Vasomotor reactivity (VMR) and autoregulation define the physiological compensatory mechanisms when flow is impaired. Identification of exhausted VMR can be a good indication for high risk for stroke.
VMR can be assessed with TCD under two specific conditions: hypercapnia or CO2 reactivity, and with intravenous injections of Acetazolamide or the Diamox test. Note that the Diamox test is not accepted in some countries.
Typically, an increase in peak velocities above 40% during induced increase in CO2 reflects intact VMR, whereas a smaller increase reflects different degrees of impaired VMR. Absence of flow increase reflects a complete exhaustion of the autoregulatory capacity.
The Viasonix Dolphin is ideally set with dedicated Unilateral and Bilateral protocols to determine the autoregulatory capacity of the cerebral circulation of the patient. Doppler waveforms are captured automatically during baseline, and peak (hypercapnia) and minimal (hypocapnia) flows for immediate evaluation, as well as a display of the blood flow fluctuations during entire test process. The respective parameters are automatically shown in a dedicated table with the VMR index readily displayed.
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