Use of Resistance-Area Product Derived from Doppler MCA Velocity to Estimate the Range of Active Cerebrovascular Regulation

Summary

The purpose of the present study was to explore the development of a method to estimate the range of active cerebrovascular regulation using resistance-area product (RAP) derived from transcranial Doppler ultrasound recordings of middle cerebral artery blood velocity (MCAV) obtained before and after physiologic challenge.

Intracranial pressure (ICP), arterial blood pressure (ABP), and MCAV were monitored on 9 patients before and after challenges with either Noradrenlin or CO2 inhalation. One patient was monitored at 24,48, 72, and 96 hrs. For each cardiac cycle a value of RAP was computed from the inverse of the slope of the regression line of paired values of aligned MCAV and ABP recordings. Mean values of percent change of difference of RAP (%ΔRAP) versus change of cerebral perfusion pressure (CPP) were computed. Theoretical values of %ΔRAP were derived from reported lab values of percent change diameter of arterioles versus ABP. Of the nine patients, 22% (2/9) demonstrated either impaired dilation and/or constriction. Furthermore, the correlation between theoretical and experimental values of %ΔRAP and CPP (n = 34) was strong (r =.86, p <.005). The serially-monitored patient failed to dilate during all CO2 challenges and to fully constrict to the Noradrenlin challenge at 72 hrs. %ΔRAP associated with corresponding changes of CPP may have value as a clinical method to estimate the range of active cerebrovascular regulation.