Transfer function analysis of dynamic cerebral autoregulation in humans

TLDR

The study tested whether spontaneous cerebral blood flow changes are driven by arterial pressure and whether autoregulation depends on frequency by measuring arterial pressure and middle cerebral artery velocity in 10 healthy subjects during rest and induced hypotension. The authors estimated transfer function gain, phase, and coherence between arterial pressure and cerebral blood flow velocity using Welch’s method, and derived an impulse response function via inverse Fourier transform to predict transient flow changes during hypotension, which were then compared to measured velocity changes. Beat‑to‑beat cerebral blood flow velocity changes tracked arterial pressure changes, with transfer gain rising and phase falling from 0.07 to 0.20 Hz, coherence above 0.5 between 0.07–0.30 Hz, and predicted velocity changes matching measured ones, indicating that short‑term autoregulation behaves like a high‑pass filter in that frequency band.

Abstract

To test the hypothesis that spontaneous changes in cerebral blood flow are primarily induced by changes in arterial pressure and that cerebral autoregulation is a frequency-dependent phenomenon, we measured mean arterial pressure in the finger and mean blood flow velocity in the middle cerebral artery (V˙ MCA ) during supine rest and acute hypotension induced by thigh cuff deflation in 10 healthy subjects. Transfer function gain, phase, and coherence function between changes in arterial pressure andV˙ MCA were estimated using the Welch method. The impulse response function, calculated as the inverse Fourier transform of this transfer function, enabled the calculation of transient changes inV˙ MCA during acute hypotension, which was compared with the directly measured change in V˙ MCA during thigh cuff deflation. Beat-to-beat changes inV˙ MCA occurred simultaneously with changes in arterial pressure, and the autospectrum of V˙ MCA showed characteristics similar to arterial pressure. Transfer gain increased substantially with increasing frequency from 0.07 to 0.20 Hz in association with a gradual decrease in phase. The coherence function was >0.5 in the frequency range of 0.07–0.30 Hz and <0.5 at <0.07 Hz. Furthermore, the predicted change inV˙ MCA was similar to the measuredV˙ MCA during thigh cuff deflation. These data suggest that spontaneous changes inV˙ MCA that occur at the frequency range of 0.07–0.30 Hz are related strongly to changes in arterial pressure and, furthermore, that short-term regulation of cerebral blood flow in response to changes in arterial pressure can be modeled by a transfer function with the quality of a high-pass filter in the frequency range of 0.07–0.30 Hz.