Dynamic cerebral autoregulation under sinusoidal gravitational loading.

Dynamic cerebral autoregulation (CA) has been studied previously using spectral analysis of oscillations in arterial blood pressure (ABP) and cerebral blood flow velocity (CBFV). The dynamics of the CA can be modeled as a high-pass filter. The purpose of this study is to compare CA of blood pressure oscillations induced by gravitational loading to CA during resting conditions. We subjected twelve healthy subjects to repeated sinusoidal head-up (0 degrees - 60 degrees) tilts at several set frequencies (0.07 to 0.25 Hz) on a computer controlled tilt table while we recorded ABP (Finapres) and CBFV (transcranial Doppler ultrasound). We fitted the data sets to a high-pass filter model and computed an average time constant (T). Our results show similar phase leads of CBFV to ABPbrain in the rest recording and in sinusoidal tilting, in the studied frequency range. The transfer function gain of the resting spectra increased with increasing frequency, the gain of the tilting spectra did not. Fitting the phase responses of both data sets to a high pass filter model yielded similar time constants.