Skytioti Maria, Søvik Signe, Elstad Maja
Division of Physiology, Institute of Basic Medical Sciences University of Oslo, Oslo, Norway
Deptartment of Anaesthesia and Intensive Care, Akershus University Hospital, Lørenskog, Norway.
Physiol Rep. 2016 Oct;4(19). doi: 10.14814/phy2.12969.
Intact cerebral blood flow (CBF) is essential for cerebral metabolism and function, whereas hypoperfusion in relation to hypovolemia and hypocapnia can lead to severe cerebral damage. This study was designed to assess internal carotid artery blood flow (ICA-BF) during simulated hypovolemia and noninvasive positive pressure ventilation (PPV) in young healthy humans. Beat-by-beat blood velocity (ICA and aorta) were measured by Doppler ultrasound during normovolemia and simulated hypovolemia (lower body negative pressure), with or without PPV in 15 awake subjects. Heart rate, plethysmographic finger arterial pressure, respiratory frequency, and end-tidal CO (ETCO) were also recorded. Cardiac index (CI) and ICA-BF were calculated beat-by-beat. Medians and 95% confidence intervals and Wilcoxon signed rank test for paired samples were used to test the difference between conditions. Effects on ICA-BF were modeled by linear mixed-effects regression analysis. During spontaneous breathing, ICA-BF was reduced from normovolemia (247, 202-284 mL/min) to hypovolemia (218, 194-271 mL/min). During combined PPV and hypovolemia, ICA-BF decreased by 15% (200, 152-231 mL/min, P = 0.001). Regression analysis attributed this fall to concurrent reductions in CI (β: 43.2, SE: 17.1, P = 0.013) and ETCO (β: 32.8, SE: 9.3, P = 0.001). Mean arterial pressure was maintained and did not contribute to ICA-BF variance. In healthy awake subjects, ICA-BF was significantly reduced during simulated hypovolemia combined with noninvasive PPV Reductions in CI and ETCO had additive effects on ICA-BF reduction. In hypovolemic patients, even low-pressure noninvasive ventilation may cause clinically relevant reductions in CBF, despite maintained arterial blood pressure.
完整的脑血流量（CBF）对于脑代谢和功能至关重要，而与血容量减少和低碳酸血症相关的灌注不足可导致严重的脑损伤。本研究旨在评估年轻健康人在模拟血容量减少和无创正压通气（PPV）期间的颈内动脉血流量（ICA - BF）。在15名清醒受试者中，通过多普勒超声在血容量正常和模拟血容量减少（下体负压）期间逐搏测量（ICA和主动脉的）血流速度，有无PPV。还记录了心率、容积描记法手指动脉压、呼吸频率和呼气末二氧化碳（ETCO）。逐搏计算心脏指数（CI）和ICA - BF。使用中位数、95%置信区间和配对样本的Wilcoxon符号秩检验来检验不同条件之间的差异。通过线性混合效应回归分析对ICA - BF的影响进行建模。在自主呼吸期间，ICA - BF从血容量正常时（247, 202 - 284 mL/min）降至血容量减少时（218, 194 - 271 mL/min）。在PPV和血容量减少联合期间，ICA - BF下降了15%（200, 152 - 231 mL/min，P = 0.001）。回归分析将这种下降归因于CI（β：43.2，SE：17.1，P = 0.013）和ETCO（β：32.8，SE：9.3，P = 0.001）的同时降低。平均动脉压保持稳定，对ICA - BF的变化无影响。在健康清醒受试者中，模拟血容量减少联合无创PPV期间ICA - BF显著降低。CI和ETCO的降低对ICA - BF的降低具有累加效应。在血容量减少的患者中，尽管动脉血压保持正常，但即使是低压无创通气也可能导致临床上相关的CBF降低。
