Hydrodynamic properties of the Certas hydrocephalus shunt

Laboratory investigation

Restricted access


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.


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.


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.


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.

Abbreviations used in this paper:ICP = intracranial pressure; ISO = International Organization for Standardization; NPH = normal-pressure hydrocephalus; UK = United Kingdom.

Article Information

Address correspondence to: Marek Czosnyka, Ph.D., Neurosurgical Unit, Box 167, Addenbrooke's Hospital, Cambridge, United Kingdom CB2 0QQ. email: mc141@medschl.cam.ac.uk.

Please include this information when citing this paper: published online December 7, 2012; DOI: 10.3171/2012.10.PEDS12239.

© AANS, except where prohibited by US copyright law.



  • View in gallery

    Schematic diagram of the construction of the Certas valve. This figure was scanned from the leaflet provided by the manufacturer.

  • View in gallery

    Schematic diagram of the shunt testing apparatus (see Methods section in text for description).

  • View in gallery

    Pressure-flow performance curves of a valve at a fixed pressure level. A: Individual pressure-flow curve for the Certas valve set at performance Level 4. B: Summary of pressure-flow curves after 10 tests. C: Pressure-flow curves without (left) and with (right) a distal drain. D: Pressure-flow curve of the valve with SiphonGuard, with the valve set at performance Level 3. Arrows show the direction of change of flow through the shunt system.

  • View in gallery

    Graphs showing the group of pressure-flow curves for different performance levels (upper), and mean values, 95% CIs (vertical bars), and ranges (horizontal bars) for the valve's operating pressure at different performance levels (lower).

  • View in gallery

    Distortion of an MR image by a Certas valve in a water-filled container, with a diameter equivalent to an adult skull. Upper: Gradient echo image. Lower: Spin echo image.


  • 1

    Aschoff AKremer PBenesch CFruh KKlank AKunze S: Overdrainage and shunt technology. A critical comparison of programmable, hydrostatic and variable-resistance valves and flow-reducing devices. Childs Nerv Syst 11:1932021995

  • 2

    Børgesen SEGjerris F: The predictive value of conductance to outflow of CSF in normal pressure hydrocephalus. Brain 105:65861982

  • 3

    Bromby ACzosnyka ZAllin DRichards HKPickard JDCzosnyka M: Laboratory study on “intracranial hypotension” created by pumping the chamber of a hydrocephalus shunt. Cerebrospinal Fluid Res 4:22007

  • 4

    Chung SKim JKWang KCHan DCChang JK: Development of MEMS-based cerebrospinal fluid shunt system. Biomed Microdevices 5:3113212003

  • 5

    Czosnyka MCzosnyka ZWhitehouse HPickard JD: Hydrodynamic properties of hydrocephalus shunts: United Kingdom Shunt Evaluation Laboratory. J Neurol Neurosurg Psychiatry 62:43501997

  • 6

    Czosnyka ZCzosnyka MPickard JD: Hydrodynamic performance of a new siphon preventing device: the SiphonGuard. J Neurol Neurosurg Psychiatry 66:4084091999

  • 7

    Czosnyka ZCzosnyka MRichards HKPickard JD: Laboratory testing of hydrocephalus shunts—conclusion of the U.K. Shunt evaluation programme. Acta Neurochir (Wien) 144:5255382002

  • 8

    Czosnyka ZCzosnyka MRichards HKPickard JD: Posture-related overdrainage: comparison of the performance of 10 hydrocephalus shunts in vitro. Neurosurgery 42:3273341998

  • 9

    Czosnyka ZHCieslicki KCzosnyka MPickard JD: Hydrocephalus shunts and waves of intracranial pressure. Med Biol Eng Comput 43:71772005

  • 10

    Davson HWelch KSegal M: Physiology and Pathophysiology of the Cerebrospinal Fluid New YorkChurchill Livingstone1987

  • 11

    Drake JMSainte-Rose C: The Shunt Book OxfordWiley-Blackwell1995

  • 12

    Ekstedt J: CSF hydrodynamic studies in man. 2. Normal hydrodynamic variables related to CSF pressure and flow. J Neurol Neurosurg Psychiatry 41:3453531978

  • 13

    Ezkerra AFernández LJMayora KRuano-López JM: SU8 diaphragm micropump with monolithically integrated cantilever check valves. Lab Chip 11:332033252011

  • 14

    Horton R: A serious regulatory failure, with urgent implications. Lancet 379:1062012. (Letter)

  • 15

    Kremer PAschoff AKunze S: Risks of using siphon-reducing devices. Childs Nerv Syst 10:2312351994

  • 16

    Petrella GCzosnyka MSmielewski PAllin DGuazzo EPPickard JD: In vivo assessment of hydrocephalus shunt. Acta Neurol Scand 120:3173232009

  • 17

    Sainte-Rose CHooven MDHirsch JF: A new approach in the treatment of hydrocephalus. J Neurosurg 66:2132261987

  • 18

    Smielewski PCzosnyka ZKasprowicz MPickard JDCzosnyka M: ICM+: a versatile software for assessment of CSF dynamics. Acta Neurochir Suppl 114:75792012

  • 19

    Stephensen HAndersson NEklund AMalm JTisell MWikkelsö C: Objective B wave analysis in 55 patients with non-communicating and communicating hydrocephalus. J Neurol Neurosurg Psychiatry 76:9659702005




All Time Past Year Past 30 Days
Abstract Views 73 73 7
Full Text Views 152 152 3
PDF Downloads 203 203 1
EPUB Downloads 0 0 0


Google Scholar