Functional: Urodynamics

See 2019 CUA NLUTD Guideline Notes, 2017 CUA OAB Guideline Notes, and 2019 AUA OAB Guidelines

Terminology

• Physiologic filling rate (mL/min): filling rate < predicted maximum (body weight (kg)/4)
• Non-physiologic filling rate: filling rate > predicted maximum
• Cystometrography (CMG): method by which the pressure/volume relationship of the bladder is measured during filling
  • The detrusor pressure is calculated indirectly by measuring the total vesical pressure (Pves, catheter in bladder) and Pabd (catheter place in the rectum or vagina) and applying the following formula: Pdet = Pves – Pabd (Bladder is a DIVA (Order of pressures is Det Ves Abd))
    • The ability to calculate subtracted Pdet allows distinguishing between a true rise in Pdet (via either a contraction or loss of compliance) and the effect of increased Pabd (e.g. straining, Valsalva)

Conducting UDS

• Many patients undergoing UDS will have been started on medications that can affect bladder function. The clinician should decide in advance what information is desired and whether the study should be done on or off medication.
  • If the goal of the study is to determine the therapeutic effect of a medication, UDS should be done with the patient on a regular dosing schedule for that medication.
  • If the medication was started empirically to treat symptoms and the goal of the urodynamic test is to uncover the cause of those symptoms, consideration can be given to discontinuing the medication before testing because this may give the highest yield.
• UDS is performed in an “unnatural setting” and therefore does not always duplicate real-life situations.
  • Failure to record an abnormality does not always rule out its existence (e.g. failure to demonstrate detrusor overactivity (DO) in a patient with urgency incontinence).
  • Not all UDS observations are clinically significant.

Role of Urodynamics (UDS)

• Potentially dangerous UDS findings that usually require intervention to prevent upper and lower urinary tract decompensation (6):
  1. Impaired compliance
  2. Detrusor external sphincter dyssynergia (DESD)
  3. Detrusor internal sphincter dyssynergia (DISD)
  4. Detrusor leak point pressure >40 cm H2O
  5. High-pressure detrusor overactivity present throughout filling
  6. Poor emptying with high storage pressures

Analysis and interpretation

• Each phase is described separately
  • Filling/storage phase: consists primarily of CMG and provocative testing (e.g. measurement of abdominal leak point pressure, and urethral pressure measurement during storage)
  • Voiding phase: evaluates bladder contractility, bladder outlet resistance, and sphincter coordination by pressure-flow analysis and EMG
• The 9 Cs of Pressure-Flow UDS§
  • Filling and storage
    1. Contractions (involuntary detrusor)
    2. Compliance
    3. Coarse sensation
    4. Continence
    5. Cystometric capacity
  • Emptying
    1. Contractility
    2. Complete emptying
    3. Coordination
    4. Clinical obstruction

Filling/storage phase

• Normal Pdet should remain near zero during the entire filling cycle until voluntary voiding is initiated
  • Baseline pressure stays constant (and low) and there are no involuntary contractions.
    • See Figure of normal UDS
  • Contractions/detrusor overactivity (DO)
    • A urodynamic observation characterized by involuntary detrusor contractions during the filling phase.
      • See Figure of DO on UDS
    • May be characterized as:
      • Neurogenic, when DO is associated with a relevant neurologic condition (e.g. spinal cord injury, multiple sclerosis), vs. idiopathic (non-neurogenic), when there is no defined cause
      • Spontaneous vs. provoked (e.g. DO triggered by a rise in Pabd)
      • Single event vs. multiple involuntary detrusor contractions
      • Phasic, sporadic, or terminal
        • Phasic DO: characterized by contractions of increasing amplitude as the bladder volume increases.
          • Any phasic detrusor contraction during filling constitutes DO, regardless of amplitude
            • Non-phasic changes in detrusor pressure before micturition should be regarded as changes in bladder compliance rather than as DO.
        • Terminal DO is a single involuntary detrusor contraction occurring at cystometric capacity, which causes incontinence
    • Presence must be interpreted in the context of patient symptoms and condition.
      • Ideally, patient symptoms should be reproduced during UDS, so DO would be expected to be accompanied by urgency and urgency incontinence. However, DO can also be test induced or clinically insignificant.
      • It is important that the person performing the UDS study be absolutely sure that the contraction is indeed involuntary. Sometimes, patients may become confused during the study and actually void as soon as they feel the desire.
    • Failure to demonstrate DO does not rule out its existence.
      • Detection can be influenced by the patient’s position.
• Compliance
  • Definition: compliance is change in bladder volume divided by change in Pdet (∆volume/∆pressure)
  • Measured in mL/cm H2O
  • Difficult to define normal compliance, but normal considered 46-124 mL/cm H2O
  • See Figure of low compliance on UDS
  • Causes of impaired compliance:
    1. Neurologic conditions (spinal cord injury, spina bifida)
       • Usually results from increased outlet resistance (e.g. detrusor external sphincter dyssynergia or decentralization in the case of lower motor neuron lesions
    2. Long-term bladder outlet obstruction
    3. Radiation cystitis
    4. Tuberculosis
  • Causes of false-positive:
    • Rapid filling
      • If filling is stopped, and the pressure returns to baseline, the compliance is not impaired.
  • Causes of false-negative:
    • “Pop-off mechanisms”, such as vesicoureteral reflux and bladder diverticulae, can make compliance seem higher than it actually is
  • Absolute pressure is more useful than a compliance value; storage pressure > 40 cm H2O is associated with harmful effects on the upper tract
• Continence
  • Leak point pressures
    • 2 distinct types of leak point pressures can be measured in the incontinent patient:
      1. Abdominal leak point pressure
      2. Detrusor leak point pressure
    • The ALPP measures the sphincter response to increased Pabd.
      • The lower the ALPP, the weaker the sphincter.
    • The DLPP measures the injured bladder response to increased outlet resistance.
      • The higher the resistance (e.g. DESD), the higher the DLPP, which is potentially dangerous to upper tracts.
    • Abdominal leak point pressure (ALPP)
      • Definition:
        1. Intravesical pressure (Pves) at which urine leakage occurs
        2. As a result of increased Pabd
        3. In the absence of a detrusor contraction
           • i.e. how much abdominal pressure transmitted to the bladder results in SUI?
      • Measure of the sphincteric strength or the ability of the sphincter to resist changes in Pabd
        • Applicable to patients with SUI and can only be demonstrated in patients with SUI
          • There is no normal ALPP because patients without SUI will not leak at any physiologic Pabd.
          • The lower the ALPP, the weaker the sphincter.
            • ALPP < 60cm H2O: suggestive of intrinsic sphincter deficiency (ISD)
            • ALPP between 60-90 is equivocal.
            • ALPP > 90 indicates little or no ISD
      • Should be measured as the total Pabd required to cause leakage, not the change in pressure. The reading is taken from the Pves channel as long as there is no involuntary contraction.
      • Current technology does not permit a method to distinguish between ISD and urethral hypermobility in women.
        • If there is no urethral hypermobility, SUI must be caused by ISD, regardless of the ALPP. Thus, an isolated measure of ALPP without considering other factors such as CMG and urethral mobility is of limited utility in predicting success for commonly performed female SUI procedures.
      • The term ALPP has been used interchangeably with Valsalva leak point pressure; however, this is not entirely correct. An ALPP can be measured during UDS testing by a voluntary Valsalva maneuver or by a cough. In the same person, Valsalva leak point pressure tends to be significantly lower than cough leak point pressure.
    • Detrusor leak point pressure (DLPP):
      • Definition:
        1. The lowest detrusor pressure (Pdet) at which urine leakage occurs
        2. In the absence of either increased Pabd or a detrusor contraction
        • The higher the urethral resistance, the higher the DLPP will be
      • The significance of elevated DLPP is that bladder pressures are getting too high before the pop-off mechanism of urethral leakage occurs.
      • Measure of Pdet in a patient with decreased bladder compliance
      • Most useful in:
        1. Patients with upper motor neuron lesions with high storage pressures (usually secondary to DO and DESD)
        2. Patients with lower motor neuron disease causing “decentralization”
        3. Non-neurogenic patients with low bladder compliance (after multiple bladder surgeries, radiation, tuberculous cystitis).
      • Higher DLPP is associated with increased risk of upper tract injury as intravesical pressure is transferred to the kidneys.
        • When treating impaired compliance, concept is to aim for as low a pressure as is reasonably achievable, which would be considerably < 40cm H2O.

Voiding and Emptying phase

• Normal detrusor function: characterized by voluntarily initiated continuous contraction that leads to complete bladder emptying within a normal time span and in the absence of obstruction.
• Detrusor underactivity: a 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.
• Acontractile detrusor: no demonstrable contraction during UDS.

• Bethanechol supersensitivity test has been used to help distinguish the cause of detrusor underactivity as neurogenic and myogenic. However, it is unreliable and has limited role.
• Many authors recommend a minimum voided volume of 150mL to accurately assess uroflow
• Voiding pressure-flow study helps assess two critical parameters related to the bladder and bladder outlet: detrusor activity (normal vs. impaired) and outlet resistance (obstructed vs. unobstructed). Can identify 3 fundamental conditions:
  1. Low (or normal) Pdet and high (or normal) flow rate: normal, unobstructed voiding
  2. High Pdet and low (or normal) flow rate: obstruction
  3. Low Pdet and low flow rate: detrusor underactivity
• Bladder outlet obstruction and detrusor underactivity in men
  • Bladder outlet obstruction index (BOOI): Pdet@Qmax – 2(Qmax)
    • ≥ 40: obstructed
    • Equivocal if 20-40
    • ≤ 20: unobstructed
  • Bladder contractility index (BCI): Pdet@Qmax +5(Qmax)
    • >150: strong contractility
    • Normal contractility 100-150
    • Weak contractility if BCI <100
  • These measures can become problematic when both detrusor underactivity and obstruction co-exist, such as in long-standing obstruction.
  • Bladder outlet obstruction is associated with abnormalities of storage as well, presumably due to changes in ultrastructure that occur with obstruction.
    • DO and impaired compliance occur in conjunction with obstruction.
    • Approximately 2/3 of men with symptomatic BOO had detrusor overactivity that resolved 50-67% of the time with treatment of obstruction. Reduced compliance is also associated with obstruction and has been shown to improve with treatment of obstruction (TURP).
• Bladder outlet obstruction in females
  • Obstruction when Qmax ≤12mL/sec and Pdet@Qmax ≥ 25cm H2O
  • Large overlap of values between obstructed and unobstructed patients; absolute pressure and flow values are imprecise and another parameter (radiographic or clinical evidence of obstruction) is necessary for diagnosis.
  • BOOI will grossly underestimate female BOO because females normally void at much lower pressures than males
• Sphincter coordination
  • Failure of the sphincter to relax or stay completely relaxed during micturition is abnormal.
  • Normally, EMG activity decreases before a voluntary bladder contraction
    • However, it is not abnormal for EMG activity to increase with an involuntary contraction as part of a guarding reflex to inhibit the idiopathic detrusor contraction, and this is known as pseudodyssynergia
      • Pseudodyssynergia: electromyographic sphincter “flare” during filling cystometry that is secondary to attempted inhibition of an involuntary bladder contraction by voluntary contraction of the striated sphincter
  • Detrusor external sphincter dyssynergia (DESD)
    • Occurs when there is an involuntary increase of external sphincter activity associated with detrusor activity and also with voiding.
    • Caused by a neurologic lesion in the suprasacral spinal cord
      • True DESD occurs only when there is a known neurologic lesion between the pons (infrapontine) above the sacral micturition center (Onuf nucleus S2-S4; suprasacral).
      • If there is no neurologic lesion, the dyssynergia is considered to be a learned behavior and is known as dysfunctional voiding.
    • May be considered a urodynamic risk factor for upper tract deterioration.
      • DESD can produce profound changes as the detrusor involuntarily contracts against a relatively closed sphincter; over time, will result in high pressures and can even impair bladder compliance.
        • Long periods of elevated Pdet during bladder filling or voiding put the upper urinary tract at risk.
  • Detrusor internal sphincter dyssynergia
    • Lack of coordination of the detrusor and internal sphincter or bladder neck
    • Insert figure

Urethral pressure profilometry (UPP)

• Definition of urethral pressure: fluid pressure needed to just open a closed urethra
  • Clinical relevance is controversial
• Several parameters can be obtained from the UPP:
  • Urethral closure pressure profile: urethral pressure – intravesical pressure
  • Maximum urethral pressure: highest pressure measured along the UPP
  • Maximum urethral closure pressure (MUCP): maximum difference between the urethral pressure and the intravesical pressure
  • Functional profile length: length of the urethra along which the urethral pressure exceeds the intravesical pressure in women
    • In most continent women, the functional urethral length is ≈3cm and the MUCP is 40-60cm H2O, but normal values vary widely

Video-urodynamics

• Procedure of choice for confirming bladder neck dysfunction in men and women
  • The AUA/SUFU Urodynamic Guideline supports the use of VUDS in young men and women without an obvious anatomic cause of obstruction
    • Can differentiate between functional causes of obstruction such as primary bladder neck obstruction and dysfunctional voiding.
    • Can be extremely useful for the diagnosis of BOO in women
    • Primary bladder neck obstruction can be only diagnosed on VUDS
  • VUDS can confirm sphincteric dysfunction diagnosed by EMG
• In addition, patients at high risk for complicated voiding dysfunction, such as those with known or suspected neurogenic lower urinary tract dysfunction, unexplained urinary retention in women, prior radical pelvic surgery, urinary diversion, prerenal or post renal transplant status, or prior pelvic radiation, should be considered for referral to a center with VUDS capabilities if a complete and accurate diagnosis cannot otherwise be obtained.
• Other uses:
  1. Localize obstruction
  2. Detecting incontinence not seen on physical exam
  3. Evaluating VUR during storage and/or voiding
  4. Determine if a known anatomic abnormality is playing a role if voiding dysfunction (e.g. bladder or urethral diverticulum, VUR)
  5. Particularly useful in cases of neuropathic voiding dysfunction

Ambulatory urodynamics

• Used to capture more realistic or physiologic observations, especially of incontinence episodes.
• More useful when standard UDS is inconclusive and diagnosis, and more importantly treatment, are uncertain

Clinical applications of UDS

• Women with SUI
  • UDS will not provide much useful information in women with pure SUI without urgency symptoms who empty normally and demonstrate SUI on physical exam
  • Many women with SUI who are considering surgical correction have mixed symptoms or emptying difficulties; UDS may have a role in these cases
  • AUA urodynamics guideline panel recommends:
    • “Clinicians who are making the diagnosis of urodynamic stress incontinence should assess urethral function.”
      • If UDS is performed, an assessment of urethral function (e.g., ALPP or MUCP) should be performed.
        • This seems reasonable as an ALPP may for some surgeons affect the type of surgery performed, because inferior outcomes have been found for some procedures in patients with low ALPP and/or MUCP.
    • “Patients with SUI considering invasive therapy should be evaluated for PVR.”
      • An elevated PVR may prompt a change in treatment for additional testing such as UDS.
    • “Clinicians may perform multichannel UDS in patients with both symptoms and physical findings of SUI who are considering invasive, potentially morbid, or irreversible treatments.”
      • This statement allows the clinician to make a decision on the selective use of preoperative UDS based on patient symptoms, how the study will influence choice of surgery, and the degree of confidence that the surgeon has in the diagnosis.
    • “Clinicians should perform repeat stress testing with the urethral catheter removed in patients suspected of having SUI who do not demonstrate this finding with the catheter in place during urodynamic testing.”
      • It is well established that some women will not demonstrate SUI with a catheter in place. This maneuver is especially important in a woman who does not demonstrate SUI on physical examination.
    • “In women with high-grade pelvic organ prolapse but without the symptom of SUI, perform stress testing with reduction of the prolapse. Multichannel UDS with prolapse reduction may be used to assess for occult stress incontinence and detrusor dysfunction in these women with associated LUTS.”
      • Prolapse reduction is extremely important if the demonstration of occult SUI on UDS will influence the type of prolapse surgery performed (i.e., a simultaneous anti-incontinence with prolapse repair).
  • UDS may be most useful in women who have:
    1. Significant urgency and/or urgency incontinence
    2. Bladder emptying problems
    3. Prior stress incontinence surgery
    4. Uncertain diagnosis or inability to demonstrate SUI on physical examination
    5. History of pelvic radiation
    6. History of neurologic disease
    7. Very severe symptoms (total or near total).
• Men and Women with LUTS
  • AUA urodynamics guideline panel recommends:
    • “Clinicians should perform pressure-flow studies in men when it is important to determine if urodynamic obstruction is present in men with LUTS, particularly when invasive, potentially morbid, or irreversible treatments are considered.”
      • Literature mixed on UDS before surgical treatment for BPH.
    • “Clinicians may perform pressure-flow studies in women when it is important to determine if obstruction is present.”
• Significantly impaired compliance remains the only absolute urodynamic indication for treating bladder outlet obstruction.
  • AUA urodynamics guideline panel recommends:
    • “Clinicians may perform multichannel filling cystometry when it is important to determine if altered compliance, DO or other urodynamic abnormalities are present (or not) in patients with urgency incontinence in whom invasive, potentially morbid, or irreversible treatments are considered.”
    • “Clinicians may perform multi-channel filling cystometry when it is important to determine if DO or other abnormalities of bladder filling/urine storage are present in patients with LUTS, particularly when invasive, potentially morbid, or irreversible treatments are considered is consistent with the available information.”
• Evaluation of Neurogenic Lower Urinary Tract Dysfunction (See 2019 CUA NLUTD Guideline Notes)
  • In addition to symptomatic presentation, neurogenic lower urinary tract dysfunction can present as upper urinary tract decompensation with hydroureteronephrosis and renal insufficiency without bothersome symptoms. The goal of management in these patients is to prevent upper tract decompensation and relieve symptoms.
  • Not all neurogenic lower urinary tract dysfunction requires UDS before observation or treatment. Conditions in which high storage pressures are not suspected (e.g., urgency incontinence after a stroke or women with multiple sclerosis with a low PVR) often can be managed initially without UDS. But in cases in which the neurologic condition/lesion can cause potentially harmful storage situations (spinal cord injury, myelomeningocele), UDS is essential both before treatment and also in ongoing follow-up of the condition and to monitor the response to treatment. In the middle are situations in which UDS can be helpful in guiding management (e.g., men with possible BPO and Parkinson disease or multiple sclerosis).
  • The AUA Guidelines contains 5 statements regarding UDS in neurogenic lower urinary tract dysfunction:
    • "Clinicians should perform PVR assessment, either as part of complete urodynamic study or separately, during the initial urologic evaluation of patients with relevant neurologic conditions (e.g., spinal cord injury, myelomeningocele), and as part of ongoing follow-up when appropriate."
    • "Clinicians should perform a complex CMG during initial urologic evaluation of patients with relevant neurologic conditions with or without symptoms and as part of ongoing follow-up when appropriate. In patients with other neurologic diseases, physicians may consider CMG as an option in the urologic evaluation of patients with LUTS."
    • "Clinicians should perform pressure-flow analysis in patients with relevant neurologic disease with or without symptoms or in patients with other neurologic disease and elevated PVR or urinary symptoms."
    • "When available, clinicians may perform VUDS in patients with relevant neurolosgic disease at risk for neurogenic lower urinary tract dysfunction or in patients with other neurologic disease and elevated PVR or urinary symptoms."
    • "Clinicians should perform EMG in combination with CMG with or without pressure-flow studies in patients with relevant neurologic disease at risk for neurogenic lower urinary tract dysfunction or in patients with other neurologic disease and elevated PVR or urinary symptoms."

Questions

1. What is the definition of ALPP vs. DLPP?
2. List causes of decreases bladder compliance?
3. What conditions may cause bladder compliance to seem better than it actually is?

References

• Wein AJ, Kavoussi LR, Partin AW, Peters CA (eds): CAMPBELL-WALSH UROLOGY, ed 11. Philadelphia, Elsevier, 2015, chap 73