Weldon School of Biomedical Engineering, Purdue University, West Lafayette, Indiana, USA.
Rotman Research Institute, Baycrest Health Sciences, Toronto, Canada.
NMR Biomed. 2024 Jul;37(7):e5084. doi: 10.1002/nbm.5084. Epub 2023 Dec 17.
In recent years, low-frequency oscillations (LFOs) (0.01-0.1 Hz) have been a subject of interest in resting-state functional magnetic resonance imaging research. They are believed to have many possible driving mechanisms, from both regional and global sources. Internal fluctuations in the partial pressure of CO (PCO) has long been thought of as one of these major driving forces, but its exact contributions compared with other mechanisms have yet to be fully understood. This study examined the effects of end-tidal PCO (PCO) oscillations on LF cerebral hemodynamics and cerebrospinal fluid (CSF) dynamics under "clamped PCO" and "free-breathing" conditions. Under clamped PCO, a participant's PCO levels were fixed to their baseline average, whereas PCO was not controlled in free breathing. Under clamped PCO, the fractional amplitude of hemodynamic LFOs in the occipital and sensorimotor cortex and temporal lobes were found to be significantly reduced. Additionally, the fractional amplitude of CSF LFOs, measured at the fourth ventricle, was found to be reduced by almost one-half. However, the spatiotemporal distributions of blood and CSF delay times, as measured by cross-correlation in the LF domain, were not significantly altered between conditions. This study demonstrates that, while PCO oscillations significantly mediate LFOs, especially those observed in the CSF, other mechanisms are able to maintain LFOs, with high correlation, even in their absence.
近年来，低频振荡（LFOs）（0.01-0.1 Hz）一直是静息态功能磁共振成像研究的一个热点。它们被认为有许多可能的驱动机制，既有来自区域的也有来自全局的。CO 分压（PCO）的内部波动长期以来被认为是这些主要驱动力之一，但与其他机制相比，其确切贡献尚未完全理解。本研究在“夹闭 PCO”和“自由呼吸”两种条件下，考察了终末 PCO（PCO）振荡对 LF 脑血流动力学和脑脊液（CSF）动力学的影响。在夹闭 PCO 条件下，参与者的 PCO 水平被固定在其基线平均值，而在自由呼吸条件下则不控制 PCO。在夹闭 PCO 条件下，发现枕叶和感觉运动皮层及颞叶的血流 LFO 的分数幅度明显降低。此外，在第四脑室测量的 CSF LFO 的分数幅度降低了近一半。然而，通过 LF 域中的互相关测量的血液和 CSF 延迟时间的时空分布在两种条件之间没有显著改变。本研究表明，虽然 PCO 振荡显著调节 LFOs，尤其是在 CSF 中观察到的那些，但其他机制能够维持 LFOs，即使在没有 PCO 振荡的情况下也能维持高度相关的 LFOs。
