title: Pulse amplitude of intracranial pressure waveform in hydrocephalus.
abstract: BACKGROUND
  There is increasing interest in evaluation of the pulse amplitude of intracranial pressure (AMP) in explaining dynamic aspects of hydrocephalus. We reviewed a large number of ICP recordings in a group of hydrocephalic patients to assess utility of AMP.
  
  
  METHODS
  From a database including approximately 2,100 cases of infusion studies (either lumbar or intraventricular) and overnight ICP monitoring in patients suffering from hydrocephalus of various types (both communicating and non-communicating), etiology and stage of management (non-shunted or shunted) pressure recordings were evaluated. For subgroup analysis we selected 60 patients with idiopathic NPH with full follow-up after shunting. In 29 patients we compared pulse amplitude during an infusion study performed before and after shunting with a properly functioning shunt. Amplitude was calculated from ICP waveforms using spectral analysis methodology.
  
  
  RESULTS
  A large amplitude was associated with good outcome after shunting (positive predictive value of clinical improvement for AMP above 2.5 mmHg was 95%). However, low amplitude did not predict poor outcome (for AMP below 2.5 mmHg 52% of patients improved). Correlations of AMP with ICP and Rcsf were positive and statistically significant (N = 131 with idiopathic NPH; R = 0.21 for correlation with mean ICP and 0.22 with Rcsf; p< 0.01). Correlation with the brain elastance coefficient (or PVI) was not significant. There was also no significant correlation between pulse amplitude and width of the ventricles. The pulse amplitude decreased (p < 0.005) after shunting.
  
  
  CONCLUSIONS
  Interpretation of the ICP pulse waveform may be clinically useful in patients suffering from hydrocephalus. Elevated amplitude seems to be a positive predictor for clinical improvement after shunting. A properly functioning shunt reduces the pulse amplitude.
authors.affiliation: Academic Neurosurgical Unit, Addenbrooke's Hospital, Box 167, Cambridge CB2 0QQ, UK. ZC200@medschl.cam.ac.uk
authors.forename: Z
authors.initials: Z
authors.lastname: Czosnyka
authors.forename: N
authors.initials: N
authors.lastname: Keong
authors.forename: D J
authors.initials: DJ
authors.lastname: Kim
authors.forename: D
authors.initials: D
authors.lastname: Radolovich
authors.forename: P
authors.initials: P
authors.lastname: Smielewski
authors.forename: A
authors.initials: A
authors.lastname: Lavinio
authors.forename: E A
authors.initials: EA
authors.lastname: Schmidt
authors.forename: S
authors.initials: S
authors.lastname: Momjian
authors.forename: B
authors.initials: B
authors.lastname: Owler
authors.forename: J D
authors.initials: JD
authors.lastname: Pickard
authors.forename: M
authors.initials: M
authors.lastname: Czosnyka
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001703:Biophysics; D001794:Blood Pressure; D002557:Cerebrospinal Fluid Shunts / Q000379:methods; D016206:Databases, Bibliographic / Q000706:statistics & numerical data; D005260:Female; D006801:Humans; D006849:Hydrocephalus / Q000145:classification / Q000503:physiopathology* / Q000601:surgery; D007427:Intracranial Pressure / Q000502:physiology*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic; D011674:Pulse; D014160:Transducers, Pressure; D055815:Young Adult