Christoph Miethke

The dual-switch valve

The currently available hydrocephalus valves are still far from perfect. Whereas the design principles of differential pressure valves and adjustable devices involve the danger of overdrainage, hydrostatic valves have a tendency to clog. The new dual-switch valve (DSV) avoids overdrainage-related problems such as subdural hygromas/hematomas or slit-like ventricles with the high risk of proximal catheter obstruction by means of two parallel chambers in a titanium casing: one for the the horizontal and the other for the vertical position. The control chamber for the horizontal position is closed by a gravity-activated tantalum ball as soon as the patient moves into an upright position. Now the drainage of CSF is directed into the appropriate controller for the erect position. Thus, the hydrostatic differential pressure between ventricles and peritoneal cavity is counterbalanced and the intraventricular pressure (IVP) remains within physiological values independently of the CSF flow and the position of the patient. To avoid the problem of clogging, the newly designed valve introduces large-area diaphragms to create extensive acting forces. The forces generated in this way are able to overcome sticking forces set up as a result of high protein content or cellular debris. By this mechanism the IVP is maintained in physiological ranges regardless of the CSF composition. The new valve has been investigated with a computer controlled test apparatus especially designed to simulate different positions of the body. The in vitro test results according to ASTM standards document a superior performance in comparison with other valves. When the new device was interposed in external drainage systems precision of its function was confirmed even in the presence of elevated protein content and high CSF flow. Simulation of the upright position of the patient allowed documentation of the valves reliability in maintaining the IVP within physiological ranges. A clinical trial with implantation of the new dual-switch valve was started at the beginning of 1995; so far follow up has been short. Clinical and computer tomographic monitoring has provided evidence of the valves capacity to avoid the problems of overdrainage and early clogging.

An improved reservoir for the flushing test to diagnose shunt insufficiency.

OBJECTIVE Reservoirs integrated into hydrocephalus shunts are commonly used for the removal of CSF and for intra-ventricular pressure measurement. Pumping with the reservoir to diagnose shunt sufficiency is still a matter of controversy. The authors describe an improved flushing device and its characteristic features in vitro and in vivo. METHODS The flushing reservoir is constructed with a sapphire ball in a cage as a nonresistance valve to also enable the detection of distal occlusions. The most important reservoir parameters were investigated in vitro, simulating total and partial proximal and distal shunt occlusions. Then the expected advantages were assessed in vivo by evaluating the pump test data of 360 implanted reservoirs. The results were compared with those found in the literature. RESULTS The optimization of the technical parameters of the device, such as the high stroke volume in combination with moderate suction force, are obvious advantages compared with other flushing devices. Total occlusion of the ventricular catheter and the valve could be assessed with high certainty. The detection of a total obstruction of the peritoneal catheter or any partial obstruction is also possible, depending on its exact grade and location. CONCLUSIONS Shunt obstructions can be assessed using the pumping test. The reservoir construction presented here provides a clear enhancement of that diagnostic test.

The new proGAV 2.0 - a valve development based on systematical market observation

The treatment of hydrocephalus has been dramatically influenced by technical achievements which have been developed by different companies. One aspect was the principle phenomenological function of the device with the aim to lower the likelihood of negative complications like under or overdrainage. Beneath these approaches it is important to observe the performance of the different devices based on intensive communication with the user. The manufacturer is not only obligated by law to systematically collect data about the performance of the devices. It is also important for significant improvement of the product. Based on findings followed by systematical analyzes of revised valves, which have been send back to the manufacturer for investigation the proGAV 2.0 has been developed to address nearly all critical points, which can be recognized during the investigations. Whereas the principle hydraulic function is nearly unchanged versus the first generation proGAV the handling, the risk of blockage, the risk of damaging the valve, the way of adjusting the valve as well as the verification of the setting have been improved and the basic technical elements have been completely reworked. The first clinical experiences support the intention of the approach as well as the information gained by returned valves. The systematical observation of the performance of medical devices offers valuable information for improvements.

A new electronic valve for the treatment of NPH

The first shunts being successfully used for the treatment of hydrocephalus were designed to lower an overpressure within the ventricles of the brain. Later the same technology was used for the treatment of normal pressure hydrocephalus, although the background of this disease can not be compared with obstructive hydrocephalus. Since then no specific device has been developed focussing on the treatment of NPH. However, the recent knowledge of NPH and the risks behind the shunting of NPH offer interesting options. For the diagnosis of NPH an often used method is the spinal tap test. The withdrawal of up to 50 cc of spinal fluid sometime leeds to impressive clinical improvement. To address this fact a new device has been developed which can be programmed to open depending on time and body position. Consequently in contrast to valves for the treatment of obstructive hydrocephalus this device does not open depending on increased baseline ICP or ICP peaks. The device can be programmed to open for two minutes intervals over 24 hours. The valve can be programmed to remain closed, to open for two minutes within 24 hours, to open the whole 24 hours or any time between two minutes and 24 hours. In addition it can be programmed whether or not the opening should be manipulated by the body position of the patient in particular to allow an only reduced flow in the standing position. The new electronic device is the first implant developed only for NPH addressing specific aspects of this decease. The valve has been investigated in vitro simulating the condition within a patient. It has not been implanted yet, because of regulatory issues. Whether or not the device improved the clinical outcome in patients with NPH, whether or not it can lower risks for these patients and introduce new treatment options can not be answered without clinical experience. However, it promises to be a tool for scientific research, which might help to improve the understanding of NPH.

Limits and options for electronic devices for the treatment of hydrocephalus

and Spina Bifida Meeting abstracts - A single PDF containing all abstracts in this Supplement is available here . http://www. biomedcentral.co m/content/files/ pdf/174 3-8454-4-S1-info .pdf

Controversies about adjustable shunts

Background The development of valves for the optimal treatment of patients with hydrocephalus is an ongoing challenge for decades. Over drainage and reliable long-term performance has been the focus for the different engineering teams. The so called Anti-Siphon-Device, flow reducing devices like the Orbis-Sigma-Valve or the Siphon-Guard and Gravitational shunts are still competing in respect to superior long term survival. On the other hand the requirement of non-invasive readjustment depending on the clinical aspects of the individual patient has led to several new developments. Whether or not adjustable valve could lower the likelihood of revisions could up to now not be shown in clinical trials. What are the options for a combination of adjustability on the one hand and over drainage avoiding devices on the other?

Controversies about the adjustment of gravitational valves in respect to a new device

Background The essential drawback of available adjustable devices for the treatment of hydrocephalus is the fact that the adjustment is valid for both positions of the patient. If the opening pressure is increased to decrease the risk of over drainage in the upright position of the patient the same adjustment leads to a very high opening pressure while the patient is lying and consequently to an under drainage in the horizontal position. On the other hand the lowering of the opening pressure automatically increases the risk of subdural effusion as soon as the patient is in upright position.