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.