Transcranial Doppler Protocols and Procedures: Vasomotor Reactivity

Abstract

Evaluating cerebral vasomotor reactivity (VMR) using TCD provides information about cerebrovascular capacity and has utility in assessing stroke risk. It is relatively easy to perform, reliable, safe, inexpensive, and well-tolerated. While there is no significant change in the large vessel diameter with increased PCO2, the arterioles dilate or contract as needed to maintain constant brain blood flow. CO2 inhalation or breath-holding are used to evaluate the arteriolar function and provide a “stress” test for the collateral circulation during carotid high-grade stenosis or occlusion. Various methods are available to monitor intracranial hemodynamics using vasomotor reactivity. This protocol will describe the two most widely used VMR measurement techniques: CO2 challenge – This study requires inhalation of 5% medical grade CO2, 95% O2 gas mixture and a dedicated gas delivery system. Breath-holding – This study requires the patient to hold their own breath for 30 seconds.