title: Continuous cerebral autoregulation monitoring by improved cross-correlation analysis: comparison with the cuff deflation test.
abstract: OBJECTIVE
  To improve the cross-correlation method for noninvasive, continuous monitoring of cerebral autoregulation, to evaluate this method in humans with intact and impaired autoregulatory capacity, and to compare it to the cuff deflation test.
  
  
  METHODS
  Prospective study in the intensive care unit of a university hospital.
  
  
  METHODS
  Fourteen patients with severe head injury, six patients with subarachnoid hemorrhage, and nine healthy volunteers.
  
  
  METHODS
  Middle cerebral artery flow velocities and arterial blood pressure were monitored continuously. Aaslid's thigh cuff tests were performed and results were scored using Tiecks' model for autoregulation index. Data were then collected without any patient manipulation. The mean time delay between slow spontaneous oscillations of blood pressure and middle cerebral artery flow velocity was calculated by cross-correlation analysis. Data are expressed as median (lower/upper quartile).
  
  
  RESULTS
  Healthy subjects had a higher autoregulation index than patients, 5.0 (5.0/5.5) vs. 3.3 (2.0/4.5). Slow oscillations of blood pressure and middle cerebral artery flow velocity showed a time delay of -2.0 s (-2.7/-1.7) in healthy subjects but were almost synchronal in patients, -0.07 s (-0.5/0.45). Inter-method agreement in diagnosing an intact or impaired cerebral autoregulation was obtained in 108 of 147 examinations of autoregulation (73.5%) and was considered moderate.
  
  
  CONCLUSIONS
  Cross-correlation analysis may serve as a simple, noninvasive, and continuous measure of cerebral autoregulation. The time delay of -2.0[Symbol: see text]s in healthy subjects is in good agreement with other studies. Short-term autoregulation tests and monitoring techniques based on slow spontaneous oscillations should not be used interchangeably.
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine, Carl Gustav Carus University Hospital, Technical University of Dresden, Fetscherstrasse 74, 01307, Dresden, Germany. Melanie.Christ@uniklinikum-dresden.de
authors.forename: Melanie
authors.initials: M
authors.lastname: Christ
authors.forename: Frank
authors.initials: F
authors.lastname: Noack
authors.forename: Tobias
authors.initials: T
authors.lastname: Schroeder
authors.forename: Andreas
authors.initials: A
authors.lastname: Hagmueller
authors.forename: Rainer
authors.initials: R
authors.lastname: Koch
authors.forename: Sven-Axel
authors.initials: SA
authors.lastname: May
authors.forename: Ute
authors.initials: U
authors.lastname: Morgenstern
authors.forename: Maximilian
authors.initials: M
authors.lastname: Ragaller
authors.forename: Ralf
authors.initials: R
authors.lastname: Steinmeier
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001794:Blood Pressure; D001930:Brain Injuries / Q000401:mortality / Q000503:physiopathology*; D005260:Female; D006706:Homeostasis / Q000502:physiology*; D006801:Humans; D007362:Intensive Care Units; D007427:Intracranial Pressure; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic / Q000379:methods*; D011446:Prospective Studies; D013345:Subarachnoid Hemorrhage / Q000401:mortality / Q000503:physiopathology*