Transfer function analysis of dynamic cerebral autoregulation: A CARNet white paper 2022 update

Abstract

Cerebral autoregulation (CA) refers to the control of cerebral tissue blood flow (CBF) in response to changes in perfusion pressure. Due to the challenges of measuring intracranial pressure, CA is often described as the relationship between mean arterial pressure (MAP) and CBF. Dynamic CA (dCA) can be assessed using multiple techniques, with transfer function analysis (TFA) being the most common. A 2016 white paper by members of an international Cerebrovascular Research Network (CARNet) that is focused on CA strove to improve TFA standardization by way of introducing data acquisition, analysis, and reporting guidelines. Since then, additional evidence has allowed for the improvement and refinement of the original recommendations, as well as for the inclusion of new guidelines to reflect recent advances in the field. This second edition of the white paper contains more robust, evidence-based recommendations, which have been expanded to address current streams of inquiry, including optimizing MAP variability, acquiring CBF estimates from alternative methods, estimating alternative dCA metrics, and incorporating dCA quantification into clinical trials. Implementation of these new and revised recommendations is important to improve the reliability and reproducibility of dCA studies, and to facilitate inter-institutional collaboration and the comparison of results between studies.

Acute beetroot juice consumption does not alter cerebral autoregulation or cardiovagal baroreflex sensitivity during lower-body negative pressure in healthy adults

“…It is difficult to compare our results to this investigation as aerobic exercise poses a different challenge to cerebral vascular resistance and blood flow compared to LBNP. Our data align more with Horiuchi et al (2022) who had participants ingest 140 mL of BRJ per day for 4 days. CA in the internal carotid artery (ICA) was not altered using the thigh-cuff deflation technique that induces a rapid decrease in blood pressure.…”

“…Then, a 3-min recovery period was allotted before the Static-LBNP protocol commenced. Static-LBNP consisted of −40 mmHg for a total of 7 min to assess static CA ( Claassen et al, 2016 ; Panerai et al, 2022 ). Upon completion of Static-LBNP, participants were de-instrumented and consumed 500 mL of commercially available BRJ (listed as ∼1,500 mg/L of nitrate) (Biotta, Carmel, IN, USA) ( Kenjale et al, 2011 ; Bond et al, 2013 ) within 10 min.…”

“…This interval time was selected due to the cerebral vasculature’s ability to dampen changes in arterial pressure that occur slower than ∼30 s (0.03 Hz) ( Brothers et al, 2009 ; Hamner et al, 2019 ). Static CA was assessed by applying static-LBNP (−40 mmHg) for 7 min ( Claassen et al, 2016 ; Panerai et al, 2022 ). Raw data files of beat-to-beat blood pressure (input signal) and MCAv (output signal) were used to assess dynamic and static CA via transfer function analysis (WinCPRS, Absolute Aliens Oy, Turku, Finland).…”

Changes in cerebral autoregulation and vasoreactivity after surgical aortic valve replacement: a prospective study

“…To address this issue, we conducted a sensitivity analysis excluding these patients from our sample and retrieved similar results regarding baseline dCA and CVR, as well as their changes after SAVR (Supporting information). We registered low coherence recordings in the very low‐frequency range that could potentially interfere with the linear input–output relationship implied in the transfer function analysis (Panerai et al., 2022). This was particularly evident when large time‐varying changes in arterial diameter led to adaptations in the haemodynamic resistance, thereby decreasing coherence.…”

“…Data were synchronized offline using MATLAB (The Mathworks, Natick, MA, USA). Cerebral autoregulation was assessed by transfer function analysis accordingly to proposed standards (Panerai et al., 2022) and coherence, gain and phase values were reported at very low (0.02–0.05 Hz), low (0.05–0.20 Hz) and high (0.2–0.5 Hz) frequency bands. The average of the values measured on both sides was reported (Figure 1).…”