Study of micturition - helps correlate clinical symptoms with pathophysiology

  • Indicated when there is a question about the diagnosis (eg bladder vs outlet)
  • Or to predict consequences of LUT dysfunction on upper tract (eg high pressure/poor compliance)
  • For neurogenic bladder - get baseline UDS
  • Example situations
    • Prolapse (identify occult SUI)
    • Mixed incontinence
    • Woman with bothersome sx after SUI surgery
    • Man with LUTS who failed pharmacotherapy
    • Man with LUTS with bothersome sx after BOO
    • Retention/high PVR
    • Neurogenic bladder
    • Post-prostatectomy incontinence (ISD vs DO, normal vs weak bladder)

Components of urodynamics

  • Uroflow - noninvasive flow meter, screen for bladder outlet obstruction (not diagnostic)
    • Peak flow Qmax- M 20-25 ml/s, F 25-30 ml/s, about 1/3 way through flow
      • < 10 ml/s - probable obstruction; 10-15 ml/s - suspected obstruction; > 15 ml/s - normal
      • Need minimal voided volume ~ 150cc to be valid
    • Flow can be falsely augmented by: elevated abdominal pressure, minimal outlet resistance, strong detrusor + outlet resistance
    • Flow pattern: normal flow v. time is bell-shaped curve "inverted U"
      • DO - very sharp onset/cessation
      • BOO: long curve, very early peak with long tail
      • Weak bladder: long curve, peak in middle
      • Stricture: 'box pattern'
      • **hide**'Choke flow' will produce 'surge' in flow rate in DO, BOO but not DU
  • PVR > 50-100cc indicates: increased outlet resistance and/or decreased detrusor function
  • Pressure flow study (PFS) - evaluate voiding, differentiate between outlet and bladder. COntractility, compelte emptying, clincial obstruction
    • Low pressure high flow - normal
    • Low pressure low flow - weak bladder
    • High pressure low flow - obstruction
  • Filling cystometry (invasive; defer if symptomatic UTI) - parameters below (pressure-volume relationship - sensation of bladder filling, compliance, etc)
    • Physiologic rate of bladder filling: max is ~ body weight/4 mL/min. However in practice use: Slow = 10 ml/min, medium 50-75 ml/min, fast > 75 ml/min
      • Or, fill at ≤ 10% of bladder capacity per min
    • **hide**Abx prophylaxis (FQ or bactrim) only if + risk factors (age, anatomic anomaly, immunodeficient, etc.)
    • Warning in patients with spinal cord injury above T6 - can cause autonomic dysreflexia during bladder filling (brady + ↑ BP)
Pves (urethral catheter ~ 7Fr) intravesical pressure
Pabd (rectal/vaginal probe) abdominal pressure
Pdet = Pves - Pabd

detrusor pressure (max 40-60 cm M, less in F)
Look for detrusor overactivity (significant if sensed, causes leakage, or causes pressure increase > 15 cm H2O)
Elevated pressures > 40 cm are dangerous if continuous - eg patients who don't void (diapers/condom cath), not CIC or SPT 

Pmuo (pressure at minimal urethral opening) (closing pressure; good measure of obstruction)

Pdet at end of flow (when prostatic urethra closes). Normal < 20; > 40 = obstruction

(similar to AG number/BOOI)

MUCP (Maximal urethral closure pressure)

Maximal difference between urethral pressure and intravesical pressure

  • < 20 cm = weak sphincter
EMG

Voluntary sphincter function (patch on perineum; measures pelvic floor activity via anal sphincter)

  • 'Noisier' = activity, increase with bladder filling ('guarding reflex') and should be quiet during voiding
  • DSD = increase in EMG during voiding if has neurologic lesion
Bladder capacity Adults: 400-500 ml
Children: (age in years + 2) x 30 ml
Neonates: 10cc; ~ 9 mo: 60cc
Bladder compliance = volume/Pdet

≤ 20 mL/cm H2O is abnormal/poor compliance

Typically every 30 cc volume should increase P by ~ 1 cm

Leak point pressure (LPP) 

  • Abdominal - measures outlet; lowest Pves at which urine leaks with valsalva in absence of detrusor contraction. Invalid if cystocele; very variable in general.
  • Detrusor - measures compliance; lowest Pdet (passive/normal bladder filling, no contraction, no valsalva) at which urine leaks, eg 'pop-off mechanism'.

ALPP < 50 cm H2O = intrinsic sphincter dysfunction. > 100 cm = stress UI not from sphincter dysfunction (eg hypermobility)

DLPP > 40 cm H2O = risk of renal injury/hydro from functional outlet obstruction

  • Only relevant/measured in abnormal/poorly compliant bladder
Volume at first sensation of filling 100-200 ml
First sensation of fullness 350-450 ml
Desire to void 350-450 ml
Strong desire to void 400-600 ml
  • Filling phase
    • Bladder capacity
    • Bladder compliance
    • Detrusor overactivity
      • If stop filling and continue to have detrusor contractions, then this is involuntary DO
  • Emptying phase
    • Bladder contraction
      • Is there a bladder contraction, or do they empty by Valsalva/abdominal pressure, or by leaking?
    • Video UDS - 'spinning top' urethra indicates DSD, or bladder contracting against closed external sphincter → posterior urethral dilation
      • Can also see evidence of ↑ bladder pressures such as diverticula
      • Image result for video uds spinning top urethra
      • Christmas tree bladder representative of neurogenic bladder
  • Infants have 'physiologic dyscoordinated voiding' which shows up as DSD, with high voidng pressures esp in males, but this will improve with age. 

 

Abrams Griffith nomogram

  • Classifies pressure-flow relationship as obstructed, equivocal, or normal
  • Abrams-Griffith/AG number = bladder outlet obstruction index (BOOI)
    • Pdet(@Qmax) − 2(Qmax), equivalent to closing pressure = Pmuo
    • > 40 = obstructed
    • 20 - 40 = equivocal
    • < 20 = unobstructed

 Image result for abrams griffiths nomogram

Bladder contractility index = Pdet(@Qmax) + 5(Qmax)

  • > 150: strong
  • < 100: detrusor underactivity

**hide**Schafer nomogram - Pdet qmax?

Stress incontinence Leakage with abdominal pressure but no detrusor contraction
Urge incontinence Leakage with detrusor activity
  • Only 10% of women who deny UUI demonstrate DO on UDS
  • Up to 30% of women who deny SUI will have SUI on UDS
  • Up to 40% of patients with UUI do not have DO on UDS...
  • Consider UDS prior to invasive therapy

Detrusor hyperactivity and impaired contractility (DHIC, DODU)

  • Detrusor overactivity but can't pee
author: admin | last edited: Aug. 23, 2020, 1:04 p.m. | pk: 54