The Prince Charles Hospital and University of Queensland, Rode Road, Brisbane (4032), Australia.
Physiol Meas. 2011 Sep;32(9):1361-72. doi: 10.1088/0967-3334/32/9/001. Epub 2011 Jul 20.
Biological signals often exhibit self-similar or fractal scaling characteristics which may reflect intrinsic adaptability to their underlying physiological system. This study analysed fractal dynamics of cerebral blood flow in patients supported with ventricular assist devices (VAD) to ascertain if sustained modifications of blood pressure waveform affect cerebral blood flow fractality. Simultaneous recordings of arterial blood pressure and cerebral blood flow velocity using transcranial Doppler were obtained from five cardiogenic shock patients supported by VAD, five matched control patients and five healthy subjects. Computation of a fractal scaling exponent (α) at the low-frequency time scale by detrended fluctuation analysis showed that cerebral blood flow velocity exhibited 1/f fractal scaling in both patient groups (α = 0.95 ± 0.09 and 0.97 ± 0.12, respectively) as well as in the healthy subjects (α = 0.86 ± 0.07). In contrast, fluctuation in blood pressure was similar to non-fractal white noise in both patient groups (α = 0.53 ± 0.11 and 0.52 ± 0.09, respectively) but exhibited 1/f scaling in the healthy subjects (α = 0.87 ± 0.04, P < 0.05 compared with the patient groups). The preservation of fractality in cerebral blood flow of VAD patients suggests that normal cardiac pulsation and central perfusion pressure changes are not the integral sources of cerebral blood flow fractality and that intrinsic vascular properties such as cerebral autoregulation may be involved. However, there is a clear difference in the fractal scaling properties of arterial blood pressure between the cardiogenic shock patients and the healthy subjects.
生物信号通常表现出自相似或分形缩放特征，这可能反映了其对潜在生理系统的内在适应性。本研究分析了心室辅助装置（VAD）支持的患者的脑血流分形动力学，以确定血压波形的持续变化是否会影响脑血流分形。通过经颅多普勒同时记录 5 例 VAD 支持的心源性休克患者、5 例匹配的对照患者和 5 例健康受试者的动脉血压和脑血流速度。通过去趋势波动分析计算低频时间尺度上的分形标度指数（α）表明，脑血流速度在两组患者（α=0.95±0.09 和 0.97±0.12）以及健康受试者（α=0.86±0.07）中均表现出 1/f 分形缩放。相比之下，两组患者的血压波动与非分形白噪声相似（α=0.53±0.11 和 0.52±0.09），但在健康受试者中表现出 1/f 缩放（α=0.87±0.04，与患者组相比 P<0.05）。VAD 患者脑血流分形的保留表明，正常的心脏搏动和中心灌注压变化不是脑血流分形的整体来源，内在的血管特性，如脑自动调节，可能与之相关。然而，心源性休克患者和健康受试者的动脉血压分形缩放特性存在明显差异。
