Fig. 1.

Schematic drawing of the catheter described by Nasser and Zelefsky. The urinary catheter drains the bladder only when urine reaches a predefined level. First balloon fills with water (blue); second balloon fills with air and function as a float (white). A. bladder is almost empty, valve close; B. bladder is partly full, valve close; C. bladder full, valve open; D. catheter drained part of the urine, valve close. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)