On the Importance of Preserving Nonlinear Dynamics when Testing the Null Hypothesis of Cerebrovascular Pressure-Flow Uncoupling in Healthy Subjects

Dynamic cerebral autoregulation (dCA) regulates the interactions between mean arterial pressure (MAP) and mean cerebral blood velocity (MCBv). We verified the relevance of preserving nonlinear properties of MAP and MCBv when testing the null hypothesis of MCBv-MAP uncoupling in healthy subjects. A model-free cross-predictability method based on k nearest neighbors was utilized to quantify the dependence of MCBv on MAP. We exploited two surrogate generation strategies: one preserving solely distribution and autocorrelation, while the other maintaining nonlinear properties as well. We recorded MAP and MCBv in 27 healthy subjects (age: $44 \pm 11$ yrs; 14 females, 13 males) at rest in supine position (REST) and during standing. We found that the percentage of subjects featuring MCBv-MAP uncoupling does not vary with the surrogate type and this result holds regardless of experimental condition, thus indicating that nonlinear dynamics play a limited role in assessing dCA.