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Dependency of cerebrospinal fluid outflow resistance on intracranial pressure
Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics. Department of Biomedical Engineering and Informatics, Umeå University Hospital.
Umeå University, Faculty of Medicine, Department of Pharmacology and Clinical Neuroscience, Neurology.ORCID iD: 0000-0001-6451-1940
Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics. Department of Biomedical Engineering and Informatics, Umeå University Hospital.
2008 (English)In: Journal of Neurosurgery, ISSN 0022-3085, Vol. 109, no 5, 918-922 p.Article in journal (Refereed) Published
Abstract [en]

OBJECT: The outflow resistance (Rout) of the cerebrospinal fluid (CSF) system has generally been accepted by most investigators as independent of intracranial pressure (ICP), but there are also those claiming that it is not. The general belief is that this question has been investigated numerous times in the past, but few studies have actually been specifically aimed at looking at this relationship, and no study has been able to provide scientific evidence to elucidate fully this fundamental and important issue. The objective of this study was to investigate the relationship between ICP and CSF outflow in 30 patients investigated for idiopathic normal-pressure hydrocephalus. METHODS: Lumbar infusion tests with constant pressure levels were performed, and ICP and corresponding flow were measured on 6 pressure levels for each patient. All data were standardized for comparison. RESULTS: In the range of moderate increases from baseline pressure (approximately 5-12 mm Hg, mean baseline pressure 11.7 mm Hg), the assumption of a pressure-independent Rout was confirmed (p = 0.5). However, when the pressure increment from baseline pressure was larger (approximately 15-22 mm Hg), the relationship had a nonlinear tendency (p < 0.05). CONCLUSIONS: The results of this study support the classic textbook theory of a pressure-independent Rout in the normal ICP range, where the CSF system is commonly operating. However, the theory might have to be questioned in regions where ICP exceeds baseline pressure by too much.

Place, publisher, year, edition, pages
2008. Vol. 109, no 5, 918-922 p.
Keyword [en]
infusion test, intracranial pressure, linearity, normal-pressure hydrocephalus, outflow resistance
National Category
Neurology
Identifiers
URN: urn:nbn:se:umu:diva-20833DOI: 10.3171/JNS/2008/109/11/0918ISI: 000260362100020PubMedID: 18976085Scopus ID: 2-s2.0-58149168576OAI: oai:DiVA.org:umu-20833DiVA: diva2:209694
Funder
Swedish Research Council, 621-2005-304-7
Available from: 2009-03-26 Created: 2009-03-26 Last updated: 2015-02-12Bibliographically approved
In thesis
1. Cerebrospinal fluid infusion methods: development and validation on patients with idiopathic normal pressure hydrocephalus
Open this publication in new window or tab >>Cerebrospinal fluid infusion methods: development and validation on patients with idiopathic normal pressure hydrocephalus
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Cerebrospinal fluid (CSF) infusion tests can be used to estimate the dynamic properties of the CSF system. Idiopathic normal pressure hydrocephalus (INPH) is a syndrome signified by a disturbance to the CSF system, where the cause is unknown and the diagnosis is difficult to determine. As an aid in identifying patients with INPH who will improve after shunt surgery, infusion tests are commonly used to determine the outflow conductance (Cout), or outflow resistance (Rout=1/Cout), of the CSF system. The tests are also used to determine shunt function in vivo. The general aim of this thesis was to develop and validate CSF infusion methods, to investigate the dynamics of the CSF system. The methods should be applicable to patients with INPH, to aid in the quest to further improve the diagnosis and management of this syndrome.

An existing mathematical model describing the dynamics of the CSF system was further developed. The characteristics of the model were verified and the effect of expanding intracranial air on the intracranial pressure (ICP) was simulated. The simulations supported the recommendation to maintain sea-level pressure during air ambulance transportation of patients with suspected intracranial air.

A recently developed infusion apparatus was evaluated, on an experimental model as well as on a patient material. The repetitiveness in estimating Cout was found to be good. A statistically significant difference was found between the repeated Cout estimations in the patient group, indicating that there might have been a small physiological change introduced during the infusion test. A parameter, ∆Cout, was proposed and evaluated. It proved to reflect the reliability of individual Cout investigations in a clinically useful way, as well as to provide easily interpreted information.

An adaptive algorithm for assessment of Cout was developed and evaluated on a patient group. The new algorithm was shown to reduce the investigation time, from 60 minutes, by 14.3 ± 5.9 minutes (mean ± SD), p<0.01, without reducing the reliability of the estimated Cout below clinically relevant levels.

The relationship between ICP and CSF outflow was studied in a group of patients investigated for INPH. It was found that in the range of moderate increase from baseline pressure, the assumption of a pressure independent Rout was confirmed (p=0.5). However, at larger pressure increments, the relationship had a non-linear tendency (p<0.05). This indicates that the traditional view of a pressure independent Rout might have to be questioned in the region where ICP exceeds baseline pressure too much.

Infusion tests can be performed in different ways, where three main categories may be distinguished. The bolus infusion method was compared to the constant pressure and constant flow infusion methods, on an experimental model as well as on a patient material. When physiological pressure fluctuations were added to the model, significant differences were found in the determination of Cout in the range of clinical importance, i.e. low Cout (p<0.05). The finding was supported by the patient investigations, the difference was however not significant.

With the application of the new methods developed in this thesis, and the increased knowledge concerning relationships between CSF dynamic parameters, the CSF infusion test was further improved with the ability to increase measurement reliability in a reduced time. This constitutes a good basis to perform a large multi-centre study with the main goal to determine the predictive value of the parameter Cout.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2007. 74 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1116
Keyword
Infusion test, idiopathic normal pressure hydrocephalus, outflow conductance, outflow resistance, intracranial pressure, cerebrospinal fluid dynamics
National Category
Medical Engineering
Research subject
medicinsk informatik
Identifiers
urn:nbn:se:umu:diva-1367 (URN)
Public defence
2007-10-12, Betula, 6M, NUS, Umeå, 09:00 (English)
Opponent
Supervisors
Available from: 2008-09-02 Created: 2008-09-02 Last updated: 2014-05-16Bibliographically approved

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Andersson, NinaMalm, JanEklund, Anders

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