Article
Scotomization of physics in shunt-studies of gravitational and antisiphon valves
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Authors
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A. Aschoff
- Neurochirurgische Klinik, Universitätsklinikum Heidelberg
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B. Vienenkoetter
- Neurochirurgische Klinik, Universitätsklinikum Heidelberg
| Published: | May 20, 2009 |
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Outline
Text
Objective: The cerebral venous outflow resistance varies depending on the body elevation, ergo on gravity. The stepwise collapse of the big low-resistance jugular veins during verticalization lead to a shift into the small high-resistance veins. The ICP sinks to moderate negative values of -5 to -10 cmH2O only. In 1973, Portnoy and Schulte adopted this regulation when designing the antisiphon (ASD). In 1975, Hakim created his gravitational lumbar valve. Both are automatic self-adjusting valves, which work gravity- or weight-controlled, in ASDs activated by the hangig distal water column, in g-valves by inbuilt balls. In ASDs, the lenght of the hanging tube is defined mainly by implantation level, in g-valves by the pressure range, the potential deviations from the body axis either by diagonal implantations or – in case of retroauricular implantations – by elevated head positions during the night. These conditions define the “pressure-range” and are essential for correct interpretation of clinical results.
Methods: We reviewed 15 ASD- and 20 g-valve-studies looking at documentation of implantation levels of ASDs or of potential axis-deviations of g-valves.
Results: In the early ASD-literature Gruber, Chapman, Foltz, and more recently Francel stressed the importance of the implantation level. Surprisingly later studies (Drake-Kestle, Delwel, Koskinen, the UK-shunt registry, display no data on the ASD level. In the gravitational valve literature, one single paper (Park 07) described precisely the deviation angles and found a significant influence on the clinical success. Even in current German g-valves-studies, the deviation-angle was missing.
Conclusions: In the instructions of manufacturers, we found only vague recommandations. The documentation of ASD-levels or angles of g-valves vs. the body axis requires a few seconds only. Without these data, it is impossible to distinguish real valve problems from simple implantation failures. Both data are obligatory for reliable ASD- and g-valve-studies.
