title: Hydrodynamic properties of the Certas hydrocephalus shunt.
abstract: OBJECTIVE
  Independent testing of hydrocephalus shunts provides information about the quality of CSF drainage after shunt implantation. Moreover, hydrodynamic parameters of a valve assessed in the laboratory create a comparative pattern for testing of shunt performance in vivo. This study sought to assess the hydrodynamic parameters of the Certas valve, a new model of a hydrocephalus shunt.
  
  
  METHODS
  The Certas valve is an adjustable ball-on-spring hydrocephalus valve. It can be adjusted magnetically in vivo in 7 steps, equally distributed within the therapeutic limit for hydrocephalus, and the eighth step at high pressures intended to block CSF drainage. The magnetically adjustable rotor is designed to prevent accidental readjustment of the valve in a magnetic field, including clinical MRI.
  
  
  RESULTS
  The pressure-flow performance curves, as well as the operating, opening, and closing pressures, were stable, fell within the specified limits, and changed according to the adjusted performance levels. The valve at settings 1-7 demonstrated low hydrodynamic resistance of 1.4 mm Hg/ml/min, increasing to 5.1 mm Hg/ml/min after connection of a distal drain provided by the manufacturer. At performance Level 8 the hydrodynamic resistance was greater than 20 mm Hg/ml/min. External programming of the valve proved to be easy and reliable. The valve is safe in 3-T MRI and the performance level of the valve is unlikely to be changed. However, with the valve implanted, distortion of the image is substantial. Integration of the valve with the SiphonGuard limits the drainage rate.
  
  
  CONCLUSIONS
  In the laboratory the Certas valve appears to be a reliable differential-pressure adjustable valve. Laboratory evaluation should be supplemented by results of a clinical audit in the future.
authors.affiliation: Neurosurgical Unit, Department of Clinical Neurosciences, University of Cambridge, United Kingdom.
authors.forename: Zofia
authors.initials: Z
authors.lastname: Czosnyka
authors.forename: John D
authors.initials: JD
authors.lastname: Pickard
authors.forename: Marek
authors.initials: M
authors.lastname: Czosnyka
mesh_terms: D015170:Cerebrospinal Fluid Pressure; D002557:Cerebrospinal Fluid Shunts / Q000295:instrumentation / Q000379:methods / Q000592:standards; D004867:Equipment Design; D006801:Humans; D006849:Hydrocephalus / Q000601:surgery*; D057446:Hydrodynamics; D008422:Materials Testing