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Quantitative Autonomic Testing
Published on: July 19, 2011
Complex demodulation of cardiorespiratory dynamics preceding vasovagal syncope
L A Lipsitz1, J Hayano, S Sakata
1Hebrew Rehabilitation Center for Aged Research and Training Institute, Department of Medicine, Harvard Medical School, Boston, Mass 02131, USA. Lipsitz@mail.hrca.harvard.edu
Circulation
|September 16, 1998
Summary
Vasovagal syncope involves complex autonomic changes, including increased breathing and a sudden rise in vagal tone before fainting. This suggests a cardiorespiratory decoupling precedes the abrupt drop in heart rate causing syncope.
Area of Science:
- Cardiology
- Autonomic Neuroscience
- Respiratory Physiology
Background:
- The autonomic nervous system's role in vasovagal syncope is not fully understood.
- Vasovagal syncope is a common condition characterized by a sudden drop in blood pressure and heart rate.
Purpose of the Study:
- To investigate the dynamic autonomic processes preceding tilt-induced vasovagal syncope.
- To analyze cardiorespiratory variability changes before syncope in healthy individuals.
Main Methods:
- Complex demodulation was used to assess respiration, R-R interval, and arterial pressure variability during head-up tilt.
- Coherence and transfer function analyses examined the relationship between respiration and R-R interval variability.
- 25 healthy subjects with syncope and 25 controls were studied.
Main Results:
- Syncope subjects showed increased tidal volume and decreased blood pressure 3 minutes before syncope.
- An abrupt increase in vagal tone (prolonged R-R interval, increased variability) occurred 90 seconds before syncope.
- Cardiorespiratory decoupling was observed, with reduced coherence between respiratory and R-R interval variability in syncope subjects.
Conclusions:
- Vasovagal syncope is preceded by hyperpnea and cardiorespiratory decoupling.
- An abrupt increase in cardiovagal tone and subsequent bradycardia precipitate syncope.
- Respiratory changes may initially counteract reduced preload until sudden bradycardia occurs.
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