Russell H Morgan Department of Radiology and Radiological Science, Division of MR Research, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
J Cereb Blood Flow Metab. 2011 Jul;31(7):1599-611. doi: 10.1038/jcbfm.2011.35. Epub 2011 Apr 6.
The poststimulus blood oxygenation level-dependent (BOLD) undershoot has been attributed to two main plausible origins: delayed vascular compliance based on delayed cerebral blood volume (CBV) recovery and a sustained increased oxygen metabolism after stimulus cessation. To investigate these contributions, multimodal functional magnetic resonance imaging was employed to monitor responses of BOLD, cerebral blood flow (CBF), total CBV, and arterial CBV (CBV(a)) in human visual cortex after brief breath hold and visual stimulation. In visual experiments, after stimulus cessation, CBV(a) was restored to baseline in 7.9±3.4 seconds, and CBF and CBV in 14.8±5.0 seconds and 16.1±5.8 seconds, respectively, all significantly faster than BOLD signal recovery after undershoot (28.1±5.5 seconds). During the BOLD undershoot, postarterial CBV (CBV(pa), capillaries and venules) was slightly elevated (2.4±1.8%), and cerebral metabolic rate of oxygen (CMRO(2)) was above baseline (10.6±7.4%). Following breath hold, however, CBF, CBV, CBV(a) and BOLD signals all returned to baseline in ∼20 seconds. No significant BOLD undershoot, and residual CBV(pa) dilation were observed, and CMRO(2) did not substantially differ from baseline. These data suggest that both delayed CBV(pa) recovery and enduring increased oxidative metabolism impact the BOLD undershoot. Using a biophysical model, their relative contributions were estimated to be 19.7±15.9% and 78.7±18.6%, respectively.
刺激后血氧水平依赖（BOLD）下冲归因于两个主要的合理起源：基于延迟脑血容量（CBV）恢复的延迟血管顺应性和刺激停止后持续增加的氧代谢。为了研究这些贡献，采用多模态功能磁共振成像来监测短暂屏气和视觉刺激后人类视觉皮层的 BOLD、脑血流（CBF）、总 CBV 和动脉 CBV（CBV(a)）的反应。在视觉实验中，刺激停止后，CBV(a)在 7.9±3.4 秒内恢复到基线，CBF 和 CBV 分别在 14.8±5.0 秒和 16.1±5.8 秒内恢复到基线，均明显快于 BOLD 信号在下冲后的恢复（28.1±5.5 秒）。在 BOLD 下冲期间，动脉后 CBV（CBV(pa)，毛细血管和小静脉）略有升高（2.4±1.8%），且脑氧代谢率（CMRO(2)）高于基线（10.6±7.4%）。然而，在屏气后，CBF、CBV、CBV(a)和 BOLD 信号均在约 20 秒内恢复到基线。没有观察到明显的 BOLD 下冲和残余的 CBV(pa)扩张，且 CMRO(2)与基线无显著差异。这些数据表明，延迟的 CBV(pa)恢复和持续增加的氧化代谢都会影响 BOLD 下冲。使用生物物理模型，估计它们的相对贡献分别为 19.7±15.9%和 78.7±18.6%。
