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
|
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'.
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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
- 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
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