The measurement of cerebrovascular CO2 reactivity is very important to assess the pathophysiology of cerebrovascular disease. However, the conventional methods for measurement of CO2 reactivity are invasive and need radioisotope or other tracers. Transcranial Doppler(TCD) is a new method to evaluate the mean flow velocity of the middle cerebral artery(MCA) non-invasively. Cerebral blood flow(CBF) and MCA flow velocity have been measured simultaneously using laser Doppler and TCD, respectively

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... our department. This study showed changes of CBF measured by laser Doppler and velocity measured by TCD relatively. Therefore, the vasodilatory capacity to increase in PaCO2 can be tested by measurement of MCA flow velocity using TCD. The elevation of end-tidal PCO2 was achieved by re-breathing the alr expired air from a respiratory bag. The CO2 reactivity was easily calculated by a personal computer using en equation obtained from the mean flow velocoty and end-tidal PCO2 within a range of 3060 mmHg. We have studied the CO2 reactivity in patients suffering from rarious neurosurgical diseases. The reduction of CO2 reactivity was detected in patients with symptomatic vasospasm, normal pressure hydrocephalus, cerebral infarction, Moyamoya disease and chronic subdural hematoma.