title: Complexity analysis of the cerebrospinal fluid pulse waveform during infusion studies.
abstract: OBJECTIVE
  Nonlinear dynamics has enhanced the diagnostic abilities of some physiological signals. Recent studies have shown that the complexity of the intracranial pressure waveform decreases during periods of intracranial hypertension in paediatric patients with acute brain injury. We wanted to assess changes in the complexity of the cerebrospinal fluid (CSF) pressure signal over the large range covered during the study of CSF circulation with infusion studies.
  
  
  METHODS
  We performed 37 infusion studies in patients with hydrocephalus of various types and origin (median age 71 years; interquartile range 60-77 years). After 5 min of baseline measurement, infusion was started at a rate of 1.5 ml/min until a plateau was reached. Once the infusion finished, CSF pressure was recorded until it returned to baseline. We analysed CSF pressure signals using the Lempel-Ziv (LZ) complexity measure. To characterise more accurately the behaviour of LZ complexity, the study was segmented into four periods: basal, early infusion, plateau and recovery.
  
  
  RESULTS
  The LZ complexity of the CSF pressure decreased in the plateau of the infusion study compared to the basal complexity (p=0.0018). This indicates loss of complexity of the CSF pulse waveform with intracranial hypertension. We also noted that the level of complexity begins to increase when the infusion is interrupted and CSF pressure drops towards the initial values.
  
  
  CONCLUSIONS
  The LZ complexity decreases when CSF pressure reaches the range of intracranial hypertension during infusion studies. This finding provides further evidence of a phenomenon of decomplexification in the pulsatile component of the pressure signal during intracranial hypertension.
authors.affiliation: Department of Neurosurgery, University Hospital of León, León, Spain. dsantamarta@saludcastillayleon.es
authors.forename: David
authors.initials: D
authors.lastname: Santamarta
authors.forename: Roberto
authors.initials: R
authors.lastname: Hornero
authors.forename: Daniel
authors.initials: D
authors.lastname: Abásolo
authors.forename: Milton
authors.initials: M
authors.lastname: Martínez-Madrigal
authors.forename: Javier
authors.initials: J
authors.lastname: Fernández
authors.forename: Jose
authors.initials: J
authors.lastname: García-Cosamalón
mesh_terms: D000368:Aged; D015170:Cerebrospinal Fluid Pressure / Q000502:physiology*; D006801:Humans; D006849:Hydrocephalus / Q000134:cerebrospinal fluid; D007427:Intracranial Pressure / Q000502:physiology*; D008875:Middle Aged; D017711:Nonlinear Dynamics