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.

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.

Our interim results include 3 of 11 patients. It took a median 46 (range: 19 – 81) seconds to insert the UroMonitor. Cystoscopy demonstrated that the UroMonitor was easily inserted into the bladder with no insertion tool or guidewire needed (Figure 1). After UroMonitor insertion, we noted a 22% average reduction in bladder capacity during the testing period (baseline UDS: 335 cc vs. UDS + UM: 262 cc).  If phasic DO was appreciated during the baseline study, a 50% increase was noted after UroMonitor insertion (baseline average DO episodes: 3.0 vs. UDS + UM: 4.5).  No new UDS findings were elicited after UroMonitor placement during the filling phase. UroMonitor presence did not impede urinary flow (baseline average flow: 8.5 cc/s vs. UDS + UM: 9.3 cc/s, p=0.93).

The UroMonitor reliably reproduced vesical pressure data patterns during both filling cystometry and ambulatory measurements, including rise in pressure with non-voiding contractions and larger rise in pressure with voiding contractions (Figure 2).  
 
Patient reported VAS scores ranged from 0-2 throughout the study.  The most uncomfortable study segment was UroMonitor Insertion (Avg. Score: 1.33). One patient voided out the device immediately after cystoscopy without discomfort; it was replaced for study completion. No changes to OAB or voiding symptoms were noted during the ambulatory phase. All patients voided freely with the device in place and reported no discomfort. It took a median 2.5 (range: 2.2 – 3.5) seconds to remove the UroMonitor.

No post-procedure reportable complications (including UTIs) or heavy metal detection were reported. There were no other unexpected or adverse events. No changes to baseline voiding symptoms were noted 48 hours after the procedure.

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.

To our knowledge, this is the first example of wireless catheter-free bladder pressure data collection in humans. The UroMonitor enables ambulatory bladder pressure data collection without catheters or wires impeding normal activity. Preliminary results indicate the UroMonitor is able to identify urodynamically relevant bladder events.  The device is easily inserted and removed in ambulatory female patients.  While in place, it does not cause voiding obstruction nor does it cause any subjective discomfort.