Hadjistassou Constantinos, Moyle Keri, Ventikos Yiannis
Fluidics and Biocomplexity Group, Department of Engineering Science, University of Oxford, Oxford, Parks Road, Oxford, United Kingdom.
Faculty of Engineering, University of Auckland, Auckland, New Zealand.
PLoS One. 2016 Mar 3;11(3):e0149935. doi: 10.1371/journal.pone.0149935. eCollection 2016.
The advent of functional MRI in the mid-1990s has catalyzed progress pertaining to scientific discoveries in neuroscience. With the prospect of elucidating the physiological aspect of the Blood Oxygenation Level Dependent (BOLD) effect we present a computational capillary-tissue system capable of mapping venous hemoglobin saturation- a marker of the BOLD hemodynamic response. Free and facilitated diffusion and convection for hemoglobin and oxygen are considered in the radial and axial directions. Hemoglobin reaction kinetics are governed by the oxyhemoglobin dissociation curve. Brain activation, mimicked by dynamic transitions in cerebral blood velocity (CBv) and oxidative metabolism (CMRO2), is simulated by normalized changes in m = (ΔCBv/CBv)/(ΔCMRO2/CMRO2) of values 2, 3 and 4. Venous hemoglobin saturation profiles and peak oxygenation results, for m = 2, based upon a 50% and a 25% increase in CBv and CMRO2, respectively, lie within physiological limits exhibiting excellent correlation with the BOLD signal, for short-duration stimuli. Our analysis suggests basal CBv and CMRO2 values of 0.6 mm/s and 200 μmol/100g/min. Coupled CBv and CMRO2 responses, for m = 3 and m = 4, overestimate peak hemoglobin saturation, confirming the system's responsiveness to changes in hematocrit, CBv and CMRO2. Finally, factoring in neurovascular effects, we show that no initial dip will be observed unless there is a time delay in the onset of increased CBv relative to CMRO2.
20世纪90年代中期功能磁共振成像（functional MRI）的出现推动了神经科学领域的科学发现。鉴于有望阐明血氧水平依赖（BOLD）效应的生理方面，我们提出了一种计算性毛细血管-组织系统，该系统能够绘制静脉血红蛋白饱和度图——这是BOLD血流动力学反应的一个标志物。考虑了血红蛋白和氧气在径向和轴向上的自由扩散、易化扩散和对流。血红蛋白反应动力学由氧合血红蛋白解离曲线控制。通过模拟脑血流速度（CBv）和氧化代谢（CMRO2）的动态变化来模拟脑激活，通过m = (ΔCBv/CBv)/(ΔCMRO2/CMRO2) 的归一化变化来模拟，m值分别为2、3和4。对于m = 2，基于CBv和CMRO2分别增加50%和25%，静脉血红蛋白饱和度分布图和峰值氧合结果处于生理范围内，对于短时间刺激，与BOLD信号表现出极好的相关性。我们的分析表明，基础CBv和CMRO2值分别为0.6 mm/s和200 μmol/100g/min。对于m = 3和m = 4，耦合的CBv和CMRO2反应高估了峰值血红蛋白饱和度，证实了该系统对血细胞比容、CBv和CMRO2变化的响应性。最后，考虑到神经血管效应，我们表明，除非CBv相对于CMRO2增加的起始存在时间延迟，否则不会观察到初始下降。
