RESUMO
Conditional neuromodulation is a form of closed-loop bladder control where neurostimulation is applied in reaction to bladder pressure changes. Current methods based on external catheters have limited utility for chronic ambulatory therapy. We have developed a wireless pressure monitor to provide real-time, catheter-free detection of bladder contractions. The device is sized for chronic implantation in the bladder muscle. The pressure monitor consists of an ultra-low-power application specific integrated circuit (ASIC), micro-electro-mechanical (MEMS) pressure sensor, RF antennas, and rechargeable battery. Here we describe an overview of the system, including chronic in vivo test data of a non-hermetic polymer sensor package and chronic testing of the wireless sensor in large animal models. Test results show that the packaging method is viable for chronic encapsulation of implanted pressure sensors. Chronic testing of the pressure monitor revealed some obstacles relating to the chosen implant site within the bladder wall. However, chronic wireless device function was confirmed and data quality was sufficient to detect bladder compressions in large animals, with average correlation coefficient of 0.90.
RESUMO
Conditional neuromodulation in which neurostimulation is applied or modified based on feedback is a viable approach for enhanced bladder functional stimulation. Current methods for measuring bladder pressure rely exclusively on external catheters placed in the bladder lumen. This approach has limited utility in ambulatory use as required for chronic neuromodulation therapy. We have developed a wireless bladder pressure monitor to provide real-time, catheter-free measurements of bladder pressure to support conditional neuromodulation. The device is sized for submucosal cystoscopic implantation into the bladder. The implantable microsystem consists of an ultra-low-power application specific integrated circuit (ASIC), micro-electro-mechanical (MEMS) pressure sensor, RF antennas, and a miniature rechargeable battery. A strategic approach to power management miniaturizes the implant by reducing the battery capacity requirement. Here we describe two approaches to reduce the average microsystem current draw: switched-bias power control and adaptive rate transmission. Measurements on human cystometric tracings show that adaptive transmission rate can save an average of 96% power compared to full-rate transmission, while adding 1.6% RMS error. We have chronically implanted the wireless pressure monitor for up to 4 weeks in large animals. To the best of our knowledge these findings represent the first examples of catheter-free, real-time bladder pressure sensing from a pressure monitor chronically implanted within the bladder detrusor.
