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Urodynamics is the investigation of urinary function disorders of the lower urinary tract, i.e. the bladder and the urethra. Symptoms reported by the patient are often an unreliable guide to the underlying dysfunction of the lower urinary tract. The purpose of urodynamics is to provide objective confirmation of the pathology that a patient's symptoms would suggest.
For example, a patient complaining of urinary urgency (or rushing to the toilet), with increased frequency of urination can be said on the basis of their symptoms to have overactive bladder syndrome. The cause of this might be detrusor overactivity, in which the bladder muscle (the detrusor) contracts unexpectedly during bladder filling. Urodynamics can be used to confirm the presence of detrusor overactivity, which may help guide treatment.
Urodynamics is typically conducted by urologists, urogynecologists, or specialist urology nurses. A set of urodynamic tests are conducted in sequence, with the complexity of tests used depending on the indication:
Most tests begin with the insertion of a urinary catheter/transducer following complete bladder emptying by the patient. The urine volume is measured (this is the post-void residual volume, which shows how efficiently the bladder empties) and sent for microscopy and culture to check for infection. What follows depends on what the presenting problem is, but some of the common tests conducted are;
- Free uroflowmetry measures how fast the patient can empty his/her bladder.
- Multichannel cystometry measures the pressure in the rectum and in the bladder, using two pressure catheters, to deduce the presence of contractions of the bladder wall, during bladder filling, or during other provocative manouevres. The strength of the urethra can also be tested during this phase, using a cough or Valsalva manouvre, to confirm genuine stress incontinence.
- Pressure uroflowmetry again measures the rate of voiding, but with simultaneous assessment of bladder and rectal pressures. It helps demonstrate the reasons for difficulty in voiding, for example bladder muscle weakness or obstruction of the bladder outflow.
These common tests may be augmented by EMG measurement of electrical activity in the bladder neck, urethral pressure profilometry, assessing the "tightness" along the length of the urethra, and fluoroscopy (moving video x-rays) of the bladder and bladder neck during voiding.
The tests are most often arranged for men with enlarged prostate glands, and for women with incontinence that has either failed conservative treatment or requires surgery.
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