Detecting bladder volume and pressure from sacral nerve signals: the key to future artificial control

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This project is about the treatment of urinary incontinence, consequent of damage to the spinal cord. Managing the urinary bladder is of the first importance to clinicians and patients following trauma to the spinal cord. Historically, kidney damage due to high bladder pressures and/or infection was the usual cause of death resulting from such an injury. Infections still raise mortality and morbidity, exacerbated by the risk of antibiotic resistance. In order to achieve urination-i.e. complete voluntary micturition (CVM) and as an alternative to the expensive process of intermittent sterile catheterisation, a neuroprosthesis for controlling the bladder after spinal cord injury (SCI) was developed by GS Brindley at the MRC Neurological Prostheses Unit in London 30 years ago. The Brindley method employs sacral anterior root stimulation (SARS) but is not popular in Europe, in terms of the fraction of the SCI population treated, because implantation of the device is accompanied by cutting the sacral posterior (sensory) nerve roots (rhizotomy) to prevent reflex incontinence during bladder filling and improve stimulated voiding. Clearly there is a need for a new neuroprosthesis that is more widely acceptable (primarily because no rhizotomy is necessary) and which, in addition, reduces the lifetime cost of care. The aim of this project is to design and demonstrate such a device. Since its introduction, the Brindley method has been improved in several ways in attempts to address the problems mentioned. However, in spite of these developments, at present (a) no satisfactory, practical method exists for detecting the onset of bladder contractions in a chronic implant and, (b) no method is available to inform the patient of the level of bladder fullness to indicate when the bladder should be emptied. These are critical obstacles to the design of a complete prosthesis and our proposed solution is to use the bladder neural signals themselves since surgically implanted electrodes are essential anyway (i.e. for stimulation). A suitable site for the electrodes is the extradural roots; this is surgically attractive and electrodes are routinely implanted here in the Brindley procedure. In order that the nerves are similar to those in man, it is essential to use a large experimental animal as a preclinical model and we propose to use sheep for these experiments.