title: Reliability, asymmetry, and age influence on dynamic cerebral autoregulation measured by spontaneous fluctuations of blood pressure and cerebral blood flow velocities in healthy individuals.
abstract: BACKGROUND
  Cerebral autoregulation (CA) enables the brain to maintain stable cerebral blood flow (CBF). CA can be assessed noninvasively by determining correlations between CBF velocity (CBFV) and spontaneous changes in blood pressure. Postrecording signal analysis methods have included both frequency- and time-domain methods. However, the test-retest reliability, cross-validation, and determination of normal values have not been adequately established.
  
  
  METHODS
  In 53 healthy volunteers, a transfer function analysis was applied to calculate phase shift (PS) and gain in the low frequency range (.06-.12 Hz) where CA is most apparent. Correlation analysis was used to derive mean velocity index (Mx). Intraclass correlation and bivariate correlation coefficients were applied to assess asymmetry, cross-validity, and test-retest results: The bihemispheric average PS, gain, and Mx means were 45.99+/-14.24°, .62+/-.38 cm/second/mmHg, and .41+/-.13, respectively. Gain exhibited a difference by age (P = .03). PS, gain, and Mx values showed excellent interhemispheric correlation (r > .8; P < .001). PS and gain showed good reliability (R ICC = .632, L ICC = .576; P < .001). PS and Mx showed fair correlation (r = -.37; P < .001).
  
  
  CONCLUSIONS
  CA parameters obtained by time- and frequency-domain methods correlate well, and show good interhemispheric and test-retest reliability. Group means from healthy controls may provide adequate norms for determining abnormal CA in cerebrovascular patients.
authors.affiliation: From the Department of Neurology, Stroke Division, Columbia University, New York, NY.
authors.forename: Santiago
authors.initials: S
authors.lastname: Ortega-Gutierrez
authors.forename: Nils
authors.initials: N
authors.lastname: Petersen
authors.forename: Arjun
authors.initials: A
authors.lastname: Masurkar
authors.forename: Andres
authors.initials: A
authors.lastname: Reccius
authors.forename: Amy
authors.initials: A
authors.lastname: Huang
authors.forename: Min
authors.initials: M
authors.lastname: Li
authors.forename: Jae H
authors.initials: JH
authors.lastname: Choi
authors.forename: Randolph S
authors.initials: RS
authors.lastname: Marshall
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D001783:Blood Flow Velocity / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology*; D001795:Blood Pressure Determination / Q000379:methods*; D001921:Brain / Q000098:blood supply / Q000502:physiology*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D003936:Diagnosis, Computer-Assisted / Q000379:methods; D005260:Female; D006706:Homeostasis / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D017585:Ultrasonography, Doppler, Transcranial / Q000379:methods*; D014655:Vascular Resistance / Q000502:physiology
keywords: Cerebral autoregulation; autoregulatory index; gain; transcranial Doppler phase shift