Measurements can be obtained using electronic microtip transducer pressure catheters, ﬂuid-filled pressure lines, fiberoptic catheters, or air-charged catheters. All are acceptable for clinical use, but it is important to realize that when different types of catheters are used, the correlation between numbers is imperfect. Other technical factors that inﬂuence cystometry results include the choice of distending medium, filling rate, and patient position. The steps involved in a multichannel urodynamic study are outlined in Table 26.7. Normal cystometric values for women are shown in Table 26.8.
An example of detrusor overactivity seen during complex cystometry is shown in Figure 26.5. Surface or needle electromyography may be performed during filling and voiding to assess muscle activity of the urethral sphincter or pelvic ﬂoor. Electromyography as generally performed did not prove useful in neurologically intact women with symptoms of only stress urinary incontinence, and is not required in this patient population.
Both false-positive and false-negative results can occur with urodynamic studies. False-positive results occur in patients with asymptomatic detrusor overactivity, detrusor overactivity
Table 26.7 Steps in Conducting a Multichannel Urodynamic Study 1.
Insert pressure and filling catheter into bladder (may be two catheters or dual catheter) to measure intravesical pressure and to fill bladder. Insert pressure catheter into upper vagina or rectum to approximate abdominal pressure.
2.
Infuse ﬂuid (usually sterile water or saline, sometimes radiographic contrast dye) at a rate of 50 to 100 mL/min. Record the volume infused and the pressure measurements continuously. The patient’s bladder may be filled with her lying supine, in a modified lithotomy position, sitting, or standing. When possible, do cystometry in the standing position as most patients with incontinence report this problem more when they are erect.
3.
Note the point at which any leakage occurs.
4. During filling, record the first desire to void (that is, the feeling that would lead her to void at the next convenient moment, but voiding can be delayed if necessary) and the strong desire to void (that is, the persistent desire to void without the fear of leakage). The maximum cystometric capacity, in women with normal sensation, is the volume at which the woman can no longer delay micturition; filling should not be continued to the point of pain or severe discomfort.
5. If no detrusor overactivity is noted during filling, have the patient do provocative maneuvers at maximum capacity, such as coughing, heel-bouncing, and listening to the sound of running water to provoke uninhibited detrusor contractions, which may be the cause of the patient’s symptoms.
that is irrelevant to the symptom, or detrusor overactivity that is situational (e.g., caused by test anxiety). False-negative results can occur because a 20-to 40-minute cystometrogram is not always an accurate measure of 24-hour bladder activity. Looking for detrusor overactivity with such a test is like looking for an episodic cardiac arrhythmia using 12-lead electrocardiography, as opposed to looking for the arrhythmia using a 24-hour Holter monitor. The sensitivity of the latter test is far greater than that of the former. Ambulatory urodynamics can be performed and are more likely to detect detrusor overactivity than office-based studies.
Tests of Urethral Function
Several tests of urethral function, including urethral pressure profilometry, Valsalva leak-point pressures, and the ﬂuoroscopic and cystoscopic assessment of the bladder neck, are used in attempts to guide therapy in women with stress urinary incontinence. Women with poor urethral function, evidenced by low Valsalva leak-point pressures, low maximal urethral closure pressures, or a visualized open bladder neck, are thought to be at higher risk of treatment
Table 26.8 Approximate Normal Values of Female Bladder Function