title: Hydrocephalus shunt technology: 20 years of experience from the Cambridge Shunt Evaluation Laboratory.
abstract: OBJECTIVE
  The Cambridge Shunt Evaluation Laboratory was established 20 years ago. This paper summarizes the findings of that laboratory for the clinician.
  
  
  METHODS
  Twenty-six models of valves have been tested long-term in the shunt laboratory according to the expanded International Organization for Standardization 7197 standard protocol.
  
  
  RESULTS
  The majority of the valves had a nonphysiologically low hydrodynamic resistance (from 1.5 to 3 mm Hg/[ml/min]), which may result in overdrainage related to posture and during nocturnal cerebral vasogenic waves. A long distal catheter increases the resistance of these valves by 100%-200%. Drainage through valves without a siphon-preventing mechanism is very sensitive to body posture, which may result in grossly negative intracranial pressure. Siphon-preventing accessories offer a reasonable resistance to negative outlet pressure; however, accessories with membrane devices may be blocked by raised subcutaneous pressure. In adjustable valves, the settings may be changed by external magnetic fields of intensity above 40 mT (exceptions: ProGAV, Polaris, and Certas). Most of the magnetically adjustable valves produce large distortions on MRI studies.
  
  
  CONCLUSIONS
  The behavior of a valve revealed during testing is of relevance to the surgeon and may not be adequately described in the manufacturer's product information. The results of shunt testing are helpful in many circumstances, such as the initial choice of shunt and the evaluation of the shunt when its dysfunction is suspected.
authors.affiliation: Department of Neurosurgery, Cambridge University Hospital National Health Service Trust, Cambridge, United Kingdom.
authors.forename: Aswin
authors.initials: A
authors.lastname: Chari
authors.forename: Marek
authors.initials: M
authors.lastname: Czosnyka
authors.forename: Hugh K
authors.initials: HK
authors.lastname: Richards
authors.forename: John D
authors.initials: JD
authors.lastname: Pickard
authors.forename: Zofia H
authors.initials: ZH
authors.lastname: Czosnyka
mesh_terms: D002557:Cerebrospinal Fluid Shunts / Q000295:instrumentation / Q000379:methods* / Q000639:trends*; D004322:Drainage / Q000295:instrumentation / Q000379:methods; D019544:Equipment Failure Analysis / Q000379:methods*; D006801:Humans; D006849:Hydrocephalus / Q000601:surgery*; D057446:Hydrodynamics; D060526:Magnetic Fields; D008422:Materials Testing / Q000379:methods*; D011312:Pressure; D011474:Prosthesis Design / Q000379:methods; D013696:Temperature; D006113:United Kingdom