Transfer function analysis of cerebral hemodynamics in patients with carotid stenosis

This study evaluates the validity of the transfer function analysis of spon taneous fluctuations of arterial blood pressure (ABP) and blood flow veloci ty of the middle cerebral artery (MCAFV) as a simple, convenient method to assess human cerebral autoregulation in patients with carotid stenosis. Eig hty-three consecutive patients with various degrees of carotid stenosis and 37 healthy controls were enrolled. The carotid stenosis was graded based o n the diagnostic criteria of duplex ultrasound. Instantaneous bilateral MCA FV and ABP of all participants were assessed noninvasively using transcrani al Doppler sonography and the servocontrolled infrared finger plethysmograp hy, respectively. Spectral analyses of ABP and MCAFV were performed by fast Fourier transform. The fluctuations in ABP as well as in MCAFV were diffra cted into three components at specific frequency ranges designated as high- frequency (HF; 0.15 to 0.4 Hz), low-frequency (LF; 0.04 to 0.15 Hz), and ve ry low-frequency (VLF; 0.016 to 0.04 Hz). Cross-spectral analysis was appli ed to quantify the coherence, transfer phase, and magnitude in individual H F, LF, and VLF components, Transcranial Doppler CO, vasomotor reactivity wa s measured with 5% CO2 inhalation. The LF phase angle (r = -0.53, P < 0.001 ); magnitude of VLF (r = -0.29, P = 0.002), LF (r = -0.35, P < 0.001), and HF (r = -0.47 P < 0.001); and CO2 vasomotor reactivity (r = -0.66, P < 0.00 1) were negatively correlated with the severity of stenosis. Patients with unilateral high-grade (greater than 90% stenosis) carotid stenosis demonstr ated significant reduction in LF phase angle (P < 0.001) and HF magnitude ( P = 0.018) on the ipsilateral side of the affected vessel compared with the ir contralateral side. The study also revealed a high sensitivity, specific ity, and accuracy using LF phase angle and HF magnitude to detect a high-gr ade carotid stenosis. A strong correlation existed between the LF phase ang le and the CO2 vasomotor reactivity test (r = 0.62, P < 0.001), and the cor relation between the HF magnitude and the CO2 vasomotor reactivity (r = 0.4 4, P < 0.001) was statistically significant as well. We conclude that trans fer function analysis of spontaneous fluctuations of MCAFV and ABP could be used to identify hemodynamically significant high-grade carotid stenosis w ith impaired cerebral autoregulation or vasomotor reserve.