Vafaee M S, Gjedde A
McConnell Brain Imaging Centre, Montreal Neurological Institute, McGill University, Quebec, Canada.
J Cereb Blood Flow Metab. 2000 Apr;20(4):747-54. doi: 10.1097/00004647-200004000-00012.
The coupling between cerebral metabolic rate of oxygen (CMRO2) and blood flow (CBF) in response to visual stimulation was evaluated by means of a model of oxygen delivery. The model predicted a nonlinear relationship between stimulus-evoked changes of oxygen consumption and blood flow. The magnitude of the CMRO2/CBF ratio index (IO2) was used to indicate the degree of flow-metabolism coupling prevailing in specific areas of the brain during physiological stimulation. Therefore, the index provided a measure of the blood oxygenation level dependent (BOLD) magnetic resonance contrast. To evaluate the changes of IO2 in response to visual stimulation, the model was applied to the effect of a changing flicker rate of a visual stimulus on the magnitudes of CBF, CMRO2, and oxygen diffusion capacity, in the human brain. Positron emission tomography (PET) was used to measure the CBF and the CMRO2 in 12 healthy volunteers who viewed a cross-hair (baseline) or a yellow-blue annular checkerboard reversing at frequencies of 1, 4, or 8 Hz. The magnitude of CBF in the primary visual cortex increased as a function of the checkerboard reversal rate and reached a maximum at the frequency of 8 Hz (z=16.0), while the magnitude of CMRO2 reached a maximum at 4 Hz (z=4.0). Therefore, the calculated IO2 was lower at 8 Hz than at 1 and 4 Hz, in contrast to the oxidative metabolic rate that reached its maximum at 4 Hz. The model explained the increase of oxygen consumption as the combined effect of increased blood flow and increased oxygen diffusion capacity in the region of visual activation.
通过氧输送模型评估了视觉刺激下脑氧代谢率（CMRO2）与脑血流量（CBF）之间的耦合关系。该模型预测了刺激诱发的氧消耗变化与血流量之间的非线性关系。CMRO2/CBF比率指数（IO2）的大小用于指示生理刺激期间大脑特定区域中血流 - 代谢耦合的程度。因此，该指数提供了一种衡量血氧水平依赖（BOLD）磁共振对比度的方法。为了评估IO2对视觉刺激的反应变化，将该模型应用于视觉刺激闪烁频率变化对人脑CBF、CMRO2和氧扩散能力大小的影响。使用正电子发射断层扫描（PET）测量了12名健康志愿者观看十字准线（基线）或频率为1、4或8Hz反转的黄蓝环形棋盘时的CBF和CMRO2。初级视觉皮层中的CBF大小随棋盘反转频率增加而增加，并在8Hz频率时达到最大值（z = 16.0），而CMRO2大小在4Hz时达到最大值（z = 4.0）。因此，与在4Hz时达到最大值的氧化代谢率相反，计算得出的IO2在8Hz时低于1Hz和4Hz时。该模型将氧消耗的增加解释为视觉激活区域中血流量增加和氧扩散能力增加的综合作用。
