The impact of the estimation strategy of the cerebral critical closing pressure on the autoregulation index

Cerebral autoregulation (CA) encompasses a series of physiological mechanisms that are necessary to regulate blood flow in the brain. The procedure for CA assessment via the autoregulatory index (ARI) requires the estimate of the critical closing pressure (CrCP). The study aims at investigating the impact of the strategy exploited for CrCP estimation on ARI by comparing three approaches: i) fixed CrCP at 12 mmHg (CrCP12); ii) first harmonic (H1) method applied to waveforms of arterial pressure (AP) and cerebral blood velocity (CBv); iii) 2-point technique using mean and diastolic AP and CBv values (2Pm). Analysis was carried out over AP and CBv signals recorded in 25 healthy subjects (age: 44 ± 10 yrs, 12 females, 13 males) at rest in supine position and during active standing. Computation of CrCP was complemented by the assessment of the resistance-area product (RAP). We found that the H1 and 2Pm methods led to different values of CrCP and RAP. However, the strategy selected for the CrCP computation did not affect the ARI estimation, and this result held regardless of the experimental condition. We conclude that the CrCP12 strategy can be safely utilized instead of more complex methods for the CA characterization based on ARI.