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Related Experiment Videos

Simultaneous cerebrovascular and cardiovascular responses during presyncope

R L Bondar1, M S Kassam, F Stein

  • 1Centre for Advanced Technology Education, Ryerson Polytechnic University, Toronto, Ontario, Canada.

Stroke
|October 1, 1995
PubMed
Summary

During presyncope, cerebral blood flow decreases while blood pressure is maintained, indicating increased cerebral vascular tone. This suggests a downward shift in the cerebral autoregulation curve in healthy individuals.

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Area of Science:

  • Cardiovascular Physiology
  • Neuroscience
  • Cerebrovascular Regulation

Background:

  • Presyncope involves symptoms preceding syncope, with cerebral autoregulation plasticity unclear.
  • Systemic hemodynamic instability is implicated in syncope, but classic models don't fully explain observed cerebral responses.
  • Previous studies using lower body negative pressure (LBNP) showed falling mean flow velocities (MFVs) with stable mean arterial blood pressure (MABP).

Purpose of the Study:

  • To investigate the cerebrovascular and cardiovascular responses during presyncope induced by LBNP in healthy volunteers.
  • To evaluate the behavior of cerebral autoregulation under simulated central hypovolemia.
  • To clarify the role of cerebral vascular tone in the transition to presyncope.

Main Methods:

Keywords:
NASA Center JSCNASA Discipline CardiopulmonaryNon-NASA Center

Related Experiment Videos

  • Healthy volunteers (4 male, 5 female) were subjected to presyncopal LBNP.
  • Cerebrovascular and cardiovascular responses were monitored using continuous transcranial Doppler sonography for MFV.
  • Mean arterial blood pressure (MABP) and heart rate were continuously recorded.

    • Main Results:

    • At presyncope, MFV decreased by 27.3% ± 14% from baseline (P < .05).
    • MABP increased by 2.0% ± 27% above baseline.
    • Estimated cerebrovascular resistance increased, with MFV decreasing before MABP changes.

    Conclusions:

    • Increased cerebrovascular resistance, falling MFV, and stable MABP indicate heightened cerebral vascular tone and a downward shift in the cerebral autoregulation curve.
    • Cerebral vessels may exhibit differential sensitivity to sympathetic drive.
    • Further research on dynamic MABP changes during LBNP is needed to assess cerebral autoregulation plasticity.