Purpose: To evaluate the physical properties of urethral catheters that are predictive of ease of placement and risk of urethral trauma: Stiffness, buckling, and friction forces.
Materials and methods: Eleven Bard Lubri-Sil and 10 Kendall Dover 16F Foley catheters were tested using a linear motion stage driven by a stepper motor with a resolution of 5 microns/step or by hand. Force was measured at a sampling rate of 5 Hz with a Wagner FDIX digital force gauge. Friction force was measured by pulling each Foley catheter at a rate of 2.5 mm/s through a 15.6F hole drilled in 36-mm thick biologic material (Oscar Meyer Beef Light bologna 12 oz package). Ease of advancement was measured by the force necessary to maneuver a catheter around a 90-degree turn in a bulbar urethra modeled by 5/16 inch inner diameter silicone tubing and lubricant. Buckling forces were measured at the tip (8 mm), from the distal end of the balloon to the tip (30 mm), and along a 20 cm section of the shaft using the appropriate size force gauge.
Results: No significant difference was noted for friction force. The Kendall catheters (0.0686 +/- 0.102 lb(f)) took more force to advance around a 90-degree turn, compared with the Bard (0.602 +/- 0.110 lb(f), P = 0.003). Buckling force along the shaft and from the balloon to the tip was significantly greater for the Bard (0.051 +/- 0.02 lb(f), P < 0.001 and 0.892 +/- 0.166 lb(f), P < 0.001) compared with the Kendall (0.027 +/- 0.007 lb(f) and 0.803 +/- 0.129 lb(f)) catheters. Stiffness of the tip was significantly greater for the Kendall (2.644 +/- 0.552 lb(f), P < 0.001) compared with the Bard (2.101 +/- 0.437 lb(f)) Foley catheters.
Conclusions: Traumatic catheterization is a major cause of urethral stricture. Catheter stiffness may increase the risk of urethral injury and subsequent stricture formation. Ease of advancement and tip stiffness may be important at predicting clinical performance of urethral catheters.