Correlations among critical closing pressure, pulsatility index and cerebrovascular resistance

We attempted to explore the relationships among critical closing pressure (CrCP), resistance-area product (RAP) and traditional resistance indices of cerebral hemodynamics. Twenty healthy volunteers were studied. Blood pressure was obtained with servo-controlled plethysmography. Cerebral blood flow velocity (CBFV) was monitored by transcranial Doppler. Hemodynamic changes were induced by hyperventilation and by 5% CO(2) inhalation. Beat-to-beat CrCP and RAP values were extracted by linear regression analysis of instantaneous arterial blood pressure (ABP) and CBFV tracings. Gosling's pulsatility index (PI) and cerebrovascular resistance (CVR) were calculated. RAP correlated well with CVR at rest and during provocative tests (p = 0.006 approximately <0.001). There was no correlation among CrCP, CVR and PI. The changes in CVR correlated with those in RAP (p = 0.008 for the 5% CO(2) test and p = 0.014 for the hyperventilation test). The changes in PI and CrCP showed significant correlation (p = 0.004 for the 5% CO(2) test and p = 0.003 for the hyperventilation test). RAP reliably reflected cerebrovascular resistance. The changes in CrCP were valuable in assessing cerebrovascular regulation. Estimating changes in CrCP and RAP provided better understanding of the nature of cerebrovascular regulation.