Correlations among critical closing pressure, pulsatility index and cerebrovascular resistance.

Section of Neurology, Department of Internal Medicine, Veterans General Hospital-Taichung, Taichung Taiwan and the Institute of Clinical Medicine, National Yang-Ming University, Taipei 11217, Taiwan.
Ultrasound in Medicine & Biology (Impact Factor: 2.1). 11/2004; 30(10):1329-35. DOI: 10.1016/j.ultrasmedbio.2004.08.006
Source: PubMed

ABSTRACT 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.

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    ABSTRACT: Estimating changes in critical closing pressure (CrCP) and resistance area product (RAP) provided better understanding of the nature of cerebrovascular regulation (arterial stiffening or narrowing). The critical closing pressure of the cerebral circulation indicates the value of the arterial blood pressure (ABP) at which cerebral blood flow (CBF) approaches zero. Measurements in animals and in humans have shown that the CrCP is significantly greater than zero. Studies of the cerebral circulation need to take CrCP and RAP into account, to obtain more accurate estimates of cerebrovascular resistance changes, and to reflect the correct dynamic relationship between instantaneous ABP and CBF. This analysis was performed on 48 healthy subjects and 11 hypertensive subjects. Due to the non-linear shape of the complete ABP-CBF curve, most methods proposed for estimation of CrCP and RAP can only represent the linear range of the pressure-flow (or velocity) relationship.
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