Directional sensitivity of dynamic cerebral autoregulation in squat-stand maneuvers

Dynamic cerebral autoregulation (CA), the transient response of cerebral blood flow (CBF) to rapid changes in arterial blood pressure (BP), is usually modelled as a linear mechanism. We tested the hypothesis that dynamic CA can display non-linear behavior resulting from differential efficiency dependent on the direction of BP changes. CBF velocity (CBV, transcranial Doppler), heart rate (HR, 3-lead ECG), continuous BP (Finometer) and end-tidal CO2 (capnograph) were measured in 10 healthy young subjects during 15 squat-stand maneuvers (SSM) with a frequency of 0.05 Hz. The protocol was repeated with a median [IQR] of 44 [35-64] days apart. Dynamic CA was assessed with the autoregulation index (ARI), obtained from CBV step responses estimated with an autoregressive moving-average model. Mean BP, HR, and CBV were different (all p<0.001) between squat and stand, regardless of visits. ARI showed a strong interaction (p<0.001) of SSM with the progression of transients; in general, the mean ARI was higher for the squat phase compared to standing. The changes in ARI were partially explained by concomitant changes in CBV (p=0.023) and pulse pressure (p