Complexity analysis of the cerebrospinal fluid pulse waveform during infusion studies

Abstract

PURPOSE: Nonlinear dynamics has enhanced the diagnostic abilities of some physiological signals. Recent studies have shown that the complexity of the intracranial pressure (ICP) 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 minutes of baseline measurement, infusion was started at a rate of 1.5 ml/minute until a plateau was reached. Once the infusion finished, CSF pressure was recorded until it returned to baseline. We analyzed CSF pressure signals using the LempelZiv (LZ) complexity measure. To characterize 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.

Effect of infusion tests on the dynamical properties of intracranial pressure in hydrocephalus

“…Lumbar ITs were performed as a supplementary hydrodynamic study to help in the decision on the surgical management of patients [8]. Table 1 summarises the data of the population under study.…”

“…Lumbar infusion tests (ITs) are frequently performed in the preoperatory evaluation of subjects who show features of NPH [8]. In ITs, ICP is artificially raised by the injection of fluid in the lumbar CSF space.…”

“…In ITs, ICP is artificially raised by the injection of fluid in the lumbar CSF space. Then, pressure is recorded and the resistance to CSF outflow is calculated [8]. Additionally, the applications of ITs include the assessment of shunt function [9], the analysis of metabolic changes in periventricular white matter [10] and the study of the haemodynamic response associated with ICP [11].…”

“…However, it does not account for all the information contained in the ICP waveform and does not clarify the pathophysiology underlying NPH [8,12]. For this reason, prior research has been devoted to the development of alternatives to study ICP.…”

“…For this reason, prior research has been devoted to the development of alternatives to study ICP. Some of them were based on non-linear methods, including approximate entropy [13], multiscale entropy [14] and Lempel-Ziv complexity [8,15]. Results revealed that intracranial hypertension was associated with a lower ICP signal complexity in children with TBI [13,15] and in adults with hydrocephalus [8].…”