Describing the response of cerebral autoregulation to postural challenge via state space correspondence methods

Postural stimulus influences the cerebral autoregulation (CA), but it remains to be elucidated whether its impact is transient. Two nonlinear state space correspondence (SSC) methods, based on cross-predictability (CP) and cloud size ratio (CSR), were exploited to describe the CA from spontaneous variability of mean arterial pressure (MAP) and mean cerebral blood velocity (MCBv) during sustained postural challenge. We continuously recorded MAP and MCBv in 12 healthy subjects (age: 27 ± 8 yrs; 5 males) at rest in supine position and during head-up tilt (HUT) at 60° prolonged for 20 minutes after the onset of the orthostatic challenge. We found that: i) markers of MCBv-MAP association computed by CP and CSR techniques are significantly associated but they feature evident differences especially in the early phase of the HUT; ii) both the methods detect an increase of the degree of association from MAP to MCBv during the late phase of HUT. We conclude that, even though the two SSC methods cannot be considered interchangeable, both techniques indicate that HUT affects the CA, and its modifications are not limited to the early phase of HUT.