Transmission characteristics of pulse waves in the intracranial cavity of dogs.

Systems analysis of intracranial pressure pulse waveforms was carried out in six dogs under conditions of normocapnia and intracranial normotension to determine how the pressure pulse is transmitted through the intracranial cavity. Since the intracranial cavity can be regarded as a system, systems analysis was applied to it. The pressure pulse wave of the common carotid artery was used as the input signal and the epidural pressure pulse wave as the output signal. An attempt was made to randomize the input signal using a cardiac pacemaker or an aorta balloon. The transfer function of the system was estimated numerically from the autocorrelation function of the input signal and the cross-correlation function of the input and output signals by means of the least-squares method. Some characteristics of pressure transmission through the system were observed. The gain curve of the system decreased between 1 and 7 Hz, then suddenly increased to form a marked peak at about 10 to 15 Hz, where the phase curve also changed from positive to negative. These results suggest that the lower frequencies of the pulse wave were suppressed during transmission through the intracranial cavity, whereas the greatest acceleration in transmission occurred at about 10 to 15 Hz. In addition, resonance was evident in the intracranial cavity under normal intracranial conditions. This is the first report of such resonance.