A pressure-balanced radio-telemetry system for the measurement of intracranial pressure. A preliminary design report.

A fully implantable radio-telemetric differential intracranial pressure sensor is described with a zero-point calibration that can be confirmed repeatedly. Intracranial pressure (ICP) is measured with the device by the principle of applying a known external pressure to the scalp above the sensor and simultaneously detecting by radio-telemetry the zero-point of the sensor corresponding to a balance of pressures across it. The radio-telemetry is implemented by a resonant circuit in the sensor of which the resonant radiofrequency is detected outside the body. The sensor is passive, has built-in barametric compensation, negligible permeability of temperature drift, no calibration ambiguities, and fast dynamic response. The implanted sensor has been used successfully for short-term as well as long-term ICP monitoring. It has been implemented primarily for intermittent ICP measurements, but also adapted to continuous recording. Preliminary clinical experience with the system indicates that it is effective, safe, and simple to operate.