[Waveform caused by raised intracranial pressure--application of spectral analysis in the study of waveform].

Changes in spectrum of the intracranial pressure (ICP) pulse wave were studied while ICP was raised by the epidural balloon inflation. ICP and systemic blood pressure were estimated in the lateral ventricle and thoracic aorta, respectively. Transmission of pulsation from arterial pressure to ICP was estimated by the amplitude transfer function (TFa). Waveform of ICP pulse was also evaluated by distortion factor to represent how ICP pulse is different form a pure sine wave. The spectra of ICP and arterial pressure showed basically the same pattern; they consisted of fundamental wave (FW) and three harmonic waves (HW 2, HW 3, HW 4). Amplitude and values of TFa of each spectral component were increased as ICP was raised and revealed significant correlation. FW and HW 2 components showed break points when ICP was raised up to 35 mmHg, thereafter increments of amplitude and TFa became more remarkable in the range of higher ICP. TFa and amplitude of each spectral component of ICP pulse revealed significant correlation. These findings proved that changes of ICP pulse were the results of changed efficiency of pulse transmission from arterial pressure to CSF. It was already reported that the cerebrovascular tonus had decisive influences on the transmission of pulsation from arterial pressure to ICP because lowered vascular tonus would diminish the damping effect by arterial wall and facilitate the transmission of arterial pressure pulse to ICP. The break point of amplitude and TFa were considered to indicate that tonus of cerebral artery was remarkably lowered and the autoregulation of cerebral blood flow was exhausted.(ABSTRACT TRUNCATED AT 250 WORDS)