Brain Physics Laboratory, Division of Neurosurgery, Department of Clinical Neurosciences, Addenbrooke's Hospital, University of Cambridge, Cambridge, UK.
Department of Physiological Nursing, UCSF, San Francisco, CA, USA.
J Physiol. 2018 Jul;596(14):2797-2809. doi: 10.1113/JP274708. Epub 2018 Jun 13.
The brain is vulnerable to damage from too little or too much blood flow. A physiological mechanism termed cerebral autoregulation (CA) exists to maintain stable blood flow even if cerebral perfusion pressure (CPP) is changing. A robust method for assessing CA is not yet available. There are still some problems with the traditional measure, the pressure reactivity index (PRx). We introduce a new method, the wavelet transform method (wPRx), to assess CA using data from two sets of controlled hypotension experiments in piglets: one set had artificially manipulated arterial blood pressure (ABP) oscillations; the other group were spontaneous ABP waves. A significant linear relationship was found between wPRx and PRx in both groups, with wPRx providing a more stable result for the spontaneous waves. Although both methods showed similar accuracy in distinguishing intact and impaired CA, it seems that wPRx tends to perform better than PRx, although not significantly so.
We present a novel method to monitor cerebral autoregulation (CA) using the wavelet transform (WT). The new method is validated against the pressure reactivity index (PRx) in two piglet experiments with controlled hypotension. The first experiment (n = 12) had controlled haemorrhage with artificial stationary arterial blood pressure (ABP) and intracranial pressure (ICP) oscillations induced by sinusoidal slow changes in positive end-expiratory pressure ('PEEP group'). The second experiment (n = 17) had venous balloon inflation during spontaneous, non-stationary ABP and ICP oscillations ('non-PEEP group'). The wavelet transform phase shift (WTP) between ABP and ICP was calculated in the frequency range 0.0067-0.05 Hz. Wavelet semblance, the cosine of WTP, was used to make the values comparable to PRx, and the new index was termed wavelet pressure reactivity index (wPRx). The traditional PRx, the running correlation coefficient between ABP and ICP, was calculated. The result showed a significant linear relationship between wPRx and PRx in the PEEP group (R = 0.88) and non-PEEP group (R = 0.56). In the non-PEEP group, wPRx showed better performance than PRx in distinguishing cerebral perfusion pressure (CPP) above and below the lower limit of autoregulation (LLA). When CPP was decreased below LLA, wPRx increased from 0.43 ± 0.28 to 0.69 ± 0.12 (P = 0.003) while PRx increased from 0.07 ± 0.21 to 0.27 ± 0.37 (P = 0.04). Moreover, wPRx provided a more stable result than PRx (SD of PRx was 0.40 ± 0.07, and SD of wPRx was 0.28 ± 0.11, P = 0.001). Assessment of CA using wavelet-derived phase shift between ABP and ICP is feasible.
大脑容易因血流不足或过多而受损。为了保持血流稳定，即使脑灌注压（CPP）发生变化，也存在一种称为脑自动调节（CA）的生理机制。目前还没有一种可靠的方法来评估 CA。传统的测量方法——压力反应性指数（PRx）仍然存在一些问题。我们引入了一种新的方法，即小波变换法（wPRx），用于评估仔猪两组控制性低血压实验中的 CA：一组人为地操纵动脉血压（ABP）波动；另一组为自发的 ABP 波。在这两组中，wPRx 与 PRx 之间均存在显著的线性关系，wPRx 为自发波提供了更稳定的结果。尽管这两种方法在区分完整和受损的 CA 方面都具有相似的准确性，但似乎 wPRx 比 PRx 表现更好，尽管差异并不显著。
我们提出了一种使用小波变换（WT）监测脑自动调节（CA）的新方法。该新方法在两项具有控制性低血压的仔猪实验中与压力反应性指数（PRx）进行了验证。第一项实验（n=12）进行控制性出血，人工固定动脉血压（ABP）和颅内压（ICP）在正呼气末压（PEEP）缓慢正弦变化下产生波动（“PEEP 组”）。第二项实验（n=17）在自发的、非固定的 ABP 和 ICP 波动期间进行静脉球囊充气（“非 PEEP 组”）。在 0.0067-0.05 Hz 的频率范围内计算 ABP 和 ICP 之间的小波变换相位差（WTP）。小波相似性，即 WTP 的余弦值，用于使值与 PRx 相媲美，并将新指数命名为小波压力反应性指数（wPRx）。计算了传统的 PRx，即 ABP 和 ICP 之间的运行相关系数。结果表明，在 PEEP 组（R=0.88）和非 PEEP 组（R=0.56）中，wPRx 与 PRx 之间存在显著的线性关系。在非 PEEP 组中，当 CPP 下降到低于自动调节下限（LLA）时，wPRx 从 0.43±0.28 增加到 0.69±0.12（P=0.003），而 PRx 从 0.07±0.21 增加到 0.27±0.37（P=0.04）。此外，wPRx 比 PRx 提供了更稳定的结果（PRx 的标准差为 0.40±0.07，wPRx 的标准差为 0.28±0.11，P=0.001）。使用 ABP 和 ICP 之间的小波衍生相位差评估 CA 是可行的。
