PRESSURE MICROSENSOR SYSTEM USING A CLOSED-LOOP CONFIGURATION

Pressure measurements in orthopaedics are hampered by the fact that th e required measuring range is a factor of 20 higher than the common ph ysiological range. A sensor system has been designed, based on a previ ously reported microsensor placed in a closed-loop configuration, in w hich the pressure across the microsensor membrane is kept constant. Th e backside of this membrane is connected to a pneumatic unit, with a h igh-pressure source and an electromagnetic valve, controlled by the ou tput signal from the microsensor. The prototype system has excellent l inearity, and a dynamic range of 67 dB, a 24 dB improvement compared w ith the open-loop system. Rise and fall times are 0.6 and 0.2 s, respe ctively, limited by the compliance and flow resistance of the pneumati c system. Recordings of intradiscal pressure have been made on animal carcasses, and on patients suffering from lumbar back pain. Intradisca l pressure measurements could, potentially, be valuable in the diagnos is and understanding of the pathogenesis of this disease.