Application of Transcranial Doppler Sonography to Evaluate Cerebral Hemodynamics in Carotid Artery Disease

Abstract

Background and Purpose Transcranial Doppler sonography in combination with manipulation of cerebral resistance vessels is widely used to screen patients with suspected intracranial hemodynamic disturbances. Maximal flow velocity (V max ), mean flow velocity (V mean ), cerebral pulsatility index (CP i ), and cerebral resistance index (CR i ) have all been used to describe cerebral hemodynamics. The present study examined CO 2 reactivity of the above hemodynamic variables with respect to its variability between different age groups and its capability to discriminate between normal and abnormal findings. Methods Absolute and relative CO 2 reactivity of V max , V mean , CR i , and CP i were determined in both hemispheres in 30 young and 37 elderly control subjects and in 245 consecutive patients with strictly unilateral symptomatic (n=101) or asymptomatic (n=144) carotid artery disease (>80% stenosis or occlusion). Results Hemispheric reactivities of V mean , CR i , and CP i were significantly age dependent. Hemispheric V max reactivity and interhemispheric differences of individual reactivities (except absolute CP i reactivity) did not vary with age and could therefore be used to define normal values. Patient classification according to these values revealed different frequencies of subjects with pathological findings (3% for hemispheric V max reactivity, 5% to 7% for interhemispheric differences of V max or V mean reactivity, 39% and 45% for interhemispheric differences of relative CR i and CP i reactivity, respectively). Conclusions Hemispheric reactivities are less suitable to evaluate cerebral hemodynamics than interhemispheric differences, since most of the latter do not vary with age. However, interhemispheric differences vary with respect to their discriminatory power. Power is low for interhemispheric differences of V max and V mean reactivity, since the corresponding frequencies of abnormal findings do not differ from the 5% frequency expected in the reference population (reference range defined as mean±2 SD). With respect to the discriminatory power, interhemispheric differences of relative CR i and CP i reactivity may be superior to other parameters.