The influence of dynamic cerebral autoregulation efficiency on its directional sensitivity.

Dynamic cerebral autoregulation (dCA) demonstrates directional sensitivity (DS_CA), depending on increases or reductions in mean arterial blood pressure (MAP). DS_CA dependence on the efficiency of dCA has not been reported. A retrospective study of 172 healthy subjects (88 female, age 19-82 years), with five-minute recordings of MAP, cerebral blood velocity (middle cerebral artery, MCAv), end-tidal CO₂, and electrocardiogram, led to estimates of the MCAv step response to changes in MAP. The strength of DS_CA was expressed by the difference between the MCAv step responses for the positive derivative component of MAP and the corresponding negative derivative component. The efficiency of dCA was expressed by the original autoregulation index (ARI_orig), ranging from 0 to 9, calculated from the original MAP. For the entire population, DS_CA strength was not associated with ARI_orig, or any other parameters. However, when taking biological sex and age into account, markers of DS_CA strength showed significant linear regressions with ARI_orig, with negative slopes for younger females (p=0.0037 to 0.011, late phase of the step responses), no influence in older females (p> 0.69), and positive slopes for both younger and older males (early phase of the step responses, p=0.003 to 0.041). This contrasting pattern of the influences of sex and age is in agreement with the known effects of gonadal hormones on the myogenic response and endothelial function of the cerebral circulation. Clinical studies of the diagnostic and/or prognostic value of DS_CA parameters need to take into account the influences of sex, age and the ARI_orig.