Document Detail

Cerebral autoregulation is compromised during simulated fluctuations in gravitational stress.
MedLine Citation:
PMID:  14574578     Owner:  NLM     Status:  MEDLINE    
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 -40 mmHg and then to oscillating LBNP at the same pressures. The oscillatory LBNP was applied at 0.1 and 0.2 Hz. We made continuous recordings of RR-interval, blood pressure, cerebral blood flow velocity (CBFV), respiratory frequency and end-tidal CO(2). Oscillations in mean arterial pressure (MAP) and CBFV were assessed by autoregressive spectral analysis. Respiration was paced at 0.25 Hz to avoid interference from breathing. Steady-state LBNP at -40 mmHg significantly increased low-frequency (LF, 0.03-0.14 Hz) powers of MAP ( P<0.01) but not of CBFV. Oscillatory 0.1 Hz LBNP (0 to -40 mmHg) 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 0.2 Hz induced oscillations in MAP and CBFV at 0.2 Hz. Cross-spectral analysis showed that the transfer of LBNP-induced oscillations in MAP onto the CBFV was significantly greater at 0.2 Hz than at 0.1 Hz ( 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.
Clive M Brown; Matthias Dütsch; Susanne Ohring; Bernhard Neundörfer; Max J Hilz
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Publication Detail:
Type:  Clinical Trial; Journal Article     Date:  2003-10-22
Journal Detail:
Title:  European journal of applied physiology     Volume:  91     ISSN:  1439-6319     ISO Abbreviation:  Eur. J. Appl. Physiol.     Publication Date:  2004 Mar 
Date Detail:
Created Date:  2004-03-01     Completed Date:  2004-10-19     Revised Date:  2008-11-21    
Medline Journal Info:
Nlm Unique ID:  100954790     Medline TA:  Eur J Appl Physiol     Country:  Germany    
Other Details:
Languages:  eng     Pagination:  279-86     Citation Subset:  IM; S    
Autonomic Laboratory, Dept. of Neurology, University of Erlangen-Nuremberg, Germany.
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MeSH Terms
Adaptation, Physiological / physiology
Blood Flow Velocity / physiology
Blood Pressure / physiology
Brain / blood supply*,  physiology*
Cerebrovascular Circulation / physiology*
Heart Rate / physiology
Hemostasis / physiology*
Homeostasis / physiology*
Lower Body Negative Pressure / methods*
Stress, Physiological / physiopathology
Supine Position / physiology

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