Objectives: The critical closing pressure (CrCP) defines arterial blood pressure below which cerebral arteries collapse. It represents a clinically relevant parameter for the estimation of cerebrovascular tone. Although there are few methods to assess CrCP, there is no consensus which of them estimates this parameter most accurately. The aim of present retrospective, experimental study was to compare three methods of CrCP estimation: conventional Aaslid’s formula and methods based on the cerebrovascular impedance: the established continuous flow forward (CFF) and a new pulsatile flow forward (PFF) model.

Methods: The effects of the following physiological manoeuvres on the CrCP were studied in New Zealand white rabbits: lumbar infusion of Hartmann’s solution to induce mild intracranial hypertension, sympathetic blockade to induce arterial hypotension, and modulation of respiratory tidal volume to induce hypocapnia or hypercapnia.

Results: During intracranial hypertension, all CrCP estimates were significantly higher than at baseline, decreased with decreasing ABP and increased with gradual hypocapnia. During hypercapnia, all CrCP estimates were significantly decreased but only in the case of CrCP_A the negative, non-physiological values were observed (16% of the cases). The Bland–Altman analysis revealed that a good agreement between each impedance method and Aaslid’s method deteriorated significantly in the low range of the average numerical value of the estimates.

Discussion: Our results confirm the limited usage of Aaslid’s formula for the calculation of CrCP. Although both impedance methods seem to be equivalent, the fact that PFF model better describes cerebrovascular hemodynamic allows the recommendation of this model for the calculation of CrCP.

目的：临界闭合压力（CrCP）定义了动脉血压，低于此血压脑动脉就会塌陷。它代表用于评估脑血管张力的临床相关参数。尽管评估CrCP的方法很少，但尚无共识，其中哪种方法最准确地估计了该参数。本回顾性实验研究的目的是比较CrCP估算的三种方法：常规Aaslid公式和基于脑血管阻抗的方法：已建立的连续向前流动（CFF）和新的搏动向前流动（PFF）模型。

方法：在新西兰白兔中研究了以下生理学动作对CrCP的影响：腰部输注Hartmann溶液可诱发轻度颅内高压，交感神经阻滞可引起动脉低血压以及调节呼吸潮气量可导致低碳酸血症或高碳酸血症。

结果：在颅内高压期间，所有CrCP估计值均显着高于基线，随着ABP的降低而降低，并随着逐渐的低碳酸血症而升高。在高碳酸血症期间，所有CrCP的估计值均显着降低，但仅在CrCP _A的情况下，观察到阴性，非生理性的值（占病例的16％）。Bland–Altman分析表明，在估计平均值的低范围内，每种阻抗方法与Aaslid方法之间的良好一致性会显着恶化。

讨论：我们的结果证实了Aaslid公式在CrCP计算中的使用有限。尽管两种阻抗方法似乎是等效的，但PFF模型可以更好地描述脑血管血流动力学这一事实允许将该模型推荐用于CrCP的计算。