The cerebrovasculature responds to blood gas challenges. Regional differences (anterior vs. posterior) in cerebrovascular responses to increases in CO₂ have been extensively studied. However, regional cerebrovascular reactivity (CVR) responses to low O₂ (hypoxia) are equivocal, likely due to differences in analysis. We assessed the effects of acute isocapnic hypoxia on regional CVR comparing absolute and relative (%-change) responses in the middle cerebral artery (MCA) and posterior cerebral artery (PCA). We instrumented 14 healthy participants with a transcranial Doppler ultrasound (cerebral blood velocity), finometer (beat-by-beat blood pressure), dual gas analyzer (end-tidal CO₂ and O₂), and utilized a dynamic end-tidal forcing system to elicit a single 5-min bout of isocapnic hypoxia (∼45 Torr P_ETO₂, ∼80% SpO₂). During exposure to acute hypoxia, absolute responses were larger in the anterior compared to posterior cerebral circulation (P < 0.001), but were not different when comparing relative responses (P = 0.45). Consistent reporting of CVR to hypoxia will aid understanding normative responses, particularly in assessing populations with impaired cerebrovascular function.

脑血管系统应对血气挑战。已经广泛研究了脑血管对 CO ₂增加的反应的区域差异（前部与后部） 。然而，可能由于分析的差异，对低 O ₂ （缺氧）的局部脑血管反应性 (CVR) 反应是模棱两可的。我们评估了急性等碳酸缺氧对区域 CVR 的影响，比较了大脑中动脉 (MCA) 和大脑后动脉 (PCA) 的绝对和相对 (%-变化) 反应。我们对 14 名健康参与者进行了经颅多普勒超声（脑血流速度）、finometer（逐搏血压）、双气体分析仪（呼气末 CO ₂和 O ₂)，并利用动态呼气末强迫系统引发单次 5 分钟的等碳酸缺氧 (~45 Torr P _ET O ₂，~80% SpO ₂ )。在暴露于急性缺氧期间，与后脑循环相比，前脑循环的绝对反应更大（P < 0.001），但在比较相对反应时没有差异（P = 0.45）。CVR 对缺氧的一致报告将有助于理解规范反应，特别是在评估脑血管功能受损的人群时。