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Carotid baroreflex function ceases during vasovagal syncope.
Shigehiko Ogoh1, Stefanos Volianitis, Peter B Raven
1Department of Integrative Physiology, University of North Texas, Health Science Centre, Fort Worth, Texas, USA.
Summary
Vasovagal syncope, a common cause of fainting, involves a loss of consciousness. This study found that arterial baroreflex function completely ceases during these episodes.
Area of Science:
- Cardiovascular physiology
- Autonomic nervous system function
Background:
- Vasovagal syncope is a frequent cause of transient loss of consciousness.
- It is often triggered by stimuli that decrease central blood volume, like head-up tilt.
- Arterial baroreflex normally regulates heart rate and blood pressure.
Purpose of the Study:
- To evaluate carotid baroreflex function during head-up tilt-induced vasovagal syncope.
- To assess changes in baroreceptor responsiveness during presyncope and syncope.
Main Methods:
- Utilized rapid pulse train of neck pressure and suction to assess carotid baroreflex.
- Measured carotid-heart rate and carotid-blood pressure baroreflex function curves.
- Evaluated three conscious volunteers experiencing vasovagal episodes during head-up tilt.
Main Results:
- Bradycardia and hypotension during presyncope/syncope indicated a shift in cardiac and vasomotor response curves.
- Baroreflex control was suppressed during vasovagal syncope, with low blood pressure during neck pressure stimuli.
- Maximal gain of baroreflex function curves decreased, indicating reduced baroreceptor responsiveness.
Conclusions:
- Arterial baroreflex function is suppressed during vasovagal syncope.
- The findings highlight a critical failure of autonomic cardiovascular regulation during fainting episodes.