Lorenz I H, Kolbitsch C, Hörmann C, Schocke M, Kremser C, Zschiegner F, Felber S, Benzer A
Department of Anesthesia and Intensive Care Medicine, University of Innsbruck, Austria.
Magn Reson Imaging. 2001 Jan;19(1):7-11. doi: 10.1016/s0730-725x(00)00229-0.
Changes in both blood flow and blood oxygenation determine the functional MRI (fMRI) signal. In the present study factors responsible for blood oxygenation (e.g., FiO(2)) were held constant so that changes in pixel count would above all reflect changes in regional cerebral blood flow (rCBF). Continuous positive airway pressure (CPAP) breathing at 12 cm H(2)O, which was previously shown to influence rCBF, was applied in human volunteers (n = 19) to investigate the sensitivity of fMRI for changes in rCBF caused by increased mean airway pressure. Increasing the mean airway pressure decreased the pixel count in the primary visual cortex (median (range)): baseline: 219 (58-425) pixels vs. CPAP (12 cm H(2)O): 92 (0-262) pixels). These findings indicate that fMRI is sensitive to detect a reduced rCBF-response in the primary visual cortex. The underlying mechanism is likely to be a reduced basal rCBF due to constriction and/or compression of postcapillary venoles during CPAP breathing. These findings are important for interpreting fMRI results in awake and in artificially respirated patients, in whom positive airway pressure is used to improve pulmonary function during the diagnostic procedure.
血流和血液氧合的变化决定了功能磁共振成像（fMRI）信号。在本研究中，负责血液氧合的因素（如FiO₂）保持恒定，以便像素计数的变化首先反映局部脑血流（rCBF）的变化。在19名人类志愿者中应用12 cm H₂O的持续气道正压通气（CPAP）呼吸，先前已证明其会影响rCBF，以研究fMRI对平均气道压力升高引起的rCBF变化的敏感性。平均气道压力升高会降低初级视觉皮层中的像素计数（中位数（范围））：基线：219（58 - 425）像素，而CPAP（12 cm H₂O）时：92（0 - 262）像素。这些发现表明，fMRI对检测初级视觉皮层中rCBF反应降低很敏感。潜在机制可能是在CPAP呼吸期间，由于毛细血管后微静脉的收缩和/或受压导致基础rCBF降低。这些发现对于解释清醒和人工通气患者的fMRI结果很重要，在这些患者中，在诊断过程中使用正压气道来改善肺功能。
