Phase shift between respiratory oscillations in cerebral blood flow velocity and arterial blood pressure.

We aim to investigate whether phase shift between respiratory oscillations in cerebral blood flow velocity (CBFV) and arterial blood pressure (ABP) is associated with changes in cerebral autoregulation (CA) or reflects the mechano-elastic properties of the cerebrovascular bed. The relationships between respiratory phase shift and slow wave phase shift versus cerebrovascular time constant (the product of cerebrovascular resistance and compliance) and the index of CA (Mx) were analyzed during breathing at 6, 10, and 15 breaths min in 39 volunteers. With increasing respiratory rate the time constant, Mx, and respiratory phase shift decreased, whereas slow wave phase shift increased. The time constant correlated moderately strongly with the respiratory phase shift (R  =  0.49, p [Formula: see text] 0.001) and did not correlate with the slow wave phase shift. The slow wave phase shift was significantly associated with Mx (R  =  -0.46, p [Formula: see text] 0.001). The respiratory phase shift more accurately reflects the mechano-elastic properties of the cerebrovascular bed, whereas CA is better described by the slow wave phase shift.