Non-Invasive and Minimally-Invasive Cerebral Autoregulation Assessment: A Narrative Review of Techniques and Implications for Clinical Research

Abstract

The process of cerebral vessels regulating constant cerebral blood flow over a wide range of systemic arterial pressures is termed cerebral autoregulation (CA). Static and dynamic autoregulation are two types of CA measurement techniques, with the main difference between these measures relating to the time scale used. Static autoregulation looks at the long-term change in blood pressures, while dynamic autoregulation looks at the immediate change. Techniques that provide regularly updating measures are referred to as continuous, whereas intermittent techniques take a single at point in time. However, a technique being continuous or intermittent is not implied by if the technique measures autoregulation statically or dynamically. This narrative review outlines technical aspects of non-invasive and minimally-invasive modalities along with providing details on the non-invasive and minimally-invasive measurement techniques used for CA assessment. These non-invasive techniques include neuroimaging methods, transcranial Doppler, and near-infrared spectroscopy while the minimally-invasive techniques include positron emission tomography along with magnetic resonance imaging and radiography methods. Further, the advantages and limitations are discussed along with how these methods are used to assess CA. At the end, the clinical considerations regarding these various techniques are highlighted.

Cerebral Autoregulation Monitoring in Traumatic Brain Injury: An Overview of Recent Advances in Personalized Medicine

“…Similarly, literature assessing the association between continuous CA metrics and NIRSbased rSO 2 delivery is underdeveloped. 79,[89][90][91][92][93][94] In general, studies assessing the utility of NIRS in moderate/severe TBI are limited, as highlighted in a recent systematic review on the topic. 79 NIRS-based CA metrics do closely co-vary with standard ICP-derived versions.…”

High spatial and temporal resolution cerebrovascular reactivity for humans and large mammals: A technological description of integrated fNIRS and niABP mapping system

“…The main difference between them is the time scale where static autoregulation looks at changes from minutes to hours while dynamic autoregulation examines changes from seconds to minutes. Both techniques assess autoregulation by looking at pulsatile cerebral blood volume (CBV) or CBF and changes in driving pressure, however, static autoregulation looks at these measures after they have reached steady state while dynamic autoregulation assesses CA during rapid manipulation of CPP/MAP or spontaneous oscillations of CPP/MAP ( Tiecks et al, 1995 ; Purkayastha and Sorond, 2012 ; Sainbhi et al, 2022 ). It is important to note that these two techniques do not define their temporality, so static vs. dynamic does not refer to the technique being continuous vs. intermittent.…”

“…Traditionally, CA has been assessed intermittently but with the advancement of technology, continuous measures of CA are becoming more popular since they can provide more detail on the evolution of CA over long periods of time. Recently, we have conducted a narrative review on various non-invasive and minimally-invasive modalities which assess CA in an intermittent, semi-intermittent, or continuous manner ( Sainbhi et al, 2022 ), and we refer the interested reader to this piece for more details and various methodologies of CA measurement.…”

“…Such invasive modalities include intracranial pressure (ICP) ( Czosnyka et al, 1997 ; Jaeger et al, 2006 ; Zweifel et al, 2008 ; Sorrentino et al, 2012 ), brain tissue oxygen (PbtO 2 ) ( Jaeger et al, 2006 ; Dengler et al, 2013 ), thermal diffusion flowmetry (TDF) ( Rosenthal et al, 2011 ; Dias et al, 2015 ; Highton et al, 2015 ), and laser Doppler flowmetry (LDF) ( Brady et al, 2008 ; Zweifel et al, 2010c ; Lee et al, 2011 ; 2012 ; Zeiler et al, 2018a ; 2018c ). The minimally-invasive modalities include magnetic resonance imaging (MRI) ( Saeed et al, 2011 ), positron emission tomography (PET) ( Steiner L. et al, 2003 ; 2003a ; 2003b ; Coles et al, 2004 ; Zweifel et al, 2008 ), and computed tomography (CT) ( Wintermark et al, 2006 ; Chieregato et al, 2007 ; Peterson and Chesnut, 2009 ) while the non-invasive modalities include transcranial Doppler (TCD) ( Czosnyka et al, 1997 ; 2003 ; Schmidt et al, 2003 ) and near-infrared spectroscopy (NIRS) ( Zweifel et al, 2010b ; Diedler et al, 2011 ; Zeiler et al, 2017a ; Chen et al, 2020 ; Sainbhi et al, 2022 ). CVR metrics based in time-domain from various modalities have seen widespread adoption by clinicians at bedside due to their simple, natural interpretation over the frequency-domain metrics.…”

“…Thus, to improve the understanding of continuously assessed CA in humans and large mammals, a tool is needed with both improved spatial and temporal resolution which can facilitate real-time imaging of cerebrovascular function. With recent advances in NIRS technology, custom functional NIRS (fNIRS) ( Reinhard et al, 2014 ; Chen et al, 2020 ; Sainbhi et al, 2022 ) systems are available that offer multi-channel capabilities and a sampling frequency of 250 Hz, facilitating full cerebral pulse-waveform data acquisition simultaneously from multiple brain regions. Multi-channel fNIRS systems have been used with non-invasive ABP measurement for CA assessment in the frequency domain along with visualizing CA changes ( Reinhard et al, 2014 ; Schumacher et al, 2019 ; Tian et al, 2021 ).…”