Electromagnetic field hazards involving adjustable shunt valves in hydrocephalus.

OBJECT: Standard therapy for hydrocephalus involves shunts and valves, which are frequently adjustable. Because of increasing "electromagnetic smog" (for example, that generated by cellular phones), these valves are often exposed to electromagnetic fields.
METHODS: Various magnetic fields were tested for their effects on two different kinds of adjustable valves. The minimum magnetic flux density affecting the adjustment of the valve was determined. Results were compared with magnetic fields found in contemporary everyday life. In homogeneous magnetic fields the adjustment of one valve (Sophysa model SM8) was changed at 5 mT, whereas the second valve (Codman Hakim model CM) was not affected. In nonhomogeneous fields the SM8 valve was affected at 25 mT and the CM valve at 15 mT. Thus, these valves may be affected by headphones and telephone receivers. Surroundings such as the Japanese magnetic suspension railway and the lead cabin of electrical railway engines, in which critical levels of magnetic flux may be present, may also affect adjustable valves. The high-frequency fields of cellular phones, however, have no effect on these valves.
CONCLUSIONS: Every surgeon who implants these valves and every patient who receives them should know the possible hazards. The valve selection should be adapted to the environment of the patient. Devices with critical levels of electromagnetic flux that are used in the homes of patients should be replaced by ones with lower magnetic fields. The future construction of these valves should be modified in such a way that their adjustment requires a higher magnetic flux density, so that the valves become less sensitive to unwanted effects from environmental magnetic fields.