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(Stroke. 2003;34:2138.)
© 2003 American Heart Association, Inc.

Original Contributions

Cerebral Autoregulation in Carotid Artery Occlusive Disease Assessed From Spontaneous Blood Pressure Fluctuations by the Correlation Coefficient Index

M. Reinhard, MD; M. Roth, PhD; T. Müller, PhD; M. Czosnyka, PhD; J. Timmer, PhD A. Hetzel, MD

From the Department of Neurology and Clinical Neurophysiology (M.R., A.H.) and Center for Data Analysis and Modeling, Department of Physics (M. Roth, T.M., J.T.), University of Freiburg, Freiburg, Germany, and Department of Neurophysics, Academic Neurosurgery Unit, Addenbrooke’s Hospital, University of Cambridge, Cambridge, UK (M.C.).

Correspondence to Andreas Hetzel, MD, Associate Professor of Neurology, Department of Neurology and Clinical Neurophysiology, University of Freiburg, Neurocenter, Breisacherstr 64, D-79106 Freiburg, Germany. E-mail Hetzel{at}nz.ukl.uni-freiburg.de

Background and Purpose— Estimation of dynamic cerebral autoregulation from spontaneous fluctuations of arterial blood pressure (ABP) and cerebral blood flow velocity (CBFV) is an attractive monitoring option for cerebral hemodynamic impairment. We evaluated the correlation coefficient index method in patients with severe obstructive carotid disease and compared it with transfer function analysis (frequency domain approach to cerebral autoregulation) and CO₂ vasomotor reactivity.

Methods— In 139 patients with severe unilateral carotid stenosis (70%) or occlusion, CBFV (transcranial Doppler) and ABP (Finapres method) were recorded over 10 minutes. Correlations between systolic pressure, diastolic pressure, and mean ABP and CBFV oscillations over 1-minute epochs were averaged over 10 minutes to form the correlation coefficient indexes (Sx, Dx, Mx, respectively). Transfer function parameters (phase shift and gain between ABP and CBFV oscillations) were determined from the entire 10-minute period. CO₂ reactivity was assessed by inhalation of 7% CO₂.

Results— The correlation indexes Dx and Mx were significantly higher ipsilateral to stenosis and increased with degree of stenosis, indicating increasing dependence of CBFV on ABP and thus impairment of cerebral autoregulation. Dx and Mx correlated moderately but highly significantly with transfer function parameters and CO₂ reactivity and showed a good level of agreement in detecting pathological values. Patients with a small variance of the 1-minute source correlations of Dx and Mx showed clearly better correlation values. Transfer function parameters and CO₂ reactivity but not Dx and Mx were significantly poorer in patients with symptomatic stenosis or occlusion.

Conclusions— The potential of the correlation coefficient indexes Dx and Mx in detecting hemodynamic impairment in patients with carotid stenosis is comparable to that of transfer function analysis and CO₂ reactivity testing. In future, a combination of various hemodynamic tests might help to identify patients at risk for ischemic events.

Key Words: autoregulation • carbon dioxide • carotid stenosis

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