Telemetered epidural pressure.

An implantable transducer capable of telemetering epidural brain pressure during long periods of time is described. The transducer is constructed from conventionally available materials, and routine workshop techniques are used. The coplanarity principle has been applied while the described mounting clamp allows discrete positioning of the transducer relative to the brain. Basically, the transducer consists of a coil-capacitor circuit in which alterations of epidural pressure induce changes in capacity and, thus, the transducer's resonance frequency. An external electromagnetically coupled impedance-measuring device converts the resonance frequency to a pressure analogous voltage. In vitro tests showed that the transducer had good accuracy and reliability for a period of more than 1 month. An in vivo experiment with a cat showed that the measured epidural pressure was linearly related to ventricular fluid pressure.