The current study aims to investigate the potential physiological mechanisms underlying the effectivity of an air-filled intravesical balloon as an intervention for stress urinary incontinence (SUI) in women. Previous studies have indicated that an intravesical balloon alleviates much of the complaints caused by SUI in women [1, 2], but the current study is the first to investigate the in vivo physiological mechanisms underlying this therapy in female SUI patients. The hypothesis of the mechanism of action is that the air-filled balloon would absorb part of the intravesical pressure, thus, reducing the stress incontinence episodes. 
We investigated an additional or alternative hypothesis that an intravesical balloon will inwardly push the bladder wall upwards causing the organ to acquire a more vertically oriented shape. This may result in a decreased exposure of the cranial bladder wall to downward pressure and a possible increased exposure of the urethral sphincters to changes in sideways intra-abdominal pressure, which aids the urethral sphincters in successfully preventing the loss of urine during episodes of high intra-abdominal pressure.

The current study was approved by the local ethical committee, and informed consent was obtained from each of our participants. We recruited 10 female patients with SUI (mean age: 55.6, SD: 7.8) according to ICS criteria. 6 patients (mean age: 52.5, SD: 4.7) could be evaluated before and after balloon implantation (4 had missing data due to technical difficulties). In order to visualize differences in bladder shape before and after implantation of the intravesical balloon, our participants were subjected to two video urodynamic studies in which the bladder was filled with 100 ml of saline: the first before implantation of the intravesical balloon, and the second one week following implantation of the balloon (fig. 1).

For each video urodynamic study, the maximum bladder diameters in the horizontal and vertical directions were measured and the maximum vertical diameter was expressed as a ratio of the maximum horizontal diameter. Before and after implantation ratios were subsequently statistically compared using a Wilcoxon Signed-Rank Test. Ratios before implantation of the intravesical balloon had a mean of 92.637 (SD: 30.24) and ratios one week following implantation had a mean of 136.605 (SD: 39.784). The difference between the maximum vertical diameter expressed as a ratio of the maximum horizontal diameter before and after implantation after the intravesical balloon was significant at the 0.05 level (2-tailed, p = 0.028). Furthermore, after intravesical balloon intervention the participants’ average daily pad use decreased from 3 pads per day before the intervention to 1.3 pads per day after the intervention.

Our results indicate that the shape of the bladder changes significantly after implantation of an intravesical balloon, obtaining a more vertically oriented shape. We propose that this change in bladder shape is an additional contributor to the alleviation of SUI symptoms. Future studies should aim to establish a causal link between bladder shape and sphincter function.

Implantation of an intravesical balloon causes the bladder to obtain a significantly more vertically oriented shape. This change in shape may be related to an alleviation of SUI symptoms.

Wyndaele, J. J., De Wachter, S., Tommaselli, G. A., Angioli, R., de Wildt, M. J., Everaert, K., ... & Van Koeveringe, G. A. (2016). A randomized, controlled clinical trial of an intravesical pressure-attenuation balloon system for the treatment of stress urinary incontinence in females. Neurourology and urodynamics, 35(2), 252-259.
Rovner, E., Jacoby, K., Kalota, S., Snyder, J. A., Cline, K., Robertson, K., ... & Zuckerman, J. (2017). Three-month primary efficacy and six-month treatment arm results from the SUCCESS study of an intravesical balloon to treat female stress urinary incontinence (SUI). European Urology Supplements, 16(3), e1504-e1505.