Hypothesis / aims of study
Urodynamics (UDS) is the gold-standard method of quantitatively evaluating the ability of the lower urinary tract to efficiently store and empty urine. However, performing UDS poses numerous challenges including requiring specialized equipment and staff as well as causing patient discomfort. We have developed a wireless catheter-free intravesical pressure sensor, the UroMonitor (Figure 1), to enable bladder monitoring for patients whose symptoms are not confirmed through UDS and to enhance our diagnostic capabilities. In this first ever human subject trial, we aim to evaluate the accuracy of UroMonitor generated pressure data and the feasibility of using the device in humans. We hypothesized that the device would obtain pressure data to describe detrusor activity and be safely placed, well tolerated, and easily extracted in all study participants.
Study design, materials and methods
This is a proof-of-concept pilot study with an intended sample of 11 subjects from a single institution. Ambulatory adult female patients undergoing evaluation for refractory overactive bladder (OAB) with multi-channel UDS were recruited, excluding those with an active urinary tract infection (UTI), > stage 2b pelvic organ prolapse (POP), neurogenic bladder, interstitial cystitis/bladder pain syndrome (IC/BPS), or history of radical pelvic or anti-incontinence surgery.
The UroMonitor uses low-power flexible electronics housed in a medical silicone housing which curles into a pigtail shape after insertion to remain in the bladder (Figure 1). It wirelessly transmits vesical pressure data at 10 Hz to a small pager-like radio receiver taped to the subject’s abdomen. The radio receiver stores the data on a micro secure digital (microSD) memory card and simultaneously transmits it wirelessly to a nearby laptop using Bluetooth. A silk suture was attached to one end of the UroMonitor to aid in transurethral retrieval from the bladder.
A pre-procedure urine culture confirmed the absence of infection. After a baseline standard multi-channel UDS was performed, the UroMonitor was transurethrally inserted into the bladder. The attached suture was taped to the subject’s thigh. Flexible cystoscopy confirmed appropriate UroMonitor positioning. The radio was placed on the subject’s abdomen and taped at the location of best reception using Tegaderm. An experimental second multi-channel UDS was performed with the device in place while UroMonitor data were received by the radio. Then, the UDS catheters were removed, and the patient was allowed to ambulate and void with only the UroMonitor in place while data were collected wirelessly and catheter-free. A repeat voided urine sample was obtained for culture and heavy metal assay. Then, the UroMonitor was manually extracted from the bladder by pulling on the attached suture. Visual-analog pain scales (VAS) assessed patient discomfort at baseline and after baseline UDS, cystoscopy, UroMonitor insertion, repeat UDS + UroMonitor, the UroMonitor monitoring period, and UroMonitor removal. Overall comfort during testing was also assessed. A follow-up phone call 48-hours post-procedure re-evaluated pain, lower-urinary tract symptoms, or changes in voiding habits.
Interpretation of results
The UroMonitor can be inserted and extracted safely without difficulty in women. The device may initially exacerbate OAB symptoms but subjectively causes minimal patient discomfort during testing and after removal. The changes to urodynamic findings after initial UroMonitor placement are confounded by potential irritation caused by cystoscopy and the necessity to repeat the UDS procedure for study purposes. UroMonitor data showed strong correlation to measured catheter pressures and voiding behaviors. Detrusor force interaction with the UroMonitor device potentially limits static pressure accuracy and accentuates voiding pressures, but more subjects are needed for definitive conclusions.