Paul C. Fletter

Low-Power Wireless Micromanometer System for Acute and Chronic Bladder-Pressure Monitoring

This letter describes the design, fabrication, and testing of a wireless bladder-pressure-sensing system for chronic, point-of-care applications, such as urodynamics or closed-loop neuromodulation. The system consists of a miniature implantable device and an external RF receiver and wireless battery charger. The implant is small enough to be cystoscopically implanted within the bladder wall, where it is securely held and shielded from the urine stream. The implant consists of a custom application-specific integrated circuit (ASIC), a pressure transducer, a rechargeable battery, and wireless telemetry and recharging antennas. The ASIC includes instrumentation, wireless transmission, and power-management circuitry, and on an average draws less than 9 μA from the 3.6-V battery. The battery charge can be wirelessly replenished with daily 6-h recharge periods that can occur during the periods of sleep. Acute in vivo evaluation of the pressure-sensing system in canine models has demonstrated that the system can accurately capture lumen pressure from a submucosal implant location.

Comparison of air‐charged and water‐filled urodynamic pressure measurement catheters

Catheter systems are utilized to measure pressure for diagnosis of voiding dysfunction. In a clinical setting, patient movement and urodynamic pumps introduce hydrostatic and motion artifacts into measurements. Therefore, complete characterization of a catheter system includes its response to artifacts as well its frequency response. The objective of this study was to compare the response of two disposable clinical catheter systems: water‐filled and air‐charged, to controlled pressure signals to assess their similarities and differences in pressure transduction.

Wireless, Ultra-Low-Power Implantable Sensor for Chronic Bladder Pressure Monitoring

The wireless implantable/intracavity micromanometer (WIMM) system was designed to fulfill the unmet need for a chronic bladder pressure sensing device in urological fields such as urodynamics for diagnosis and neuromodulation for bladder control. Neuromodulation in particular would benefit from a wireless bladder pressure sensor which could provide real-time pressure feedback to an implanted stimulator, resulting in greater bladder capacity while using less power. The WIMM uses custom integrated circuitry, a MEMS transducer, and a wireless antenna to transmit pressure telemetry at a rate of 10 Hz. Aggressive power management techniques yield an average current draw of 9 μA from a 3.6-Volt micro-battery, which minimizes the implant size. Automatic pressure offset cancellation circuits maximize the sensing dynamic range to account for drifting pressure offset due to environmental factors, and a custom telemetry protocol allows transmission with minimum overhead. Wireless operation of the WIMM has demonstrated that the external receiver can receive the telemetry packets, and the low power consumption allows for at least 24 hours of operation with a 4-hour wireless recharge session.

Wireless micromanometer system for chronic bladder pressure monitoring

This paper describes a wireless system to monitor urinary bladder pressure comprising an implantable device with an external receiver and wireless battery charger. The device is intended to be implanted within the bladder wall, sealed behind the urothelial lining. This location is protected from the urine stream, thus avoiding mineral encrustation and stone formation, and is suitable to measure intravesical pressure in chronic applications. The implant is dimensionally designed to gain access to the bladder using conventional urological tools, e.g. a cystoscope. The active circuit implant features a custom application-specific integrated circuit (ASIC), rechargeable battery and wireless telemetry. Inductive charging, novel power management schemes and innovative packaging allow this device to be inserted through the urethra, implanted within the bladder wall, and operate for a lifetime of up to 10 years.

Suburothelial bladder contraction detection with implanted pressure sensor

Aims Managing bladder pressure in patients with neurogenic bladders is needed to improve rehabilitation options, avoid upper tract damage, incontinence, and their associated co-morbidities and mortality. Current methods of determining bladder contractions are not amenable to chronic or ambulatory settings. In this study we evaluated detection of bladder contractions using a novel piezoelectric catheter-free pressure sensor placed in a suburothelial bladder location in animals. Methods Wired prototypes of the pressure monitor were implanted into 2 nonsurvival (feline and canine) and one 13-day survival (canine) animal. Vesical pressures were obtained from the device in both suburothelial and intraluminal locations and simultaneously from a pressure sensing catheter in the bladder. Intravesical pressure was monitored in the survival animal over 10 days from the suburothelial location and necropsy was performed to assess migration and erosion. Results In the nonsurvival animals, the average correlation between device and reference catheter data was high during both electrically stimulated bladder contractions and manual compressions (r = 0.93±0.03, r = 0.89±0.03). Measured pressures correlated strongly (r = 0.98±0.02) when the device was placed in the bladder lumen. The survival animal initially recorded physiologic data, but later this deteriorated. However, endstage intraluminal device recordings correlated (r = 0.85±0.13) with the pressure catheter. Significant erosion of the implant through the detrusor was found. Conclusions This study confirms correlation between suburothelial pressure readings and intravesical bladder pressures. Due to device erosion during ambulatory studies, a wireless implant is recommended for clinical rehabilitation applications.

Conversion of urodynamic pressures measured simultaneously by air-charged and water-filled catheter systems.

The objective of this study was to compare the simultaneous responses of water‐filled (WFC) and air‐charged (ACC) catheters during simulated urodynamic pressures and develop an algorithm to convert peak pressures measured using an ACC to those measured by a WFC.

Urothelial Biomechanics: Submucosal Sensing of Intravesical Pressure

Measurement of physiological pressures is fundamental to many forms of medical diagnosis and monitoring in the cardiovascular, respiratory, gastrointestinal, urological and other systems. Pressure is usually measured via catheters, either connected to transducers outside the body or more recently by micro-transducers mounted on the tip of such catheters. However, this requires that the catheters be inserted and maintained without infection and that the patient be tethered to a recording device. While this may be manageable during short term tests such as urodynamics, the measurement of bladder pressure to diagnose incontinence, chronic monitoring poses an additional set of obstacles.Copyright

Fluid Volume Conductance for Determination of Bladder Volume

Clinical urodynamics is the present standard for diagnosing voiding dysfunction. The nonphysiological nature of this exam often hinders symptom reproduction in the laboratory. Currently, a small intrabladder device is being developed to conduct ambulatory urodynamics. This study investigates the feasibility of using fluid volume conductance for the realtime intravesical volume measurement needed in urodynamics. Prototype devices are polymer bodies having 4 electrodes. Electrode configurations and probe geometries were tested in bladder-like latex vessels using saline having conductivity similar to urine. Sensitivity to temperature and fluid concentration were determined using fresh pig bladders in vitro. The voltage across the fluid volume was found to be inversely related to volume. The ideal probe configuration was found to be an ellipsoid having strip electrodes spaced at 25deg. Increasing fluid temperature and concentration increased solution conductivity, significantly decreasing the measured voltage. Urines dynamic chemical properties therefore necessitate real-time compensation of conductivity in clinical application; which could be accomplished with another smaller electrode array.