Orthostasis as a test for cerebral autoregulation in normal persons and patients with carotid artery disease
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Published on: January 19, 2020
M Stoll1, A Seidel, K Schimrigk
1Department of Neurology, Saarland University, Homburg, Germany.
Insights
Orthostatic testing reveals reduced cerebral blood flow velocity in patients with carotid artery disease. This method may help evaluate cerebrovascular reserve and autoregulation.
Area of Science:
- Neurology
- Vascular Medicine
- Medical Diagnostics
Background:
- Orthostasis (standing up) normally reduces cerebral blood flow velocity.
- Carotid artery disease (CAD) affects blood flow to the brain.
- Cerebrovascular reserve (CVR) indicates the brain's ability to maintain blood flow under stress.
Purpose of the Study:
- To investigate if orthostasis can serve as a provocation test for cerebral hemodynamics in patients with unilateral carotid artery disease (CAD).
- To assess the relationship between orthostatic changes in cerebral blood flow and cerebrovascular reserve (CVR).
Main Methods:
- Transcranial Doppler was used to measure mean flow velocity (FVmean) in middle cerebral arteries (MCAs) during a tilt table test in 21 CAD patients and 21 controls.
- Blood pressure (BP) and heart rate (HR) were monitored.
- Cerebrovascular reserve (CVR) was assessed using an acetazolamide test.
Main Results:
- Orthostasis reduced MCA FVmean in both controls and patients.
- The decrease in FVmean during orthostasis was significantly smaller in patients with impaired CVR compared to those with normal CVR and controls.
- Heart rate increased significantly, while blood pressure remained unchanged.
Conclusions:
- Orthostasis induces a decrease in MCA FVmean, which is attenuated in patients with impaired CVR.
- This suggests that impaired cerebrovascular autoregulation may limit vasoconstriction during orthostasis in these patients.
- Orthostatic testing, combined with CVR assessment, may be a valuable tool for evaluating cerebral autoregulation in CAD patients.
Abstract:
Orthostasis reduces mean flow velocity (FVmean) in cerebral arteries. This might be used as an alternative provocation test for cerebral hemodynamics in patients with carotid artery disease (CAD). In 21 unilateral CAD patients and 21 controls, FVmean in both middle cerebral arteries (MCA) was measured by transcranial Doppler, together with blood pressure (BP) and heart rate (HR) during a tilt table test. Cerebrovascular reserve (CVR) was measured by an acetazolamide test. In all cases, FVmean dropped to a lower level (controls: 81.9 +/- 9.4% of baseline; patients: 84.3 +/- 7.9% symptomatic side, 85.6 +/- 9.0% contralateral). Impaired CVR patients showed a smaller (p < 0.01) decrease (90.6 +/- 3.3%) compared to contralateral (84.9 +/- 6.0%), to normal CVR patients (81.1 +/- 7.8%) and to controls. Heart rate increased in both groups (controls: +16.6 +/- 9.9%, patients +10.3 +/- 9.9%; p < 0.01); BP showed no change. Orthostasis induces a decrease of MCA FVmean as already previously described. This decrease is significantly smaller in patients with impaired CVR. Since BP does not change, some authors explain the lower MCA Fvmean during orthostasis as caused by sympathetic induced vasoconstriction of cerebral resistance vessels. The authors speculate that in impaired CVR-patients autoregulative protection against ischemia might limit vasoconstriction. In combination with standard tests for measurement of CVR, this test might be useful for evaluation of cerebral autoregulation.
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