theory of operation of cystometry

8/9/2019 Theory of Operation of Cystometry

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cyctometry

Introduction:

Cystometry is a test that measures the pressure inside of the bladder tosee how well the bladder is working. Cystometry is done when a muscleor nerve problem may be causing problems with how well the bladder holds or releases urine.

Urination is a complex process. As the bladder fills, nerves in the bladder wall send a message to the spinal cord and brain that you need to urinate.In response, your spinal cord sends a signal for the bladder to contract(voiding reflex). When you hold in your urine, your brain is overriding

this reflex. When you allow the reflex to occur, urination occurs. A problem affecting this nerve pathway or the muscles of the bladder wallcan cause bladder dysfunction.

During cystometry, your bladder is filled with water or gas to measure itsability to hold in and push out the water or gas. Medicine may also begiven to see whether your bladder contracts or relaxes normally inresponse to the medicine. A small tube (catheter) can be placed in your rectum to measure pressure as the bladder fills. A small pad or needlemay be placed near your anus to measure muscle function in this area.

Why it is done?Cystometry is done to:

Find the cause of problems with the bladder or the muscle that holdsurine in the bladder (bladder sphincter). Problems in one or both of theseareas may cause uncontrolled urine leakage, an urgent feeling that youhave to urinate, or a weak urine stream.

Measure how much urine your bladder can store and how much urine

remains in your bladder after you feel you have completely emptied it(residual volume.(

Help you and your doctor make decisions about how to treat your urinarysymptoms.

See how well the bladder works in people with progressive neurologicaldiseases, such as multiple sclerosis.

How it is done?


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Cystometry is done in a doctor's office or hospital urology department bya urologist , gynecologist , or other trained health professional.

You will need to take off most of your clothes below the waist. You will

be given a cloth or paper covering to use during the test.At the beginning of the test, you will be asked to urinate into a toilet thatis connected to a machine called a uroflowmeter . This machine measureshow much urine passes and how long it takes. The time and effort neededto start the flow of urine, the number of times you start and stop the flowof urine, and the presence of dribbling near the end of urinating are alsorecorded.

Next you will be asked to lie on your back on an examining table. After the urethra is thoroughly cleaned, a well-lubricated thin, flexible tube(catheter ) is gently inserted and slowly advanced into your bladder. Anyurine remaining in your bladder (residual volume) will be drained andmeasured.

Next, a catheter is used to fill your bladder with sterile, room-temperaturewater. The catheter is also attached to a device called a cystometer, whichmeasures how much your bladder can hold and the pressure in your

bladder. You will be asked to report any feelings such as warmth, bladder

fullness, or an urge to urinate. The process may be repeated.

Sometimes a gas (usuall ycarbon dioxide ) is used instead of water.

A contrast material may be used if X-rays are taken during the test.

Another catheter may be placed in your rectum to measure the pressure inyour abdomen as your bladder fills. A small pad or needle may be placednear your anus to measure muscle function in this area.

Each time your bladder is filled, you will be asked to report when youfirst feel the urge to urinate. Your bladder will then continue to be filleduntil you report that you feel you must urinate. Then the catheter will beused to drain the bladder, or you will be asked to urinate.

After all the liquid is drained out of your bladder, and if no additionaltests are required, the catheter is removed.

While the catheter is in place, other tests may also be done to help find out whether the nerves that control urination are working properly. These include:
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Ice water test. Ice-cold water is injected through the catheter into your bladder.

Bethanechol sensitivity test. Bethanechol is a medicine that normallymakes the bladder muscles contract. In this test, bethanechol will be injectedunder your skin . Bulbocavernosus reflex test. To test nerve function, a gloved finger isinserted into your rectum and then the penis or clitoris is gently squeezed. Saddle sensation test. The skin around your anus is stroked or lightly

pricked with a pin. Maximum urethral closure pressure (MUCP). Urethral pressure isrecorded as the catheter is gently pulled out of your urethra. This test helpsdetermine whether the muscles around the bladder and urethra are functioning

properly. Leak point pressure (LPP). Approximately 200ml of sterile water isinjected into the catheter in your bladder, and then the pressures are measuredwhile you bear down (as if having a bowel movement). This test helps find outwhether the muscles around the bladder and urethra are working properly. Alow pressure reading may mean that poor muscle function is causing urinaryincontinence .

Another test that may be done is the stress incontinence test. In thistest, your bladder is filled with water and the catheter is withdrawn.You are then asked to cough , bend over, or lift a heavy object.Dribbling urine indicates stress incontinence .

Cystometry testing usually takes 30 to 60 minutes, but it may takeslightly longer if any of the special tests are done.

After cystometry, you will need to keep track of how much you drink and how much you urinate for the next 24 hours. A burning sensationduring urination is a common but temporary side effect. Drinking lotsof fluids will help relieve this sensation. You may be given anantibiotic to help prevent a urinary tract infection.

How it feels?

You may feel embarrassed at having to urinate in front of other people, but you needn't be because this procedure is quite routine for the medical staff. If you find yourself feeling embarrassed, take deep,slow breaths and try to relax.

You will feel a strong urge to urinate at times during the test. You mayalso find it somewhat uncomfortable when the catheter is inserted andleft in place, and you may be sore afterward. If so, soaking in a warmtub bath may help.
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Risks:

Cystometry usually does not cause problems. There is always a slightrisk of developing a urinary tract infection when a catheter is inserted

into the bladder. In rare cases, a bladder infection can spread to akidney and into the blood, leading to a life-threatening infection. If aninfection occurs, it can be treated with antibiotics.

If you have a high spinal cord injury, you may have low heart rate,high blood pressure, headache , and feel flushed or sweaty during thetest. Report these symptoms to the health professional conducting thetest, since further testing may cause complications.

After the procedure:

You may have a small amount of blood in your urine for 1 to 2 days after the test. You also may feel that you need to urinate often or have a senseof urgency to urinate or have some burning on urination (especially if carbon dioxide gas was used). However, contact your doctor immediatelyif you have symptoms of a urinary tract infection. These symptomsinclude:

Pain or burning when you urinate. An urge to urinate frequently, but usually passing only smallquantities of urine. Dribbling or leaking urine. Urine that is reddish or pinkish, foul-smelling, or cloudy. Pain or a feeling of heaviness in the lower belly. Pain in the back just below the rib cage on one side of the

body (flank pain). Fever or chills. Nausea or vomiting.

Results:

Cystometry is a test that measures the pressure inside of the bladder tosee how well the bladder is working.

Some results may be available right away. Full results are usuallyavailable in 1 to 2 days.

normal :

The rate at which urine flows from your bladder when you urinate is normal.
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The point at which you first feel the urge to urinate is within the normal range, whenthe amount of liquid in your bladder is between 150ml and 200ml.

The maximum amount of liquid your bladder can hold is within the normal range:400ml to 500ml.

Tests of the function of the nerves that control your bladder are normal.

Urine does not leak from your bladder during the stress test .

abnormal :

The rate at which urine flows from your bladder when you urinate is slower thannormal.

You have trouble starting the flow of urine.

The point at which you first feel the urge to urinate is more or less than normal or does not occur.

The maximum amount of liquid your bladder can hold is less than normal or youcannot feel it.

Normal sensations and reactions do not occur when the nerves that control your

bladder are tested.

Urine leaks from your bladder during the stress test.

What affects the test?

Reasons you may not be able to have the test or why the results may not be helpfulinclude:

Having a urinary tract infection (UTI) . Cystometry should not be doneif you have a UTI. Straining when urinating. Not being able to urinate while sitting or lying down. Not being able to urinate in front of other people. Taking medicines, such as antihistamines and cough and coldmedicines, that interfere with your bladder function. Having surgery for a spinal cord injury within 6 to 8 weeks before thistest.

Cystometry
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Clinical Introduction

Cystometry is carried out to categorise the bladder. The main issue isthe stability of the detrusor. The normal bladder should be stable under

all conditions of filling or stress. The compliance of the bladder (

Vol / P) is also of interest as is its capacity and the patient's sensations of strength of desire to void. Two pressure Channels are typicallymeasured, rectal pressure and bladder(intravesical). The rectal pressureresponds to any changes of the abdominal cavity due to straining or stress. These can then be subtracted from the intravesical to give thetrue intrinsic bladder pressure from the detrusor muscle (detrusor pressure). Quality control is important during cystometry. The cancellation fromthe rectal catheter must be accurate. Click here for an example of perfect rectal cancellation

NB All the images in thiscolumn are clickable

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

The diagram shows an unstable bladder with lowcapacity. In such a case the height of thecontractions are of interest as they may exceedthe maximum urethral pressure leading toincontinence. The unstable bladder is a sign thatthe micturition reflex is triggered and the reflexlowers urethral pressure. For leakage to takeplace the detrusor pressure just has to exceedthis lowered urethral pressure. The patient in thediagram had a static urethral pressure of 100 cmwater when the bladder was stable. Thecontraction has almost reached this height, soleakage had almost certainly taken place.Patients with unstable bladders may also carrythe risk of urine refluxing up the ureters causingkidney damage. This would be tested for by x raycontrast cystometry. Although a large pressurerise has taken place, this type of bladder wouldnot be termed low compliance. This term isreserved for the stable bladder with a large

pressure rise.
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An example of a low compliance bladder isshown. Note how the pressure drops after fillingis stopped. This is termed accommodation. Thistype of behaviour is a consequence of theviscoelastic nature of the bladder. It has beenobserved for years using standard urodynamicstechniques and much debate has been had over what it means. Some would assert that the lowcompliance bladder is unstable. In ambulatoryurodynamics filling rates are physiological i.e. afew ml per minute instead of a few tens of ml.Bladders are never found to be low compliancewith ambulatory urodynamics. Low compliancebehaviour is a consequence of filling the bladder faster than it can accommodate. At present workstill needs to be done into this phenomenon.

The hyperreflexic detrusor is one which isunstable in the presence of confirmedneuropathy

Cystometry Instrumentation

Pressure measurements in the Bladder and Urethra

Pressure is measured with strain gauge transducers . In these thepressure sensitive elements form the arms of a Wheatstone bridge.Pressure raises the resistance of one arm and lowers the resistance of the other.

The pressure is typically conveyed to the sensors via fluidfilled lines. These lines will damp the pressure waveform, removing

high frequencies. In diagnostic cystometry, the characteristic pressures of interest - e.g. detrusor instability are low frequency. Some damping from the lines is acceptable. The transducers can be zeroed to atmospheric pressure bybalancing the bridge. For most urodynamic measurements a sampling rate of 30Hz is more than adequate. Although the transducer will satisfythis, care must be taken interpreting results from a fluid filledsystem as air in the lines can cause damping which isunacceptable. In cases where fast frequency response is required,catheter tip transducers are used - see ambulatory urodynamics .
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CystometryRectal cancellation working well

The rectal pressure responds to any changes of the abdominal cavitydue to straining or stress. These can then be subtracted from the intravesical to give the trueintrinsic bladder pressure from the detrusor muscle (detrusor pressure).

Quality control is important during cystometry. The cancellation fromthe rectal catheter must be accurate. The examples below shows severalartefacts on t he rectal and vesical traces all of which are completelyremoved from the detrusor pressure by subtraction.

This is a stable bladder. All the artefacts in these traces derive fromabdominal pressure. Unfortunately , the rectum "has a life of its own"and can generate its own pressures.


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Click here to seerectal cancellationworking badly

Click here to seerectal cancellationworking well but withsome rectal pressurecontractions whichcan confuse

CystometryBoth the images below show rectal cancellation working well but withconfusing rectal contractions
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Click here to seerectal cancellationworking well

Click here to seerectal cancellation

working badly

Click here to seerectal cancellationworkin

CystometryThe image below shows rectal cancellation working badly
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The two coughs in the middle of the trace are recorded very unfaithfullyon the rectal channel. Uaually this is a result of air in the system and is cured fairly easily byflushing the lines and transducer dome.

Click here to seerectal cancellationworking well

Click here to seerectal cancellationworking well but with

rectal contractions which can confuse

Click here to seerectal cancellationworking badly but withsufficient response tostill diagnose instability

Cystometry
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The image below shows rectal cancellation working badly but Detrusor Instability is still diagnosed

The three coughs in the first half of the trace are recorded veryunfaithfully on the rectal channel. Usually this is a result of air in the system and is cured fairly easily byflushing the lines and transducer dome. However, damping might only apply to high

frequencies. If the damped rectal is responding well to low frequenciessuch as bodliy movement might produce, there us no problem beingsure about the diagnosis of detrusor Instability based on the contractionat the right

Click here to see Click here to see Click here to see
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rectal cancellationworking well

rectal cancellationworking well but with

rectal contractions which can confuse

rectal cancellationworking badly
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theory of operation of cystometry

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