Urodynamics: The Study of Motion and Flow of Urine
Urodynamics is the term that describes the study of the motion and flow of urine. 1
Definition and Purpose of Urodynamics
Urodynamics (UDS) is an interactive diagnostic study of the lower urinary tract composed of a number of tests that can be used to obtain functional information about bladder filling, urine storage, and emptying. 1 It is specifically defined as the dynamic study of the storage and voiding function of the urinary tract. 2
The main goal of urodynamic testing is to:
- Reproduce the patient's symptoms when present
- Determine the cause of these symptoms through urodynamic measurements and observations
- Identify the pathophysiology of lower urinary tract dysfunction 1
Components of Urodynamic Testing
According to the American Urological Association (AUA) and Society for Urodynamics, Female Pelvic Medicine and Urogenital Reconstruction (SUFU) guidelines, urodynamic testing includes several specialized tests that evaluate different aspects of urinary function:
- Uroflowmetry: Measures the volume of urine expelled from the bladder per unit of time (ml/s) 3
- Post-void residual (PVR): Measures remaining urine in the bladder after voiding
- Cystometry (CMG): Evaluates bladder function during filling and storage
- Pressure-flow studies (PFS): Assesses the relationship between pressure and flow during voiding
- Videourodynamic studies (VUDS): Combines imaging with pressure measurements
- Electromyography (EMG): Records electrical activity of pelvic floor muscles
- Urethral function tests: Including Valsalva leak point pressure (VLPP) and urethral pressure profile 1
Clinical Applications of Urodynamics
Urodynamic testing is valuable in evaluating:
- Lower urinary tract symptoms (LUTS)
- Urinary incontinence (stress, urgency, and mixed)
- Pelvic organ prolapse
- Neurogenic bladder
- Detrusor-sphincter dyssynergia 1, 4
In patients with pelvic floor dysfunction, urodynamic studies typically reveal:
- Staccato or intermittent flow patterns
- Reduced maximal flow rates
- Prolonged flow times
- EMG activity during voiding 4
Advanced Techniques in Urodynamics
Recent advances in urodynamic testing include:
- Home uroflowmetry techniques that allow multiple measurements in real-life conditions, addressing the limitations of single-visit office testing 5
- Visualization of the intravesical urine stream using transrectal ultrasound, which can provide additional information about urodynamics by measuring the velocity of urine flow within the bladder 6
Importance in Clinical Decision Making
The AUA/SUFU guidelines emphasize that urodynamic testing should be performed when specific urodynamic questions are formulated after appropriate evaluation and symptom characterization. 1 Proper urodynamic testing often aids in diagnosis when urinary symptoms and physical findings do not adequately predict the underlying pathophysiology.
Urodynamic findings have important treatment implications, particularly in conditions like detrusor-sphincter dyssynergia, where treatments such as pelvic floor physical therapy, biofeedback therapy, and management of associated conditions like constipation may be indicated. 4
In summary, urodynamics is the specialized field that studies the motion and flow of urine through the lower urinary tract, providing critical diagnostic information that guides clinical management of various urologic conditions.