Cerebral autoregulation and neurovascular coupling are progressively impaired during septic shock: an experimental study

Background: Alteration of the mechanisms of cerebral blood flow (CBF) regulation might contribute to the pathophysiology of sepsis-associated encephalopathy (SAE). However, previous clinical studies on dynamic cerebral autoregulation (dCA) in sepsis had several cofounders. Furthermore, little is known on the potential impairment of neurovascular coupling (NVC) in sepsis. The aim of our study was to determine the presence and time course of dCA and NVC alterations in a clinically relevant animal model and their potential impact on the development of SAE. Methods: Thirty-six anesthetized, mechanically ventilated female sheep were randomized to sham procedures (sham,n= 15), sepsis (n= 14), or septic shock (n= 7). Blood pressure, CBF, and electrocorticography were continuously recorded. Pearson's correlation coefficient Lxa and transfer function analysis were used to estimate dCA. NVC was assessed by the analysis of CBF variations induced by cortical gamma activity (E gamma) peaks and by the magnitude-squared coherence (MSC) between the spontaneous fluctuations of CBF and E gamma. Cortical function was estimated by the alpha-delta ratio. Wilcoxon signed rank and rank sum tests, Friedman tests, and RMANOVA test were used as appropriate. Results: Sepsis and sham animals did not differ neither in dCA nor in NVC parameters. A significant impairment of dCA occurred only after septic shock (Lxa,p= 0.03, TFA gainp= 0.03, phasep= 0.01). Similarly, NVC was altered during septic shock, as indicated by a lower MSC in the frequency band 0.03-0.06 Hz (p< 0.001). dCA and NVC impairments were associated with cortical dysfunction (reduction in the alpha-delta ratio (p= 0.03)). Conclusions: A progressive loss of dCA and NVC occurs during septic shock and is associated with cortical dysfunction. These findings indicate that the alteration of mechanisms controlling cortical perfusion plays a late role in the pathophysiology of SAE and suggest that alterations of CBF regulation mechanisms in less severe phases of sepsis reported in clinical studies might be due to patients' comorbidities or other confounders. Furthermore, a mean arterial pressure targeting therapy aiming to optimize dCA might not be sufficient to prevent neuronal dysfunction in sepsis since it would not improve NVC.