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Tilt Testing with Combined Lower Body Negative Pressure: a "Gold Standard" for Measuring Orthostatic Tolerance
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Progressive baroreflex dysfunction and hypotension preceding VVS: a vicious cycle?

D L Jardine1,2,3, V Stott4, C Frampton5

  • 1Department of General Medicine, Christchurch Hospital, Riccarton Rd, Christchurch, 8041, New Zealand. david.jardine@cdhb.health.nz.

Clinical Autonomic Research : Official Journal of the Clinical Autonomic Research Society
|August 30, 2025
PubMed
Summary
This summary is machine-generated.

Presyncope, the precursor to vasovagal syncope, is initiated by a drop in sympathetic baroreflex gain. This occurs despite elevated sympathetic activity at baseline and during early tilt in patients with vasovagal syncope.

Keywords:
BaroreflexSympathetic nerve activityVasodilatationVasovagal syncope

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Area of Science:

  • Cardiovascular physiology
  • Autonomic nervous system function
  • Neuroscience

Background:

  • Presyncope, characterized by a gradual drop in blood pressure, precedes vasovagal syncope.
  • The precise control of sympathetic nervous system activity during presyncope remains unclear.
  • Understanding presyncope mechanisms is crucial for managing vasovagal syncope.

Purpose of the Study:

  • To elucidate the mechanism of presyncope, specifically the role of sympathetic activity.
  • To investigate the changes in sympathetic and cardiovagal baroreflex gain during presyncope.
  • To differentiate autonomic responses in patients with vasovagal syncope compared to healthy controls.

Main Methods:

  • Retrospective analysis of tilt tests in patients with vasovagal syncope and controls.
  • Measurement of haemodynamics and muscle sympathetic nerve activity.
  • Utilized sequence methods to assess vascular sympathetic and cardiovagal baroreflex gain at various stages (baseline, tilt, presyncope, recovery).

Main Results:

  • Patients with vasovagal syncope exhibited increased sympathetic and cardiovagal baroreflex gain at baseline and early tilt compared to controls.
  • During presyncope, sympathetic baroreflex gain significantly decreased, losing correlation with mean arterial pressure.
  • In some patients, sympathetic nerve activity fell below baseline levels upon recovery (tilt-back).

Conclusions:

  • Presyncope appears to be triggered by a decline in sympathetic baroreflex gain.
  • This fall in gain occurs despite initially heightened sympathetic baroreflex sensitivity in vasovagal syncope patients.
  • The findings highlight a critical shift in autonomic regulation during the transition to syncope.