This is considered the cornerstone of urodynamic testing and it refers to the measurement of intravesical bladder pressure during bladder filling, for the assessment of bladder storage function [19].

Position of patient: The sitting position is more provocative for abnormal detrusor activity than the supine position. At some point in the test, filling might desirably take place with the woman standing.

Filling rate: The filling rate, including any changes during testing, should be noted on the urodynamic report [9, 16, 17].

The graphical recording of bladder pressures and volumes over time. Several standard parameters are evaluated during a cystometrogram, including bladder storage pressure, capacity, bladder sensation, bladder stability, and compliance [10, 16].

In preparation for this phase of urodynamics, both urethral and rectal (or vaginal) catheters are placed. The bladder is then filled with contrast, saline or sterile water through the urethral catheter.

This is the direct measurement of bladder storage pressure during cystometry. Pves is measured by the urethral catheter.

The intra-abdominal pressure ( Pabd) is measured by a rectal or vaginal catheter. The simultaneous measurement of abdominal pressure is essential for interpretation of the intravesical pressure trace [16, 17].

This is the component of intravesical pressure created by the bladder wall (passive and active). Pdet is calculated by subtracting the abdominal pressure from the intravesical pressure [17]. Whereas the calculated Pdet represents the viscoelastic properties and tone of the bladder wall, when looking at the urodynamic study all three tracings (Pves, Pabd, and Pdet) should be evaluated to monitor for artifacts and other factors contributing to the Pdet tracing [1].

This is assessed by questioning the woman during the filling cystometry about fullness of the bladder. Sensation during cystometry is subjective and can be influenced by the rate of filling, temperature of the fluid medium, position of the patient (supine vs. upright), and the patient’s level of concentration [18].

Determining the volumes at which different degrees of fullness occur, the occurrence of pain during filling and evidence of decreased sensation during filling, may all be subtle predictors of disease processes. The greatest value of the cystometrogram with respect to sensation occurs when a symptom arises, and when sensation is correlated to actual Pves changes [28]. Understanding the accuracy of bladder sensation during the exam and its correlation with the patient’s symptoms is a key factor in analyzing results, specifically in cases of OPF patients. The way patients describe their symptoms and the simulation of these sensations during cystometry allow the examiner to understand the objective pressure/volume measurements related to pain, pressure, or urgency symptoms. Sensations evoked during the urodynamic exam that are new to the patient or do not mirror her/his usual complaints should be probably ignored in most cases since they do not represent the etiology of the patient’s symptoms.

The volume at which the patient first becomes aware of bladder filling.

The volume at which the patient first wishes to pass urine [16].

The volume at which the patient wishes to pass urine at the next convenient moment, but voiding can be delayed if necessary.

The volume at which a persistent desire to pass urine occurs, without the fear of leakage.

A sudden, compelling desire to pass urine, which is difficult to defer.

Also known as “increased bladder sensation” or “sensory urgency” [17]. Increased perceived bladder sensation during bladder filling with an early first desire to void or an early strong desire to void, which occurs at low bladder volume or at low maximum cystometric bladder capacity, in the absence of abnormal increases in detrusor pressure.

Diminished bladder sensation during filling cystometry.

Absent bladder sensation during filling cystometry.

The complaint of pain during filling cystometry. It is considered abnormal and needs to be investigated.

Measured during urodynamics, it reflects the volume at which a subject with normal bladder sensation can no longer delay voiding [17]. This measurement is different from the functional bladder capacity, which is usually determined by the voiding diary, and the maximum anesthetic capacity, which is obtained under anesthesia [18].

This refers to the accommodation of the detrusor to increasing bladder volumes without evidence of an involuntary detrusor contraction. If the detrusor is normal then there is little or no change in detrusor pressure with filling, and there are no involuntary phasic contractions despite provocation with activities (postural changes, coughing, hearing the sound of running water or hand washing) [15].

The occurrence of involuntary detrusor contractions during filling cystometry. These contractions, which may be spontaneous or provoked, produce a waveform of variable duration and amplitude on the cystometrogram. The contractions may be phasic or terminal. Symptoms like urgency and/or urgency incontinence may or may not occur. If a relevant neurological cause is present, then neurogenic detrusor overactivity is noted, otherwise the term idiopathic detrusor overactivity should be used [15].

This defines detrusor overactivity with evidence of a relevant neurological disorder (according to the definition from the ICS) [15].

The change in bladder pressure for a given change in bladder volume [18]. Compliance (C) is calculated by dividing the volume change (ΔV) by the change in detrusor pressure (ΔPdet), C = ΔV/ΔPdet and is expressed as cmH₂O [16, 17].

A normal bladder displays low pressure during filling because of its viscoelastic properties. Bladder compliance can be affected by various factors such as bladder filling rate (faster filling is more provocative), contractile/relaxant properties of the detrusor, and starting and ending points for compliance calculations.

Loss of elasticity is a result of muscle being replaced by collagen and can be caused by a number of disease processes including neurologic conditions, prolonged catheter drainage, radiation therapy, prior pelvic or urethral surgery, interstitial cystitis, and obstructive uropathy [29]. A poorly compliant bladder displays an abnormal, often linear increase in Pdet during filling. This can result in dangerously high detrusor storage pressures. High storage pressures can distort the normal detrusor anatomy resulting in the development of vesicoureteral reflux and can be transmitted to the upper tracts, with development of hydronephrosis and renal failure. Early studies by McGuire and associates [30] have shown that sustained Pdet greater than 40 cmH₂O is specifically linked to renal or upper tract damage.

Urethral pressure and urethral closure pressure represent the ability of the urethra to prevent leakage. Normal urethral pressure value is higher than bladder pressure during non-voiding periods.

Urethral pressure is currently measured by a number of different techniques, which tend to lack consistent results either between methods or for a single method [31]. Urethral pressure might be measured at rest with the bladder at a given volume, during coughing or straining or during the process of voiding [10, 16, 17]. Urethral pressure values summarize all the components that participate in the continence mechanism and include also pressure of the pelvic floor muscles surrounding the urethra. The urethral pressure profile (UPP), maximum urethral pressure (MUP), and maximum urethral closure pressure (MUCP) may be used as part of the urodynamic evaluation for stress urinary incontinence.

This static test measures the lowest value of detrusor pressure at which leakage is observed, in the absence of increased abdominal pressure or a detrusor contraction. High detrusor LPP (>40 cmH₂O) may put patients at risk for upper urinary tract deterioration or secondary damage to the bladder in the cases of known underlying neurological disorders such as paraplegia or MS [32]. There are no data on any correlation between detrusor LPP and upper tract damage in non-neurogenic patients.

This dynamic test is defined by the ICS as the intravesical pressure at which urine leakage occurs due to increased abdominal pressure, in the absence of a detrusor contraction [15, 33].

Abdominal leak point pressure (ALPP ) is used for the definition of intrinsic sphincter deficiency (ISD) and low abdominal LPP is suggestive of a poor urethral function, corresponding to more severe stress urinary incontinence [15]. The ALPP can be induced either by cough (cough leak point pressure = CLPP), or by Valsalva maneuver (Valsalva leak point pressure = VLPP). ALPP values can be used to quantify the severity of stress urinary incontinence and this information can be used to guide treatment selection [16, 32, 33].

LPP values can be affected by many other factors such as the technique used to confirm urine loss, location of catheter, type of pressure sensor, bladder volume, rate of bladder filling, and patient position. The catheter size also has an important influence on the measurement of ALPP values and should be standardized. A trans-urethral catheter can partially occlude the urethral lumen, potentially distorting the value of the ALPP. Although there is no standard catheter size recommended for urodynamic testing, it is generally agreed that smaller catheters have less occlusive potential and are usually preferred.

Urethral pressure measurements are used to assess urethral competence and incontinence severity. Although it is fully accepted that urethral pressure is an important and integral component to urinary continence, it remains challenging to measure and characterize this pressure in a reliable manner [34, 35].

Normal detrusor function: Normal voiding in women is achieved by an initial (voluntary) reduction in intra-urethral pressure (urethral relaxation) [36]. This relaxation is part of pelvic floor muscle relaxation, which simultaneously eliminates the inhibiting effect on the detrusor. This is generally followed by a continuous detrusor contraction that leads to complete bladder emptying. Many women will void successfully (normal flow rate and low PVR) by urethral relaxation, with a low rise in detrusor pressure [37]. The amplitude of the detrusor contraction will tend to increase to cope with any degree of bladder outflow obstruction (BOO) [38].

Detrusor under activity: Detrusor contraction of reduced strength and/or duration, resulting in prolonged bladder emptying and/or a failure to achieve complete bladder emptying within a normal time span. Occasionally patients will void by increasing intra-abdominal pressure compensating for detrusor under activity [16, 17].

Acontractile detrusor: The detrusor cannot be observed to contract during urodynamic studies, resulting in prolonged bladder emptying and/or a failure to achieve complete bladder emptying. The term “areflexia” has been used where there is a neurological cause [16, 17].

This technique may assist in determining the nature of urethral obstruction to voiding. Pressure is recorded in the urethra during voiding. This may be at one specific point, e.g., high-pressure zone or it may be measured as a profile. A voiding urethral pressure profile (VUPP) uses a similar technique to that described above for the UPP measured during bladder filling. Simultaneous intravesical pressure measurement is required. Localization of the site of the intraurethral pressure measurement is useful [10, 16, 17].

Bladder outflow obstruction is the generic term for obstruction during voiding. It presents as reduced urine flow rate and/or presence of a raised PVR and an increased detrusor pressure. It is usually diagnosed by studying the synchronous values of urine flow rate and detrusor pressure and any PVR measurements.

Outlet obstruction in women is most likely caused by pelvic organ prolapse, as a complication after surgery for stress incontinence, or from pelvic floor or external sphincter pathology such as detrusor-sphincter dyssynergia [18].

Dysfunctional voiding is characterized by an intermittent and/or fluctuating flow rate due to involuntary intermittent contractions of the periurethral striated muscles or levator muscles during voiding in neurologically normal women. This type of voiding may also be the result of an acontractile detrusor (abdominal voiding), with an EMG or videourodynamics required to distinguish between the two entities [15]. This is a common finding in patients with OPFS symptoms but can be used to differentiate different etiologies under this category.

Detrusor sphincter dyssynergia (DSD) is defined as lack of coordination between detrusor and urethral sphincter mechanism during voiding due to a neurological abnormality. This is a feature of neurological voiding disorders. Videocystoure-thrography is usually required to establish a diagnosis of DSD [15].