Frequency Stability of an Implantable Pressure Telemetry Capsule

An implantable pressure telemetry capsule was developed to permit monitoring cuff pressure in an artificial urethral sphincter during chronic conditions. Following implantation, the baseline frequency of the capsule was observed to increase by nearly 2 percent. A series of experiments was then conducted to determine whether this increase was caused by the temperature rise after implant, by fluid migration through the Silastic diaphragm, or by permeation of water vapor through the epoxy encapsulating the electronics. Elevated temperatures accounted for 84.5 percent of the frequency increase, migration through the diaphragm 11.85 percent of the total, and water permeation through the epoxy 3.65 percent.