Figure 2 . Exponential nature of urine flow is related to urethral diameter [7,8]. For a flow rate of 50 ml/sec (thick blue line), closing the urethral diameter from 4 mm to 3.5 mm (for example, by an overtight tape) increases the head of pressure required by the detrusor to expel urine from the bladder from 100 cm to 172 cm water. Expanding urethral diameter to 6 mm (yellow lines), reduces the head of pressure to 20 cm water. The blue line represents the total urethral resistance to flow.