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Physiology of Micturition
• Low bladder volumes: SNS is stimulated and PNS is
• Bladder full: PNS stimulated (bladder contracts) SNS
inhibited (internal sphincter relaxes).
• Intravesical pressure > resistance within the urethra: urine
• Pudendal nerve innervates external sphincter.
Urodynamics describes a group of physiological tests that
are used in clinical practice to investigate abnormalities of
lower urinary tract function.
Dynamic study of transport, storage & evacuation of
Main goal of UDS: to reproduce pt.'s symptoms and
determine their cause by various tests.
-incontinence in whom surgery is planned.
-mixed ,urge & stress symptoms.
-associated voiding problems.
-pts. with neurologic disorders.
-pt with LUTS, at least uroflow study.
-all neurologically impaired patients with
neurogenic bladder dysfunction.
Children with voiding dysfunction:
-kids with daytime urgency and urge incontinence,
recurrent infection, reflux, or upper tract changes.
Characterization of detrusor function.
Evaluation of bladder outlet.
Evaluation of voiding function.
Diagnosis and characterization of neuropathy.
Three important rules before starting UDS
1. Decide on questions to be answered before starting a
2. Design the study to answer these questions.
3. Customize the study as necessary.
Terminology for Common Urodynamic Terms and Observations
According to the International Continence
Society Standardization Subcommittee
The ICS has now defined the term urodynamic
observations to denote observations that occur during
and are measured by the urodynamics(UDS) test itself.
Two principal methods of urodynamic investigation
Conventional urodynamic studies: normally take place
in the urodynamic laboratory involving artificial
Ambulatory urodynamic studies: a functional test of
the lower urinary tract using natural filling and
reproducing the subject’s everyday activities.
The following are required of both types of studies:
Intravesical pressure: the pressure within the bladder.
Abdominal pressure: the pressure surrounding the bladder; currently it
is estimated from rectal, vaginal, or extraperitoneal pressure or a bowel
Detrusor pressure: the component of intravesical pressure created by
forces on the bladder wall that are both passive and active.
Filling cystometry: the method by which the pressure and volume
relationship of the bladder is measured during bladder filling.
Physiologic filling rate: a filling rate less than the predicted maximum.
Predicted maximum is the body weight in kilograms divided by 4 and
expressed as milliliters per minute.
Nonphysiologic filling rate: a filling rate greater than the predicted
Urodynamic stress incontinence: noted during filling cystometry and
defined as the involuntary leakage of urine during increased abdominal
pressure in the absence of a detrusor contraction. This currently replaces
genuine stress incontinence.
Urethral pressure measurements:
Urethral pressure: the fluid pressure needed to just open a closed urethra.
Urethral pressure profile: a graph indicating the intraluminal pressure along
the length of the urethra.
Urethral closure pressure profile: the subtraction of intravesical pressure from
Maximum urethral pressure: the maximum pressure of the measured profile.
Maximum urethral closure pressure (MUCP): the maximum difference
between the urethral pressure and the intravesical pressure.
Functional profile length: the length of the urethra along which the urethral
pressure exceeds intravesical pressure in women.
Abdominal leak point pressure(ALPP): the
intravesical pressure at which urine leakage occurs
because of increased abdominal pressure in the
absence of a detrusor contraction.
Detrusor leak point pressure(DLPP): the lowest
detrusor pressure at which urine leakage occurs in the
absence of either a detrusor contraction or increased
Measurement of intravesical bladder pressure during
bladder filling(measures volume-pressure relationships).
Used to assess bladder sensation, capacity, compliance,
Bladder access by transurethral catheter, or rarely by
percutaneous suprapubic tube.
Filling medium either gas (CO2) or liquid (water, saline, or
contrast material at body temp).
Liquid cystometry is more physiologic.
Ideally, filling should be performed in standing position.
Bladder filling either by diuresis or filling through a catheter.
slow (up to 10 ml/min), physiologic
medium (10 to 100 ml/min)
fast (> 100 ml/min)
Children and pts with known bladder hyperactivity require
slow fill rates.
All systems should be zeroed to atmospheric pressure.
No air bubbles.
- Capacity 350-600ml
- First desire to void between
150- 200 ml.
- Constant low pressure that
does not reach more than 6-
10 cm H2O above baseline
at the end of filling.
maneuvers(cough, fast fill
etc.) should not provoke a
- No leakage on coughing .
- A voiding detrusor pressure
rise of < 70 cm H2O with a
peak flow rate of > 15 ml /
s for a volume > 150 ml.
- Residual urine of < 50 ml.
Single Vs multi-channel UDS:
-single: Pves only
-multi: Pves, Pdet, Pabd
Intravesical pressure(Pves): Total Pressure within the
Abdominal pressure(Pabd): Pressure surrounding the
bladder; currently estimated from rectal, vaginal, or
extraperitoneal pressure or a bowel stoma.
Detrusor pressure(Pdet): Component of intravesical
pressure created by forces on the bladder wall, both
passive and active.
True detrusor pressure = Intravesical pressure -
Intraabdominal pressure.(Pdet = Pves-Pabd)
Physiologic filling rate: A filling rate < predicted maximum.
Predicted maximum = body weight in kg divided by 4 and
expressed as ml/min.
Nonphysiologic filling rate: A filling rate > predicted
First sensation of bladder filling: Volume at which patient first
becomes aware of bladder filling.
First desire to void: Feeling during filling cystometry that
would lead the patient to pass urine at the next convenient
Strong desire to void: Persistent desire to void without fear of
- Relationship between change in bladder volume and
change in Pdet (Δvolume/Δpressure); measured in
- Normal bladder is highly compliant, and can hold
large volumes at low pressure.
- Normal pressure rise during the course of CMG in
normal bladder will be only 6-10 cm H2O.
- Decrease compliance < 20 ml/cm H2O, poorly
Impaired compliance is seen in:
neurologic conditions: spinal cord injury/lesion, spina
bifida, usually results from increased outlet resistance
(e.g., detrusor external sphincter dyssynergia [DESD])
or decentralization in the case of lower motor neuron
Long-term BOO (e.g., from benign prostatic
Structural changes- radiation cystitis or tuberculosis.
Impaired compliance with prolonged elevated storage
pressures is a urodynamic risk factor and needs
treatment to prevent renal damage.
Neurogenic detrusor overactivity: Overactivity
accompanied by a neurologic condition; also k/a
Idiopathic detrusor overactivity: Detrusor
overactivity without concurrent neurologic cause; also
k/a detrusor instability.
Abdominal leak point pressure(ALPP): Intravesical
pressure at which urine leakage occurs because of
increased abdominal pressure in the absence of a
ALPP is a measure of sphincteric strength or ability
of the sphincter to resist changes in Pabd
Applicable to stress incontinence; ALPP can be
demonstrated only in a patient with SUI.
There is no normal ALPP, because patients without
stress incontinence will not leak at any physiologic
Lower the ALPP, weaker is the sphincter.
ALPP<60 cm H2O: significant ISD
ALPP 60-90 cm H2O: equivocal
ALPP>90 cm H2O: urethral hypermobility;
little or no ISD
Detrusor leak point pressure(DLPP): Lowest
detrusor pressure at which urine leakage occurs in the
absence of either a detrusor contraction or increased
abdominal pressure (risk with > 40cm H2O).
Its a measure of Pdet in a patient with decreased
Higher the urethral resistance, higher the DLPP, the
more likely is upper tract damage as intravesical
pressure is transferred to the kidneys.
Non invasive study.
Measurement of the rate of urine flow over time.
Estimate of effectiveness of the act of voiding along with PVR.
effectiveness of detrusor contraction
completeness of sphincteric relaxation
patency of the urethra
3 methods used
Recorded variables during UFM study:
Voided volume (VV in milliliters)
• Flow rate (Q in milliliters per second)
• Maximum flow rate (Qmax in milliliters per second)
• Average flow rate (Qave in milliliters per second)
• Voiding time (total time during micturition in seconds)
• Flow time (the time during which flow occurred in seconds)
• Time to maximum flow (onset of flow to Qmax in seconds)
• Optimal voids 200 to 400cc.
• Voids < 150cc are difficult to interpret.
• Pt. should be well hydrated with full bladder, but
not overly distended bladder.
• Should be performed in privacy and pt.encouraged
to void in his normal fashion.
• Qmax & shape of curve- more reliable indicators of
• Qmax- most reliable variable in detecting abnormal
Post Void Residual Urine
Excellent assessment of bladder emptying.
Performed by ultrasound (bladder scan) or
Normally, it is < 0.5ml, but < 10% of voided volume
is considered insignificant.
Urethral pressure profilometry
Urethral pressure profile (UPP): a graph indicating
intraluminal pressure along the length of urethra.
Urethral pressure: fluid pressure needed to just open a
UPP is obtained by withdrawal of a pressure sensor
(catheter) along the length of urethra.
Urethral closure pressure profile is given by subtraction of
intravesical pressure from urethral pressure.
Maximum urethral pressure is highest pressure measured
along the UPP.
• Maximum urethral closure pressure (MUCP) : maximum
difference between urethral pressure and intravesical
Functional profile length: length of urethra along which
urethral pressure exceeds intravesical pressure in women.
In most continent women,
functional urethral length:approx.3 cm &
MUCP is 40 to 60 cm H2O.
MUCP is not always indicative of severity of incontinence
hence not used commonly.
Simultaneous measurement of bladder pressure and
flow rate throughout the micturition cycle.
Best method of quantitatively analyzing voiding
Access to bladder via transurethral or SPC 8F or less.
Intra-abdominal pressure measured by balloon
catheter in rectum or vagina.
Men should void in standing position, while women
seated on commode.
Detrusor pressure at maximal flow(Pdet at Qmax):
Magnitude of micturition contraction at the time when
flow rate is at its maximum.
Pressure <100 cm H2O indicate outlet obstruction
even if the flow rate is normal.
Normal male generally voids with Pdet 40-60 cm H2O
and woman with lower pressure.
Pdet more accurately measures bladder wall
Indications for pressure-flow studies:
- to differentiate between pts with a low Qmax sec. to
obstruction, from those sec.to poor contractility.
- Identify pt.with normal flow rates but high pressure
- LUTS in pt with hx of neurologic disease(CVA,
- LUTS with normal flow rates (Qmax > 15cc/min).
younger men with LUTS.
- Men with little endoscopic evidence of prostate
UDS with simultaneous fluoroscopic image of lower
Equipment and technique:
- CMG + PFS same as before but the study is conducted
on a fluoroscopy table, and the filling medium is a
radiographic contrast agent.
evaluation of VUR during storage &/or filling.
neurogenic bladder dysfunction
identification of associated pathology
Primary BNO diagnosis & differentiation from
dysfunctional voiding in women: only on VUDS.
Study of the electric potentials produced by depolarization of
In case of UDS, EMG measurement of striated sphincteric
muscles of the perineum is done to evaluate possible
abnormalities of pelvic floor muscle function.
EMG activity is measured during both filling and emptying.
EMG is performed via electrodes placed in (needle
electrodes) or near (surface electrodes) the muscle to be
Most important information obtained from sphincter EMG
is whether there is coordination or not between the
external sphincter and the bladder.
EMG activity gradually increases during filling
cystometry (recruitment) and then cease and remains so
for the time of voiding.
Failure of the sphincter to relax or stay completely relaxed
during micturition is abnormal.
In pt with neurologic disease, this is called detrusor-
In the absence of neurologic disease, it is called pelvic
floor hyperactivity,or dysfunctional voiding.