Impact of carotid arterial pressure measurements for cerebrovascular impedance estimation.

Cerebrovascular impedance quantifies the relationship between pulsatile changes in arterial pressure and cerebral artery blood flow velocity, reflecting the Windkessel effect in dampening blood flow oscillations. For its estimation, arterial pressure can be measured at either the common carotid artery (CCA) or the internal carotid artery (ICA) using applanation tonometry. However, due to pressure wave propagation and potential waveform distortions, even over short vascular distances, pressure waveforms recorded at the ICA may differ from those at the CCA. Therefore, this study investigated the impact of measurement site (CCA vs. ICA) on cerebrovascular impedance estimation. Sixteen healthy young adults (18-25 years, nine women) underwent simultaneous recordings of ipsilateral CCA and ICA pressure and CBF velocity in the middle cerebral artery using B-mode ultrasound and transcranial Doppler. The transfer function gain from CCA to ICA pressures remained close to 1.0 up to 2.34 Hz and then declined slightly and linearly, reaching approximately 0.6 at 7.80 Hz, whereas both phase and coherence remained stable up to approximately 7 Hz. Repeated-measures correlation showed strong intra-individual agreement in cerebrovascular impedance estimates from both pressure sites, although ICA-derived values tended to be lower at higher frequencies. Importantly, no significant differences were observed below 6 Hz. Thus, the choice of carotid arterial pressure measurement site (CCA vs. ICA) has minimal impact on cerebrovascular impedance estimation within this lower frequency range.