Functional transcranial Doppler sonography of cerebral autoregulation - Basics and clinical applications

Functional transcranial Doppler sonography (fTCD) examines changes in cereb ral blood flow velocity (CBFV) caused by varying physiological and patholog ical influences. The study of cerebral autoregulation to determine the rela tionship between changes in arterial blood pressure (ABP) and CBFV is one o f the most important clinical aspects of fTCD. Various paradigms for fTCD a utoregulation tests are established: the phenylephrine method for static au toregulation; the leg-cuff, Valsalva, and carotid compression methods, are examples of dynamic autoregulation tests. In the present contribution we in troduce cross-spectrum analysis of spontaneous Mayer waves in ABP and CBFV as a recent method of dynamic autoregulation. In normal subjects autoregula tion causes a positive phase shift (Delta phi) by about 60 degrees of CBFV in relation to blood pressure waves due to highpass filtering. Patients wit h disturbed autoregulation (occlusive cerebrovascular diseases, arterioveno us malformations) show a pathologically reduced or complete lack of Delta p hi due to blood-pressure passive CBN changes. This method allows continuous autoregulation monitoring, for example on the stroke unit.