title: Cerebral autoregulation among patients with symptoms of hydrocephalus.
abstract: OBJECTIVE
  To study the relationship between the resistance to cerebrospinal fluid (CSF) outflow and cerebral autoregulation.
  
  
  METHODS
  We examined 35 patients who presented with ventricular dilation and clinical symptoms of communicating hydrocephalus. For all of these patients, CSF compensatory reserve was investigated by using a computerized infusion test, with simultaneous recording of blood flow velocity wave forms (by using transcranial Doppler ultrasonography) and arterial blood pressure (with a Finapress finger cuff). The resistance to CSF outflow was calculated as the absolute increase in intracranial pressure (interpolated over vasogenic waves) divided by the infusion rate (1.5 ml/min in most cases). The index of autoregulation was assessed as a correlation coefficient (moving time window of 5 min) between slow waves (with periods of 20 s to 2 min) in mean blood flow velocity and cerebral perfusion pressure.
  
  
  RESULTS
  The mean intracranial pressure increased during the test, from 6 mm Hg (standard deviation, 6 mm Hg) to 20 mm Hg (standard deviation, 10 mm Hg) (P < 0.0001). The index of autoregulation was significantly correlated with the resistance to CSF outflow (r = -0.41, P < 0.03), indicating better autoregulation with greater resistance to CSF outflow.
  
  
  CONCLUSIONS
  Patients presenting with ventricular dilation may exhibit either decreased (atrophy) or increased (normal-pressure hydrocephalus) resistance to CSF outflow. Increased resistance is correlated with preserved autoregulation. Patients with low resistance, suggesting brain atrophy, more often have disturbed autoregulation in the middle cerebral artery territory, as assessed by transcranial Doppler ultrasonography.
authors.affiliation: Academic Neurosurgical Unit and Wolfson Brain Imaging Centre, Addenbrooke's Hospital, Cambridge, England. ZC200@MEDSCHL.CAM.AC.UK
authors.forename: Zofia H
authors.initials: ZH
authors.lastname: Czosnyka
authors.forename: Marek
authors.initials: M
authors.lastname: Czosnyka
authors.forename: Peter C
authors.initials: PC
authors.lastname: Whitfield
authors.forename: Tim
authors.initials: T
authors.lastname: Donovan
authors.forename: John D
authors.initials: JD
authors.lastname: Pickard
mesh_terms: D000328:Adult; D000368:Aged; D002555:Cerebrospinal Fluid / Q000502:physiology; D002560:Cerebrovascular Circulation; D005260:Female; D006439:Hemodynamics; D006706:Homeostasis; D006801:Humans; D006849:Hydrocephalus / Q000000981:diagnostic imaging / Q000503:physiopathology*; D007427:Intracranial Pressure; D008297:Male; D008875:Middle Aged; D017585:Ultrasonography, Doppler, Transcranial