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Related Experiment Videos

Dynamic cardiorespiratory interaction during head-up tilt-mediated presyncope.

S Krishnamurthy1, X Wang, D Bhakta

  • 1No. 2, Wenner-Gren Research Laboratory, Center for Biomedical Engineering, Univ. of Kentucky, Lexington, KY 40506-0070, USA.

American Journal of Physiology. Heart and Circulatory Physiology
|August 7, 2004
PubMed
Summary

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Altered cardiorespiratory interactions, specifically enhanced blood pressure influences on cerebral blood flow and reduced CO2 reactivity, may precede presyncope during head-up tilt (HUT). These changes in cerebral hemodynamics could contribute to unexplained syncope.

Area of Science:

  • Cardiovascular Physiology
  • Autonomic Nervous System Function
  • Cerebrovascular Regulation

Background:

  • Head-up tilt (HUT) is used to study autonomic responses and syncope.
  • Cerebral autoregulation maintains stable cerebral blood flow (CBF) despite blood pressure (BP) fluctuations.
  • The interaction between respiration, BP, and CBF during HUT is not fully understood.

Purpose of the Study:

  • To compare dynamic cardiorespiratory and cerebral hemodynamic interactions between presyncopal and non-presyncopal subjects during HUT.
  • To investigate alterations in the relationship between BP and CBF in individuals prone to presyncope.
  • To assess the role of end-tidal CO2 (ETco2) and its reactivity in presyncope.

Main Methods:

  • 28 healthy adults underwent 70-degree HUT.

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  • Measurements included airflow, CO2, cerebral blood flow velocity (CBF), ECG, and BP.
  • Coherency and transfer function analyses quantified BP-CBF interactions.
  • Relative CO2 reactivity was calculated.

    • Main Results:

    • Presyncopal subjects showed higher BP-CBF coherence and transfer function gains during HUT.
    • Presyncopal individuals exhibited reduced relative CO2 reactivity before symptom onset.
    • Lower ETco2 in presyncopal subjects correlated with reduced CO2 reactivity.

    Conclusions:

    • Enhanced dynamic interactions between systemic BP and CBF, alongside attenuated CO2-mediated cerebral vasodilation, may precede presyncope.
    • These cardiorespiratory and cerebrovascular alterations likely contribute to the development of syncope during HUT.
    • Findings suggest a potential mechanism for unexplained syncope involving impaired cerebral autoregulation.