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Decrease in cardiac output and muscle sympathetic activity during vasovagal syncope.

D L Jardine1, I C Melton, I G Crozier

  • 1Department of General Medicine, Christchurch Hospital, Christchurch, New Zealand. David.Jardine@cdhb.govt.nz

American Journal of Physiology. Heart and Circulatory Physiology
|April 18, 2002
PubMed
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Cardiac output (CO) significantly drops before vasovagal syncope, but mean blood pressure is more closely linked to sympathetic nerve activity and total peripheral resistance. A falling CO may precede hypotension in vasovagal reactions.

Area of Science:

  • Cardiovascular Physiology
  • Autonomic Nervous System
  • Clinical Medicine

Background:

  • Vasovagal syncope is a common condition characterized by a sudden drop in blood pressure and heart rate.
  • The precise role of cardiac output (CO) in the development of hypotension during vasovagal syncope remains unclear.
  • Understanding the interplay between cardiac output, blood pressure, and sympathetic activity is crucial for managing syncope.

Purpose of the Study:

  • To investigate the relationship between cardiac output (CO), mean blood pressure (MBP), and sympathetic nerve activity (MSNA) during head-up tilt in patients with recurrent syncope.
  • To determine whether a decline in CO precedes the hypotensive event in vasovagal syncope.

Main Methods:

  • Twenty-six patients with recurrent syncope underwent 60-degree head-up tilt testing.

Related Experiment Videos

  • Measurements included thermodilution cardiac output (CO), mean blood pressure (MBP), and leg muscle mean sympathetic nerve activity (MSNA), recorded every minute.
  • Patients were divided into those who tolerated tilt (TT) and those who developed syncope (TS).

    • Main Results:

    • In patients who developed syncope (TS), cardiac output (CO) showed a significant progressive decline starting minutes before the event.
    • In contrast, CO remained relatively stable after an initial drop in patients who tolerated tilt (TT).
    • Mean blood pressure (MBP) was more strongly correlated with total peripheral resistance and sympathetic nerve activity (MSNA) than with cardiac output (CO).

    Conclusions:

    • A progressive decline in cardiac output (CO) may contribute to the hypotension observed in vasovagal reactions.
    • While CO decreases before syncope, mean blood pressure regulation appears more dependent on sympathetic activity and vascular resistance.
    • These findings highlight the complex hemodynamic changes during vasovagal syncope and suggest CO as a potential predictor of impending syncope.