What is Urodynamics?

Urodynamics is a series of diagnostic tests to evaluate the bladder’s function and efficiency.  Urodynamic testing may be performed when: 1) the patient experiences a moderate to severe involuntary loss of urine; 2) other tests do not determine the cause of incontinence; 3) the physician suspects there is more than one cause of incontinence and; 4) the patient is considering surgery.  Urodynamics will assess bladder filling, bladder storage, transportation, and emptying/micturition of urine.  The urodynamic study goal is to reproduce and identify the underlying causes of lower urinary tract dysfunction.  According to the Standardization Committee of the International Continence Society, a good urodynamic study is comprised of three main elements: 1) a clear indication for an appropriate selection of relevant test measurements and procedures; 2) precise measurements with data quality control and complete documentation and; 3) accurate analysis and critical reporting of results.  The different urodynamic studies are; 1) Uroflowmetry; 2) Cystometrogram3Electromyography; 4) Leak Point Pressures; 5) Urethral Pressure Profiles and; 6) Pressure Flow Studies.

  • The cystometrogram (CMG) is a test that measures how well the bladder can store and release urine. The bladder is filled with sterile water by an infusion pump with a catheter inserted into the bladder through the urethra.  The sterile water infusion is controlled at a steady rate and vesical pressures (Pves) are monitored.  A second catheter is placed in the rectum or vagina to measure intra-abdominal pressure (PAbd).  As the bladder is filled with sterile water, bladder sensations from the patient’s first urge to urinate to the maximum tolerated bladder capacity are measured.  During the study, vesical pressure (Pves) is subtracted from intra-abdominal pressure (PAbd) to obtain a measurement of true detrusor pressure (Pdet).

 1.  Vesical Pressure is the pressure exerted on the contents of the bladder.  Vesical pressure is the sum of the intra-abdominal pressure from outside the bladder and the detrusor pressure exerted by the bladder wall musculature.

2.  Intra-Abdominal Pressure is the steady state pressure within the abdominal cavity.  Various factors such as coughing and sneezing can cause intra-abdominal pressure to increase drastically for short periods.  Intra-abdominal pressure is also increased in patients who are morbidly obese, have chronic ascites, or are pregnant.    

3. Detrusor Pressure is that component of vesical pressure created by the tension (active and passive) exerted by the bladder wall estimated by subtracting abdominal pressure from vesical pressure.

1.Detrusor/Sphincter Dyssynergia (DSD) is a disturbance of the normal synergistic coordination between bladder contraction and external urethral sphincter muscle relaxation during voiding.  In patients with a neurogenic bladder the urethral sphincter muscles contract during voiding instead of completely relaxing.  This results in alteration of normal flow and the rise of bladder pressure
  • Leak Point Pressure is a measurement taken of the bladder pressure at the point where leakage occurs.  Leak point pressure tests the amount of abdominal pressure required to drive fluid across the urethral sphincter.  This study is used to differentiate between genuine stress incontinence caused by bladder neck hypermobility versus that caused by intrinsic sphincter deficiency.  This is accomplished by abdominal pressure on the bladder with a provocative maneuver such as Valsalva (VLPP) or cough (CLPP).  Leak Point Pressure is particularly helpful in evaluating Stress Urinary Incontinence (SUI).
1. Valsalva Leak Point Pressure measures the competency of the urethral closure mechanism.  This test is dependent on the patient’s ability to bear down slowly at an increasing force until appropriate pressures are generated.
2. Cough Leak Point Pressure is a measure of the stress competence of the urethral with the expulsive force of abdominal pressure produced by a cough.
  • Urethral Pressure Profile (UPP) can be employed to assess sphincter closure pressure and urethral competence during filling, voiding and abdominal pressure.  The urethral pressure profile (UPP) will also measure the functional length of the urethra.  This is done by manually or mechanically by pulling a specialized catheter through the urethra while monitoring and recording pressures.  The UPP indicates the intraluminal pressure along the length of the urethra with the bladder at rest.
  • Pressure Flow Study is the voiding or bladder emptying phase of the urodynamic study.  A pressure flow study will measure the detrusor and vesical pressure during the voiding phase.  Electromyography (sEMG) of the pelvic floor may also be useful during the voiding phase to measure detrusor/sphincter synergy.  Once the voiding is complete, a Post Void Residual (PVR) measurement is taken.

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