Wireless implantable pressure monitor for conditional bladder neuromodulation

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, realtime bladder pressure sensing from a pressure monitor chronically implanted within the bladder detrusor.