Determinants of the dynamic cerebral critical closing pressure response to changes in mean arterial pressure.

Abstract

Objective. Cerebral critical closing pressure (CrCP) represents the value of arterial blood pressure (BP) where cerebral blood flow (CBF) becomes zero. Its dynamic response to a step change in mean BP (MAP) has been shown to reflect CBF autoregulation, but robust methods for its estimation are lacking. We aim to improve the quality of estimates of the CrCP dynamic response.Approach. Retrospective analysis of 437 healthy subjects (aged 18-87 years, 218 males) baseline recordings with measurements of cerebral blood velocity in the middle cerebral artery (MCAv, transcranial Doppler), non-invasive arterial BP (Finometer) and end-tidal CO₂(EtCO₂, capnography). For each cardiac cycle CrCP was estimated from the instantaneous MCAv-BP relationship. Transfer function analysis of the MAP and MCAv (MAP-MCAv) and CrCP (MAP-CrCP) allowed estimation of the corresponding step responses (SR) to changes in MAP, with the output in MCAv (SRV_MCAv) representing the autoregulation index (ARI), ranging from 0 to 9. Four main parameters were considered as potential determinants of the SRV_CrCPtemporal pattern, including the coherence function, MAP spectral power and the reconstruction error for SRV_MAP, from the other three separate SRs.Main results. The reconstruction error for SRV_MAPwas the main determinant of SRV_CrCPsignal quality, by removing the largest number of outliers (Grubbs test) compared to the other three parameters. SRV_CrCPshowed highly significant (p< 0.001) changes with time, but its amplitude or temporal pattern was not influenced by sex or age. The main physiological determinants of SRV_CrCPwere the ARI and the mean CrCP for the entire 5 min baseline period. The early phase (2-3 s) of SRV_CrCPresponse was influenced by heart rate whereas the late phase (10-14 s) was influenced by diastolic BP.Significance. These results should allow better planning and quality of future research and clinical trials of novel metrics of CBF regulation.