Dynamic autoregulation testing in patients with middle cerebral artery stenosis

Background and Purpose-Cross-spectral analysis (CSA) of spontaneous oscillations in cerebral blood flow velocity (CBFV) and arterial blood pressure is considered a sensitive and convenient method for dynamic autoregulation testing. So far, it has been unclear whether CSA can be used to assess stenoses of the intracranial arteries. Methods-This study for the first time applies CSA to 26 patients with low-, moderate-, and high-degree M1 stenoses and 14 normal control subjects. Using CSA, we studied spontaneous oscillations (M waves, 3 to 9 cpm; B waves, 0.5 to 3 cpm) in continuous recordings of transcranial Doppler of the middle cerebral artery and simultaneously recorded beat-to-beat blood pressure. Results-A gradual decrease in pulsatility indexes confirmed the increasing hemodynamic relevance of the stenoses. Compared with control subjects, M-wave phase shifts between CBFV and blood pressure were gradually reduced with increasing degree of M1 stenosis (control subjects, 44.6+/-21.1degrees; high-degree stenosis, 16.7+/-19.5degrees). The phase relation between B waves in blood pressure and CBFV was shifted to positive values (low- degree stenosis, -9.7+/-108.4degrees; high-degree stenosis, 50.9+/-43.8degrees). Conclusions-Because B- and M-wave phase shifts seem to characterize the degree of autonomy of CBFV modulation, this study suggests that with increasing degree of M1 stenosis, the arteriolar function is impaired. It shows that CSA is of indicative use for the assessment of intracranial artery stenosis.