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Altered cerebral vasoregulation in hypertension and stroke
V Novak1, A Chowdhary, B Farrar
1Division of Gerontology, Harvard Medical School, Beth Israel Deaconess Medical Center, Boston, MA 02215, USA. vnovak@caregroup.harvard.edu
Neurology
|May 29, 2003
Summary
Cerebral vasoregulation is impaired in stroke patients, especially during orthostatic stress. Blood flow velocity asymmetry indicates risk of hypoperfusion.
Area of Science:
- Neurology
- Cardiovascular Physiology
- Cerebrovascular Regulation
Background:
- Stroke compromises the brain's ability to regulate blood flow.
- Maintaining steady cerebral perfusion across blood pressure ranges is crucial.
Purpose of the Study:
- To investigate if cerebral vasoregulation is impaired in stroke patients during orthostatic stress.
- To assess the impact of minor stroke on the brain's blood flow control mechanisms.
Main Methods:
- Transcranial Doppler was used to measure bilateral middle cerebral artery blood flow velocities (BFVs).
- Subjects (controls, hypertension, stroke) underwent supine and tilted (80 degrees) assessments with CO2 challenges.
- Calculations included side-to-side BFV difference, vasomotor range (VMR), and cerebrovascular resistance (CVR).
Main Results:
- BFVs decreased on the stroke side during tilt and hypercapnia, indicating impaired vasoregulation.
- Cerebrovascular resistance increased, and vasomotor range decreased on the stroke side.
- BFV asymmetry between sides clearly differentiated stroke patients and correlated with lower orthostatic blood pressure.
Conclusions:
- Minor stroke significantly impairs cerebral vasoregulation.
- Cerebral blood flow in stroke patients is highly dependent on blood pressure.
- Reduced blood flow velocities during orthostatic stress may signal a risk for silent hypoperfusion.