ICP Versus Laser Doppler Cerebrovascular Reactivity Indices to Assess Brain Autoregulatory Capacity

F A Zeiler,F A Zeiler,F A Zeiler,D Cardim,D Cardim,D K Menon,D K Menon,D K Menon,D K Menon,J Donnelly,J Donnelly,P Smielewski,P Smielewski,M Czosnyka,M Czosnyka,M Czosnyka

doi:10.1007/s12028-017-0472-x

Abstract

BackgroundTo explore the relationship between various autoregulatory indices in order to determine which approximate small vessel/microvascular (MV) autoregulatory capacity most accurately.MethodsUtilizing a retrospective cohort of traumatic brain injury patients (N = 41) with: transcranial Doppler (TCD), intracranial pressure (ICP) and cortical laser Doppler flowmetry (LDF), we calculated various continuous indices of autoregulation and cerebrovascular responsiveness: A. ICP derived [pressure reactivity index (PRx)—correlation between ICP and mean arterial pressure (MAP), PAx—correlation between pulse amplitude of ICP (AMP) and MAP, RAC—correlation between AMP and cerebral perfusion pressure (CPP)], B. TCD derived (Mx—correlation between mean flow velocity (FVm) and CPP, Mx_a—correlation between FVm and MAP, Sx—correlation between systolic flow velocity (FVs) and CPP, Sx_a—correlation between FVs and MAP, Dx—correlation between diastolic flow index (FVd) and CPP, Dx_a—correlation between FVd and MAP], and LDF derived (Lx—correlation between LDF cerebral blood flow [CBF] and CPP, Lx_a—correlation between LDF-CBF and MAP). We assessed the relationship between these indices via Pearson correlation, Friedman test, principal component analysis (PCA), agglomerative hierarchal clustering (AHC), and k-means cluster analysis (KMCA).ResultsLDF-based autoregulatory index (Lx) was most associated with TCD-based Mx/Mx_a and Dx/Dx_a across Pearson correlation, PCA, AHC, and KMCA. Lx was only remotely associated with ICP-based indices (PRx, PAx, RAC). TCD-based Sx/Sx_a was more closely associated with ICP-derived PRx, PAx and RAC. This indicates that vascular-derived indices of autoregulatory capacity (i.e., TCD and LDF based) covary, with Sx/Sx_a being the exception, whereas indices of cerebrovascular reactivity derived from pulsatile CBV (i.e., ICP indices) appear to not be closely related to those of vascular origin.ConclusionsTranscranial Doppler Mx is the most closely associated with LDF-based Lx/Lx_a. Both Sx/Sx-a and the ICP-derived indices appear to be dissociated with LDF-based cerebrovascular reactivity, leaving Mx/Mx-a as a better surrogate for the assessment of cortical small vessel/MV cerebrovascular reactivity. Sx/Sx_a cocluster/covary with ICP-derived indices, as seen in our previous work.

Highlights

Continuous assessments of autoregulation/cerebrovascular reactivity in traumatic brain injury (TBI) patients focus on the calculation of moving Pearson correlation coefficients between physiologic variables that characterize systemic and cerebrovascular dynamics [1,2,3]
Utilizing a retrospective cohort of traumatic brain injury patients (N = 41) with: transcranial Doppler (TCD), intracranial pressure (ICP) and cortical laser Doppler flowmetry (LDF), we calculated various continuous indices of autoregulation and cerebrovascular responsiveness: A
Transcranial Doppler mean flow index (Mx) is the most closely associated with LDF-based LDF-based autoregulatory index (Lx)/Lx_a

Summary

Introduction

Continuous assessments of autoregulation/cerebrovascular reactivity in traumatic brain injury (TBI) patients focus on the calculation of moving Pearson correlation coefficients between physiologic variables that characterize systemic and cerebrovascular dynamics [1,2,3] These indices are derived by comparing slow wave changes of a surrogate for cerebral blood volume (CBV)/cerebral blood flow (CBF), to the intravascular driving force, mean arterial pressure (MAP) or cerebral perfusion pressure (CPP) [1, 3]. Pressure reactivity index (PRx), derived from ICP and MAP, and mean flow index (Mx), derived from transcranial Doppler-derived CBFV and CPP, are the two most commonly quoted continuous indices of cerebrovascular reactivity in TBI. To explore the relationship between various autoregulatory indices in order to determine which approximate small vessel/microvascular (MV) autoregulatory capacity most accurately

Methods

Results

Conclusion