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Real-time estimation of cerebrospinal fluid system parameters via oscillating pressure infusion
Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics. (Computer Science and Artificial Intelligence Laboratory, Massachusetts Institute of Technology, Cambridge, MA, USA)
Umeå University, Faculty of Medicine, Department of Pharmacology and Clinical Neuroscience, Neurology.ORCID iD: 0000-0001-6451-1940
Umeå University, Faculty of Science and Technology, Centre for Biomedical Engineering and Physics (CMTF). Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
2010 (English)In: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 48, no 11, 1123-1131 p.Article in journal (Refereed) Published
Abstract [en]

Hydrocephalus is related to a disturbed cerebrospinal fluid (CSF) system. For diagnosis, lumbar infusion test are performed to estimate outflow conductance, C (out), and pressure volume index, PVI, of the CSF system. Infusion patterns and analysis methods used in current clinical practice are not optimized. Minimizing the investigation time with sufficient accuracy is of major clinical relevance. The aim of this study was to propose and experimentally evaluate a new method, the oscillating pressure infusion (OPI). The non-linear model of the CSF system was transformed into a linear time invariant system. Using an oscillating pressure pattern and linear system identification methods, C (out) and PVI with confidence intervals, were estimated in real-time. Forty-two OPI and constant pressure infusion (CPI) investigations were performed on an experimental CSF system, designed with PVI = 25.5 ml and variable C (out). The ARX model robustly estimated C (out) (mean C (out,OPI) - C (out,CPI) = 0.08 μl/(s kPa), n = 42, P = 0.68). The Box-Jenkins model proved most reliable for PVI (23.7 ± 2.0 ml, n = 42). The OPI method, with its oscillating pressure pattern and new parameter estimation methods, efficiently estimated C (out) and PVI as well as their confidence intervals in real-time. The results from this experimental study show potential for the OPI method and supports further evaluation in a clinical setting.

Place, publisher, year, edition, pages
Springer, 2010. Vol. 48, no 11, 1123-1131 p.
Keyword [en]
normal pressure hydrocephalus, system identification, outflow resistance, outflow conductance, intracranial pressure, infusion test
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:umu:diva-36898DOI: 10.1007/s11517-010-0670-6ISI: 000282830000007PubMedID: 20690044OAI: oai:DiVA.org:umu-36898DiVA: diva2:356591
Available from: 2010-10-13 Created: 2010-10-13 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Assessment of cerebrospinal fluid system dynamics: novel infusion protocol, mathematical modelling and parameter estimation for hydrocephalus investigations
Open this publication in new window or tab >>Assessment of cerebrospinal fluid system dynamics: novel infusion protocol, mathematical modelling and parameter estimation for hydrocephalus investigations
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Patients with idiopathic normal pressure hydrocephalus (INPH) have a disturbance in the cerebrospinal fluid (CSF) system. The treatment is neurosurgical – a shunt is placed in the CSF system. The infusion test is used to assess CSF system dynamics and to aid in the selection of patients that will benefit from shunt surgery. The infusion test can be divided into three parts: a mathematical model, an infusion protocol and a parameter estimation method. A non-linear differential equation is used to mathematically describe the CSF system, where two important parameters are the outflow conductance (Cout) and the Pressure Volume Index (PVI). These are used both for clinical and research purposes. The analysis methods for the non-linear CSF system have limited the infusion protocols of presently used infusion investigations. They come with disadvantages such as long investigation time, no estimation of PVI and no measure of the reliability of the estimates.

The aim of this dissertation was to develop and evaluate novel methods for infusion protocols, mathematical modelling and parameter estimation methods for assessment of CSF system dynamics.

The infusion protocols and parameter estimation methods in current use, constant pressure infusion (CPI), constant infusion and bolus infusion, were investigated. The estimates of Cout were compared, both on an experimental set-up and on 20 INPH patients. The results showed that the bolus method produced a significantly higher Cout than the other methods. The study suggested a method with continuous infusion for estimating Cout and emphasized that standardization of Cout measurement is necessary.

The non-linear model of the CSF system was further developed. The ability to model physiological variations that affect the CSF system was incorporated into the model and it was transformed into a linear time-invariant system. This enabled the use of methods developed for identification of such systems. The underlying model for CSF absorption was discussed and the effect of baseline resting pressure (Pr) in the analysis on the estimation of Cout was explored using two different analyses, with and without Pr.

A novel infusion protocol with an oscillating pressure pattern was introduced. This protocol was theoretically better suited for the CSF system characteristics. Three new parameter estimation methods were developed. The adaptive observer was developed from the original non-linear model of the CSF system and estimated Cout in real time. The prediction error method (PEM) and the robust simulation error (RSE) method were based on the transformed linear system, and they estimated both Cout and PVI with confidence intervals in real time. Both the oscillating pressure pattern and the reference CPI protocol were performed on an experimental set-up of the CSF system and on 47 hydrocephalus patients. The parameter estimation methods were applied to the data, and the RSE method produced estimates of Cout that were in good agreement with the reference method and allowed for an individualized and considerably reduced investigation time.

In summary, current methods have been investigated and a novel approach for assessment of CSF system dynamics has been presented. The Oscillating Pressure Infusion method, which includes a new infusion protocol, a further developed mathematical model and new parameter estimation methods has resulted in an improved way to perform infusion investigations and should be used when assessing CSF system dynamics. The advantages of the new approach are the pressure-regulated infusion protocol, simultaneous estimation of Cout and PVI and estimates of reliability that allow for an individualized investigation time.

Place, publisher, year, edition, pages
Umeå: Umeå university, 2011. 50 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1413
Keyword
Medicinsk teknik, hydrocefalus, infusionstest, utflödeskonduktans, systemidentifiering
National Category
Biomedical Laboratory Science/Technology
Identifiers
urn:nbn:se:umu:diva-42383 (URN)978-91-7459-175-0 (ISBN)
Public defence
2011-05-06, Bergasalen, by 27, Umeå universitetssjukhus, Umeå, 09:00 (Swedish)
Opponent
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Available from: 2011-04-13 Created: 2011-04-07 Last updated: 2014-05-16Bibliographically approved

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