FREQUENCY-DOMAIN ANALYSIS OF CEREBRAL BLOOD-FLOW VELOCITY AND ITS CORRELATION WITH ARTERIAL BLOOD-PRESSURE

We applied frequency domain analysis to detect and quantify spontaneou s fluctuations in the blood flow velocity of the middle cerebral arter y (MCAFV). Instantaneous MCAFV of normal volunteers was detected using transcranial Doppler sonography. Spectral and transfer function analy ses of MCAFV and arterial blood pressure (ABP) were performed by fast Fourier transform. We found the fluctuations in MCAFV, like ABP, could be diffracted into three components at specific frequency ranges, des ignated as high-frequency (HF, 0.15 to 0.4 Hz), low-frequency (LF, 0.0 4 to 0.15 Hz), and very low frequency (VLF, 0.016 to 0.04 Hz) componen ts. The HF and LF components of MCAFV exhibited high coherence with th ose of ABP, indicating great similarity of MCAFV and ABP fluctuations within the two frequency ranges. However, it was not the case for the VLF component. Transfer function analysis revealed that the ABP-MCAFV phase angle was frequency-dependent in the LF range (r = -0.79, P < 0. 001) but not in the HF range. The time delay between LF fluctuations o f ABP and those of MCAFV was evaluated as 2.1 seconds. We conclude tha t in addition to traditional B-wave equivalents, there are at least tw o different mechanisms for MCAFV fluctuations: the HF and LF fluctuati ons of MCAFV are basically secondary to those of ABP, and cerebral aut oregulation may operate efficiently in LF rather than HF range, Freque ncy domain analysis offers an opportunity to explore the nature and un derlying mechanism of dynamic regulation in cerebral circulation.