Increased blood pressure variability upon standing up improves reproducibility of cerebral autoregulation indices

Abstract

Dynamic cerebral autoregulation, that is the transient response of cerebral blood flow to changes in arterial blood pressure, is currently assessed using a variety of different time series methods and data collection protocols. In the continuing absence of a gold standard for the study of cerebral autoregulation it is unclear to what extent does the assessment depend on the choice of a computational method and protocol. We use continuous measurements of blood pressure and cerebral blood flow velocity in the middle cerebral artery from the cohorts of 18 normotensive subjects performing sit-to-stand manoeuvre. We estimate cerebral autoregulation using a wide variety of black-box approaches (including the following six autoregulation indices ARI, Mx, Sx, Dx, FIR and ARX) and compare them in the context of reproducibility and variability. For all autoregulation indices, considered here, the intra-class correlation was greater during the standing protocol, however, it was significantly greater (Fisher's Z-test) for Mx (p < 0.03), Sx (p < 0.003) and Dx (p < 0.03). In the specific case of the sit-to-stand manoeuvre, measurements taken immediately after standing up greatly improve the reproducibility of the autoregulation coefficients. This is generally coupled with an increase of the within-group spread of the estimates.

The Effects of Gradual Change in Head Positioning on the Relationship between Systemic and Cerebral Haemodynamic Parameters in Healthy Controls and Acute Ischaemic Stroke Patients

“…This is supported by Panerai et al (2001) who demonstrated that, intact CA was present in all manoeuvres that induced sudden changes in BP in healthy subjects [ 34 ]. A study investigating 18 normotensive patients with intact CA in response to a large increase in arterial BPv (three times greater during standing protocol) showed that CBFVv did not increase by a large amount [ 29 ]. Additionally, Lam et al (2018) observed that in nonstroke patients, CA remained intact in response to GHP [ 18 ].…”

“…Studies have shown that in the hyperacute, acute and subacute stages of AIS patients, pre-existing BPv is present and therefore insensitive to the effects of changes in head position [26][27][28]. However, a significant difference in MABPv observed over time (visits 2 and 3) could be explained by the temporal relationship seen during stroke recovery, however, in healthy controls, a significant increase in BPv in response to GHP was seen [18,29]. Assuming this is the response in healthy individuals, it would mean that a physiological improvement post-stroke would lead to responses closer to those of a healthy individual.…”

“…Significant results of visits 2 and 3 are in agreement with a study examining BPv and CBFVv in normotensive subjects performing a sit-to-stand manoeuvre compared to resting (sitting) state. Results showed arterial BPv increased three times as much, in response to the sit-to-stand manoeuvre [29]. In a recent post-hoc analysis of the HeadPoST study, Minhas et al (2019) looked at how BPv affects clinical outcome in AIS and haemorrhagic stroke.…”

Incomplete recovery of cerebral blood flow dynamics in sufficiently treated high blood pressure

“…Hence, these manoeuvres expose transfer function analysis to the risk of too low gain and phase values in the VLF and low-frequency ranges. Indeed, in a very recent work, by Mahdi et al [27], nearly all of the dynamic cerebral autoregulation (dynCA) parameters investigated decreased in parts significantly after stand up. Similarly, Barnes et al [28] demonstrated that the autoregulatory index (ARI) they used, was significantly reduced after squat/stand manoeuvres compared with the baseline recordings at standing.…”

Influence of Induced Blood Pressure Variability on the Assessment of Cerebral Autoregulation in Patients after Cardiac Arrest

“…In the current study we demonstrated a significant increase in CV of MAP during tilting of the bed compared to the resting position. Previous literature showed an improvement of reproducibility of the autoregulation coefficients by inducing blood pressure variability due to a sit-to-stand manoeuvre [ 17 , 18 ]. However, those manoeuvres lead to consistent oscillatory changes that enhance reliability, in contrast with bed tilting.…”