Frequency-dependent properties of cerebral blood transport--an experimental study in anaesthetized rabbits

Carotid arterial blood pressure and blood flow velocity in the basilar artery were studied in nine New Zealand rabbits under general anaesthesia. The cerebrovascular impedances for mean and maximal flow velocity were defined as the ratios of the respiratory and pulse waveforms of arterial blood pressure and blood flow velocities. The absolute values of these impedances were expressed and analysed as functions of frequency. Both functions decreased as frequency increased, demonstrating that a pulsatile blood movement need a lower energy expenditure than a continuous one. A minimum absolute value of impedance for flow velocity mean was found near 2.5-4 Hz in each rabbit. The impedance for mean flow velocity could be modelled by a second-order circuit, whereas the distribution of impedance for the maximal velocity had a more uniform character and could be approximated by a first-order model. A method of assessment of changes in cerebrovascular resistance using frequency properties of calculated impedance was proposed.