title: The continuous assessment of cerebrovascular reactivity: a validation of the method in healthy volunteers.
abstract: Using transcranial Doppler ultrasonography, we investigated the moving correlation between slow waves in arterial blood pressure (ABP) and blood flow velocity (FV) at different levels of cerebrovascular vasodilation provoked by changing PETCO2. Fourteen healthy volunteers were examined. The FV in middle cerebral arteries, PETCO2, and ABP were recorded during normocapnia, hypercapnia, and hypocapnia. The moving correlation coefficients between ABP and mean FV (FVm) or systolic FV (FVs) during spontaneous fluctuations in ABP were calculated for 3-min epochs and averaged for each investigation, thus yielding the mean index (Mx) and systolic index (Sx). As a reference method, Aaslid's cuff tests were performed to obtain the rate of regulation (RoR). RoR, Mx, and Sx significantly depended on PETCO2 (analysis of variance, P < 0.00001). At high PETCO2, cerebrovascular reactivity was disturbed as reflected in RoR values of < 0.17/s for all volunteers and increased values of Mx (> 0.4 in 86% of volunteers) and Sx (> 0.2 in 79% of volunteers). Overall, there was a reasonably good correlation of both Mx and Sx with RoR (R2 = 0.65 and 0.58, respectively).
  
  
  CONCLUSIONS
  Indices derived from the correlation between spontaneous fluctuations of blood flow velocity wave form and arterial blood pressure may be used for the noninvasive continuous monitoring of cerebrovascular reactivity.
authors.affiliation: Wolfson Brain Imaging Centre, Cambridge Medical Research Council's Centre for Brain Repair and Academic Neurosurgery Unit, Addenbrooke's Hospital, United Kingdom. S.K.Piechnik@iname.com
authors.forename: S K
authors.initials: SK
authors.lastname: Piechnik
authors.forename: X
authors.initials: X
authors.lastname: Yang
authors.forename: M
authors.initials: M
authors.lastname: Czosnyka
authors.forename: P
authors.initials: P
authors.lastname: Smielewski
authors.forename: S H
authors.initials: SH
authors.lastname: Fletcher
authors.forename: A L
authors.initials: AL
authors.lastname: Jones
authors.forename: J D
authors.initials: JD
authors.lastname: Pickard
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001783:Blood Flow Velocity / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology; D002245:Carbon Dioxide / Q000008:administration & dosage / Q000097:blood; D002536:Cerebral Arteries / Q000502:physiology; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005260:Female; D006801:Humans; D006935:Hypercapnia / Q000503:physiopathology; D016857:Hypocapnia / Q000503:physiopathology; D008297:Male; D015203:Reproducibility of Results; D012815:Signal Processing, Computer-Assisted; D013599:Systole; D017585:Ultrasonography, Doppler, Transcranial; D014664:Vasodilation / Q000502:physiology
chemical_list: D002245:Carbon Dioxide