Key Components in Urodynamic Testing of Overactive Bladder

After the decision is made to proceed with urodynamic testing, the next consideration is the type of testing to be conducted. Most current urodynamic machines offer only multiple-channel testing because single-channel testing is prone to considerable artifacts.

In general, because it is difficult to predict for the presence of specific voiding dysfunction in women based on urinary symptoms alone ⁽⁹⁾, it is good urodynamic practice always to perform a pressure flow study at the end of filling to assess for voiding disturbance. Although controversial, the use of patch or needle electromyographic perineal electrodes can assess for lack of pelvic floor relaxation or external sphincter dyssynergia in patients at risk. 

The addition of simultaneous cystourethrography (videourodynamics), although clearly not always mandated, does allow further evaluation of the outlet during voiding,  which can aid in determining the level of obstruction and evaluating the bladder for foreign bodies, vesicoureteral reflux, and diverticula. Although it may not be universally available, the addition of imaging of the lower urinary tract during urodynamic testing may be most useful when evaluating patients with known neurological conditions, young men with severe LUTS, and women with possible pelvic floor dysfunction.

Typically, a 6- or 7-French dual-lumen urethral urodynamic catheter is used, along with either a rectal or vaginal catheter to assess extravesical pressure fluctuations.

Patients are typically standing for the study, particularly if they are also complaining of stress incontinence, or they sit in a urodynamics chair. 

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Fluid (room temperature sterile water or radiographic contrast) is instilled at 25–100 mL/min, keeping in mind that OAB contractions can be elicited by more rapid rates of filling, by utilizing a cold filling solution, and by performing certain provocative maneuvers during filling (such as heel bouncing). The threshold volume for OAB contractions should be noted in addition to the amplitude of the overactive contraction because there are some data to suggest that the severity of the contraction may correlate with the nature of the disease process responsible for detrusor overactivity (DO) ⁽¹³⁾.

Many patients will attempt to suppress leakage that may accompany the contraction, and if leakage still ensues, it should be recorded, as should the maximum bladder capacity. Compliance should also be assessed because altered compliance may be responsible for upper tract deterioration, particularly in neuropathic bladders. Although widely accepted cutoff values for outlet obstruction in women are still lacking, a number of strategies have been proposed ^(14–16), and a properly conducted voiding study (adjust transducers as the patient sits to void) is imperative after the conclusion of filling.

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Gary E. Lemack, MD
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