Analysis of dynamic system compliance for the therapy of Normal Pressure Hydrocephalus

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The number of patients suffering from Normal Pressure Hydrocephalus (NPH), a pathological enlargement of the inner cerebrospinal fluid (CSF) spaces without accompanying pressure rise, has increased in recent years. Currently the pathophysiology is not completely understood, but it is known that reduced intracranial compliance plays an important role in the pathogenesis. Therefore, this research project aims to investigate the intracranial compliance especially concerning its dynamics, which has only been insufficiently analyzed in its relation to NPH, and to develop new therapeutic and diagnostic options for this disease. In order to understand the underlying mechanism leading to a reduced intracranial compliance better, this project initially focuses on the modeling of parameters so far not investigated to perform a sensitivity analysis. Since existing models reproduce the dynamic compliance insufficiently and simplify the reabsorption of cerebrospinal fluid and the formation of the pulse wave, the dynamics of the entire system are distorted. Against this background, a new model will be created, which maps the craniospinal system with a morphologically and functionally justified dynamic compliance. In a finite element model the coupling of the arterial pulse wave over large cranial arteries to the CSF will be modeled, based on the structural mechanical behavior of the different arterial wall layers of connective tissue, and the influence of age-related changes of connective tissue will be analyzed in simulation. Parameter studies should shed light on the influence of various factors on the compliance, on tissue-damaging dynamic loads on the parenchyma and thus on the formation of NPH. On the basis of these findings from the parameter studies an existing real-time capable model with concentrated parameters of the craniospinal system including autoregulation and dynamic spinal compliance will be adapted accordingly. In this model in particular age-related or pathologically altered outflow resistance at the spinal reabsorption sites caused by an age-related shortening of the spinal cord and other effects will be taken into account. Based on an improved understanding of the influencing parameters and a correspondingly extended modeling an artificial compliance and a bioimpedance measuring catheter aiming at an improved therapy will be developed. The real-time model serves to configure the artificial compliance, the newly developed finite element model to design the bioimpedance catheter. Using bioimpedance to measure the ventricular size and the change in size conclusions can be drawn on the overall compliance, which subsequently can be used to control the existing drainage system when necessary. Parallel to the investigation, a modular phantom model will be developed in order to validate the correlations shown in bioelectrical and biomechanical simulation as well as to test both the artificial compliance and the bioimpedance catheter.