title: Pulse pressure waveform in hydrocephalus: what it is and what it isn't.
abstract: OBJECTIVE
  Apart from its mean value, the pulse waveform of intracranial pressure (ICP) is an essential element of pressure recording. The authors reviewed their experience with the measurement and interpretation of ICP pulse amplitude by referring to a database of recordings in hydrocephalic patients.
  
  
  METHODS
  The database contained computerized pressure recordings from 2100 infusion studies (either lumbar or intraventricular) or overnight ICP monitoring sessions in patients suffering from hydrocephalus of various types (both communicating and noncommunicating), origins, and stages of management (shunt or no shunt). Amplitude was calculated from ICP waveforms by using a spectral analysis methodology.
  
  
  RESULTS
  The appearance of a pulse waveform amplitude is positive evidence of a technically correct recording of ICP and helps to distinguish between postural and vasogenic variations in ICP. Pulse amplitude is significantly correlated with the amplitude of cerebral blood flow velocity (R = 0.4, p = 0.012) as assessed using Doppler ultrasonography. Amplitude is positively correlated with a mean ICP (R = 0.21 in idiopathic normal-pressure hydrocephalus [NPH]; number of cases 131; p < 0.01) and resistance to cerebrospinal fluid outflow (R = 0.22) but does not seem to be correlated with cerebrospinal elasticity, dilation of ventricles, or severity of hydrocephalus (NPH score). Amplitude increases slightly with age (R = 0.39, p < 0.01; number of cases 46). A positive association between pulse amplitude and increased ICP during an infusion study is helpful in distinguishing between hydrocephalus and predominant brain atrophy. A large amplitude is associated with a good outcome after shunting (positive predictive power 0.9), whereas a low amplitude has no predictive power in outcome prognostication (0.5). Pulse amplitude is reduced by a properly functioning shunt.
  
  
  CONCLUSIONS
  Proper recording, detection, and interpretation of ICP pulse waveforms provide clinically useful information about patients suffering from hydrocephalus.
authors.affiliation: Academic Neurosurgical Unit, Addenbrooke's Hospital, Cambridge, United Kingdom. mc141@medschl.cam.ac.uk <mc141@medschl.cam.ac.uk>
authors.forename: Marek
authors.initials: M
authors.lastname: Czosnyka
authors.forename: Zofia
authors.initials: Z
authors.lastname: Czosnyka
authors.forename: Nicole
authors.initials: N
authors.lastname: Keong
authors.forename: Andreas
authors.initials: A
authors.lastname: Lavinio
authors.forename: Piotr
authors.initials: P
authors.lastname: Smielewski
authors.forename: Shahan
authors.initials: S
authors.lastname: Momjian
authors.forename: Eric A
authors.initials: EA
authors.lastname: Schmidt
authors.forename: Gianpaolo
authors.initials: G
authors.lastname: Petrella
authors.forename: Brian
authors.initials: B
authors.lastname: Owler
authors.forename: John D
authors.initials: JD
authors.lastname: Pickard
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging; D001284:Atrophy; D001783:Blood Flow Velocity; D001921:Brain / Q000473:pathology; D002560:Cerebrovascular Circulation; D016208:Databases, Factual; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D006849:Hydrocephalus / Q000175:diagnosis / Q000503:physiopathology*; D007427:Intracranial Pressure; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D018608:Ultrasonography, Doppler