Urodynamics are a means of evaluating the pressure-flow relationship between the bladder and the urethra for the purpose of defining the functional status of the lower urinary tract. The ultimate goal of urodynamics is to aid in the correct diagnosis of urinary incontinence based on pathophysiology.
Urodynamic studies should assess both the filling-storage phase and the voiding phase of bladder and urethral function. In addition, provocative tests can be added to try to recreate symptoms and to assess pertinent characteristics of urinary leakage.
Simple urodynamic tests involve performing a noninvasive uroflow study, obtaining a postvoid residual (PVR) urine measurement, and performing single-channel cystometrography (CMG). A single-channel CMG (ie, simple CMG) is used to assess the first sensation of filling, fullness, and urge. Bladder compliance and the presence of uninhibited detrusor contractions (eg, phasic contractions) can be noted during this filling CMG. A simple CMG may be performed using water or gas (carbon dioxide). Water is the most common filling medium.
Multichannel urodynamic studies are more complex than simple urodynamics and can be used to obtain additional information, including a noninvasive uroflow, PVR urine, filling CMG, abdominal leak-point pressure (ALPP), voiding CMG (pressure-flow), and electromyography (EMG). Water is the fluid medium used for multichannel urodynamics.
The most sophisticated study is videourodynamics, the criterion standard in the evaluation of a patient with incontinence. In this study, the following are obtained:
- Noninvasive uroflow
- PVR urine
- Filling CMG
- Voiding CMG (pressure-flow)
- Static cystography
- Voiding cystourethrogram (VCUG)
The fluid medium used for videourodynamics is radiographic contrast.
Selection of patients for complex urodynamic testing can be difficult. Universally agreed-upon criteria for complex testing do not exist. The criteria that do exist are rooted more in expert opinion than in evidence-based scientific findings.
Urodynamic testing is expensive and requires specialized equipment and expertise. The availability of testing facilities is not universal.
The potential importance of urodynamic testing lies in the fact that the outcome of therapy is tied to understanding the pathophysiology in any given case and to making the correct and complete diagnosis. Surgery for incontinence carries with it substantial failure and complication rates. Many poor outcomes may be attributed to diagnostic failures.
Urodynamic studies are, by their nature, unphysiologic. Studies have shown that the reference range in such tests as uroflowmetry and cystometry is wide. Urodynamic findings of significance must be associated with reproduction of the patient’s symptoms. Studies that do not reproduce the patient’s symptoms are inconclusive. Likewise, studies that result in abnormalities with no associated symptoms, or symptoms differing from the patient’s complaints, are not conclusive. Nevertheless, these are the best tests available for examination of lower urinary tract function.