Study of threee urethral pressure recording devices: theoretical considerations.

Using a bladder-urethra model, 2 perfusion catheters (open side and open tip) were compared to the balloon catheter. The most accurate results were obtained using the balloon catheter. Based on the law of continuity and Bernouilli's law, the disadvantage of the open side catheter is due to the inconstant diameter of the sum of the side holes. Therefore, the measured pressure is not necessarily identical to the real pressure. The open tip catheter measures the opening pressure and the recorded pressure does not necessarily reflect the pressure at the site of the tip hole. The balloon catheter has elastic and plastic characteristics. Optimum results were obtained only with prestretch of the balloon and with calibration before and after each study. This catheter was the most complicated, but produced the best results and gave rise to the least irritation.