Advanced Platform Technology Center
Wireless Implantable Pressure Monitor for Clinical Applications
Wireless Implantable Pressure Monitor for Clinical Applications
Principal Investigator: Margot Damaser, Ph.D.
Co-Principal Investigators: Darrin Young, Ph.D. and Steve Garverick, Ph.D.
Co-Investigators: Wen Ko, Ph.D., Graham Creasey, M.D., Hui Zhu, M.D., Sc.D., Kenneth J. Gustafson, Ph.D.
Staff: Paul Fletter, B.S., James Buckett, M.S., Brad Boggs, M.S., Paul Zaszczurynski, B.S.
Students: Steve Majerus, Peng Cong
Description
Measurement of physiological pressures is fundamental to many forms of medical diagnosis and monitoring in cardiovascular, respiratory, gastrointestinal, urological and other systems. One example is urodynamics, the measurement of bladder pressure to diagnose incontinence. 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. It would be a great advantage to continuously measure pressure using a miniature device that transmits wirelessly to an external receiver. Existing monitors are either passive devices, with no onboard power source and required to be near their external power source, or active devices with a battery onboard that are too large for our primary application in the bladder. A miniaturized, active device, or one with a creative wireless powering method, could be implanted in internal organs. Such a device could either be inserted into an internal organ or could be implanted endoscopically. This device would have application for many purposes including diagnostic, monitoring, biofeedback, and as a mechanism to improve control of rehabilitative systems, such as those using functional electrical stimulation or neuromodulation. Since no such systems currently exist, this technology development project will result in a novel medical device that clearly serves an important, but yet unmet, clinical need.
Objectives
The objectives of this project are to design, fabricate, and test a wireless, implantable pressure monitor.
Research Plan & Methodology
Research Plan: We have created a large prototype using PC Board technology and have tested it in a pressure chamber. We have also tested methods and devices for insertion of the device into the bladder. We have determined that salt water (to simulate the body) does not degrade transmission of the signal. We have used these preliminary data to support a VA Merit Review proposal to build an appropriately sized prototype using integrated circuit technology. Experiments are being performed to further assess the attenuation of intravesical pressure signals as sensed through the mucosa and derive methods to compensate for any losses due to the this tissue layer. We are currently investigating the geometries and spatial relationships of internal and external coil designs to be used for wireless RF powering and data telemetry. Testing is currently underway on the first generation Application Specific Integrated Circuit (ASIC) and will lay the ground work toward on-board implant control circuitry. Methodology: APT Center funding had enabled us to form an investigative team, formulate a research plan, and obtain the preliminary data needed to submit for external funding. We will continue to make progress toward the objectives above over the next three years. In addition, VA Merit review funding enables us to continue pursuing methods of inserting and implanting the pressure sensor in the bladder (the initial target organ).
Milestones
This research project has been awarded VA Merit Review funding of $750,000 over three years, beginning October 2007.
We have determined that bladder pressure measured submucosally reflects lumen pressure by placing a catheter with a custom latex diaphragm under the mucosa in a pig bladder placed in our in vitro bladder testing apparatus. We have developed a large prototype using PC board technology and have tested in a pressure chamber. The results demonstrate high repeatability with low hysteresis. Fabrication of the device using an unpackaged pressure sensor, ASIC technology for the circuitry, and a different battery during the proposed project will significantly reduce the size of the device.
We have designed and tested an insertion tool to demonstrate implantation of a submucosal device into the bladder wall. We have demonstrated this concept in preliminary experiments inserting mock devices (i.e. steel pellets) into pig bladders in vitro.
We have fabricated the first generation ASIC to test the circuitry components that will be incorporated into the final design.
Clinical Relevance
The ability to continuously record pressures from within the body without catheters would have dramatic significance in many medical specialties. In intensive care units, besides eliminating inconveniences associated with tethering of patients by catheters, wireless implanted monitors have the potential to reduce catheter line infections and associated morbidity and mortality. Ambulatory monitoring, home monitoring, and telemedicine would be greatly enhanced by long term monitoring of pressure. In addition, pressure measurement could be used as feedback for biofeedback training
and rehabilitation systems. This device would allow improved therapeutic control of many conditions such as urinary incontinence, pulmonary hypertension, chest pain of non-cardiac origin, and lack of bowel and bladder control due to spinal cord injury. The
initial application to ambulatory urodynamics would have great significance for improving diagnosis and treatment of incontinence, which is endemic among the elderly.
The special features of the veteran population, such as traumatic injuries to the brain and spinal cord, increasing age, and prevalence of cardiovascular disease and diabetes suggest opportunities for improved monitoring and treatment of complications such as urinary and fecal incontinence, constipation, and pulmonary hypertension. As an example of relevance, 25% of the 250,000 people with spinal cord injuries in the U.S. are veterans and there are 10,000 people with new spinal cord injuries incurred each year. The aging veteran population includes many with disabilities as well as decreased bladder and bowel control, resulting in urinary and fecal incontinence.
Continence and pelvic health are especially important to the health and well being for these at-risk segments of the disabled veteran population. The proposed device will improve the health and quality of life for disabled veterans by enabling new treatment interventions and diagnostic modalities that will improve their standard of care.
