engleski

Assessment of cerebral vasoreactivity by functional transcranial doppler

Transcranial Doppler (TCD) is an excellent noninvasive method for evaluation of cerebral blood flow (CBF) in real time, but TCD in basal conditions is sometimes insufficient for complete estimation of cerebral circulation. CBF is coupled with neuronal activity and brain metabolism, therefore newer approach in investigation of CBF and cerebral vascular reserve is through the evaluation of cerebral autoregulation and vasoreactivity by means of TCD. Number of tests are introduced - response to blood pressure changes, C02, acetazolamide, hyperventilation, breathholding. In numerous studies results showed impaired autoregulatory response in patients with carotid artery disease, dementia, migraine and other conditions. Because of high temporal resolution functional TCD gives us more information about regional CBF and regulatory mechanisms related to functional neuronal activity; the changes are visible in seconds. Aaslid first described CBF velocities increase using TCD in the posterior cerebral artery (PCA) during visual stimulation in healthy subjects. Afterwards difterent stimuli were applied for monitoring the changes in regional CBF-color and checkerboard stimulation, auditory and vibratory stimulation, stimulation with associative tasks, memory test, speaking and complex tasks. Results clearly showed that these changes detected by TCD are specific to the type of stimuli - during cognitive testing changes in middle cerebral artery (MCA) of dominant hemisphere appear, and in the PCA during visual stimulation. Visually evoked response of CBF in PCA is of special interest because it is known that light is the most powerful stimulus for metabolism in the visual cortex that is almost exclusively irrigated by PCA so the influence of additional factors on flow responses is low. Performed studies presented results about cerebral lateralization according to the type of visual stimuli and results about decreased response in patients with posterior circulation ischemia. This difterences in response could be used as additional diagnostic indicator of cerebral vascular reserve condition.

transcranial doppler; functional tests; vasoreactivity

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