Urodynamics
Key points
Components of multi-channel urodynamics:
1. Uroflowmetry
2. Cystometry
3. Pressure flow study
4. Urethral pressure profile
5. Electromyography
Start with uroflow:
Qmax = mighest flow measured - >15ml/s normal
Decreased flow - obstruction or weak detrusor
Plateau flow - stricture
Intermittent flow - similar to decreased flow
Saw tooth - detrusor-sphincter dyssynergia
High flow - wide urethra/bladder neck - normal in asymptomatic females
Staccato uroflow = dysfunctional voiding
Then 6Fr multilumen catheter per urethra
Measure residual
Rectal catheter
Calibrate pressure transducers - vesicle pressure should be zero
Cough - make sure vesicle and abdo pressure peaks go to same height - check if good subtraction
Fill 10% bladder vol/min
Filling and voiding phase
Detrusor pressure (Pdet) = Bladder pressure (Pves) minus Abdo pressure (Pabd)
Pdet = Pves - Pabd
Resting detrusor pressure: between -5 and +5 cm H2O
Bladder compliance = change of bladder volume divided by change in detrusor pressure during filling phase
The detrusor line should be flat during most of filling phase - If it rises, suggests poor compliance
Non-neurogenic bladders
Normal compliance: >40 ml/cm H20
Low compliance: <30 ml/cm H2O
Neurogenic bladders
Normal compliance: >30 ml/cm H2O
Low compliance: <10 ml/cm H2O
Leak point pressure >40cmH20 is unsafe bladder
Patterns
Stress incontinence: Pabd raised when coughing then leak seen
Detrusor overactivity: increase in Pdet and Pves during filling but Pabd normal
Detrusor sphincter dyssynergia: Sphincter contractions during detrusor contraction
Interpretation
Look at -
1. Faithful study? can you see 3 lines with good subtraction of Pves from Pabd?
2. In filling phase: Total capacity
3. Size and shape on video cystogram
4. Max pressure at end just before void
5. Compliance: end fill pressure minus start fill pressure
6. Emptying - reflux, shape, uroflow, sphincter, residual
Do basic history and examination
Oxybutynin
Biofeedback
For abnormal traces - get an MRI
References
Yao M, Simoes A. Urodynamic Testing and Interpretation. [Updated 2023 Aug 14]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK562310/