Ogawa Yojiro, Iwasaki Ken-ichi, Aoki Ken, Shibata Shigeki, Kato Jitsu, Ogawa Setsuro
Department of Hygiene and Space Medicine, Nihon University School of Medicine, Tokyo, Japan.
Anesth Analg. 2007 Nov;105(5):1389-96, table of contents. doi: 10.1213/01.ane.0000281910.95740.e4.
Frequent changes in the perioperative central blood volume could affect cerebral autoregulation through alterations in sympathetic nerve activity, cardiac output, blood viscosity, and cerebral vasomotor tone. However, the effect of dynamic cerebral autoregulation has not been studied during acute wide-ranging changes in central blood volume, especially with respect to central hypervolemia with hemodilution.
We evaluated dynamic cerebral autoregulation during central hypovolemia and central hypervolemia with hemodilution using spectral and transfer function analysis between mean arterial blood pressure (MBP) and cerebral blood flow (CBF) velocity variability in 12 individuals. Rapid changes in central blood volume were achieved using two levels of lower body negative pressure (-15 and -30 mm Hg) and two discrete infusions of normal saline (15 mL/kg and total 30 mL/kg). We then estimated changes in central blood volume as central venous pressure (CVP) and/or cardiac output using impedance cardiography.
Steady-state CBF velocity and cardiac output decreased at -30 mm Hg lower body negative pressure (changes of CVP approximately -4 mm Hg) or were increased by each saline infusion (changes of CVP 4-6 mm Hg), without a significant change in MBP. However, transfer function gain (magnitude of transfer) between MBP and CBF velocity variability significantly increased only after saline infusion, suggesting an increased magnitude of transfer from MBP oscillations to CBF fluctuations during central hypervolemia with hemodilution.
Our results suggest that, although steady-state CBF velocity changes under both central hypervolemia and hypovolemia, only hypervolemic hemodilution impairs dynamic cerebral autoregulation.
围手术期中心血容量的频繁变化可通过交感神经活动、心输出量、血液粘度和脑血管运动张力的改变影响脑自动调节。然而，在中心血容量急性大幅变化期间，尤其是在伴有血液稀释的中心性高血容量情况下，动态脑自动调节的影响尚未得到研究。
我们使用频谱和传递函数分析，在12名个体中评估了中心性低血容量和伴有血液稀释的中心性高血容量期间的动态脑自动调节，该分析是基于平均动脉血压（MBP）和脑血流（CBF）速度变异性之间进行的。通过两种水平的下肢负压（-15和-30 mmHg）以及两次分别输注生理盐水（15 mL/kg和总计30 mL/kg）实现中心血容量的快速变化。然后，我们使用阻抗心动图估计中心血容量作为中心静脉压（CVP）和/或心输出量的变化。
在下肢负压为-30 mmHg时（CVP变化约-4 mmHg），稳态CBF速度和心输出量降低，或者每次输注生理盐水后均增加（CVP变化4-6 mmHg），而MBP无显著变化。然而，仅在输注生理盐水后，MBP与CBF速度变异性之间的传递函数增益（传递幅度）显著增加，这表明在伴有血液稀释的中心性高血容量期间，从MBP振荡到CBF波动的传递幅度增加。
我们的结果表明，尽管在中心性高血容量和低血容量状态下稳态CBF速度均发生变化，但只有高血容量血液稀释会损害动态脑自动调节。
