title: Symmetry of cerebral hemodynamic indices derived from bilateral transcranial Doppler.
abstract: OBJECTIVE
  The authors evaluated with bilateral transcranial Doppler (TCD) ultrasonography the norm of interhemispheric difference for several cerebrovascular hemodynamic parameters.
  
  
  METHODS
  Forty-four volunteers (33 male, 11 female; average age = 21 years; range, 20-23 years) were studied. The authors recorded bilateral systolic, diastolic, and mean flow velocity (FV) and noninvasive systolic, diastolic, and mean arterial blood pressure. Calculated indices included Gosling's pulsatility index (GPI), an index of autoregulation (Mx), critical closing pressure (CCP), and a noninvasive estimator of cerebral perfusion pressure (nCPP). All indices were averaged per side and patient. For each parameter, the left-right correlation coefficient (r2) and the 95% confidence limit of the left-right differences were calculated.
  
  
  RESULTS
  All TCD-derived indices displayed significant correlations between the left and right sides: r2 = 0.49 for mean FV (FVm), r2 = 0.66 for GPI, r2 = 0.79 for Mx, r2 = 0.93 for CCP, and r2 = 0.94 for nCPP. The 95% confidence intervals for the left-right differences were 20 cm/s for FVm, 0.16 for GPI, 0.18 for Mx, 13 mm Hg for CCP, and 4.6 mm Hg for nCPP.
  
  
  CONCLUSIONS
  This study gives the reference values for the assessment of left-right symmetry of cerebral hemodynamics using various TCD-derived indices. These reference values should be useful for clinical studies assessing the left-right asymmetry of cerebral hemodynamics on a daily basis.
authors.affiliation: Academic Neurosurgery Unit, PO Box 167, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2QQ, United Kingdom. eas49@cam.ac.uk
authors.forename: Eric A
authors.initials: EA
authors.lastname: Schmidt
authors.forename: Stefan K
authors.initials: SK
authors.lastname: Piechnik
authors.forename: Piotr
authors.initials: P
authors.lastname: Smielewski
authors.forename: Andreas
authors.initials: A
authors.lastname: Raabe
authors.forename: Basil F
authors.initials: BF
authors.lastname: Matta
authors.forename: Marek
authors.initials: M
authors.lastname: Czosnyka
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity / Q000502:physiology; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005260:Female; D006801:Humans; D007427:Intracranial Pressure / Q000502:physiology; D008297:Male; D011673:Pulsatile Flow / Q000502:physiology; D012016:Reference Values; D012044:Regression Analysis; D017585:Ultrasonography, Doppler, Transcranial