Ch62 UDS

• ● To reproduce the patient’s symptomatic complaints during urodynamics, and
• ● To provide a pathophysiological explanation by correlating the patient’s symptoms with the urodynamic findings

• 1. To identify or rule out factors contributing to lower urinary tract dysfunction (e.g., urinary incontinence) and assess their relative importance
• 2. To obtain information about other aspects of lower urinary tract function or dysfunction
• 3. To predict the consequences of lower urinary tract dysfunction on the upper urinary tract
• 4. To predict the outcome including undesirable side effects of a contemplated treatment
• 5. To confirm the effects of intervention or understand the mode of action of a particular type of treatment (especially a new one)6. To understand the reasons for failure of previous treatments for symptoms (e.g., urinary incontinence)or for lower urinary tract function in general.

• ● Maximum flow rate (Qmax) is the maximum measured value of the flow rate.
• ● Voided volume (VV) is the total volume expelled via the urethra.
• ● Flow time is the time over which measurable flow occurs
• ● Average flow rate (Qave) is voided volume divided by flow time.
• ● Time to maximum flow is the elapsed time from onset of flow to maximum flow.
• ● Intermittent flow

• 1. using the weight transducer (a)
• 2. spinning disc (b) and
• 3. capacitance methods (c).

• Bell shaped
• Maximum flow is reached in the first 30% of any trace and within 5 seconds from the start of flow.
• The flow rate varies according to the volume voided
• The final phase of a normal flow trace shows a rapid fall from high flow, together with a sharp cutoff at the termination of flow

Flow rates are highest and most predictable in the volume range between 200 ml and 400 ml. Through this range the maximum flow tends to be constant

Normally detrusor pressure should remain near zero during the entire filling cycle until voluntary voiding is initiated. That means baseline pressure stays constant (and low) and there are no involuntary contractions.

As mentioned previously, the simultaneous measurement of Pabd, usually by a rectal or vaginal catheter, and Pves during urodynamics provides a means of calculating the true Pdet. The ability to calculate subtracted Pdet allows one to distinguishbetween a true rise in detrusor pressure (eithervia a contraction or loss of compliance) and the effectof increased abdominal pressure (e.g., straining, Valsalva).This is especially important when rises in detrusor pressure aresmall or when they are accompanied by changes in abdominalpressure.

• Supranormal flow is established almost immediately and cessation of flow is equally rapid as the bladder neck closes suddenly. 
• In this and subsequent figures the height of the calibration mark indicates 10 ml/s flow rate and the width of the mark is 2 s.
• 

• Plateau shaped curve - Maximum flow is established soon after the onset of voiding
• 

• Maximum flow is established near the middle of the voiding time.
• 

• Straining makes the flow trace irregular.With straining the changes in flow tend to be relatively slow and the stream is usually continuous. Straining flow traces are very variable in appearance. 
• 

This abnormality is generally seen in patients with a neurological problem, most commonly multiple sclerosis.The detrusor contraction, instead of producing an approximately constant pressure throughout voiding, fluctuates. This produces either a continuous but varying flow or,more commonly, an interrupted flow.

• Detrusor Overactivity, and 
• Impaired Compliance

Detrusor overactivity (DO) is a urodynamic observation characterized by Involuntary detrussor contractions (IDCs) during the filling phase,which may be spontaneous or provoked.

• Neurogenic DO - associated with a relevant neurologic condition(e.g., spinal cord injury, multiple sclerosis) or
• Idiopathic DO - there is “no defined cause”

Compliance is the relationship between change in bladder volume and change in detrusor pressure (Δ volume/Δ pressure) and is measured in mL/cm H2O.

Mean values for compliance in healthy subjects range from 46 to 124 mL/cm H2O. 

In practical terms, absolute pressure is probably more useful than a “compliance number” or value. For example, it has been shown that storage greater than 40 cm H2O is associated with harmful effects on the upper tracts. Also, depending on the clinical scenario, a particular compliance in terms of mL/cm H2O can mean different things. As a general rule, prolonged storage at high pressures can lead to upper tract deterioration.

• ALPP and DLPP, although both called “leak point pressure,” are completely different.
• The ALPP measures the sphincter response to increased abdominal pressure. 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., detrusor-external sphincter dyssynergia), the higher the DLPP, which is potentially dangerous to the upper tracts.

It is defined as the lowest detrusor pressure at which urine leakage occurs in the absence of either a detrusor contraction or increased abdominal pressure.

DLPP > 40 cm H2O result in hydronephrosis or vesicoureteral reflux in 85% of myelodysplastic patients.

ICS - International continence society

According to the ICS, normal detrusor function is characterized by a voluntarily initiated continuous contraction that leads to complete bladder emptying within anormal time span, and in the absence of obstruction.

Detrusor underactivity is defined as 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.Finally, an acontractile detrusor is when there is no demonstrable contraction during UDS.

High-pressure and low-flow voiding

BOOI = PdetQmax− 2(Qmax).

• Obstructed - >40
• Unobstructed - <20, and
• Equivocal -  20 to 40.

BCI = PdetQmax + 5(Qmax)

• Strong contractility - >150
• Normal contractility - 100 to 150, and
• Weak contractilitya - <100

The following urodynamics findings are potentially dangerous and usually require intervention to prevent upper and lower urinary tract decompensation:

• Detrusor-external sphincter dyssynergia
• Detrusor-internal sphincter dyssynergia
• High-pressure detrusor overactivity present throughout filling
• Elevated detrusor leak point pressure (>40 cm H2O)
• Poor emptying with high storage pressures
• Impaired compliance

pdet = pves – pabd

• The pressure changes seen on the pves trace of Fig. 3.26 allow simple rules to be devised:
• ● If a pressure change is seen in both pves and pabd but not in pdet then it is due to raised abdominal pressure (event S).
• ● If a pressure change is seen on pves and pdet but not on pabd then it is due to a detrusor contraction (event U).
• ● If a pressure change is seen on pves pabd and pdet then there is both a detrusor contraction and increased abdominal pressure (event C + U).
• ● If a pressure change is seen on pabd with no change in pves and a consequent fall in pdet then this due to a rectal contraction

• Cystometry trace showing the patient straining (S), a cough superimposed on an involuntary detrusor contraction (C + U) and an involuntary detrusor
• contraction (U).

• A convenient rate, which does not prolong the test unduly,is 50 ml/min to 60 ml/min. In children and patients with neurological abnormalities, and in particular patients with detrusor overactivity secondary to spinal trauma, the bladder should be filled very slowly (less than 10 ml/min) because faster flow rates may produce artefactual low compliance. 
• The fastest physiological urine production for any individual can be calculated by dividing the body weight (in KG) by four (e.g., 20 ml/min for an 80-KG man).

Prior to catheterisation the patient is asked to empty the bladder as fully as possible. If thepatient self-catheterises, then the patient is asked to do this before urodynamics commencesand to empty the bladder.However if the patient has neurological disease and does not selfcatheterise,the bladder should not be emptied. In these patients, the post-void residual(PVR) can be measured by passing a catheter after the voiding phase of urodynamic studies.If a patient without neurological abnormalities has evidence of hydronephrosis, whichcould be secondary to elevated bladder pressure, the bladder should not be drained at thebeginning of the filling phase of urodynamic studies. Removing the PVR and/or filling tooquickly can fundamentally change the results, particularly in respect of bladder compliance,detrusor overactivity and cystometric capacity. In patients with neurological disease and/orupper tract dilatation, the artefacts of low compliance and reduced capacity are likely to beproduced if the standard technique is used

This means there should be a continuous dialogue between the investigator and the patient throughout the investigation. It is particularly important when assessing the sensations the patient experiences during cystometry.

• During bladder filling the following should be assessed:
• ● Bladder sensation
• ● Detrusor activity
• ● Bladder compliance
• ● Urethral function
• ● Bladder capacity

• Certain terms have been accepted, but it should be emphasised that relating a precise bladder volume to one of them is subjective and is likely to vary considerably. These terms are:
• ● First sensation of filling (FSF). This sensation is often difficult to interpret duringcystometry because the mere presence of the urethral catheter is often interpreted as adesire to void. It occurs at approximately 50% of cystometric capacity.
• ● Normal desire to void (NDV). This is defined as the feeling that leads the patient to passurine at the next convenient moment, but voiding can be delayed if necessary. It is felt atabout 75% of cystometric capacity.
• ● Strong desire to void (SDV). This is defined as a persistent desire to void without the fearof leakage. It is felt at approximately 90% capacity.
• ● Urgency. This is defined as a sudden compelling persistent desire to void which isdifficult to defer (ICS 2002).
• ● Pain. The site and character should be specified. Pain during bladder filling or micturitionis abnormal.

Sensation can be said to be abnormal if it is one of the following:

• ● Increased (hypersensitive). Bladder hypersensitivity is a term we have used and founduseful.We define it as the condition of a bladder in which there is an early first sensationof filling (FSF) at less than 100 ml which, instead of passing away until the normal desireto void (NDV) occurs, persists and increases, limiting the cystometric capacity to lessthan 250 ml.
• ● Reduced. Reduced sensation is characterised by a later FSF and NDV, with the patientnever experiencing a strong desire to void (SDV) or urgency.
• ● Absent. Absent sensation necessitates the patient passing urine “by the clock” and isusually indicative of a neurological condition such as spinal cord trauma ormeningomyelocele.

The normal detrusor remains quiescent during filling and detrusor overactivity does notoccur under any circumstances (e.g., during the provocation tests used in an effort touncover detrusor overactivity (DO)). In normal function the detrusor relaxes and stretchesto allow the bladder to increase in size without any change in pressure (accommodation)(Fig. 3.49). This ability is essential for two reasons. The first is to allow normal urine transportfrom the kidneys; ureteric muscle is relatively weak, being capable of generating amaximum pressure of approximately 30 cmH2O. The second is that increased bladder pressuresduring filling would be likely to compromise continence.

The overactive detrusor is one that is shown objectively to contract spontaneously or on provocation, during the filling phase. The overactive detrusor may be asymptomatic, and its presence does not necessarily imply a neurological disorder. Idiopathic DO is the commonest form of detrusor overactivity.

If an involuntary contraction has occurred but the patient either is unaware of the contraction or feels the contraction as a normal desire to void, then the DO is probably not clinically significant.

This can be classified as follows:

• ● Normal when the detrusor contracts to empty the bladder with a normal flow rate
• ● Underactive when either the detrusor contraction is unable to empty the bladder or thebladder empties at a lower than normal speed 
• ● Acontractile when no measured detrusor pressure change occurs during voiding