Depression of dynamic cerebral autoregulation during neural activation: the role of responders and non-responders

Neurovascular coupling (NVC) interaction with dynamic cerebral autoregulation (dCA) remains unclear. Sixteen healthy participants (31.6 ± 11.6 years) performed verbal fluency (naming words (NW)) and serial subtraction (SS) paradigms, of varying complexity, at durations of 05, 30 and 60s. Bilateral middle cerebral artery blood velocity (MCAv, transcranial Doppler), blood pressure (BP, Finapres) and end-tidal CO2 (EtCO2, capnography), were recorded continuously. The autoregulation index (ARI), was estimated from the MCAv step response, calculated by transfer function analysis (TFA), for each paradigm during unstimulated (2min) and neuroactivated (1min) segments. Intraclass correlation (ICC) determined reproducibility for two visits. ARI was averaged across visits, and objective criteria were applied to classify responders (R) and non-responders (NoR) to task-induced MCAv increase. MCAv, BP and heart rate increased during all cognitive tasks (p<0.001). ICC values demonstrated fair reproducibility in all tasks. ARI decreased in right (RH) and left (LH) hemispheres during all cognitive activations, irrespective of paradigm complexity and duration (p<0.0001). Bilateral ARI estimates were significantly decreased during NW for the R group only (5.9 vs 4.3 for RH and 5.8 vs 4.2 for LH, p<0.0001) but were reduced in both R (5.9 vs 4.5 for RH and 5.8 vs 4.2 for LH, p<0.0001) and NoR (5.9 vs 4.6 for RH and 5.8 vs 5.0 for LH, p=0.03) groups for SS tasks compared with baseline. The reproducible attenuation of dCA efficiency due to paradigm-induced NVC response, its interaction, and different behaviour in R and NoR subjects, warrant further research in different physiological and clinical conditions.