McKetton Larissa, Sam Kevin, Poublanc Julien, Crawley Adrian P, Sobczyk Olivia, Venkatraghavan Lakshmikumar, Duffin James, Fisher Joseph A, Mikulis David J
Division of Neuroradiology, Joint Department of Medical Imaging, University Health Network, Toronto, ON, Canada.
The Russell H. Morgan Department of Radiology & Radiological Science, The John Hopkins University School of Medicine, Baltimore, MD, United States.
Front Physiol. 2021 May 13;12:639782. doi: 10.3389/fphys.2021.639782. eCollection 2021.
The normal variability in breath size and frequency results in breath-to-breath variability of end-tidal PCO (PCO), the measured variable, and arterial partial pressure of carbon dioxide (PaCO), the independent variable affecting cerebral blood flow (CBF). This study examines the effect of variability in PaCO on the pattern of resting-state functional MRI (rs-fMRI) connectivity. A region of interest (ROI)-to-ROI and Seed-to-Voxel first-level bivariate correlation, hemodynamic response function (hrf)-weighted analysis for measuring rs-fMRI connectivity was performed during two resting-state conditions: (a) normal breathing associated with breath-to-breath variation in PaCO (poikilocapnia), and (b) normal breathing with breath-to-breath variability of PCO dampened using sequential rebreathing (isocapnia). End-tidal PCO (PCO) was used as a measurable surrogate for fluctuations of PaCO. During poikilocapnia, enhanced functional connections were found between the cerebellum and inferior frontal and supramarginal gyrus (SG), visual cortex and occipital fusiform gyrus; and between the primary visual network (PVN) and the hippocampal formation. During isocapnia, these associations were not seen, rather enhanced functional connections were identified in the corticostriatal pathway between the putamen and intracalacarine cortex, supracalcarine cortex (SCC), and precuneus cortex. We conclude that vascular responses to variations in PCO, account for at least some of the observed resting state synchronization of blood oxygenation level-dependent (BOLD) signals.
呼吸大小和频率的正常变异性导致呼气末二氧化碳分压（PETCO₂）（测量变量）和动脉血二氧化碳分压（PaCO₂）（影响脑血流量（CBF）的自变量）逐次呼吸的变异性。本研究考察了PaCO₂变异性对静息态功能磁共振成像（rs-fMRI）连接模式的影响。在两种静息状态下进行了感兴趣区（ROI）到ROI以及种子点到体素的一级双变量相关性分析，以及用于测量rs-fMRI连接性的血流动力学响应函数（hrf）加权分析：（a）与PaCO₂逐次呼吸变化相关的正常呼吸（波动二氧化碳血症），以及（b）通过序贯重复呼吸抑制PCO₂逐次呼吸变异性的正常呼吸（等二氧化碳血症）。呼气末二氧化碳分压（PETCO₂）被用作PaCO₂波动的可测量替代指标。在波动二氧化碳血症期间，发现小脑与额下回和缘上回（SG）、视觉皮层与枕颞梭状回之间以及初级视觉网络（PVN）与海马结构之间的功能连接增强。在等二氧化碳血症期间，未观察到这些关联，而是在壳核与距状沟内皮层、距状沟上皮层（SCC）和楔前叶皮层之间的皮质纹状体通路中发现功能连接增强。我们得出结论，对PCO₂变化的血管反应至少部分解释了观察到的静息状态下血氧水平依赖（BOLD）信号的同步性。
