Related Experiment Videos
Cerebral autoregulation in orthostatic intolerance.
R Schondorf1, J Benoit, R Stein
1Autonomic Reflex Laboratory, Department of Neurology, McGill University, Sir Mortimer B. Davis Jewish General Hospital, Montreal, Quebec, Canada H3T 1E2. ronald.schondorf@mcgill.ca
Annals of the New York Academy of Sciences
|July 19, 2001
Summary
Cerebral hypoperfusion may cause orthostatic intolerance symptoms. Transcranial Doppler studies show varied results in neurally mediated syncope and POTS, questioning current interpretations of cerebral blood flow and autoregulation.
Area of Science:
- Neurology
- Cardiology
- Physiology
Background:
- Orthostatic intolerance symptoms like fatigue and poor concentration are linked to reduced cerebral blood flow.
- Neurally mediated syncope (NMS) and postural orthostatic tachycardia syndrome (POTS) are conditions affecting blood pressure regulation.
- Transcranial Doppler (TCD) is used to measure middle cerebral artery blood velocity (CBV) for assessing cerebral blood flow and dynamic cerebral autoregulation.
Purpose of the Study:
- To examine the interpretation of CBV changes during syncope and orthostatic stress.
- To evaluate dynamic cerebral autoregulation in patients with NMS and POTS.
- To address controversies in understanding cerebral blood flow dynamics in these conditions.
Main Methods:
- Utilizing Transcranial Doppler (TCD) to measure middle cerebral artery blood velocity (CBV).
- Analyzing blood velocity pulsatility and mean flow changes relative to blood pressure during head-up tilt and syncope.
- Applying transfer-function analysis to assess dynamic cerebral autoregulation.
Main Results:
- Controversy exists on whether increased CBV pulsatility during syncope indicates increased cerebrovascular resistance or intact autoregulation.
- Studies show no evidence of impaired dynamic cerebral autoregulation in NMS patients.
- Some POTS patients exhibit excessive CBV decrease during head-up tilt, but others with similar symptoms show normal CBV and autoregulation.
Conclusions:
- Current interpretations of CBV data during syncope need further clarification.
- Dynamic cerebral autoregulation appears intact in NMS, despite symptoms potentially linked to cerebral hypoperfusion.
- Discrepancies in CBV responses in POTS patients suggest potential underlying heterogeneity in the condition's pathophysiology.