Cerebral autoregulation (CA) maintains stable cerebral blood flow (CBF) despite mean arterial pressure (MAP) fluctuations. Transcranial Doppler ultrasonography (TCD) and Near-Infrared Spectroscopy (NIRS) report CBF surrogates and facilitate CA assessment. This study aimed to investigate the distinct information they provide about dynamic CA (dCA) responses to MAP step changes Approach: Simultaneous TCD-NIRS was performed on 28 healthy older participants alongside continuous measurements of beat-to-beat and breath-to-breath MAP, heart rate (HR) and end-tidal CO2. Transfer function analysis (TFA) was performed, varying input/output metrics including MAP, middle and posterior cerebral artery blood flow velocity (MCAv/PCAv) and oxyhaemoglobin (HbO2), comparing macro- and microvasculature dCA, respectively. Main Results: No differences in regional MAP step change HbO2 responses were found across eight pre-frontal (p=0.14) or four averaged regions (p=0.69). There was a significant effect of time in HbO2 responses to MAP step change (p<0.001), and to MCAv step change (p=0.016). There were also significant differences between HbO2 and MCAv and PCAv responses (p<0.001). Distinct TCD and NIRS step responses suggest much slower dCA responses in the microvasculature, compared to MCA and PCA, without regional differences. Significance: Further investigation into regional dCA differences is needed alongside potential benefits of simultaneous TCD-NIRS in pathological states.
Ball et al. (Wed,) studied this question.