Müller Martin W-D, Österreich Mareike, Müller Andreas, Lygeros John
Department of Neurology and Neurorehabilitation, Kantonsspital Lucerne Lucerne, Switzerland.
Automatic Control Laboratory, ETH Zurich Zurich, Switzerland.
Front Physiol. 2016 May 9;7:162. doi: 10.3389/fphys.2016.00162. eCollection 2016.
At present, there is no standard bedside method for assessing cerebral autoregulation (CA) with high temporal resolution. We combined the two methods most commonly used for this purpose, transcranial Doppler sonography (TCD, macro-circulation level), and near-infrared spectroscopy (NIRS, micro-circulation level), in an attempt to identify the most promising approach.
In eight healthy subjects (5 women; mean age, 38 ± 10 years), CA disturbance was achieved by adding carbon dioxide (CO2) to the breathing air. We simultaneously recorded end-tidal CO2 (ETCO2), blood pressure (BP; non-invasively at the fingertip), and cerebral blood flow velocity (CBFV) in both middle cerebral arteries using TCD and determined oxygenated and deoxygenated hemoglobin levels using NIRS. For the analysis, we used transfer function calculations in the low-frequency band (0.07-0.15 Hz) to compare BP-CBFV, BP-oxygenated hemoglobin (OxHb), BP-tissue oxygenation index (TOI), CBFV-OxHb, and CBFV-TOI.
ETCO2 increased from 37 ± 2 to 44 ± 3 mmHg. The CO2-induced CBFV increase significantly correlated with the OxHb increase (R (2) = 0.526, p < 0.001). Compared with baseline, the mean CO2 administration phase shift (in radians) significantly increased (p < 0.005) from -0.67 ± 0.20 to -0.51 ± 0.25 in the BP-CBFV system, and decreased from 1.21 ± 0.81 to -0.05 ± 0.91 in the CBFV-OxHb system, and from 0.94 ± 1.22 to -0.24 ± 1.0 in the CBFV-TOI system; no change was observed for BP-OxHb (0.38 ± 1.17 to 0.41 ± 1.42). Gain changed significantly only in the BP-CBFV system. The correlation between the ETCO2 change and phase change was higher in the CBFV-OxHb system [r = -0.60; 95% confidence interval (CI): -0.16, -0.84; p < 0.01] than in the BP-CBFV system (r = 0.52; 95% CI: 0.03, 0.08; p < 0.05).
The transfer function characterizes the blood flow transition from macro- to micro-circulation by time delay only. The CBFV-OxHb system response with a broader phase shift distribution offers the prospect of a more detailed grading of CA responses. Whether this is of clinical relevance needs further studies in different patient populations.
目前，尚无用于评估具有高时间分辨率的脑自动调节（CA）的标准床边方法。我们将最常用于此目的的两种方法，经颅多普勒超声（TCD，宏观循环水平）和近红外光谱（NIRS，微循环水平）相结合，试图确定最有前景的方法。
在8名健康受试者（5名女性；平均年龄38±10岁）中，通过向呼吸空气中添加二氧化碳（CO₂）来实现CA紊乱。我们同时记录呼气末CO₂（ETCO₂）、血压（BP；指尖无创测量），并使用TCD记录双侧大脑中动脉的脑血流速度（CBFV），以及使用NIRS测定氧合血红蛋白和脱氧血红蛋白水平。为了进行分析，我们在低频带（0.07 - 0.15Hz）中使用传递函数计算来比较BP - CBFV、BP - 氧合血红蛋白（OxHb）、BP - 组织氧合指数（TOI）、CBFV - OxHb和CBFV - TOI。
ETCO₂从37±2mmHg增加到44±3mmHg。CO₂诱导的CBFV增加与OxHb增加显著相关（R² = 0.526，p < 0.001）。与基线相比，BP - CBFV系统中平均CO₂给药相移（以弧度为单位）从 - 0.67±0.20显著增加（p < 0.005）到 - 0.51±0.25，CBFV - OxHb系统中从1.21±0.81降低到 - 0.05±0.91，CBFV - TOI系统中从0.94±1.22降低到 - 0.24±1.0；BP - OxHb无变化（从0.38±1.17到0.41±1.42）。仅BP - CBFV系统中的增益发生了显著变化。CBFV - OxHb系统中ETCO₂变化与相变化之间的相关性高于BP - CBFV系统[r = - 0.60；95%置信区间（CI）： - 0.16， - 0.84；p < 0.01]（r = 0.52；95%CI：0.03，0.08；p < 0.05）。
传递函数仅通过时间延迟表征从宏观循环到微循环的血流转变。具有更宽相移分布的CBFV - OxHb系统响应为更详细地分级CA响应提供了前景。这是否具有临床相关性需要在不同患者群体中进一步研究。
