Leak point pressure measurements often are performed at a bladder volume of 200 or 300 mL. Patients are asked to cough with gradually increasing force (cough leak-point pressure) and finally to strain slowly (Valsalva) to increase intravesical pressure gradually. The lowest pressure at which leakage occurs is recorded as the cough or the Valsalva leak-point pressure (Fig. 26.7). If leakage is not demonstrated, the highest pressure that was obtained can be recorded with the notation “no leakage” to the specified pressure as measured in centimeters of water pressure. Many clinicians use a cutoff point of 60 cm water pressure to separate women who have intrinsic sphincter deficiency from those who do not. This is problematic for two reasons: (i) the marked variability of results that depend on all the aforementioned factors and (ii) the lack of prospective studies that demonstrate the predictive value of leak point pressure values on surgical outcomes. Results from this and other urodynamics tests must be evaluated as one piece of the patient’s puzzle, along with the history, physical examination, voiding diary, and other tests. Medicare guidelines require that when bulking agents, such as collagen, are considered to treat stress incontinence, the intra-abdominal leak point pressure when the bladder has been filled with at least 150 mL of ﬂuid must be less than 100 cm H2O.
Fluoroscopy and cystourethroscopy were used to visualize the bladder neck because many clinicians and investigators believe that a closed bladder neck is important in maintaining continence. However, studies of continent women reveal that many individuals with normal urethral function show evidence of bladder neck opening with physical stress (43). Neither test is recommended in the routine evaluation of women with straightforward incontinence.
Figure 26.7 Leak point pressure. The abdominal leak point pressure (LPP) is 114 cm H2O (the abdominal pressure at which the patient leaked urine).
Urodynamic testing usually concludes with an instrumented voiding study (also known as a pressure-ﬂow study or voiding cystometrogram), in which the vesical, abdominal, and urethral pressures are measured simultaneously during bladder emptying (Fig. 26.8). Various studies identified Valsalva voiding, low preoperative ﬂow rate, and high preoperative detrusor pressures during voiding as risk factors for postoperative voiding dysfunction; however, findings often are contradictory.
Imaging Tests The role of imaging techniques in studying female urinary incontinence is not yet established. Researchers are evaluating the potential roles of ultrasonography, ﬂuoroscopy, functional neuroimaging, and magnetic resonance imaging (MRI). These tests should not be done routinely but are useful in certain conditions. If the patient’s symptoms (easily remembered by the three Ds: dysuria, dribbling, and dyspareunia) or examination suggests a urethral diverticulum, MRI is the test of choice (44).
Neurophysiologic Tests The neuromuscular function of the pelvic ﬂoor is dependent on the integrity of the nervous system. Injury can theoretically occur anywhere along these nerves, from the cell body located in Onuf’s nucleus in the ventral part of the spinal cord, along its axon, to the neuromuscular junction. Pelvic ﬂoor neurophysiology utilizes techniques applied to nerves and skeletal muscles elsewhere in the body to document neuromuscular integrity or evidence of injury. These tests are not routinely used in the clinical evaluation of most incontinent women.
Figure 26.8 Voiding cystometrogram. This patient voids in an uninterrupted ﬂow pattern by means of a prolonged bladder contraction. She does not strain to void, with the exception of minimal straining toward the end of the ﬂow.