Urodynamics (UDS) remains the gold-standard method for functional assessment of the lower urinary tract (LUT).  However, UDS has many limitations and often fails to replicate patients’ symptoms [1–3]. We have developed a wireless, catheter-free intravesical pressure sensor, the UroMonitor (UM) to perform telemetric ambulatory bladder monitoring.  Our aims were to evaluate the accuracy of UM-measured pressure data and assess the safety and feasibility of use in a first in human study. We hypothesized that UM-obtained pressure data would correlate with that of standard multi-channel UDS and that the UM could be safely placed, well tolerated, and easily extracted in women with overactive bladder.  Herein we report the results of our completed first in human study (preliminary reports on the first 3 patients were presented at the 2020 ICS meeting).

This was an observational pilot study which included 11 adult female patients undergoing evaluation for overactive bladder (OAB) with multi-channel UDS. Women with a diagnosis of interstitial cystitis/bladder pain syndrome, neurogenic lower urinary tract dysfunction, recurrent UTI (3 or more culture proven UTI in 1 year), > stage 2b pelvic organ prolapse, significant obesity (BMI >35), or a history of radical pelvic surgery were excluded from the study. All patients had a negative urine culture prior to any study-related procedures.  

All patients had baseline, multi-channel UDS performed including uroflowmetry, cystometry, pressure-flow studies, and electromyography (EMG). Following baseline UDS, the UM was inserted transurethrally into the bladder. The UM’s pre-curled, flexible silicone housing allowed it to be straightened during insertion and then coil back into a more circular shape upon entering the bladder. Flexible cystoscopy was performed to confirm appropriate positioning of the UM within the bladder. A pre-placed silk suture through one of the UM’s end caps allowed for device retrieval at the conclusion of the study. 

A second UDS was performed with both UDS catheters and UM simultaneously recording vesical pressure data, allowing for direct comparison between the two modalities. Throughout the study, the UM wirelessly transmitted vesical pressure data at 10 Hz to a small radio receiver secured to the subject’s abdomen. The receiver stored the data on a memory card and transmitted the data wirelessly to a nearby laptop using Bluetooth for real-time assessment of vesical pressure data.  

Next, the UDS catheters were removed and the subject was able to ambulate and void with only the UM in place. Vesical pressure data from the UM were collected wirelessly and catheter-free via telemetry and the subjects voided in privacy on a toilet.  At least one voided urine sample was obtained from all subjects and sent for urine culture and urine heavy metal assay. The UM was manually extracted transurethrally via the pre-attached suture and a post-void residual (PVR) urine volume was obtained. Visual-analog pain scales (0-5) were used to assess patient discomfort during each study phase. A follow-up phone call was made 2 days post-procedure to reassess for pain and/or any changes in LUT symptoms. 

Descriptive statistics were utilized to define patient and UDS characteristics. A paired t-test compared UDS data before and after UM insertion, with p < 0.05 indicating statistical significance. The simultaneously obtained UDS and UM data were evaluated by 2 urologists and UDS relevant events were identified for both pressure tracings to qualitatively assess the accuracy of the UM.  Linear regression was performed to assess correlation between UDS- and UM-recorded pressure data.

UDS and UM data from 11 subjects were obtained. The mean age of subjects was 65 [range 44-83 years] and all subjects self-identified as white. Average BMI was 30.2 [25.0-35.8]. Mean time for UM insertion was 24.5 s [7-66 s]. Urodynamic data obtained during baseline UDS was compared to UDS with the UM in place (Table 1). Only 1 patient demonstrated worsening detrusor overactivity (DO) on UDS following UM insertion and cystoscopy. No new or concerning urodynamic findings were elicited during the filling or voiding phase with the UM in place.  

Qualitatively, the UM was able to accurately reproduce vesical pressure data patterns during cystometry, capturing 98% (85/87) of voiding and non-voiding urodynamic events (i.e. DO, stress maneuvers, and voiding contractions). Overall, UM-recorded pressure events aligned well in time and morphology with those from simultaneous UDS (Figure 1). On initial analysis during early filling, a consistent divergence between UM and UDS pressure data was noted. However, when analyzing only pressure data during UDS relevant pressure events, UM pressure data correlated closely with that of UDS and improved significantly over the course of the study as device modifications and data acquisition methods improved (mean r2: 0.61, [0.1-0.94]).

Subjects ambulated with only the UM in place for an average of 60 minutes [range 30-90 mins] (Figure 1).  All subjects voided with the UM in place with a mean number of 1.7 voids [1-4 voids]. This was in contrast to 4 subjects who were unable to void with UDS catheters in place. When assessing the catheter-free UM-measured pressures for the 5 subjects with DO demonstrated on baseline UDS, 71% fewer DO episodes were noted during the catheter-free phase (38 cumulative baseline DO events vs. 11 cumulative catheter-free DO events) despite almost two times the duration of monitoring (103 mins cumulative baseline UDS time vs 205 mins cumulative catheter-free time).  Mean PVR following the catheter-free, ambulatory phase (11cc, [0-50cc]) was less than during baseline UDS (21cc, [0-100cc]), but the difference was not statistically significant (p=0.38). Two subjects voided the UM out but neither reported pain associated with this. A second sterile UM was replaced in both instances to complete the study.

The most painful portion of the procedural intervention was flexible cystoscopy, with a median pain score of 3 [range 0-5]. Pain during ambulation with only UM, UM removal, post-procedure, and 48 hours after the procedure all had median pain scores <1. Mean time for UM removal was 2.1 s [1.5-3 s].  There were no post-procedure UTIs or detection of heavy metals within the urine. There were no adverse events or peri-procedural complications. There were no significant changes to baseline voiding behaviors 48 hours post-procedure.

Use of the UM is safe with no associated peri-procedural urinary tract infections, complications, or heavy metal detection in the urine. The UM was inserted and extracted without difficulty in women via techniques familiar to urologists. The UM was well-tolerated, with the most painful portion of the study being flexible cystoscopy. Presence of the UM did not significantly alter either urinary storage or emptying ability.  While there appears to be subtle differences in pressure measurement between UM and UDS during the early filling phase, this did not impact the UM’s ability to identify clinically relevant UDS events, and it accurately detected 98% of events on qualitative assessment by 2 urologist. When focusing on these clinically relevant pressure events, the UM pressure data correlates closely with UDS.

The UM is the first device to enable catheter-free telemetric ambulatory bladder pressure monitoring in humans. The UM appears safe, is well tolerated by patients, and does not impede LUT function. The UM enables ambulatory bladder pressure data collection without catheters or UDS equipment that may impede normal activity. Preliminary data suggest the UM can reliably identify urodynamic relevant bladder events.

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A. M. Suskind et al., “Patient perceptions of physical and emotional discomfort related to urodynamic testing: A questionnaire-based study in men and women with and without neurologic conditions,” Urology, vol. 85, no. 3, pp. 547–551, Mar. 2015, doi: 10.1016/j.urology.2014.11.001.