Conformation and mechanics of the polymeric cuff of artificial urinary sphincter

In silico assessment of the reliability and performance of artificial sphincter for urinary incontinence

BACKGROUND

The standard artificial urinary sphincter (AUS) is an implantable device for the treatment of urinary incontinence by applying a pressure loading around the urethra through an inflatable cuff, often inducing no-physiological stimulation up to tissue degenerative phenomena. A novel in silico approach is proposed to fill the gap of the traditional procedures by providing tools to quantitatively assess AUS reliability and performance based on AUS-urethra interaction.

METHODS

The approach requires the development of 3D numerical models of AUS and urethra, and experimental investigations to define their mechanical behaviors. Computational analyses are performed to simulate the urethral lumen occlusion by AUS inflation under different pressures, and the lumen opening by applying an intraluminal pressure progressively increased under the AUS action (Abaqus Explicit solver). The AUS reliability is evaluated in terms of tissue stimulation by the mechanical fields potentially responsible for vasoconstriction and tissue damage, while the performance by the intraluminal pressure that causes the lumen opening for a specific occlusive pressure, showing the maximum urethral pressure for which continence is guaranteed.

RESULTS

The present study implemented the procedure considering the gold standard AMS 800 and a novel patented AUS. Results provided the comparison between two sphincteric devices and the evaluation of the influence of different building materials and geometrical features on the AUS functionality.

CONCLUSIONS

The approach was developed for the AUS, but it could be adapted also to artificial sphincters for the treatment of other anatomical dysfunctions, widening the analyzable device configurations and reducing experimental and ethical efforts.

Characterizing and Quantifying Material Fatigue of the Artificial Urinary Sphincter Pressure Regulating Balloon

OBJECTIVE

To characterize and quantify changes in elastic properties and in vivo pressure characteristics of pressure regulating balloons (PRB) over time, we conducted an analysis of the mechanical characteristics of the PRB after removal from patients for revision surgery.

METHODS

Pressure and elasticity characteristics of new and used 61-70 cm H2O PRBs were analyzed. Pressure-volume curves were generated using commercially available urodynamics equipment. PRB pressures were measured at a standard fill volume (23 cc). Elastance was calculated by the slope of the tangent line at the inflection point of the pressure-volume curve. Tests were repeated 5 times per PRB and intraclass correlations were used to gauge test-retest reliability. Regression models were used for continuous variables based on data distribution.

RESULTS

Twenty-seven used PRBs were analyzed after excluding 3 for alternative pressure ratings and 2 for occult pinpoint leaks. Time from artificial urinary sphincter placement to removal ranged from 0.02-17.6 years (median 8.4, interquartile range (IQR) 5.7-10.0). The mean pressure of all extracted PRBs: 58.8 cm H=O (± 7.4), 17 (62.9%) below the standard operating range. Each year of use in-vivo was associated with 1.09 cm H2O pressure loss on linear regression (P <.01 CI -1.52 to -0.65). PRB pressures were not significantly different according to indication for removal (1-way analysis of variance (ANOVA) P = .11). Loss of elastance was non-linear, decreasing by 1.9% per year on Poisson regression (P <.01, CI -0.03 to -0.01). When accounting for PRB age, PRB pressure was independently associated with detrusor overactivity.

CONCLUSION

In PRBs tested for pressure-volume characteristics, increasing PRB age was associated with decreased pressure and elasticity.