Cardiovascular Systems Laboratory, University of Otago, Wellington South, New Zealand.
Am J Physiol Heart Circ Physiol. 2012 Sep 15;303(6):H658-71. doi: 10.1152/ajpheart.00328.2012. Epub 2012 Jul 20.
We assessed the convergent validity of commonly applied metrics of cerebral autoregulation (CA) to determine the extent to which the metrics can be used interchangeably. To examine between-subject relationships among low-frequency (LF; 0.07-0.2 Hz) and very-low-frequency (VLF; 0.02-0.07 Hz) transfer function coherence, phase, gain, and normalized gain, we performed retrospective transfer function analysis on spontaneous blood pressure and middle cerebral artery blood velocity recordings from 105 individuals. We characterized the relationships (n = 29) among spontaneous transfer function metrics and the rate of regulation index and autoregulatory index derived from bilateral thigh-cuff deflation tests. In addition, we analyzed data from subjects (n = 29) who underwent a repeated squat-to-stand protocol to determine the relationships between transfer function metrics during forced blood pressure fluctuations. Finally, data from subjects (n = 16) who underwent step changes in end-tidal P(CO2) (P(ET)(CO2) were analyzed to determine whether transfer function metrics could reliably track the modulation of CA within individuals. CA metrics were generally unrelated or showed only weak to moderate correlations. Changes in P(ET)(CO2) were positively related to coherence [LF: β = 0.0065 arbitrary units (AU)/mmHg and VLF: β = 0.011 AU/mmHg, both P < 0.01] and inversely related to phase (LF: β = -0.026 rad/mmHg and VLF: β = -0.018 rad/mmHg, both P < 0.01) and normalized gain (LF: β = -0.042%/mmHg(2) and VLF: β = -0.013%/mmHg(2), both P < 0.01). However, Pet(CO(2)) was positively associated with gain (LF: β = 0.0070 cm·s(-1)·mmHg(-2), P < 0.05; and VLF: β = 0.014 cm·s(-1)·mmHg(-2), P < 0.01). Thus, during changes in P(ET)(CO2), LF phase was inversely related to LF gain (β = -0.29 cm·s(-1)·mmHg(-1)·rad(-1), P < 0.01) but positively related to LF normalized gain (β = 1.3% mmHg(-1)/rad, P < 0.01). These findings collectively suggest that only select CA metrics can be used interchangeably and that interpretation of these measures should be done cautiously.
我们评估了常用于评估脑自动调节 (CA) 的常用指标的会聚有效性，以确定这些指标在多大程度上可以互换使用。为了研究低频 (LF；0.07-0.2 Hz) 和极低频 (VLF；0.02-0.07 Hz) 传递函数相干性、相位、增益和归一化增益的受试者间关系，我们对 105 个人的自发性血压和大脑中动脉血流速度记录进行了回顾性传递函数分析。我们描述了自发性传递函数指标之间的关系 (n = 29) 以及源自双侧大腿袖带放气试验的调节指数和自动调节指数之间的关系。此外，我们分析了进行重复深蹲到站立方案的受试者 (n = 29) 的数据，以确定在强制血压波动期间传递函数指标之间的关系。最后，分析了进行呼气末二氧化碳 (P(ET)(CO2) 阶跃变化的受试者 (n = 16) 的数据，以确定传递函数指标是否可以可靠地跟踪个体内 CA 的调制。CA 指标通常没有关系或仅显示弱到中度相关性。P(ET)(CO2) 的变化与相干性呈正相关[LF：β=0.0065 任意单位 (AU)/mmHg 和 VLF：β=0.011 AU/mmHg，均 P < 0.01]，与相位呈负相关[LF：β=-0.026 rad/mmHg 和 VLF：β=-0.018 rad/mmHg，均 P < 0.01]，与归一化增益呈负相关[LF：β=-0.042%/mmHg(2) 和 VLF：β=-0.013%/mmHg(2)，均 P < 0.01]。然而，Pet(CO(2))与增益呈正相关[LF：β=0.0070 cm·s(-1)·mmHg(-2)，P < 0.05；VLF：β=0.014 cm·s(-1)·mmHg(-2)，P < 0.01]。因此，在 P(ET)(CO2) 变化期间，LF 相位与 LF 增益呈负相关[β=-0.29 cm·s(-1)·mmHg(-1)·rad(-1)，P < 0.01]，但与 LF 归一化增益呈正相关[β=1.3%mmHg(-1)/rad，P < 0.01]。这些发现共同表明，只有选定的 CA 指标可以互换使用，并且应该谨慎解释这些指标。
