Detecting the Onset of Urinary Bladder Contractions Using an Implantable Pressure Sensor
ABSTRACT 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.
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ABSTRACT: The aim of this study was to investigate the feasibility of using external urethral sphincter electromyogram (EMG) (EUSEMG) to detect the onset of detrusor contractions in patients with both neurogenic detrusor overactivity (NDO) and detrusor sphincter dyssynergia (DSD). Detrusor pressure (Pdet) and EUSEMG was recorded in 23 neurogenic patients during slow artificial bladder filling. The time delay between the onset of a detrusor contraction and the onset of EUSEMG activity was calculated together with the detrusor pressure increase related to this delay. Of 23 patients enrolled, 12 patients showed both NDO and DSD. Of these 12 patients, 10 had a strong correlation between detrusor pressure and EUSEMG. One patient in this group was excluded due to a storage pressure above 30 cm H2O. Two detection methods were applied on the remaining 9 patients. Method 1 was a root mean square (RMS)-integrator with simple thresholding. This approach had a good sensitivity but also a poor specificity (many false-positive detections). Detection method 2 included a kurtosis-based scaling function, which was multiplied to a similar RMS-integrator as used in method 1. Onset detection occurred before Pdet exceeded 18 cm H2O with both methods. However, method 1 resulted in 14.1 +/- 12.8 false-positive detections during one bladder filling. Pdet at onset detection was on average 1.0 +/- 1.1 cmH2 0 higher with detection method 2 but the number of false-positives was reduced by 95.8%. This paper demonstrates the feasibility of using EUSEMG to estimate the onset of a detrusor contraction in selected patients.IEEE Transactions on Biomedical Engineering 08/2007; 54(7):1212-9. · 2.35 Impact Factor