Kim Mi Ok, Li Jonathan, Qasem Ahmad, Graham Stuart L, Avolio Alberto P
Australian School of Advanced Medicine, Macquarie University, Sydney, Australia.
Annu Int Conf IEEE Eng Med Biol Soc. 2012;2012:5614-7. doi: 10.1109/EMBC.2012.6347267.
The pulsatile energy transmission between arterial blood pressure (BP) and intracranial pressure (ICP) is affected by cerebrospinal fluid (CSF) and brain tissue. Studies in dogs have shown that the transfer function (TF) between BP and ICP shows damping of pulsatile energy around heart rate frequency (1-3Hz) with notch filter characteristics, and the amount of damping is sensitive to cerebral compliance. This investigation aimed to assess whether this notch filter characteristic is an intrinsic property of the brain enclosed in a rigid skull and therefore applies across species with a large difference in body size. This was done by determining the TF between BP and ICP in rats with corresponding significantly smaller body size and higher heart rate (5-7 Hz) compared to dogs. Arterial BP and ICP waveforms were recorded in 8 anaesthetized (urethane) adult male Sprague-Dawley rats with solid state micro-sensor transducer catheters. The TF was computed as the ratio of ICP and arterial BP waveform amplitudes for the first 4 harmonics. Arterial BP and ICP signals were normalized for pulse amplitude such that attenuation or amplification is detected for any TF values significantly different to unity. Mean cardiac frequency was 5.72 Hz (range 4.6 - 7.11 Hz). Of the 4 harmonics only the heart rate frequency band showed a statistically significant attenuation of 17%, while the higher harmonics showed a progressive amplification. Findings show that the rat brain acts as a selective frequency pulsation absorber of energy centered at heart rate frequency. This similarity with larger animals indicates a possible allometric mechanism underlying this phenomenon, with notch filter characteristic frequency scaled to body size. This study suggests that the TF between arterial BP and ICP is an intrinsic property of the brain tissue and CSF enclosed in a rigid compartment and can be used to assess changes in cerebral compliance due to abnormal CSF pressure and flow as occur in hydrocephalus.
动脉血压（BP）与颅内压（ICP）之间的脉动能量传递受脑脊液（CSF）和脑组织的影响。对犬类的研究表明，BP与ICP之间的传递函数（TF）在心率频率（1 - 3Hz）附近呈现脉动能量的衰减，具有陷波滤波器特性，且衰减量对脑顺应性敏感。本研究旨在评估这种陷波滤波器特性是否是封闭在坚硬颅骨内的大脑的固有属性，因此是否适用于体型差异较大的不同物种。通过测定体型明显小于犬类且心率较高（5 - 7Hz）的大鼠的BP与ICP之间的TF来实现。使用固态微传感器导管在8只麻醉（乌拉坦）的成年雄性Sprague - Dawley大鼠中记录动脉BP和ICP波形。TF计算为前4个谐波的ICP与动脉BP波形幅度之比。对动脉BP和ICP信号进行脉冲幅度归一化，以便检测到任何与1显著不同的TF值的衰减或放大。平均心率为5.72Hz（范围4.6 - 7.11Hz）。在4个谐波中，只有心率频段显示出17%的统计学显著衰减，而更高的谐波则呈现逐渐放大。研究结果表明，大鼠大脑起到了以心率频率为中心的能量选择性频率脉动吸收器的作用。与较大动物的这种相似性表明了这种现象背后可能存在的异速生长机制，陷波滤波器特征频率与体型成比例。本研究表明，动脉BP与ICP之间的TF是封闭在刚性腔室内的脑组织和CSF的固有属性，可用于评估由于脑脊液压力和流量异常（如脑积水时发生的情况）导致的脑顺应性变化。
