Control of urine leakage is of major importance after spinal cord injury (SCI) since SCI patients are highly susceptible to pressure ulcers. Pressure ulcers exposed to urine are more susceptible to infection since urine alters the pH balance of the skin and reduces resistance to bacterial invasion. Septicemia resulting from infected pressure ulcers is a major cause of rehospitalization or death among individuals with SCI. SCI patients characteristically develop detrusor overactivity and striated sphincter dyssynergia, leading to uncontrolled leakage of urine, putting the patient at increased risk for contact dermatitis and infected pressure ulcers. In addition, these bladder complications of SCI can lead to autonomic dysreflexia, renal failure, and stroke. Therefore, control of urine leakage is of major importance after SCI. Electrical stimulation of pudendal sensory pathways can arrest unwanted reflex bladder contractions in SCI patients. Open-loop continuous electrical stimulation can inhibit overactive bladder activity and several devices are approved by the FDA. However, patients must frequently return to the doctor to have their electrical stimulation system adjusted when its effectiveness wanes due to habituation or accommodation to an electrical stimulation signal that is always on. Conditional or closed-loop stimulation that only stimulates when triggered to do so has been shown to be more effective than open-loop continuous stimulation, resulting in greater bladder capacity and utilizing less power. However, conditional stimulation is presently only utilized acutely for research purposes using a catheter-based pressure-sensing system since a chronic bladder sensor is not currently available. During the initial VA Merit funding period of this project, we developed a miniature, implantable, wireless, catheter-free, battery-powered, rechargeable pressure monitor for chronic submucosal implantation which could provide the feedback for chronic conditional stimulation. We have achieved most of the objectives of the initial proposal period. However, several hurdles remain to be overcome for application of the pressure monitor to provide closed-loop control for prevention of urinary incontinence, including assessment of feasibility of implantation, optimization of the pressure monitor for chronic implantation, creation of an algorithm for differentiating important bladder events from artifacts, validating our micro-packaging method for chronic implantation, and testing of this novel system in a chronic in vivo model. The goal of this extensively revised design and development renewal proposal is to accomplish these goals, thereby optimizing our pressure monitor for chronic submucosal implantation in the bladder for closed-loop bladder control after SCI. Four specific objectives are designed to accomplish the necessary work: 1. Assess clinical aspects of pressure monitor implantation;2. Optimize the implantable pressure monitor for chronic implantation;3. Develop feature extraction methods for distinguishing important bladder events from artifact;and 4. Develop micro-packaging for chronic implantation of the pressure monitor. Completion of the proposed research will put us in a strong position to proceed to clinical testing of our closed loop control system, after which, we will begin clinical trials of our pressure monitor.
Spinal cord injury (SCI) patients characteristically develop detrusor overactivity and striated sphincter dyssynergia, leading to overactive bladder (OAB) and uncontrolled leakage of urine. These same patients are at high risk for pressure ulcers, which can lead to sepsis and potentially death when in continuous contact with urine. In addition, chronic bladder hyperreflexia can also lead to autonomic dysreflexia and renal failure. Electrical stimulation is currently used in an open loop configuration to treat OAB but the effectiveness is reduced because it must be on continuously. We have developed a wireless catheter-free pressure monitor for submucosal implantation in the bladder. In the proposed project, we will further develop it to provide the necessary feedback for closed loop control of electrical stimulation systems for bladder control in SCI patients. Veterans constitute one quarter of the 250,000 people with SCI in the U.S. and there are 10,000 new SCI patients each year. Therefore this proposal is of high relevance to the VA.