg, Germany
    • Öhring, Susanne. Autonomic Laboratory, Dept. of Neurology, University of Erlangen-Nuremberg, Germany
    • Neundörfer, Bernhard. Autonomic Laboratory, Dept. of Neurology, University of Erlangen-Nuremberg, Germany
    • Hilz, Max. Autonomic Laboratory, Dept. of Neurology, University of Erlangen-Nuremberg, Germany
    Document Type
    • Postprint
    Language
    • English
    Published in
    • European Journal of Applied Physiology, 2004, vol. 91, no. 2-3, p. 279-286. Springer-Verlag
    Other Version
    OAI-PMH Identifier
    • oai:doc.rero.ch:313632
    Summary
    Gravity places considerable stress on the cardiovascular system but cerebral autoregulation usually protects the cerebral blood vessels from fluctuations in blood pressure. However, in conditions such as those encountered on board a high-performance aircraft, the gravitational stress is constantly changing and might compromise cerebral autoregulation. In this study we assessed the effect of oscillating orthostatic stress on cerebral autoregulation. Sixteen (eight male) healthy subjects [aged 27 (1)years] were exposed to steady-state lower body negative pressure (LBNP) at −15 and −40mmHg and then to oscillating LBNP at the same pressures. The oscillatory LBNP was applied at 0.1 and 0.2Hz. We made continuous recordings of RR-interval, blood pressure, cerebral blood flow velocity (CBFV), respiratory frequency and end-tidal CO2. Oscillations in mean arterial pressure (MAP) and CBFV were assessed by autoregressive spectral analysis. Respiration was paced at 0.25Hz to avoid interference from breathing. Steady-state LBNP at −40mmHg significantly increased low-frequency (LF, 0.03-0.14Hz) powers of MAP (P<0.01) but not of CBFV. Oscillatory 0.1Hz LBNP (0 to −40mmHg) significantly increased the LF power of MAP to a similar level as steady-state LBNP but also resulted in a significant increase in the LF power of CBFV (P<0.01). Oscillatory LBNP at 0.2Hz induced oscillations in MAP and CBFV at 0.2Hz. Cross-spectral analysis showed that the transfer of LBNP-induced oscillations in MAP onto the CBFV was significantly greater at 0.2Hz than at 0.1Hz (P<0.01). These results show that the ability of the cerebral vessels to modulate fluctuations in blood pressure is compromised during oscillatory compared with constant gravitational stress. Furthermore, this effect seems to be more pronounced at higher frequencies of oscillatory stress