Marian Walter

Der Stellenwert hydrostatischer Ventile in der Therapie des chronischen Hydrozephalus

ZusammenfassungFrühere Designänderungen an den Hydrozephalusventilen, die darauf zielten, die gefürchtete Komplikation der Überdrainage zu verhindern, erwiesen sich als ungeeignet. Seit Mitte der 90er Jahre stehen neue Hydrozephalusventile – sog. hydrostatische Ventile –, die diese Problematik verringern sollen, zur Verfügung. Mit der vorliegenden Studie sollte untersucht werden, ob das Problem der Überdrainage durch diese neuen Ventilkonstruktionen zu verringern ist.Bei 45 Patienten mit chronischem Hydrozephalus wurde der klinische Status sowie die Ventrikelweite an Hand von CCT oder MRI vor und in festen Intervallen (1, 6, 26 Wochen) nach Shuntimplantation evaluiert. 35 Patienten erhielten ein Miethke Dual-Switch-Ventil (Therapiegruppe 1), die übrigen ein programmierbares Codmann-Hakim-Ventil mit einem Miethke-Shuntassistenten (Therapiegruppe 2) als Antigravitationseinheit. Eine 3. Therapiegruppe stellten Patienten (n=6) dar, die bereits seit längerem ein Ventil hatten und unter Überdrainagebeschwerden litten, die auf konservative Maßnahmen nicht ansprachen. Diesen Patienten wurde zum existierenden Ventil zusätzlich ein Miethke-Shuntassistent implantiert.Eine permanente deutliche Besserung trat bei Patienten in Behandlungsgruppe 1 und 2 in etwa 80% auf, etwas mehr als 10% zeigten eine mäßige Besserung. Klinische oder radiologische Zeichen der Überdrainage traten bei 3 Patienten in der 1. postoperativen Woche auf, verschwanden jedoch ohne jegliche operative Intervention bis zur nächsten Untersuchung. Die Ventrikelweite änderte sich bei den meisten Patienten nach der Shuntimplantation nicht oder marginal. Bei den Patienten der 3. Behandlungsgruppe verschwand innerhalb weniger Tage nach OP die präexistente Überdrainagesymptomatik.Die Studie zeigt, dass gravitationsgesteuerte Ventile die Überdrainagegefahr beim chronischen Hydrozephalus sehr effektiv verhindern.SummaryEarlier design changes in hydrocephalus valves focusing on reducing overdrainage failed. Since the middle of the 1990s, hydrostatic valve constructions have been available which are claimed to solve this problem. The objective of this study was to evaluate the efficiency of these constructions.Clinical status and ventricular size were evaluated in 45 patients with chronic hydrocephalus before and 1, 6, and 26 weeks after operation. In 35 of these, a Miethke dual-switch valve was implanted (treatment group 1), and the others received a combination of a programmable Codman-Hakim valve and a Miethke shunt assistant as the hydrostatic element of the configuration (treatment group 2). A third group (n=6) had already been shunted but suffered from overdrainage symptoms which could not be overcome by conservative measures. In these cases, the only operative treatment was the implantation of a Miethke shunt assistant adjunctively to the existing valve.In groups 1 and 2, there was a significant permanent improvement in the clinical state in nearly 80% of cases and a moderate permanent improvement in about 10%. Mild clinical and radiological signs of overdrainage occurred in three patients during the first postoperative week but resolved without further operative measures within the next 5 weeks. Typically, the ventricular width was not or only marginally reduced in these 45 patients. In the patients treated for symptoms of overdrainage (group 3), complaints resolved within the first week after implantation of the shunt assistant.The study indicates that gravitational shunts may be very effective in preventing overdrainage in chronic hydrocephalus, and therefore these constructions could represent the gold standard in the treatment of chronic hydrocephalus.

Online Analysis of Intracranial Pressure Waves

Brain pressure waves, particularly B-waves, as they were described by Lundberg contain valuable diagnostic information about the patients status. So far, this information cannot be used on a daily routine basis because manual analysis of the recorded ICP data is very time consuming. Furthermore, the analysis is only retrospective, after incidents of interest occurred. To overcome these drawbacks, an automated B-wave detection system has been developed. Using a direct spectral estimation method (so called ARMA approach) the most significant spectral components and their amplitudes in the ICP signal are identified. The frequency with the biggest amplitude inside the B-wave band is a reliable indicator of B-wave activity and can be displayed on-line on a bedside computer.

Evaluation of Bioelectrical Impedance Spectroscopy for the Assessment of Extracellular Body Water

This study evaluates bioelectrical impedance spectroscopy (BIS) measurements to detect body fluid status. The multifrequency impedance measurements were performed in five female pigs. Animals were connected to an extracorporeal membrane oxygenation device during a lung disease experiment and fluid balance was recorded. Every 15 min the amount of fluid infusion and the weight of the urine drainage bag was recorded. From the fluid intake and output, the fluid balance was calculated. These data were compared with values calculated from a mathematical model, based on the extracellular tissue resistance and the Hanai Mixture theory. The extracellular tissue resistance was also measured with BIS. These experimental results strongly support the feasibility and clinical value of BIS for in vivo assessment of the hydration status.

A Simulation Model for Intracranial Fluid Dynamics

Abstract Most parameters inside the human body are regulated with biological control systems in order to maintain an optimal environment for the body cells. This paper aims at the development of models which interpret these control loops in a technical manner so they may be used in a technical simulation environment. As an example, a model for intracranial fluid dynamics is presented. Starting from first order principles (like conservation of mass, …) and constitutive equations models for the liquor circulation system and the autoregulation of cerebral blood flow are derived and implemented in a simulation environment under Matlab/Simulink. The simulation may be used for educational purposes or the development of new treatment and diagnostic strategies.