An pilot study on lower limit of cerebral blood flow autoregulation by transcranial Doppler ultrasonography

Objective To study a new usage of transcranial Doppler (TCD) to assess the lower limit of cerebral blood flow autoregulation and widen the field of TCD.Methods The blood velocities of MCA were probed by transcranial Doppler in SD rat, and femoral blood pressure was recorded simultaneously by physiological multimeter. Then lower limit of cerebral blood flow autoregulation was figured out by the clinical closing pressure (CCP) and compared with the results obtainea by hemorrhage hypotension.Results In the process of hemorrhage hypotension, both of the velocity of MCA and the blood quality of common carotid artery were reduced, and the decreasing rate of velocity was almost equal to the one of blood quality (r= 0.951 16 ± 0.057 36 ,P 0.001 ). So the velocity of MCA probed by TCD could replace the blood quality to calculate CCP. The lower limit of autoregulation of normal SD rats working out by CCP was ( 70.88 ± 24.05 )mm Hg(1 mm Hg= 0.133 kPa). It highly correlated to the results measured by hemorrhage hypotension [velocity of MCA:( 72.88 ± 26.26 )mm Hg and quality of CCA:( 75.63 ± 22.22 )mm Hg]. The latter should be replaced by the former.Conclusions The cerebral blood flow can be evaluated conveniently and exactly by lower limit of autoregulation figured out from MCA velocities and arterial blood pressure recorded simultaneously.