A completely implantable intracranial pressure sensor was designed for chronic measurement of intraventricular pressure (IVP) in hydrocephalic patients. It is a passive-resonant circuit transducer and the implantable sensor does not contain an active element such as an electric battery. The size and shape of the sensor are nearly those of Pudenz's single flushing device, so that the transducer can be used in place of a traditional flushing device in the ventriculo-peritoneal shunt system. The IVP meter is sensitive to 1 mmH2O of pressure and it has a linear pressure range from -500 to + 1, 000 mmH2O. The zero drift of the sensor was negligible during a 104 hour running test. The errors induced by changes in external atmospheric pressure were automatically corrected by placing a accurate barometer in the line of pressure-calculation.
The intraventricular pressure of hydrocephalic dogs was measured by this new IVP meter and by the LADD transducer simultaneously, and the reliability of this IVP sensor was confirmed.
These sensors were applied to eight hydrocephalic patients, and chronic and continuous measurements of the ventricular pressure were performed. These preliminary clinical experiences disclosed; (1) this IVP meter offers a method almost ideal for simple, safe and accurate, recording of the intraventricular pressure of hydrocephalic patients, (2) patency of the ventricular tube can be easily demonstrated by a steep rise of intracranial pressure at the time of jugular compression, and (3) abnormal pressure waves with obstructed shunt and their disappearance when the shunt is working are easily recognized.
