Figure 5.

Exponential effect of the external striated muscle mechanism on urethral resistance explains Fowler's syndrome (FS) retention. The arrows represent simplified vector forces which close the urethra during continence (forward arrow) or open it during micturition (backward arrow). The indicated pressures required to drive the urine through the changed diameter, are based on a nominal pressure of 160 cm for radius ‘r’. Pressures to expel through diameters r/2 (closure) and 2r (micturition) are calculated using the 4^th power law of Poiseuille. Halving the radius (r/2) increases the expulsion force required by a factor of 16, to 2560 cm H₂O. Doubling the radius (2r), decreases that force by a factor of 16 to 10 cm H₂O. If we take the front arrow to represent overcompensation by the distal urethral closure mechanism in FS patients, very little extra activity is required to close the urethra sufficiently to make it impassable to urine flow. This explains the clinical ‘retention’ of FS. After Petros PE, The Female Pelvic Floor, 3^rd Ed Springer 2010.