Chapter 1 Figure 1The relationship of cerebral blood flow versus cerebral perfusion pressure as regulated by an intact cerebral autoregulation mechanism (from Aaslid, 2006). Only after the introduction of transcranial Doppler sonography (TCD) 5 cere- bral blood flow waveform and its beat-to-beat changes could be acquired due to the high temporal resolution of TCD. However, by means of the Doppler effect only blood velocity can be measured and since the diameter of the insonated vessel is unknown cerebral blood flow can not be quantified. Under the assump- tion of a constant diameter in the insonated supplying vessel, cerebral blood flow velocity can be used as parameter for assessing cerebral blood flow changes. Due to the high time resolution of TCD cerebral blood flow velocity (CBFV) can now be recorded noninvasively as continuous waveform. This enables recording of transient changes in cerebral blood flow. Aaslidet al 4 were the first to study dynamic cerebral autoregulation in humans. They measured transient behavior of cerebral blood flow in response to a sudden drop in arterial blood pressure evoked by deflating leg cuffs that were inflated above systolic blood pressure for 10
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