Detecting the Onset of Urinary Bladder Contractions Using an Implantable Pressure Sensor

This study investigates whether signals obtained from an implantable pressure sensor placed in the urinary bladder wall could be used to detect the onset of bladder contractions. The sensor assembly was custom made using a small piezoresistive sensor die. The die was mounted on ceramic substrate (8 mm × 8 mm) and encapsulated in silicone by a two-part moulding process. The final sensor was lens shaped with a diameter of 13.6 mm and height of 2.0 mm. Experiments were performed in six pigs that had one or more sensors placed in the bladder wall. An external reference sensor was used to simultaneously monitor intravesical pressure via a transurethral catheter. Bladder contractions were evoked by unilateral electrical stimulation of the pelvic nerve. Onset latency was computed using both signals. In addition, the correlation between wall pressure and intravesical pressure was calculated. On average, the onset latency was -307 ms using the wall sensors compared to the intravesical pressure, i.e., the detection occurred earlier using the wall sensors than the intravesical sensor. In 91 of 114 recordings the correlation coefficient was above 0.90. In conclusion, the implantable sensor performs similar to the reference sensor when used to detect the onset of bladder contractions.