Telemetry of intracranial pressure.

In the care of patients with abnormal intracranial pressure, it is important to continuously and accurately measure the intracranial pressure so that treatment can be instituted. Strain gage pressure cells have successfully replaced the open-end manometer for chronic use but have lacked the stability for accurate long-term measurements. The system described uses a capacitive pressure transducer with excellent long-term stability. The transducer, electronics, and transmitter package can be implanted to telemeter the pressure transcutaneously, reducing the danger of infection by the elimination of transcutaneous leads. The pressure modulates the frequency of an oscillator in the 8-10 MHz region and provides an easily telemetered signal. To eliminate the problems of periodic battery replacement, the system is energized inductively by a coil placed externally over the implant device, so that the operating life is virtually unlimited.