Hypothesis / aims of study
Conventional Urodynamic studies (UDS) are widely utilized in evaluating neurogenic bladder (NGB) and refractory overactive bladder (OAB). However, UDS requires invasive monitoring via an indwelling urethral catheter and a significant time commitment for patients in the outpatient setting. In addition, insertion of urethral catheters for vesical pressure monitoring and back-filling has a potential risk of urinary tract infection and its associated morbidity. In this pilot study, we combined the expertise of bioengineers, translational scientists and urologists to determine the feasibility and sensitivity of a novel non-invasive UDS (NI-UDS) system for dynamic bladder physiology assessment in healthy volunteers. Our goal is to present high-resolution, non-invasive multi-channel urodynamic study (NI multi-channel UDS) as an equivalent but entirely non-invasive diagnostic tool that can be offered in lieu of conventional, invasive UDS. In this study, we aimed to test the ability of NI multi-channel UDS to monitor OAB in individuals. We hypothesized that NI multi-channel UDS has sufficient resolution to sense dysfunctional changes in the bladder and provides diagnostic value of OAB in individuals.
Study design, materials and methods
Our NI multi-channel UDS was prepared with eight surface electrodes, Cyton (a data collecting device), ECG/EMG snap electrode cables, OpenBCI USB Dongle, OPENBCI_GUI software and a laptop (Figure 1). In details, ECG/EMG snap electrode cables are connected to the electrode pins located in the Cyton board. OPENBCI USD Dongle is connected to the laptop and the OPENBCI_GUI software is turned on upon data collection. Cutaneous myoelectric recordings of the urinary bladder were measured from ten healthy subjects consisting of seven females (mean age 37.175.02 years) and three males (mean age 30.330.88 years) using NI-UDS. NI-UDS is performed with an array of eight surface electrodes (Ambu Blue Sensor-N) placed on the suprapubic region and left flank (ground) after reporting a full bladder. Data is recorded in three phases: (1) 5 mins 30 secs storage phase, (2) voluntary voiding, and (3) 5 minutes post-void phase. Real time data is sent to OpenBCI_GUI software wirelessly over the course of voiding phases and the recording is paused between each of these periods to minimize movement artifact as the subject enters and exits the lavatory. Statistical signal processing is performed with Python to determine spatial and temporal patterns in the three phases associated with wave propagation. Features include wave speed and whether or not a sustained wave is present at any point in time.
Movement artifacts was successfully eliminated using Jupiter software and Python program language for noise filtering of signals at 60 Hz and the desired urodynamic parameters from original data were sorted out. Average percentages of sustained wave in the bladder of female subjects during storage, voiding and post-void phases were 0.710.05, 0.740.06 and 0.730.05, respectively. Interestingly, male subjects had lower average percentages of sustained wave compared to females (0.660.03, 0.680.03 and 0.67+0.03 for storage/filling phase, voluntary voiding and post-voiding phase, respectively). Direction of electrical activity (wave propagation) in urinary bladder was consistent over the course of pre-, voluntary, and post- voiding (Figure 2). Interestingly, the number of wave propagation at various speed was noticeably decreased during voluntary voiding as compared to pre- and post- voiding phase. Strikingly, we observed this pattern in all subjects.
Interpretation of results
Given that several factors including age and hormonal change may affect urodynamic parameters at the time of NI multi-channel UDS recording, it is striking that our system revealed a signature pattern of electrical signals from urinary bladder over the course of pre-, voluntary and post- voiding, which was consistent in all subjects. In other words, NI multi-channel UDS is sensitive enough to monitor electrical signals of the healthy human bladder.