Principles of modern urodynamic studies.

Modern urodynamic equipment should have at least three channels to record the cystometrogram, the electromyogram of the periurethral striated sphincter, and intrarectal pressure. The addition of simultaneous transrectal ultrasonography is helpful. The bladder should not be irritated when introducing the urodynamics catheter. Variables affecting the performance of the catheter used for measuring the urethral pressure profile include the size of the lumen, the size of the side hole, the speed with which the catheter is withdrawn, and the rate of infusion. The entire curve of the cystometrogram should be examined, not simply initial rise. Initial overshoots can occur if older apparatus is used or if the urodynamics catheter is partially blocked; such overshoots should be disregarded.