title: A method of evaluating the lower limit of cerebral autoregulation and its correlation with blood pressure by transcranial Doppler in rats.
abstract: The aim of present study was to validate the assessment of lower limit of cerebral autoregulation (LLCA) as derived from mean artery blood pressure (MABP) and cerebral zero flow pressure (ZFP) by means of transcranial Doppler (TCD) and to determine the accurate relationship between LLCA and MABP in stroke-prone renovascular hypertensive rats (RHRSP). We studied two groups of rats: RHRSP and normal controls. Blood flow velocity of middle cerebral artery was monitored by TCD and arterial blood pressure was recorded in right femoral artery to compute the ZFP. The value of LLCA was determined as the difference between MABP and ZFP and validated by the value determined by blood withdrawal-induced cerebral autoregulation. In normal rats, the LLCA derived from the new method was 69.8 ± 8.7 mm Hg, from the change of blood velocity was 69.4 ± 9.8 mmHg and from blood volume flow after blood withdrawal was 68.8 ± 9.7 mmHg. In the RHRSP group, the corresponding values of LLCA were 109.1 ± 17.2 mm Hg, 110.0 ± 18.0 mm Hg and 109.0 ± 19.3 mm Hg, respectively. In each group, there was no statistically significant difference among the three values. LLCA in RHRSP began to increase 6 weeks after hypertension-induced operation, significantly higher than controls (p < 0.05), and stabilized at 110 mm Hg, 10 weeks after operation. The increase of LLCA was positively correlated with MABP, following an "S" curve, demonstrating that the change of LLCA was more obvious in the middle range of MABP in RHRSP (R(2) = 0.8848, p < 0.05). In conclusion, TCD is a valid and noninvasive method for determination of LLCA compared with the classic method in rats. Our data demonstrated that the change of LLCA may be correlated with MABP, following an "S" curve relationship.
authors.affiliation: Institute of Neuroscience, the Second Affiliated Hospital, Guangzhou Medical University, Guangzhou, P.R. China. qcgao@263.net
authors.forename: Qing Chun
authors.initials: QC
authors.lastname: Gao
authors.forename: Xian
authors.initials: X
authors.lastname: Fu
authors.forename: Xiang Yan
authors.initials: XY
authors.lastname: Chen
authors.forename: Jin Sheng
authors.initials: JS
authors.lastname: Zeng
authors.forename: Ru Xun
authors.initials: RX
authors.lastname: Huang
mesh_terms: D000818:Animals; D001783:Blood Flow Velocity; D001794:Blood Pressure; D002560:Cerebrovascular Circulation; D006706:Homeostasis; D019586:Intracranial Hypertension / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D013223:Statistics as Topic; D017585:Ultrasonography, Doppler, Transcranial / Q000379:methods*