Urodynamic evaluation of voluntary detrusor response in healthy subjects

The ability of healthy subjects to voluntarily inhibit a bladder detrusor contraction was evaluated using standard urodynamic techniques. Ten healthy subjects (five men and five women) were appraised using trichannel techniques which included measuring bladder volume, bladder pressure, intraabdominal pressure, and electromyographic activity of the anal or external urethral sphincter. Each subject was first evaluated to determine normalcy of urine flow rate. All subjects were assessed in three positions: supine, sitting, and standing. All ten subjects were able to inhibit their detrusor responses without increasing external urethral or anal sphincter activity or raising the tonus pressure limb of the bladder. Three of the subjects were unable to void during any part of the urodynamic evaluation. In one subject, voiding was accomplished by Valsalva maneuver which mimicked detrusor contraction. At least two subjects did not demonstrate their first urge to void until 300 to 400 cc, and one of these individuals was unable to void until his bladder capacity reached 600cc. These results indicated that normal subjects can inhibit their detrusor response during urodynamic studies. Inability to inhibit this response would therefore appear to be an abnormal pattern. Conversely, inability to produce a detrusor response cannot be called an abnormal retention pattern. Bladder volumes in healthy subjects may be higher than the traditional norms, and this must be taken into account during urodynamic evaluations.