The Novel Development of Continuous Bladder Volume Measurement System

Neurogenic bladder is a dysfunction developed as a consequence of the injury to nervous systems controlling the voiding and storage function. The disease plagues especially the spinal cord injury patients, causing long term morbidities and complications such as urinary tract infection, renal impairment, or urinary stones. Traditionally neurogenic bladder is treated with medication, behavioral treatment, and catheterizations to divert the urine, either indwelled or intermittent. However, current treatments have the shortcomings of compliance and medication side effects. A new technology, sacral nerve electric stimulation, appears to be a promising treatment option for this patient group. Currently available products include Interstim by Medtronic, and Vocare by Finetech-Brindley. The major concern in the patients with neurogenic bladder is the lack of accurate bladder sensation. Therefore, a system providing continuous and accurate bladder volume measurement becomes important. The information of bladder volume is important in electric stimulation treatment, in which the bladder volume can serve as an input to trigger voiding stimulation when the volume reaches the voiding threshold. If this can be achieved, the electric stimulation system can be configured into a closed loop system and will not require external control, as practiced now. Currently this technology of continuous measurement is not available. In addition, if the patient is under intermittent catheterization to divert the urine, the information of bladder volume is also essential. Currently because of lack of bladder sense, this group of patients has to perform catheterization on a timed schedule basis, i.e. catheterization every 4 hours. If continuous bladder measurement system is available, the patient can then determine when is the best time to perform catheterization, and avoid unnecessary catheterizations or bladder overdistension injury. We propose the establishment of a method to directly measure the bladder volume. The measurement principle for this novel technology utilizes the change of bladder strain when the bladder is distended. A strip of strain volume sensor is composed of connection of 4 strips of strain gages to measure the distension of the bladder. The full sensor system consists of the sensor, power supply, and signal output port. A pair (two strips) of sensors is constructed. One sensor strip is positioned at the half equator across the fluid-filled artificial bladder. The other sensor strip is positioned at the half meridian. The actual volume of the bladder is compared with the volume estimated from the calculation. Continuous measurement is also performed. This project will have two stages. The first stage is through the use of an artificial bladder system, in which we should experiment and determine the best design and parameters on an artificial bladder. The second stage is in vitro study, in which 4 sets of swine ex vivo bladders will be used as animal models to evaluate the actual application of the design. The objective of this work is to demonstrate the feasibility of continuous measurement of bladder volumes directly based on the change of strain on bladder wall. Direct volume measurements would also permit active volume control using feedback principles.