CHAPTER 116 Urodynamic Testing (Multichannel)

Incontinence, dysuria, urinary retention and frequency, and other urinary symptoms are common problems among a growing population, the elderly. Given the broad range of etiologic factors that can cause incontinence (Box 116-1) and other urinary symptoms, accurate diagnosis is the cornerstone for formulating an effective treatment plan. In addition to a careful history and physical examination, urodynamic testing—the study of hydrodynamics and muscle activity to define the functional status of the lower urinary tract—can quantify abnormalities in order to make an accurate diagnosis. Urodynamic testing is also useful for objective assessment of patient improvement after a prescribed treatment protocol.

Although simple urodynamics (see Chapter 115, Bedside Urodynamic Studies), which can be performed in the office setting and provide objective qualitative data, are useful for conservative treatment in the uncomplicated patient, some patients require more precise quantitative analysis of lower urinary tract function. Formal, multichannel urodynamics (MCUD) provides specific quantitative information about detrusor and urethral function during filling, storage, and emptying of urine.

MCUD involves the simultaneous measurement of pressure from multiple sites during bladder filling and emptying and allows precise measurement of intravesical, intraurethral, and intra-abdominal pressure (Fig. 116-1). Complex uroflowmetry measures and graphs urine volume voided over time, allowing detection of anatomic (obstructive) and physiologic (functional) voiding abnormalities. Complex cystometry, a filling test of the bladder, measures and graphs the pressure–volume relationship of the bladder as it distends and contracts, determining abnormalities of detrusor activity, sensation, capacity, and compliance consistent with urge incontinence or detrusor instability. Urethral pressure profilometry evaluates the urethral continence mechanism as a possible cause of stress urinary incontinence (SUI). Pressure–flow studies allow determination and quantification of a patient’s voiding mechanism, helping establish the etiology of voiding dysfunction. Electromyography (EMG) evaluates contractile activity and innervation of the perineal muscles involved with voiding. Bethanechol testing can be used to diagnose a neurogenic bladder. If a contrast medium is used for the infusion, a voiding cystourethrogram can be performed.

Figure 116-1 Multichannel urodynamics (MCUD) with measurement of vesical and abdominal pressure using separate catheters. P_abd, intra-abdominal pressure; P_det, detrusor pressure; P_ves, bladder pressure.

When performing MCUD, bladder (P_ves) and urethral (P_ura) pressures are measured directly with a single intravesical catheter that contains two microtransducers, one located in the bladder and the other in the urethra. A separate, single microtransducer catheter is placed in either the rectum or the vagina and indirectly measures simultaneous intra-abdominal pressure (P_abd). Detrusor pressure (P_det) and urethral closure pressure (P_ucp) are derived from electronic subtraction of one measured pressure from a second measured pressure. Detrusor pressure is derived by subtracting intra-abdominal pressure from intravesical pressure (P_det = P_ves − P_abd), whereas urethral closure pressure is the difference between urethral pressure and intravesical pressure (P_ucp = P_ura − P_ves; Fig. 116-2).

Figure 116-2 Mathematical formulas deriving detrusor pressure and urethral closure pressure from multichannel urodynamics measurements. P_abd, intra-abdominal pressure; P_det, detrusor pressure; P_ucp, urethral closure pressure; P_ura, urethral pressure; P_ves, bladder pressure.

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