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Urodynamic Terminology

The Many Cs of Urodynamics

• Capacity: volume
• Compliance: DLPP
• Contractility: DO, DUA
• Coordination: DESD
• Continence: VLPP
• Conscious sensation: increased/decreased
• Complete emptying: DUA, BOO
• Clinical obstruction: BOO

Broad classifications for voiding dysfunction

• Storage dysfunction vs emptying dysfunction
• Bladder dysfunction vs bladder outlet dysfunction

Urodynamic components

• Cystometry: pressure/volume relationship of the bladder during filling, measures sensation, compliance, capacity, and presence of detrusor activity
• Electromyography (EMG): measurement of sphincter (and pelvic) muscle depolarization
• Pressure-flow studies: bladder pressure and urine flow rate during emptying
• Uroflowmetry: measurement of urine flow rate
• Video UDS: fluoroscopy during UDS

Normal urodynamics

Measurements

• Compliance: change in volume over change in pressure, < 6cm water increase considered normal
• Cough leak point pressure (CLPP): urinary leakage with cough, considered superior to VLPP
• Detrusor leak point pressure (DLPP): detrusor pressure at which urine leakage occurs in the absence of detrusor contraction or increased abdominal pressure, 40cm water usually used as cutoff for concern for renal injury
• Maximum urethral closure pressure (MUCP): max difference between urethral and intravesical pressures
• Post Void Residual: amount of urine left in bladder after urination, no universal definition, elevated PVR caused by DUA and/or BOO
• Urethral pressure profile: fluid pressure needed to open a closed urethra
• Valsalva leak point pressure (VLPP): intravesical pressure at which urine leakage occurs in the absence of a detrusor contraction, tends to be lower than CLPP
• Volumes: first sensation, sensation of fullness, desire to void, capacity

Filling phase

• Detrusor pressure should remain near zero until voiding is initiated
• Detrusor pressure (Pdet): differentiate between Valsalva (Pdet unchanged) and true detrusor contraction (Pdet rises)
• Impaired compliance: > 40, needs treatment to prevent upper tract injury, may be artificially decreased if reflux or diverticulum present
• Abdominal leak point pressure (ALPP): ability of sphincter to resist changes in abdominal pressure, can only be seen with SUI, < 60 indicates ISD, > 90 indicates minimal/no ISD
• Stress induced detrusor overactivity (SIDO): triggered by rise in abdominal pressure

Emptying phase

• Normal voiding: relaxation of striated sphincter, detrusor contraction, opening of bladder neck and urethra, onset of urination
• Minimum volume 150mL recommended to assess uroflow curve
• Detrusor underactivity (DUA): low pressure and low flow, reduced contraction strength leading to prolonged emptying time
• Detrusor acontractility: no detrusor contraction on UDS
• Bladder outlet obstruction: high pressure and low flow
• Abrams Griffiths nomogram: BOOI = PdetQmax - 2 * Qmax
• Bladder contractility index (BCI, Schafer's lines): PdetQmax + 5 * Qmax

VideoUDS

• Indications: localize level of obstruction, detect incontinence, evaluate for reflux
• Findings: bladder contour, trabeculations, diverticula, stones, reflux, bladder neck, urethra
• The only method available for diagnosing primary bladder neck obstruction