In an apparatus for determining the actual status of a piezoelectric sensor
in a medical implant, electrical charges generated in the sensor, in
response to changes in acceleration and/or gravitational force or other
loads acting on the sensor, are continuously detected and the charges are
then removed from the sensor, thereby maintaining the voltage across the
sensor at a substantial constant zero level. The detected charges, both
negative and positive, are integrated, thereby providing a resulting
integrated signal representing the actual status of the sensor. The
integrated signal is then evaluated for determining the physical activity
and/or the posture of a patient in whom the medical implant is implanted.
