Abstract: The present invention relates to an apparatus for monitoring the intracranial pressure of a patient. The apparatus includes an implantable sensor implanted in the skull of a patient. The implantable sensor senses pressure and outputs a signal indicative of the pressure in the patient's skull. The apparatus further includes a probe receiving the signal output by the implantable sensor when the probe is positioned near the implantable sensor. The probe outputs a signal indicative of the pressure sensed by the implantable sensor. An interrogation circuit is provided for receiving the signal output by the probe and automatically outputting a digital signal proportional to the pressure sensed by the implantable sensor.

Abstract: A pressure sensor for measuring pressure of a body at a selected site is provided wherein radiopaque means shift in response to pressure. The body is X-rayed using conventional techniques and the shifting of the radiopaque means is observed to indicate the change in pressure. Several embodiments of the present invention are suited for biomedical applications.

Abstract: An implantable transensor device containing a passive RF resonant circuit having a natural frequency influenced by the pressure of the sensor's environment in a body cavity of a living entity. The circuit of the transensor includes an inductor and a capacitor, at least one of which varies in value in direct relation to variation of environmental pressure to change the resonant frequency of the circuit. The circuit can be externally interrogated to determine the resonant frequency thereof at any point in time by the imposition thereon of swept frequency electromagnetic radiation provided by a monitoring device which determines when some of the radiation is absorbed as a result of the frequency of the radiation being the same as the resonant frequency of the transensor circuit. An imposed relationship exists between the sensed environmental pressure, and the reactance of the reactive components of the circuit.

Abstract: Pressure monitoring apparatus implantable in the cranium to measure intracranial pressure, the apparatus comprises a passive resonant circuit having a natural frequency influenced by ambient pressure. The resonant circuit has inductance and capacitance capability for comparing the local environmental pressure to that of a volume of gas trapped inside the apparatus, the environmental pressure being measured by observation of the frequency at which energy is absorbed from an imposed magnetic field located externally of the cranium.