Basic Urodynamic Information

URODYNAMICS refers to a group of diagnostic procedures that are performed to evaluate voiding disorders. The goal of diagnosis and treatment of these disorders is to (1) protect the kidneys and (2) keep the patient dry.

The PARAMETERS that are measured during a urodynamic procedure can include:

• PRESSURE
• FLOW
• EMG
• VIDEO IMAGE

URODYNAMICS are primarily performed for evaluation of the lower urinary tract.

These tests include Uroflow, CMG, Flow/Pressure, UP, UPP and EMG.

DECISIONS ON THERAPEUTIC INTERVENTION ARE BASED, IN LARGE PART, ON THE RESULTS OF THESE URODYNAMIC PROCEDURES.

 

URINARY TRACT STRUCTURES SIGNIFICANT TO URODYNAMICS

KIDNEYS:

FILTER WATER SOLUBLE WASTE PRODUCTS AND EXCESS WATER FROM THE BLOOD STREAM, IN THE FORM OF URINE

URETERS:

TUBE SHAPED STRUCTURES THAT TRANSPORT URINE FROM THE KIDNEYS TO THE BLADDER, THROUGH PERISTALTIC ACTION AT 1CC/MIN

BLADDER:

MUSCULAR "SACK" THAT STORES URINE

URETHRA:

TUBE THAT CLOSES TO HOLD URINE IN BLADDER AND OPENS TO RELEASE URINE (MICTURITION) WHEN BLADDER HAS REACHED CAPACITY

Each urodynamic procedure attempts to answer the following questions about bladder function:

• Can normal and appropriate bladder contractions be voluntarily initiated?

• Are involuntary detrusor contractions present?

• Is the detrusor muscle adequate or inadequate?

• Is the bladder capacity normal?

• Does the bladder accommodate adequate volume without significant pressure rise?

• Is sensation normal? Is hypoesthesia or hyperesthesia present?

With regard to the outlet, each study attempts to answer these questions:

• Is the sphincter mechanism intact? If incompetent, is it only so under certain circumstances, such as when supine, standing, or coughing?

• What are the sphincter dynamics? How strong are the sphincter contractions? Are they voluntary or involuntary? Are they sustained or interrupted?

• Is there evidence of neurologic dysfunction?

• During the bladder contraction, is there evidence of outlet obstruction? If so, where (bladder neck, proximal urethra, external sphincter, anterior urethra)? Why? Is it neurologic (detrusor sphincter dyssynergia), structural (stricture, BPH), or psychologic?

Anatomy and Physiology

Normal Male Urinary Tract

 Normal Female Urinary Tract

Normal Bladder Anatomy and Physiology

 The bladder is a sack, made of many thin layers of smooth muscle cells.

The smooth muscles are layered in different directions, so that the bladder can contract downward, while the bladder neck opens for voiding.

Even though the bladder is usually illustrated as a round "balloon," it is actually an oval, flattened at the top. The abdominal contents press downward on the bladder, causing it to flatten as it empties.

The urethra and urethral sphincter are striated muscle. These muscles contract to hold the urethra and bladder neck closed during filling. They relax just prior to urination. The combined action of the contraction of the bladder’s smooth muscles and the relaxation of these striated muscles causes the bladder neck to raise and open, and the bladder to empty (2).

The SPHINCTER STRIATED MUSCLES are structured and placed differently in males and females. The sphincter is stronger in the male and has a function in the ejaculatory process.

 MICTURITION REFLEX

The MICTURITION REFLEX is a two-phase cycle that serves as a protective mechanism for the kidneys. It consists of the FILLING (or storage) PHASE and the EMPTYING PHASE. This reflex is uninhibited when we are born, and we learn to inhibit (or control) it as we mature.

The ability to control the MICTURITION REFLEX is dependent upon two "systems" being intact. These are

·         RECEPTORS and CHEMICALS that must maintain a delicate balance for the muscles to operate properly

·         A NEURO/SENSORY PATHWAY that must be intact between the brain, spinal cord and bladder, so that the receptors can elicit an appropriate response

RECEPTORS in the bladder communicate with RECEPTORS in the brain, via the spinal cord, to control the MICTURITION REFLEX.

RECEPTORS

Alpha Receptors

• Located in the bladder neck area
• Chemically stimulated during the FILLING PHASE to contract and keep bladder neck closed
• Chemically blocked during the EMPTYING PHASE to relax and open the bladder neck and urethra

Beta Receptors

• Located in the bladder
• Chemically stimulated during the
  FILLING PHASE to relax muscles
• Chemically blocked during the
  EMPTYING PHASE to contract
  and "collapse" the bladder

Cholinergic Receptors

• Located throughout the bladder
• Chemically blocked during the
  FILLING PHASE to relax muscles
• Chemically stimulated during the EMPTYING PHASE to strengthen the contraction of the bladder muscle

 NEUROSENSORY REGULATION

There are 2 electrical pathways that operate as part of the MICTURITION REFLEX. These are the REFLEX LOOP and the SENSORY/REGULATORY LOOP.

The REFLEX LOOP is composed of peripheral nerves in the bladder and their connections to the spinal cord. The REGULATORY/SENSORY LOOP is composed of ascending sensory neurons in the spinal cord connected, through the motor cortex in the brain, to motor neurons in the regulatory tract of the spinal cord.

 

PROPRIOCEPTIVE NERVE ENDINGS in the bladder are stretched during the FILLING PHASE and send information to the cortex that is perceived as fullness, discomfort, or pain.

 Voiding Disorders

URODYNAMIC  tests will provide answers to clinical questions that arise about a patient's bladder and outlet function, after they have visited the physician with specific complaints. The typical patient complaints that lead to an urodynamic evaluation include:

These complaints, or symptoms, have multiple causes, to include:

• SIDE EFFECTS OF MEDICATION

• OBSTRUCTION
• Tumor/carcinoma
• Polyp
• Scarring
• Infection
• Abscess

• FISTULA

• DIVERTICULUM

• NEUROMUSCULAR
• Neuromuscular disease (i.e. ms)
• Detrusor instability
• Hypersensitivity

Male Urinary Obstructions

Female Urinary Obstructions

 A URODYNAMIC procedure could include measurement of FLOW, PRESSURE, ELECTRICAL ACTIVITY and RADIOGRAPHIC IMAGING during one or more of the following tests:

The illustration below depicts the sequence of events during micturition as measured and displayed during the various urodynamic procedures.

 FLOW

Flow information can be utilized two ways as part of an urodynamic procedure:

• UROFLOW W/RESIDUAL is performed when the patient arrives at the lab with a full bladder and voids into a beaker that is placed on a weight transducer or load cell.

• FLOW/PRESSURE studies are typically performed immediately following a filling cystometrogram and require the use of smallest catheter practical, to measure pressure in the bladder while the patient voids.

The UROFLOW is a screening test only. It demonstrates the result of the micturition reflex and the information obtained will indicate the presence of dysfunction. An abnormal UROFLOW indicates a voiding dysfunction and should be followed by for further testing.

The ICS recommendations for standardization in the comparison and interpretation of Uroflow test results state that the following data should always be documented as part of a flow study:

• Patient's name and the date of the test
• Maximum Flow Rate
• Volume Voided
• Time: Voiding Time (always); Flow Time (if intermittent)
• Average Flow Rate > Total Voided Volume Total Voiding Time (cc/sec)
• Patient's opinion of normality of voiding
• Residual urine, if measured

The diagram shows a stable bladder. The traces are from top to bottom rectal (abdominal) pressure, Intravesical pressure, detrusor pressure, and infused volume

  The diagram shows an unstable bladder with low capacity. In such a case the height of the contractions are of interest as they may exceed the maximum urethral pressure leading to incontinence. The unstable bladder is a sign that the micturition reflex is triggered and the reflex lowers urethral pressure. For leakage to take place the detrusor pressure just has to exceed this lowered urethral pressure. The patient in the diagram had a static urethral pressure of 100 cm water when the bladder was stable. The contraction has almost reached this height, so leakage had almost certainly taken place. Patients with unstable bladders may also carry the risk of urine refluxing up the ureters causing kidney damage. This would be tested for by x ray contrast cystometry. Although a large pressure rise has taken place, this type of bladder would not be termed low compliance. This term is reserved for the stable bladder with a large pressure rise.

When the abnormal Uroflow is due to intermittent flow, both VOIDING TIME and FLOW TIME need to be documented. Voiding time is defined as the total time from beginning to end of micturition. Flow time is defined as the total time when urine is actually flowing.

FLOW/PRESSURE

A FLOW/PRESSURE study is typically performed immediately after the cystometrogram. To obtain optimum results, the study should be performed with a small catheter, to prevent flow obstruction artifact.

Abnormally high voiding pressure. Indicates outflow tract obstruction when associated with a low initial flow rate. High flow rates, in excess of 40 cc/sec may be associated with exceptionally powerful detrusor contractions and higher than normal voiding pressure, in both sexes. This is most often seen in patients with long standing bladder over activity and detrusor hypertrophy, but no outflow obstruction.
In women, voiding commonly occurs with a low voiding pressure. The detrusor may be proven to be contracting by measuring the isometric pressure on interruption of flow.
A poorly sustained voiding pressure may be related to a failing detrusor. An unsustained contraction is likely to lead to residual urine.
A bladder with instability often contracts before the patient is ready to void. The detrusor pressure usually falls as the sphincter is relaxed and voiding begins
Fluctuating detrusor contractions result in an interrupted or irregular flow. This situation occurs most often in neurologically abnormal patients, particularly those with multiple sclerosis.

CMG

The CYSTOMETROGRAM is basically performed to evaluate the COMPLIANCE and STABILITY of the detrusor muscle. 85% of all incontinence occurs in women, and 75% of that is stress incontinence (i.e., LEAKAGE IN THE ABSENCE OF OVERACTIVITY).

COMPLIANCE is simply the elastic property of the DETRUSOR muscles. An evaluation of COMPLIANCE is an evaluation of the ability of the bladder to "stretch" to "normal" capacity while maintaining low pressures.

STABILITY is evaluated by observing the DETRUSOR while filling the bladder to normal capacity. The evaluation determines the presence or absence of DETRUSOR OVERACTIVITY (or INSTABILITY).

A CMG evaluation routinely involves two pressure measurements and 1 subtracted pressure, with which detrusor activity is evaluated. Urethral pressure a subtracted urethral closure pressure may also be added for certain specialized studies.

*SUBTRACTED PRESSURES are calculated in an effort to evaluate the pressures generated by specified structures.

VESICAL PRESSURE (pves) is the pressure that is measured inside the bladder, with a catheter that was specifically designed for pressure monitoring in the urinary tract. The pressure information obtained is a combination of the pressure being exerted on the bladder by the abdominal contents, the weight or pressure of any urine in the bladder and the force that the detrusor muscle is exerting on that fluid. The pressure in an empty bladder is usually called RESTING PRESSURE. Resting pressure changes with position. The normal bladder resting pressures may vary between 8 and 40 cmH2O, depending upon the particular patient and position during study.

ABDOMINAL PRESSURE (pabd) is measured by placing a special catheter either in the rectum or the vagina. Abdominal pressure information is significant because the bladder is contained in the floor of the abdominal cavity and it is important to isolate pressures and activities occurring in the bladder itself.

The DETRUSOR PRESSURE is a subtracted pressure that is calculated by subtracting the abdominal pressure from the vesical pressure. A detrusor pressure channel will display a waveform tracing that represents the actual activities taking place in the bladder during the CMG. Artifact from abdominal straining, gas and the weight of the abdominal contents are removed from the information being processed from the catheter in the bladder. The ability to provide this calculated information is one of the many benefits of using digital urodynamic equipment.

The dynamics of the urinary tract structures are readily illustrated when looking at the pressures in the various "chambers." This is particularly important in the female patient because relaxation of the pelvic floor and subsequent displacement of the bladder and urethra is the leading cause of stress incontinence. Illustrated below are the dynamics of the intra-abdominal cavity during a cough in a patient with a normal pelvic floor and then a relaxed pelvic floor.

When the bladder is properly positioned in the abdominal cavity, both it and the bladder neck are above the pelvic floor. As illustrated below, during a valsalva (either abdominal straining or cough), the intra-abdominal pressure rises. This rise is reflected into the vesical pressure. If the bladder is properly suspended, the increased

	Intra-abdominal pressure is also reflected in the urethra. For a patient to remain dry, the pressures in the urethra must remain greater than the pressure in the bladder, during filling. The average URETHRAL CLOSURE PRESSURE for a female is 60 cmH20 and for a male it is 80 cmH20.
	With aging, or after childbearing, the female pelvic floor can relax, causing the base of the bladder and the bladder neck to fall below the pelvic floor. A valsalva will usually lead to pressures in the bladder being higher than in the urethra. The result of this is stress incontinence, which is illustrated to the left.

Surgical procedures can be used to raise the bladder and urethra. These suspensory procedures are typically successful, however, occasionally result in complications. Those include a permanently open bladder neck with complete incontinence or worsened incontinence in the event that the problem was DETRUSOR INSTABILITY. Instability is readily controlled by medication.

The COMPLIANCE and STABILITY of the DETRUSOR muscle are most easily visualized on a subtracted, DETRUSOR channel..

A bladder with NORMAL COMPLIANCE will demonstrate NO GREATER than 15cm H2O increase in DETRUSOR pressure as it progresses from empty to capacity during a CMG.

A bladder with LOW COMPLIANCE will demonstrate an INCREASE in DETRUSOR pressure GREATER than 15cm H2O as it progresses from empty to capacity during a CMG. A poorly compliant bladder typically has a low capacity. INSTABILITY should not be confused with LOW COMPLIANCE. Incontinence.

A bladder with HIGH COMPLIANCE will demonstrate a MINIMAL INCREASE in DETRUSOR pressure with a capacity above normal limits.

NORMAL COMPLIANCE
<15cm H20 pressure increase to capacity

NORMAL COMPLIANCE w/DETRUSOR
OVERACTIVITY as capacity is reached

NORMAL COMPLIANCE w/ DETRUSOR
OVERACTIVITY Stress (cough) induced

LOW COMPLIANCE
pdet > 15cm H20 w/ low capacity

LOW COMPLIANCE w/ DETRUSOR
OVERACTIVITY Unstable contractions at
capacity (~ 100cc) due to muscle hypertrophy
(radiation tx)

LOW COMPLIANCE
Bladder does not distend normally to
accommodate filling. This can be due
to an infusion rate that is too fast

HIGH COMPLIANCE w/ DETRUSOR
OVERACTIVITY High capacity bladder
w/terminal overactivity. Probably neurogenic

HIGH COMPLIANCE Stable w/ large capacity

HIGH INTRAVESICAL PRESSURE
Associated w/ stress incontinence &
obesity

 EMG

ELECTROMYOGRAPHY is used in urodynamics to evaluate the electrical activity of the sphincter muscle. The sphincter’s striated muscles undergo a reversal of polarity during contraction.

This electrical activity is known as MOTOR UNIT POTENTIAL and can be picked up by needle electrodes and displayed on a monitor screen or audibly on special speakers. The sound that is generated is a rapid metallic tap.

The common EMG modality for Urodynamics is a gross recruitment pattern, relating to storage and voiding. Increased sphincter muscle activity sounds like machine gun fire and looks like the trace below:

EMG audio can be utilized during the CMG as a tool to assist the incontinent patient in identifying proper sphincter relaxation and contraction techniques.

There are three types of electrodes used for EMG:

The needle and wire electrodes are placed directly in the sphincter muscle and provide the most reliable information. The placement in male and female sphincter is illustrated below:

	The female urethral sphincter muscle bands are located about 1" in from the meatus. Needle or wire electrodes are placed in the folds along side the meatus at 1:00 and 11:00 position.
	Wire or needle electrodes are placed in the male urethral sphincter by inserting them, as shown by the "X." They should be inserted between the base of the scrotum and the rectum, parallel to the rectum, about 2" deep.

Patch electrodes may be used, but provide the least reliable information. Skin preparation and placement are both critical. Two patches are placed on either side of the external anal sphincter. The buttocks should be spread and the area on and around the anal orifice should be thoroughly wiped with alcohol and then dried. Without releasing the buttocks, the electrodes need to be placed at 3:00 and 9:00 position, as close to the rectal mucosa as possible. The third electrode is placed on the inner thigh.

 URETHRAL PRESSURES & UPP

Pressure information from the urethra can be obtained and utilized in several ways. As stated in the CMG section, the pressure in the urethra should be equal or greater than the vesical pressure, during bladder filling. When the bladder and urethra are in their proper anatomical place, any pressure increases in the abdominal cavity, from strain or any other cause, will also affect the urethra, preventing leakage.

Urethral pressure information can be taken a step further and, through the use of catheters with depth markings, turned into a URETHRAL PRESSURE PROFILE.

The UPP is a pressure curve that is obtained by withdrawing the catheter at a constant rate, which is ideally mechanically controlled by a PROFILOMETER. URETHRAL COUGH PRESSURE PROFILES may also be recorded by having the patient cough repeatedly while the catheter is being withdrawn. These studies provide information about the transmission of increased abdominal pressure to the upper urethra, as well as the FUNCTIONAL URETHRAL LENGTH, MAXIMUM URETHRAL PRESSURE and MAXIMUM URETHRAL CLOSURE PRESSURE.

MAXIMUM URETHRAL PRESSURE is the major pressure represented in the profile. MAXIMUM URETHRAL CLOSURE PRESSURE is the maximum urethral pressure minus the simultaneously recorded vesical pressure. TOTAL PROFILE LENGTH is the anatomic length of the urethra. FUNCTIONAL PROFILE LENGTH is the length of the urethra where the urethral pressure is equal to or exceeds the vesical pressure.

Urethral pressure studies can be done with water perfused catheters or micro-tip catheters. When using water-perfused catheters, solution should be run through the urethral lumen at 4-12 cc/min. This is to provide backpressure for the transducer to measure pressure against.

  URODYNAMIC TERMS & DEFINITIONS

ARREFLEXIC - Diminished or absent reflex. A bladder that fails to react or has diminished reactions is arreflexic. Also called flaccid.

ATONIC - Same as arreflexic. Also, a bladder that shows no "tone" or muscle strength. Again, flaccid.

AUTONOMOUS - Acting independently. Used to describe a bladder that acts on its own, with no control by the patient.

BLADDER - A vessel-like smooth muscle organ that collects and stores urine from the kidneys, then contracts to expel the urine through the urethra.

BLADDER NECK - The area of the bladder where the bladder muscle converges to form the urethra.

CONTINENCE - The successful storage of urine.

CONTRACTION - The shortening of the bladder muscle causing the bladder to get smaller and force urine out.

CYSTO - Refers to the bladder.

CYSTOMETRY - Measurement of the bladder. Bladder pressure is measured as the bladder is filled. A volume versus pressure graph is produced called a cystometrogram.

DENERVATION - Resection (cutting) or removal of the nerves to a certain organ or part of the body.

DETRUSOR - The smooth muscle that forms the bladder.

DETRUSOR PRESSURE - The pressure in the bladder caused exclusively by the contraction of the detrusor muscle.

DILATE - To open or stretch a tubular organ (such as the urethra) beyond its normal dimensions.

DISTEND - To stretch outward. For example, when the bladder is filled, it is distended.

DYSPAREUNIA - Difficult or painful coitus.

DYSURIA - Difficult or painful urination.

ELECTROMYOGRAPHY - The measurement of relative nerve activity by electronically measuring and amplifying nerve signals.

FREQUENCY - The need to empty one's bladder frequently.

INCONTINENCE - The failure to store urine when desired.

INCOMPLETE VOIDING - The failure of the lower urinary tract to expel all the urine in the bladder (a 20-50 cc residual normally remains).

HYPERREFLEXIC - Refers to the bladder that contracts too soon or too much.

HYPERTONIC - Similar to hyperreflexic. A bladder with unusually high pressure or one that contracts too soon.

HYPERTROPHY - Enlarged above normal size.

HYPOREFLEXIC - The opposite of hyperreflexic. Similar to arreflexic.

HYPOTONIC - The opposite of hypertonic. Similar to atonic.

INHIBIT - Refers to conscious effort that keeps the bladder from contracting. Conscious inhibition of the detrusor reflex.

INTEGRATED EMG - A technique of averaging the signals received from electromyography in order to be able to graph the information with standard recording devices. This is as opposed to direct EMG, which shows individual nerve impulses. The individual pulses happen too fast to record on paper with most devices.

INTRA-ABDOMINAL PRESSURE - Refers to the pressure in the abdomen that in turn applies pressure to the bladder. It is sometimes important to know how much this pressure is when measuring pressure in the bladder.

INTRINSIC - Pertaining exclusively to a part. Intrinsic bladder pressure is pressure created only by the bladder, not for example, abdominal pressure.

NEURO - Pertaining to the nervous system. Certain parts of urodynamics are referred to as neuro-urology, as the tests evaluate the nervous system that affects and operates the lower urinary tract.

OBSTRUCTION - Refers to something blocking the urethra and restricting or preventing urine outflow.

OUTLET - Refers to the bladder neck, urethra, and sphincter as a combined mechanism.

OVERFLOW INCONTINENCE - A type of incontinence brought about because of incomplete emptying and a large amount of urine always being present in the bladder.

PROSTATE - A gland in men that surrounds the urethra, distal to the bladder neck. This gland sometimes enlarges and obstructs the urethra.

RESIDUAL - The urine remaining in the bladder just after urination.

RETENTION - The symptom of retaining too much urine in the bladder. Incomplete voiding or complete inability to void.

SENSATION - The feeling of the bladder filling. During a cystometrogram, the patient will be asked to describe how much they can sense their bladder getting full.

SPHINCTER - A circular muscle that acts as the mechanism to close the urethra when voiding is not desired.

STRESS INCONTINENCE - A symptom of losing urine when there is a sudden increase in pressure on the bladder, such as from a cough or running down stairs.

STRIATED - Refers to skeletal muscle. The sphincter is often referred to as the striated sphincter, as it is made up of skeletal type muscle.

STRICTURE - Scar tissue. Used to describe scarring in the urethra that blocks urine flow.

SUBTRACTED PRESSURE - Refers to pressure created only by the detrusor muscle. Abdominal pressure is electronically subtracted from total bladder pressure to get this value.

TRANS URETHRAL RESECTION OF THE PROSTATE - An operation that cuts away enlarged prostate tissue to maintain an adequate urine outlet in the urethra.

TRIGONE - A sensitive area in the bladder, defined as the area bounded by the two urethral orifices and the bladder neck.

UNINHIBITED - Acting without conscious inhibition.

URETER - The tube that drains urine from the kidney to the bladder.

URETHRA - The tube that carries urine from the bladder to the outside.

URETHRAL PRESSURE PROFILE - A test that measures pressures along the length of the urethra.

URETHRAL PRESSURE: STATIC - Refers to measurement of pressure at a single point in the urethra.

URGE - The feeling of the need to urinate.

URGENCY - The symptom of sudden onset of a strong urge to urinate.

VASALVA - Bearing down to apply pressure to the bladder.

VOID - Urinate