Department of Pediatrics, New York Medical College, Valhalla, NY, USA.
Am J Physiol Heart Circ Physiol. 2013 Jun 1;304(11):H1576-83. doi: 10.1152/ajpheart.00114.2013. Epub 2013 Apr 5.
The modified Oxford maneuver is the reference standard for assessing arterial baroreflex function. The maneuver comprises a systemic bolus injection of 100 μg sodium nitroprusside (SNP) followed by 150 μg phenylephrine (PE). On the one hand, this results in an increase in oxyhemoglobin and total hemoglobin followed by a decrease within the cerebral sample volume illuminated by near-infrared spectroscopy (NIRS). On the other hand, it produces a decrease in cerebral blood flow velocity (CBFv) within the middle cerebral artery (MCA) during SNP and an increase in CBFv during PE as measured by transcranial Doppler ultrasound. To resolve this apparent discrepancy, we hypothesized that SNP dilates, whereas PE constricts, the MCA. We combined transcranial Doppler ultrasound of the right MCA with NIRS illuminating the right frontal cortex in 12 supine healthy subjects 18-24 yr old. Assuming constant O₂ consumption and venous saturation, as estimated by partial venous occlusion plethysmography, we used conservation of mass (continuity) equations to estimate the changes in arterial inflow (ΔQa) and venous outflow (ΔQv) of the NIRS-illuminated area. Oxyhemoglobin and total hemoglobin, respectively, increased by 13.6 ± 1.6 and 15.2 ± 1.4 μmol/kg brain tissue with SNP despite hypotension and decreased by 6 ± 1 and 7 ± 1 μmol/kg with PE despite hypertension. SNP increased ΔQa by 0.36 ± .03 μmol·kg(-1)·s(-1) (21.6 μmol·kg(-1)·min(-1)), whereas CBFv decreased from 71 ± 2 to 62 ± 2 cm/s. PE decreased ΔQa by 0.27 ± .2 μmol·kg(-1)·s(-1) (16.2 μmol·kg(-1)·min(-1)), whereas CBFv increased to 75 ± 3 cm/s. These results are consistent with dilation of the MCA by SNP and constriction by PE.
改良的牛津手法是评估动脉压力反射功能的参考标准。该手法包括系统地注射 100μg 硝普钠（SNP），然后注射 150μg 去氧肾上腺素（PE）。一方面，这会导致氧合血红蛋白和总血红蛋白增加，随后近红外光谱（NIRS）照射的脑样本体积减少。另一方面，它会导致 SNP 期间大脑中动脉（MCA）内的脑血流速度（CBFV）下降，而 PE 期间 CBFV 增加，这是通过经颅多普勒超声测量得出的。为了解决这个明显的差异，我们假设 SNP 扩张，而 PE 收缩 MCA。我们在 12 名仰卧健康受试者中，将右侧 MCA 的经颅多普勒超声与右侧额皮质的 NIRS 结合起来，这些受试者年龄在 18-24 岁之间。假设通过部分静脉闭塞体积描记术估计的 O₂消耗和静脉饱和度保持不变，我们使用质量守恒（连续性）方程来估计 NIRS 照射区域的动脉流入（ΔQa）和静脉流出（ΔQv）的变化。尽管存在低血压，但 SNP 使氧合血红蛋白和总血红蛋白分别增加了 13.6±1.6μmol/kg 脑组织和 15.2±1.4μmol/kg 脑组织，而尽管存在高血压，但 PE 却使它们分别减少了 6±1μmol/kg 和 7±1μmol/kg。SNP 使 ΔQa 增加了 0.36±0.03μmol·kg(-1)·s(-1)（21.6μmol·kg(-1)·min(-1)），而 CBFv 从 71±2cm/s 降至 62±2cm/s。PE 使 ΔQa 减少了 0.27±0.2μmol·kg(-1)·s(-1)（16.2μmol·kg(-1)·min(-1)），而 CBFv 增加到 75±3cm/s。这些结果与 SNP 扩张 MCA 和 PE 收缩 MCA 的结果一致。
