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Urodynamic studies (UDS) are a group of diagnostic tests that assess the function of the lower urinary tract, specifically the bladder (detrusor) and urethral sphincter during filling and voiding phases.
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These are functional tests, complementing anatomical imaging like VCUG, ultrasound, or MRI.
Urodynamic testing is indicated in both adults and children for:
| Domain | Condition |
|---|---|
| Storage dysfunction | • Urinary incontinence (stress, urge, mixed) |
| • Overactive bladder | |
| • Nocturia | |
| Voiding dysfunction | • Incomplete emptying |
| • Urinary retention | |
| • Recurrent urinary tract infections (UTIs) | |
| Neurologic bladder evaluation | • Spinal cord injury |
| • Multiple sclerosis | |
| • Spina bifida / tethered cord | |
| • Diabetic autonomic neuropathy | |
| Pre-operative evaluation | Prior to incontinence or prolapse surgery |
| Component | Function Assessed | Description |
|---|---|---|
| Uroflowmetry | Voiding pattern | Measures urine flow rate vs. time during natural void |
| Cystometry (CMG) | Bladder filling/storage | Evaluates detrusor pressure, capacity, compliance, and sensation during filling |
| Pressure-flow study (PFS) | Voiding phase | Measures detrusor pressure and flow rate during micturition |
| Electromyography (EMG) | External sphincter activity | Detects coordination between detrusor and sphincter (esp. in neurogenic bladder) |
| Post-void residual (PVR) | Efficiency of bladder emptying | Often measured by ultrasound or catheterization |
| Leak point pressure (LPP) | Incontinence mechanism | Assesses when urine leakage occurs without/with detrusor contraction |
Key Parameters in UDS
| Parameter | Normal Value | Interpretation |
|---|---|---|
| Bladder capacity | ~400–600 mL | Low = poor compliance or overactivity |
| Detrusor compliance | >20 mL/cm H₂O | Low = risk for upper tract damage |
| Max detrusor pressure (voiding) | <40 cm H₂O | High = obstruction or DSD |
| Flow rate (Qmax) | >15 mL/s | Low = obstruction or weak detrusor |
| PVR | <50 mL | >100 mL = incomplete emptying |
| Detrusor leak point pressure (DLPP) | <40 cm H₂O safe | >40 = risk to kidneys in children |
| Condition | Urodynamic Pattern |
|---|---|
| Overactive bladder (OAB) | Detrusor overactivity during filling |
| Stress urinary incontinence | Low leak point pressure without detrusor contraction |
| Neurogenic bladder (UMN lesion) | Detrusor-sphincter dyssynergia (DSD); high voiding pressures |
| Neurogenic bladder (LMN lesion) | Areflexic detrusor; large capacity, high residual |
| Bladder outlet obstruction | High detrusor pressure + low flow rate |