According to the presenter, there are 3 primary urodynamic pressures: intravesical (Pves), abdominal (Pabd), and detrusor pressures (Pdet). While Pves reflects detrusor pressure and abdominal pressure affecting LUT, Pdet is a difference between Pabd and Pves.
Dr. Gray stressed an importance of understanding basic concepts of bladder storage, filling, and emptying for the successful interpretation of the tests. Bladder storage function should be determined by cystometric capacity (large, small, within normal limits), detrusor response to bladder filling (normal or overactive), patient-reported sensations during bladder filling (normal, increased, decreased or absent), and capability of urethral sphincter mechanism (incompetence corresponds with the urodynamic stress urinary incontinence).
Bladder capacity encompasses functional bladder capacity (FBC) (urine volume in the bladder when a patient elects to urinate), anatomic capacity (infused volume), and cystometric capacity (intravesical volume). Data show that functional bladder capacity is 330ml in the U.S. females and 382 in the U.S. males. Normal adult cystometric capacity is 300-600ml.
Dr. Gray introduced a technique on documenting individual’s sensation during bladder filling. The patient should report the first sensation of filling, first desire to urinate, strong urge to void, and imminent desire to void.
Urethral sphincter competence can be examined by abdominal leak point pressure or urethral pressure profilometry (UPP). Abdominal leak point pressure is a magnitude of abdominal force necessary to drive urine across a closed urethral sphincter mechanism. Testing usually begins at 150-200ml with Valsalva. UPP determines maximum urethral closure pressure.
Bladder evacuation is evaluated by uroflowmetry (screening study to assess obstruction or underactive detrusor function) and voiding pressure-flow study (UPFS) (uroflowmetry combined with pelvic floor muscle EMG).
Finally, Dr. Gray stressed that a computer is a great mathematician, but a very poor clinician, thus continuous education is essential for the interactive interpretation of urodynamic studies.
Presented by: Mikel Gray, Ph.D., RN, Professor, Department of Urology, University of Virginia
Written by: Hanna Stambakio, BS, Clinical Research Coordinator, Division of Urology, University of Pennsylvania, @PennUrology at the 2018 ICS International Continence Society Meeting - August 28 - 31, 2018 – Philadelphia, PA USA