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 Q_max- 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)

• 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 = P_muo
• > 40 = obstructed
• 20 - 40 = equivocal
• < 20 = unobstructed

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

• > 150: strong
• < 100: detrusor underactivity

**hide**Schafer nomogram - Pdet qmax?

• 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