Abstract
Parameters describing dynamic cerebral autoregulation (DCA) have limited reproducibility. In an international, multi-center study, we evaluated the influence of multiple analytical methods on the reproducibility of DCA. Fourteen participating centers analyzed repeated measurements from 75 healthy subjects, consisting of 5 min of spontaneous fluctuations in blood pressure and cerebral blood flow velocity signals, based on their usual methods of analysis. DCA methods were grouped into three broad categories, depending on output types: (1) transfer function analysis (TFA); (2) autoregulation index (ARI); and (3) correlation coefficient. Only TFA gain in the low frequency (LF) band showed good reproducibility in approximately half of the estimates of gain, defined as an intraclass correlation coefficient (ICC) of >0.6. None of the other DCA metrics had good reproducibility. For TFA-like and ARI-like methods, ICCs were lower than values obtained with surrogate data (p < 0.05). For TFA-like methods, ICCs were lower for the very LF band (gain 0.38 ± 0.057, phase 0.17 ± 0.13) than for LF band (gain 0.59 ± 0.078, phase 0.39 ± 0.11, p ≤ 0.001 for both gain and phase). For ARI-like methods, the mean ICC was 0.30 ± 0.12 and for the correlation methods 0.24 ± 0.23. Based on comparisons with ICC estimates obtained from surrogate data, we conclude that physiological variability or non-stationarity is likely to be the main reason for the poor reproducibility of DCA parameters.
Highlights
The importance of cerebral autoregulation (CA) has been clearly established, as a cerebro-protective mechanism to alterations in blood pressure (BP) by keeping cerebral blood flow (CBF) relatively constant (van Beek et al, 2008)
No significant differences were found for MAP, CBF velocity (CBFv), and EtCO2 for the two measurements (T1 and T2)
By comparing real physiological measurements with those where physiological variability was reduced by use of surrogate data, we have been able to assess the contribution of physiological non-stationary to the reproducibility of Dynamic CA (DCA) parameters
Summary
The importance of cerebral autoregulation (CA) has been clearly established, as a cerebro-protective mechanism to alterations in blood pressure (BP) by keeping cerebral blood flow (CBF) relatively constant (van Beek et al, 2008). Maneuvers that induce relatively large and rapid changes in BP, such as the sudden release of compressed thigh cuffs (Aaslid et al, 1989), lead to recordings with better signal-to-noise ratio and the possibility of visualizing and quantifying the DCA response with measurements as short as 30 s. On the other hand, using the spontaneous fluctuations in BP and CBF, that can be observed in most individuals, allows estimation of DCA parameters at rest, without the need for a physiological disturbance or challenge. This can lead to better acceptance and feasibility in most clinical conditions
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