Urodynamic studies

Question 1

Micturition pathway

Answer 1

• Voiding under voluntary control mediated by pontine reticular formation centre in cerebellum
• Storage/filling phase
  o Sensory receptors -> pelvic nerve -> S2-S4 -> pontine storage centre
  o Sympathetic descending fibres
• Via hypogastric nerve and plexus (T10-L2)
• Alpha adrenergic to bladder neck and urethra to increase resistance
• Beta adrenergic to detrusor muscle to cause smooth muscle relaxation
  o Somatic descending fibres
• Pudendal nerve innervates external sphincter to voluntarily increase tone
  o First urge to void at half bladder capacity
  o Suppression of detrusor contraction may be accompanied by voluntary pelvic floor contraction
• Initiation phase
  o Relaxation of pelvic floor muscle
  o Inhibition of the pontine mictuition centre allows parasympathetic system to become activated
  o Parasympathetic fibres (S2-S4) via pelvic nerve, release acetylcholine which binds to M2 and M3 receptors causing detrusor muscle contraction and
  inhibition of intrinsic sphincter
• Voiding phase
  o Rising intravesical and falling urethral pressure results in bladder emptying

Question 2

Urodynamics

Answer 2

• Pressure measurements
  o Pves – intravesical pressure
• Measured with bladder pressure transducer
  o Pabd – abdominal pressure
• Estimated with catheter in rectum
• Not a ‘true’ pressure as not intra-abdominal
  o Pdet – detrusor pressure
• = Pves – Pabd
• Involuntary detrusor activity during filling diagnoses detrusor overactivity
• Usually accompanied by feeling of urge
  o Pura – urethral pressure
  o Reference level at pubic symphysis
  o Pressure measurements recorded simultaneously over time
  o Pt should be asked to cough early in filling
• Observe for increased Pabd and Pves without increase in Pdet to confirm correct placement
• Filling measurements – patient sensations
  o Slow bladder (30-60mL/min) filling with normal saline
  o Pt reports first desire to void, strong desire and urgency
• Cystometric capacity
  o Either record volume infused at urgency (ignores urine production during procedure) or add voided volume and residual volume
  o Higher than functional capacity
  o Cystometric capacity is reduced in detrusor overactivity and low bladder wall compliance
• End-filling pressure
  o A measure of bladder compliance
  o Bladder compliance means the detrusor muscle remains relaxed over a wide volume
  o Low compliance means the intravesical pressure rises at low volumes
  o Causes include fibrosis of bladder wall, upper urinary tract disease
  o In this case there will be a high end-filling pressure
• Detrusor leak point pressure
  o The Pdet at which overflow urinary incontinence occurs
  o Ie, the detrusor pressure where leakage occurs without a voluntary increase in abdominal pressure or detrusor contraction
  o High detrusor LPP is a feature in people with neurogenic bladder and places them at increased risk of upper urinary tract disease (essentially a measure of urinary retention!)
• Abdominal leak point pressure
  o The Pabd required to drive urine across a closed urethral sphincter
  o May be assessed with cough or valsalva
  o Any measureable abdominal LPP suggests stress urinary incontinence
  o More suggestive of intrinsic sphincter deficiency
  o Urodynamic stress incontinence diagnosed when involuntary loss of urine occurs with raised abdominal pressure in the absence of detrusor contraction
• Urethral opening pressure
  o The Pdet required to open urethra when voluntary micturition initiated
• Maximal urethral closure pressure
  o The difference between the maximal urethral pressure and the bladderpressure
  o Measured by withdrawing a urethral pressure catheter along the length of the urethra
  o Low MUCP suggestive of intrinsic sphincter deficiency

Question 3

Uroflowmetry

Answer 3

• An assessment of voiding pattern
• Patient voids into a pan that records either weight or volume
• Measures volume voided over time to calculate flow in mL/s
• Maximal flow increases with volume voided
  o Compare to nomograms for analysis
• Assess for shape of graph
  o Should be smooth
  o Stop-start or low maximum flow suggestive of obstruction or poor detrusor activity (ie MS)
• Some UDS allow simultaneous measurement of pressures during the void
  o Allows differentiation of voiding dysfunction due to bladder outlet obstruction (good detrusor contraction) vs poor detrusor function
  (generation of abdominal pressure to empty bladder

Question 4

Basic Procedure

Answer 4

• Free uroflow
• Position patient
• Determine post-void residual (using UD catheter)
• Place rectal catheter
• Fill bladder slowly and record patient sensations of urgency
• Trial manoeuvres to provoke incontinence (Valsalva and cough) or detrusor
  overactivity (washing hands, running water)
• Measure cystometric capacity and end-filling pressure
• Uroflow with catheters in situ