Urodynamics (UDS) is presently the clinical standard for the assessment of neurogenic lower urinary tract dysfunction after spinal cord injury (SCI). However, this method presents many well-recognized limitations which may interfere with bladder function and its subsequent interpretation, particularly when working with conscious or mobile animals. To address this, we developed and tested a wireless intravesical device (the “UroMonitor”), as well as a telemetric transdetrusor pressure probe to permit continuous bladder pressure recording without the use of catheters. The aim of the presented study was to compare the UroMonitor and Telemetry system to the clinical assessment tools during UDS in a large animal model of SCI. In addition, we sought to determine how the bladder functions after SCI during ambulatory urodynamic assessment in these animals and how the testing technique compares to traditional UDS.

Female Yucatan minipigs (n=9; S&S Farms) were used under IACUC and veterinary oversight. SCI was induced via weight drop contusion (50g impactor; 16.73cm) with 5mins of additional compression (100g weight) at the 10th thoracic vertebrae (T10). UDS was performed before and 4-, 8-, and 11-weeks after SCI using clinical air-charged catheters (T-DOC; Laborie). Telemetric transdetrusor sensor was implanted under general anesthesia 4-weeks prior to SCI. UroMonitor was inserted transurethrally immediately prior to UDS under general anesthesia (dexmedetomidine, midazolam, butorphanol). Sedation was reversed with antisedan before beginning UDS. Amplitude [ΔPves (cmH2O)] and frequency of bladder contractions were quantified during UDS in the pre- and post-SCI setting. Data are expressed in mean and standard deviation. Ambulatory urodynamic monitoring (AUM) was performed unrestricted and unsedated in the animal pens. P-value of 0.05 was determined as statistically significant.

The UroMonitor was safely inserted into all 9 animals before and after SCI with little to no evidence of urethral trauma. Voiding and non-voiding contractions were reliably identified greater than 90% of the time (Table 1). Quantification of bladder contractions revealed the maximum amplitude (ΔPves) of voiding contractions (mean±stdev) in uninjured animals to be 27.2±10.8 cmH2O for UDS catheters, 25.8±8.4 cmH2O for Telemetric Transdetrusor Sensor and 26.0±10.6cmH2O for UroMonitor (Figure 1). No non-voiding contractions were observed in pre-SCI minipigs.  Maximum voiding contraction amplitudes in the post-SCI setting were measured as 15.6±6.7 cmH2O for UDS catheters, 12.7±5.7 cmH2O for the Telemetric Transdetrusor sensor and 12.5±7.1 cmH2O for the UroMonitor. Mean of differences between UDS catheter and Transdetrusor sensor was -2.9 cmH2O and mean difference between UDS catheterizations and UroMonitor was -3.1 cmH2O when assessing the amplitude of post-SCI voiding contractions. Maximum amplitude of non-voiding contractions in the post-SCI setting were measured as 15.4±5.9 cmH2O for UDS catheterizations, 11.3±5.4 cmH2O for the Telemetry sensor and 12.8±7.8 cmH2O for the UroMonitor. During AUM, voided volumes were found to be significantly reduced relative to those collected during UDS in pre-SCI animals. Further, bladder contractions were found to be greater during AUM relative to UDS assessment. UroMonitor baseline pressure demonstrated a ‘filling artifact’ causing high pressures at low bladder volumes which gradually returned to values measured by UDS and Telemetry sensors; a high-pass filter was applied to enable detection of contractions with a stable baseline. Correlation between UroMonitor and UDS air-charged catheters show moderate to strong agreement after the application of high-pass filter (pre-SCI: 0.39±0.44; post-SCI: 0.67±0.28; p<0.01).

We demonstrated that the UroMonitor and Transdetrusor telemetry sensor identified and quantified bladder events within ~4 cmH2O of the present clinical standard in a large animal model of traumatic SCI. Despite this 3-4 cmH2O decrease in contraction amplitude as measured from the sensors testing in the present study, we believe the clinical application of this device would be valuable in both ambulatory human patients and animal research models. The additional data which can be generated during ambulatory assessment along with catheter-free, anesthetic-free, restraint-free recording capabilities in pre-clinical models could significantly improve bladder assessment before and after injury. The presence of recording artefact during voiding likely contributed to poor correlations between pressure sensing modalities and is being investigated to correct in future embodiments of the UroMonitor. There were notable differences when assessing bladder function during conventional cystometry versus ambulatory urodynamic monitoring which may highlight the present gap in knowledge regarding how the bladder behaves outside of catheter-based assessment in the context of SCI.

Wireless, catheter-free devices may offer an alternative to traditional bladder assessment techniques permitting more natural, comfortable observation of lower urinary tract function in pre-clinical animals and humans. The present study demonstrates two devices that can reliably identify and quantify bladder contractions before and after SCI in a large animal model with a high degree of accuracy. The UroMonitor and Transdetrusor pressure sensors quantified bladder contractions within 5 cmH2O of the currently clinical standard.  Contraction pressures were weaker and voided volumes were greater during conventional cystometric assessment compared to ambulatory urodynamics which may further emphasize the unnatural component of catheter-based assessment

Continence 7S1 (2023) 100971
DOI: 10.1016/j.cont.2023.100971