FC092: The Relationship between Cerebrovascular Reactivity and Intradialytic Cerebral Perfusion
Authors: Richerson Wesley , Schmit Brian , Wolfgram Dawn 
Published: May 2022

Abstract

BACKGROUND AND AIMS
Cerebral perfusion can decline in hemodialysis (HD) patients during HD and may have severe consequences on cerebral integrity. The declines in cerebral perfusion are often related to intradialytic changes in blood pressure (BP), indicating that the ability of cerebrovasculature to maintain perfusion during systemic BP drop is impaired. Preliminary data using transcranial Doppler ultrasound demonstrated that cerebrovascular reactivity (CVR), a physiologic mechanism for maintaining cerebral perfusion, is impaired in HD patients. we hypothesize that CVR can serve as a measure for how a patients’ cerebrovasculature can respond to intradialytic hypotension. We aim to measure CVR in a cohort of HD patients and evaluate the relationship between CVR, intradialytic BP fluctuation and risk of intradialytic cerebral hypoperfusion.

METHOD
In a cross-sectional analysis, we used resting state fMRI to estimate CVR and determine if CVR is related to changes in cerebral oxygen saturation (ScO2) measured during HD. We recruited ESRD patients ≥50 years of age who were treated with in-center HD to complete an MRI with T1 weighted anatomical images and resting state fMRI. CVR was obtained from the resting state fMRI data by first bandpass filtering and detrending the global blood oxygenation level dependent (BOLD) signal within the frequency range that correlated with end tidal CO2 (vasoactive stimulus for CVR). The CVR was then calculated as the coefficient relating the filtered fMRI signal to each unfiltered voxel. Intradialytic ScO2 was continuously measured during an entire HD session using near-infrared spectroscopy with oximetry sensors secured to the forehead. Change in cerebral perfusion was quantified as the % change in ScO2 from baseline during the HD session. Due to the forehead placement of our sensors, we focused our CVR analysis to the frontal brain regions. Univariate linear regression models were run within each region for association with change in ScO2. Further analysis added intradialytic BP change to the model.

RESULTS
We included 26 participants with complete MRI and ScO2 data in analysis. Mean (SD) age was 65.7 (7.1), 81% had hypertension and 69% had diabetes mellitus. On average, the systolic BP (SBP) and ScO2 declined during HD. Results demonstrated that lower CVR in the anterior cingulate gyrus (ACG r2 = 0.19; P = 0.03, Figure 1), insular cortex (IC, r2 = 0.19; P = 0.03, Figure 1) and posterior parahippocampal gyrus (PPG, r2 = 0.20; P = 0.02) regions were associated with a decrease in ScO2 during HD. When adding the change in SBP during HD to the model, the ACG (r2 = 0.35, &lt;0.01) and IC (r2 = 0.26; P = 0.03) models remained significant with increased correlation coefficients.

CONCLUSION
We were able to demonstrate a relationship between lower CVR in frontal gray matter regions and greater decline in cerebral perfusion during HD. This relationship was further strengthened when adding the intradialytic change in SBP to the model. This suggests that both the hemodynamic fluctuations and the patient's ability to regulate cerebral perfusion are contributing factors for the risk of intradialytic cerebral hypoperfusion and subsequent cerebral ischemic injury in HD patients.