M-wave analysis and passive tilt in patients with different degrees of carotid artery disease

Background and Purpose - Carotid artery disease (CAD) is able to critically impair cerebral autoregulation which increases the risk for stroke. As therapeutic strategy largely depends on the degree of CAD, we investigated whether this gradation is also related to significant changes in autoregulatory capacity. We applied cross-spectral analysis (CSA) of spontaneous Mayer-wave (M-wave) oscillations and passive tilting (PT) to test cerebral autoregulation. Methods - Cerebral autoregulation was tested in 102 patients with carotid stenosis (greater than or equal to70%) or occlusion and 14 controls by comparison of continuous transcranial Doppler sonography of the middle cerebral artery and beat-to-beat arterial blood pressure (ABP) during PT to 80degrees head-up position as well as by CSA of M-waves (3-9 cpm). Results - The orthostatic decrease of cerebral blood flow velocity (CBFV) was not correlated with the degree of CAD and showed a lower sensitivity and specificity than phase angle shifts between M-waves in ABP and CBFV (sensitivity: 75-80%, specificity: 86%). Phase angles were gradually lowered in carotid stenoses > 70%, but apparently, they were only moderately correlated with the degree of CAD (r = -0.35, P < 0.01). An additional influencing factor seemed to be the sufficiency of collateralization. Conclusions - The results show that CSA of M-waves is more appropriate for testing autoregulation than PT. CSA suggests that the capacity to autoregulate depends to a certain extent on the degree of CAD but is also influenced by the sufficiency of collateral pathways and pre-existing strokes.