ICS
1999, Denver
Consensus reports - Standardisation
Committee Reports
The
Standardization of Terminology of Lower Urinary Tract Function Recommended by
the International Continence Society
P. Abrams,
J.G. Blaivas, S.L. Stanton and J.T. Andersen (Chairman)
ICS Committee on Standardization of Terminology
Copyright International Urogynecology Journal, Springer-Verlag London Limited,
UK and the International Continence Society. Reprinted with permission. Keywords:
Lower urinary tract function; Terminology; Definitions; Urinary incontinence;
Urodynamics
1 Introduction
The International Continence Society (ICS) established a committee for the standardization of terminology of lower urinary tract function in 1973. Five of the six reports from this committee, approved by the Society, have been published [1-5]. The fifth report, on quantification of urine loss, was an internal ICS document but appears, in part, in this document.
These reports are revised, extended and collated in this monograph. The standards are recommended to facilitate comparison of results by investigators who use urodynamics methods. These standards are recommended not only for urodynamic investigations carried out on human patients but also during animal studies. When using urodynamic studies in animals the type of any anesthesia used should be stated. It is suggested that acknowledgement of these standards in written publications be indicated by a footnote to the section 'Methods and Materials' or its equivalent, to read as follows: 'Methods, definitions and units conform to the standards recommended by the International Continence Society, except where specifically noted.'
Urodynamic studies involve the assessment of the function and dysfunction of the urinary tract by any appropriate method. Aspect of urinary tract morphology, physiology, biochemistry, and hydrodynamics affect urine transport and storage. Other methods of investigation such as the radiographic visualization of the lower urinary tract is a useful adjunct to conventional urodynamics. This monograph concerns the urodynamics of the lower urinary tract.
2 Clinical assessment
The clinical assessment of patients with lower urinary tract dysfunction should consist of a detailed history, a frequency/volume chart, and a physical examination. In urinary incontinence, leakage should be demonstrated objectively.
2.1 History
The general history should include questions relevant to neurological and congenital abnormalities as well as information on previous urinary infections and relevant surgery. Information must be obtained on medication with known or possible effects on the lower urinary tract. The general history should also include assessment of menstrual, sexual and bowel function, and obstetric history.
The urinary history must consist of symptoms related to both the storage and the evacuation functions of the lower urinary tract.
2.2 Frequency/Volume Chart
The frequency/volume chart is a specific urodynamic investigation recording fluid intake and urine output per 24-hour period. The chart gives objective information on the number of voidings, the distribution of voidings between daytime and nighttime and each voided volume. The chart can also be used to record episodes of urgency and leakage and the number of incontinence pads used. The frequency/volume chart is very useful in the assessment of voiding disorders, and in the follow-up of treatment.
2.3 Physical Examination
Besides a general urologic and, when appropriate, gynecologic examination, the physical examination should include the assessment of perineal sensation, the perineal reflexes supplied by the sacral segments S2-S4, and anal sphincter tone and control.
3 Procedures Related to the Evaluation of Urine Storage
3.1 Cystometry
Cystometry is the method by which the pressure/volume relationship of the bladder is measured. All systems are zeroed at atmospheric pressure. For external transducers the reference point is the level of the superior edge of the symphysis pubis. For catheter-mounted transducers the reference point is the transducer itself. Cystometry is used to assess detrusor activity, sensation, capacity, and compliance.
Before starting to fill the bladder the residual urine may be measured. However, the removal of a large volume of residual urine may alter detrusor function, especially in neuropathic disorders. Certain cystometric parameters may be significantly altered by the speed of bladder filling (see Compliance, 6.2.1).
During cystometry it is taken for granted that the patient is awake, unanesthetized and neither sedated nor taking drugs that affect bladder function. Any variations should be specified.
3.1.1. General Information. The following details should be given:
1. Access
(transurethral or percutaneous).
2. Fluid medium
(liquid or gas).
3. Temperature
of fluid (state in degrees Celsius).
4. Position of
patient (e.g., supine, sitting, or standing).
5. Filling method
- may be by diuresis or catheter. Filling by catheter may be continuous or incremental;
the precise filling rate should be stated. When the incremental method is used
the volume increment should be stated. For general discussion, the following
terms for the range of filling rate may be used:
a. Up
to 10ml/min is slow fill cystometry ('physiological' filling).
b. 10-100 ml/min is medium
fill cystometry.
c. Over 100 ml/min is rapid
fill cystometry.
3.1.2. Technical Information. The following details should be given:
1. Fluid-filled
catheter - specify number of catheters, single or multiple lumens, type of catheter
(manufacturer), size of catheter.
2. Catheter tip
transducer - list specifications.
3. Other catheters
- list specifications.
4. Measuring equipment.
3.1.3. Definitions. Cystometric terminology is defined as follows:
The term 'Capacity' must be qualified as follows:
Maximum cystometric capacity, in patients with normal sensation, is the volume at which the patient feels he/she can no longer delay micturition. In the absence of sensation the maximum cystometric capacity cannot be defined in the same terms and is the volume at which the clinician decides to terminate filling. In the presence of sphincter incompetence the maximum cystometric capacity may be significantly increased by occlusion of the urethra, e.g., by Foley catheter.
The functional bladder capacity, or voided volume, is more relevant and is assessed from a frequency/volume chart (urinary diary).
The maximum (anesthetic) bladder capacity is the volume measured after filling during a deep general or spinal / epidural anesthetic, specifying fluid temperature, filling pressure, and filling time.
Compliance indicates the change in volume for a change in pressure. Compliance is calculated by dividing the volume change ( V) by the change in detrusor pressure ( Pdet) during that change in bladder volume ( V/ Pdet). Compliance is expressed as milliliters per centimeters of water pressure. (See also Compliance, 6.2.1.)
3.2. Urethral Pressure Measurement
It should be noted that the urethral pressure and the urethral closure pressure are idealized concepts which represent the ability of the urethra to prevent leakage (see Urinary Incontinence, 6.2.3). In current uro-dynamic practice the urethral pressure is measured by a number of different techniques which do not always yield consistent values. Not only do the values differ with the method of measurement, but there is often lack of consistency for a single method; for example, the affect of catheter rotation when urethral pressure is measured by a catheter-mounted transducer.
Intraluminal urethral pressure may be measured:
At rest,
with the bladder at any given volume.
During coughing or
straining.
During the process
of voiding (see section on voiding urethral pressure profile, 4.4).
Measurements may be
made at one point in the urethra over a period of time, or at several points
along the urethra consecutively forming a urethral pressure profile (UPP).
Two types of UPP may be measured in the storage phase:
1. Resting
urethral pressure profile - with the bladder and subject at rest.
2. Stress
urethral pressure profile - with a defined applied stress (e.g., cough,
strain, valsalva).
In the storage phase the urethral pressure profile denotes the intraluminal pressure along the length of the urethra. All systems are zeroed at atmospheric pressure. For external transducers the reference point is the superior edge of the symphysis pubis. For catheter-mounted transducers the reference point is the transducer itself. Intravesical pressure should be measured to exclude a simultaneous detrusor contraction. The subtraction of intravesical pressure from urethral pressure produces the urethral closure pressure profile.
It is essential to record both intravesical and intraurethral pressures simultaneously during stress urethral profilometry.
3.2.1. General information. The following details should be given:
1. Infusion
medium (liquid or gas).
2. Rate of
infusion.
3. Stationery,
continuous, or intermittent withdrawal.
4. Rate of
withdrawal.
5. Bladder
volume.
6. Position
of patient (supine, sitting, or standing).
3.2.2. Technical Information. The following details should be given:
1. Open
catheter: Specify type (manufacturer), size, number, position, and orientation
of side or end hole.
2. Catheter-mounted
transducers: Specify manufacturer; number of transducers; spacing of transducers
along the catheter; orientation with respect to one another; transducer
design, e.g., transducer face depressed or flush with catheter surface;
catheter diameter; and material. The orientation of the transducer(s) in
the urethra should be stated.
3. Other catheters,
e.g., membrane, fiberoptic: Specify type (manufacturer), size, and number
of channels as for microtransducer catheter.
4. Measurement
technique: For stress profiles the particular stress employed should be
stated, e.g., cough or valsalva.
5. Recording
apparatus: Describe type of recording apparatus. The frequency response
of the total system should be stated. The frequency response of the total
system should be stated. The frequency response of the catheter in the perfusion
method can be assessed by blocking the eyeholes and recording the consequent
rate of change of pressure.
3.2.3. Definitions. Terminology referring to profiles measured in storage phase (see Fig. 1) is defined as follows:
3.3. Quantification of Urine Loss
Subjective grading of incontinence may not indicate reliably the degree of abnormality. However, it is important to relate the management of the individual patients to their complaints and personal circumstances, as well as to objective measurements.
In order to assess and compare the results of the treatment of different types of incontinence in different centers, a simple standard test can be used to measure urine loss objectively in any subject. In order to obtain a representative result, especially in subjects with variable or intermittent urinary incontinence, the test should occupy as long a period as possible; yet it must be practical. The circumstances should approximate to those of everyday life, yet be similar for all subjects to allow meaningful comparison. On the basis of pilot studies performed in various centers, an internal report of the ICS [6] recommended a test occupying a 1-hour period during which a series of standard activities was carried out. This test can be extended by further 1-hour periods if the result of the first 1-hour test were not considered representative by either the patient or the investigator. Alternatively, the test can be repeated, after filling the bladder to a defined volume.
The total amount of urine lost during the test period is determined by weighing a collecting device such as a nappy, absorbent pad, or condom appliance. A nappy or pad should be worn inside waterproof underpants or should have a waterproof backing. Care should be taken to use a collecting device of adequate capacity. Immediately before the test begins the collecting device is weighed to the nearest gram.
3.3.1. Typical Test Schedule:
1. Test
is started without the patient voiding.
2. Preweighed
collecting device is put on and first 1-hour test period begins.
3. Subject
drinks 500 ml sodium-free liquid within a short period (max. 15 min), then
sits or rests.
4. Half-hour
period: subject walks, including stair climbing equivalent to one flight
up and down.
5. During the
remaining period the subject performs the following activities:
a) Standing up from sitting,
10 times.
b) Coughing vigorously,
10 times.
c) Running on the spot
for 1 min.
d) Bending to pick up
small object from floor, 5 times.
e) Washing hands in running
water for 1 min.
6. At the end
of the 1-hour test the collecting device is removed and weighed.
7. If the test
is regarded as representative, the subject voids and the volume is recorded.
8. Otherwise
the test is repeated, preferably without voiding.
If the collecting device becomes saturated or filled during the test it should be removed and weighed, and replaced by a fresh device. The total weight of urine lost during the test period is taken to be equal to the gain in weight of the collecting device(s). In interpreting the results of the test it should be borne in mind that a weight gain of up to 1 g may be due to weighing errors, sweating, or vaginal discharge.
The activity program may be modified according to the subject's physical ability. If substantial variations from the usual test schedule occur, these should be recorded so that the same schedule can be used on subsequent occasions.
In principle the subject should not void during the test period. If the patient experiences urgency, then he / she should be persuaded to postpone voiding and to perform as many of the activities in section 5 as possible in order to detect leakage. Before voiding the collection device is removed for weighing. If voiding cannot be postponed, then the test is terminated. The voided volume and the duration of the test should be recorded. For subjects not completing the full test the results may require separate analysis, or the test may be repeated after rehydration.
The test result is given in grams urine lost in the 1-hour test period in which the greatest urine loss is recorded.
3.3.2. Additional Procedures. Provided that there is no interference with the basic test, additional procedures intended to give information of diagnostic value are permissible. For example, additional changes and weighing of the collecting device can give information about the timing or urine loss; the absorbent nappy may be an electronic recording nappy so that the timing is recorded directly.
3.3.3. Presentation of Results. The following details should be given:
1. Collecting
device.
2. Physical
condition of subject (ambulant, chairbound, bedridden).
3. Relevant
medical condition of subject.
4. Relevant
drug treatments.
5. Test schedule.
In some situations the timing of the test (e.g., in relation to the menstrual cycle) may be relevant.
Findings: A record should be made of the weight of urine lost during the test (in the case of repeated tests, greatest weight in any stated period). A loss of less than 1 g is within experimental error and the patient should be regarded as essentially dry. Urine loss should be measured and recorded in grams.
Statistics: When performing statistical analysis or urine loss in a group of subjects, nonparametric statistics should be employed, since the values are not normally distributed.
4 Procedures Related to the Evaluation of Micturition
4.1. Measurement of Urinary Flow
Urinary flow may be described in terms of rate and pattern and may be continuous or intermittent. Flow rate is defined as the volume of fluid expelled via the urethra per unit time. It is expressed in milliliters per second.
4.1.1. General Information. The following details should be given:
1. Voided
volume.
2. Patient environment
and position (supine, sitting, or standing).
3. Filling:
a) By diuresis (spontaneous
or forced: specify regimen).
b) By catheter (transurethral
or suprapubic).
4. Type of fluid.
4.1.2. Technical Information. The following details should be given:
1. Measuring
equipment
2. Solitary procedure
or combined with other measurements.
4.1.3. Definitions. The terminology referring to urinary flow is defined as follows:
1. Continuous flow (Fig. 2):
Voided
volume is the total volume expelled via the urethra.
Maximum flow rate is the
maximum measured value of the flow rate.
Average flow rate is voided volume divided by flow time. The calculation of average flow rate is only meaningful if flow is continuous and without terminal dribbling.
Flow time is the time over which measurable flow actually occurs.
Time to maximum flow is the elapsed time from onset of flow to maximum flow.
The flow pattern must be described when flow time and average flow rate are measured.
2. Intermittent Flow (Fig.3):
The same parameters used to characterize continuous flow may be applicable, if care is exercised, in patients with intermittent flow. In measuring flow time the time intervals between flow episodes are disregarded.
Voiding time is total duration of micturition, i.e., includes interruptions. When voiding is completed without interruption, voiding time is equal to flow time.
4.2. Bladder Pressure Measurements During Micturition
The specification of patient position, access for pressure measurement, catheter type, and measuring equipment are as for cystometry (see 3.1).
4.2.1. Definitions. The terminology referring to bladder-pressure during micturition is defined as follows (Fig. 4):
Opening time is the elapsed time from initial rise in detrusor pressure to onset of flow. This is the initial isovolumetric contraction period of micturition. Time lags should be taken into account. In most urodynamic systems a time lag occurs equal to the time taken for the urine to pass from the point of pressure measurement to the uroflow transducer.
The following parameters are applicable to measurements of each of the pressure curves - intravesical, abdominal, and detrusor pressure:
Premicturition pressure is the pressure recorded immediately before the initial isovolumetric contraction.
Opening pressure is the pressure recorded at the onset of measured flow.
Maximum pressure is the maximum value of the measured pressure.
Pressure at maximum flow is the pressure recorded at maximum measured flow rate.
Contraction pressure at maximum flow is the difference between pressure at maximum flow and premicturition pressure. Postmicturition events (e.g., after contraction) are not well understood and so cannot be defined as yet.
4.3. Pressure Flow Relationships
In the early days of urodynamics the flow rate and voiding pressure were related as a 'urethral resistance factor.' The concept of a resistance factor originates from rigid tube hydrodynamics. The urethra does not generally behave as a rigid tube; it is an irregular and distensible conduit and its walls and surroundings have active and passive elements which influence the flow through it. Therefore a resistance factor cannot provide a valid comparison between patients.
There are many ways of displaying the relationships between flow and pressure during micturition. An example is suggested in the third ICS report [3] (Fig. 5). As yet, available data do not permit a standard presentation of pressure/flow parameters.
When data from a group of patients are presented, pressure flow relationships may be shown on a graph, as illustrated in Fig. 5. This form of presentation allows lines of demarcation to be drawn on the graph to separate the results according to the problem being studied. The points shown in Fig. 5 are purely illustrative to indicate how the data might fall into groups. The group of equivocal results might include either an unrepresentative micturition in an obstructed or an unobstructed patient, or underactive detrusor function with or without obstruction. This is the group which invalidates the use of the term 'urethral resistance factors.'
4.4. Urethral Pressure Measurements During Voiding
The voiding urethral pressure profile (VUPP) is used to determine the pressure and site of urethral obstruction. Pressure is recorded in the urethra during voiding. The technique is similar to that used in the UPP measured during storage (the resting and stress profiles; see 3.2).
General and technical information should be recorded as for UPP during storage (see 3.2.).
Accurate interpretation of VUPP depends on the simultaneous measurement of intravesical pressure and the measurement of pressure at a precisely localized point in the urethra. Localization may be achieved by radiopaque marker on the catheter, which allows the pressure measurements to be related to a visualized point in the urethra. This technique is not fully developed, and a number of technical as well as clinical problems need to be solved before the VUPP is widely used.
4.5. Residual Urine
Residual urine is defined as the volume of fluid remaining in the bladder immediately following the completion of micturition. The measurement of residual urine forms and integral part of the study of micturition. However, voiding in unfamiliar surroundings may lead to unrepresentative results, as may voiding on command with a partially filled or overfilled bladder. Residual urine is commonly estimated by the following methods:
1. Catheter
or cystoscope (transurethral, suprapubic).
2. Radiography
(excretion urography, micturition cystography).
3. Ultrasonics.
4. Radioisotopes
(clearance, gamma camera).
When estimating residual urine the measurement of voided volume and the time interval between voiding and residual urine estimation should be recorded. This is particularly important if the patient is in a diuretic phase. In the condition of vesicoureteric reflux, urine may re-enter the bladder after micturition and may falsely be interpreted as residual urine. The presence of urine in bladder diverticula following micturition presents special problems of interpretation, since a diverticulum may be regarded either as part of the bladder cavity or as outside the functioning bladder.
The various methods of measurement each have limitations as to their applicability and accuracy in the various conditions associated with residual urine. Therefore it is necessary to choose a method appropriate to the clinical problems. The absence of residual urine is usually an observation of clinical value, but does not exclude infravesical obstruction or bladder dysfunction. An isolated finding of residual urine requires confirmation before being considered significant.
5 Procedures Related to Neurophysiological Evaluation of the Urinary Tract During Filling and Voiding
5.1. Electromyography
Electromyography (EMG) is the study of electrical potentials generated by the depolarization of muscle. The following refers to striated muscle EMG. The functional unit in EMG is the motor unit. This comprises a single motor neuron and the muscle fibers it innervates. A motor unit action potential is the recorded depolarization of muscle fibers which results from activation of a single anterior horn cell. Muscle action potentials may be detected either by needle electrodes or by surface electrodes.
Needle electrodes are placed directly into the muscle mass and permit visualization of the individual motor unit action potentials. Surface electrodes are applied to an epithelial surface as close to the muscle under study as possible. Surface electrodes detect the action potentials from groups of adjacent motor units underlying the recording surface.
EMG potentials may be displayed on an oscilloscope screen or played through audio amplifiers. A permanent record of EMG potentials can only be made using a chart recorder with a high-frequency response (in the range of 10 KHz).
EMG should be interpreted in the light of the patient's symptoms, physical findings, and urologic and urodynamic investigations.
5.1.1. General Information. The following details should be given:
1 EMG
(solitary procedure, part of urodynamic or other electro-physiological investigation).
2 Patient position
(supine, standing, sitting, or other).
3 Electrode placement:
a) Sampling site - intrinsic striated muscle of the urethra, periurethral striated muscle, bulbocavernosus muscle, external anal sphincter, pubococcygeus, or other. State whether sites are single or multiple, unilateral or bilateral. Also state number of samples per site.
b) Recording electrode - define the precise anatomical location of the electrode. For needle electrodes, include site of needle entry, angle of entry, and needle depth. For vaginal or urethral surface electrodes, state method of determining position of electrode.
c) Reference electrode position. Note: ensure that there is no electrical interference with any other machines, e.g., x-ray apparatus.
5.1.2. Technical Information. The following details should be given
1 Electrodes:
a) Needle electrodes
- design (concentric, bipolar, monopolar, single fiber, other); dimensions
(length, diameter, recording area); electrode material (e.g., platinum).
b) Surface electrodes
- type (skin, plug, catheter, other); size and shape; electrode material;
mode of fixation to recording surface; conducting medium (e.g., saline,
jelly).
2 Amplifier (make and specifications).
3 Signal processing (data: raw, averaged, integrated, or other).
4 Display equipment (make and specifications to include method of calibration,
time base, full scale deflection in microvolts and polarity):
a) Oscilloscope.
b) Chart recorder.
c) Loudspeaker.
d) Other.
5 Storage (make and specifications):
a) Paper.
b) Magnetic tape recorder.
c) Microprocessor.
d) Other.
6 Hard copy production (make and specifications):
a) Chart recorder.
b) Photographic / video
reproduction of oscilloscope screen.
c) Other.
5.2. EMG Findings
5.2.1. Individual motor unit action potentials. Normal motor unit potentials have a characteristic configuration, amplitude and duration. Abnormalities of the motor unit may include an increase in the amplitude, duration, and complexity of waveform (polyphasicity) of the potentials. A polyphasic potential is defined as one having more than five deflections. The EMG findings of fibrillations, positive sharp waves, and bizarre high-frequency potentials are thought to be abnormal.
5.2.2. Recruitment patterns. In normal subjects there is a gradual increase in 'pelvic floor' and 'sphincter' EMG activity during bladder filling. At the onset of micturition there is complete absence of activity. Any sphincter EMG activity during voiding is abnormal unless the patient is attempting to inhibit micturition. The finding of increased sphincter EMG activity during voiding, accompanied by characteristic simultaneous detrusor pressure and flow changes is described by the term 'detrusor-sphincter-dyssynergia.' In this condition a detrusor contraction occurs concurrently with an inappropriate contraction of the urethral and / or periurethral striated muscle.
5.3. Nerve Conduction Studies
Nerve conduction studies involve stimulation of a peripheral nerve and recording the time taken for a response to occur in muscle innervated by the nerve under study. The time taken from stimulation of the nerve to the response in the muscle is called the 'latency'. Motor latency is the time taken by the fastest motor fibers in the nerve to conduct impulses to the muscle and it depends on conduction distance and the conduction velocity of the fastest fibers.
5.3.1. General Information. Also applicable to reflex latencies and evoked potentials (see below). The following details should be given:
1 Type
of investigation:
a) Nerve conduction study
(e.g., pudendal nerve).
b) Reflex latency determination
(e.g., bulbocavernosus).
c) Spinal evoked potential.
d) Cortical evoked potential.
e) Other.
2 Is the study a solitary procedure or part of urodynamic or neurophysiological investigations?
3 Patient position and environmental temperature, noise level, and illumination.
4 Electrode
placement. Define electrode placement in precise anatomical terms. The exact
interelectrode distance is required for nerve conduction velocity calculations.
a) Stimulation site (penis,
clitoris, urethra, bladder neck, bladder, or other).
b) Recording sites (external
and sphincter, periurethral striated muscle, bulbocavernosus muscle, spinal
cord, cerebral cortex or other).
When
recording spinal evoked responses, the sites of the recording electrodes
should be specified according to the bony landmarks (e.g., L4). In cortical
evoked responses the sites of the recording electrodes should be specified
as in the international 10-20 system [6]. The sampling techniques should
be specified (single or multiple, unilateral or bilateral, ipsilateral or
contralateral, or other).
c) Reference electrode
position.
d) Grounding electrode
site. Ideally this should be between the stimulation and recording sites
to reduce stimulus artifact.
5.3.2. Technical Information. Also applicable to reflex latencies and evoked potentials (see 5.4). The following details should be given:
1 Electrodes
(make and specifications). Describe separately stimulus and recording electrodes
as below:
a) Design (e.g., needle,
plate, ring, and configuration of anode and cathode where applicable.
b) Dimensions.
c) Electrode material
(e.g., platinum).
d) Contact medium.
2 Stimulator
(make and specifications):
a) Stimulus parameters
(pulse width, frequency, pattern, current density, electrode impedance in
Kohms). Also define in terms of threshold (e.g., in case of supramaximal
stimulation).
3 Amplifier
(make and specifications):
a) Sensitivity (mV- æ
V).
b) Filters - low pass
(Hz) or high pass (kHz).
c) Sampling time (ms).
4 Averager
- make and specifications:
a) Number of stimuli
sampled.
5 Display
equipment (make and specifications to include method of calibration, time
base, full scale deflection in microvolts, and polarity):
a) Oscilloscope.
6 Storage
(make and specifications):
a) Paper.
b) Magnetic tape recorder.
c) Microprocessor.
d) Other.
7 Hard
copy production (make and specification):
a) Chart recorder.
b) Photographic / video
reproduction of oscilloscope screen.
c) XY recorder.
d) Other.
5.3.3. Description of Nerve Conduction Studies. Recordings are made from muscle, and the latency of response of the muscle is measured. The latency is taken as the time to onset of the earliest response.
To ensure that response time can be precisely measured, the gain should be increased to give a clearly defined take-off point (gain setting at least 100 æ V/div and using a short time base, e.g., 1-2ms/div).
Additional information may be obtained from nerve conduction studies, if, when using surface electrodes to record a compound muscle action potential, the amplitude is measured. The gain setting must be reduced so that the whole response is displayed and a longer time base is recommended (e.g., 1mV/div and 5 ms/div). Since the amplitude is proportional to the number of motor unit potentials within the vicinity of the recording electrodes, a reduction in amplitude indicates loss of motor units and therefore denervation. (Note: A prolongation of latency is not necessarily indicative of denervation.)
5.4. Reflex Latencies
Reflex latencies require stimulation of sensory fields and recordings from the muscle which contracts reflexly in response to the stimulation. Such responses are a test of reflex arcs, which comprise both afferent and efferent limbs and a synaptic region within the central nervous system. The reflex latency expresses the nerve conduction velocity in both limbs of the arc and the integrity of the central nervous system at the level of the synapse(s). Increased reflex latency may occur as a result of slowed afferent or efferent nerve conduction or due to central nervous system conduction delays.
5.4.1. General and Technical Information. The same technical and general details apply as discussed above under Nerve Conduction Studies.
5.4.2. Description of Reflex Latency Measurements. Recordings are made from muscle, and the latency of response of the muscle is measured. The latency is taken as the time to onset of the earliest response.
To ensure that response time can be precisely measured, the gain should be increased to give a clearly defined take-off point (gain setting at least 100 mV/div and using a short time base, e.g., 1-2 ms/div).
5.5 Evoked Responses
Evoked responses are potential changes in central nervous system neurons resulting from distant stimulation, usually electrical. They are recorded using averaging techniques. Evoked responses may be used to test the integrity of peripheral, spinal, and central nervous pathways. As with nerve conduction studies, the conduction time (latency) may be measured. In addition, information may be gained from the amplitude and configuration of these responses.
5.5.1. General and Technical Information. See under Nerve Conduction Studies (5.3).
5.5.2. Description of Evoked Responses. When describing the presence or absence of stimulus evoked responses and their configuration the following details should be given:
1. Single
or multiple response.
2. Onset of
response - defined as the start of the first reproducible potential. Since
the onset of the response may be difficult to ascertain precisely, the criteria
used should be stated.
3. Latency
to onset - defined as the time (in milliseconds) from the onset of stimulus
to the onset of response. The central conduction time relates to cortical
evoked potentials and is defined as the difference between the latencies
of the cortical and the spinal evoked potentials.
This parameter may be used to test the integrity of the corticospinal neuraxis.
4. Latencies
to peaks of positive and negative deflections in multiphasic response (Fig.
6). P denotes positive deflections. N denotes negative deflections. In multiphasic
responses, the peaks are numbered consecutively (e.g., P1, N1, P2, N2 ...)
or according to the latencies to peaks in milliseconds (e.g., P44, N52,
P66 ...)
5. The amplitude
of the responses is measured in microvolts.
5.6. Sensory
Testing
Limited information, of a subjective nature, may be obtained during cystometry by recording such parameters as the first desire to micturate, urgency, or pain. However, sensory function in the lower urinary tract can be assessed by semi-objective tests by the measurement of urethral and / or vesical sensory thresholds to a standard applied stimulus such as a known electrical current.
5.6.1. General
Information. The following details should be given:
1 Patient's
position (supine, sitting, standing, other).
2 Bladder volume
at time of testing.
3 Site of applied
stimulus (intravesical, intraurethral).
4 Number of
times the stimulus was applied and the response, e.g., the first sensation
or the sensation of pulsing.
5 Type of applied
stimulus:
a) Electrical current
- is usual to use a constant current stimulator in urethral sensory measurement.
State electrode characteristics and placement as in section on EMG (5.2);
electrode contact area and distance between electrodes if applicable; impedance
characteristics of the system; type of conductive medium used for electrode/epithelial
contact. Note: Topical anesthetic agents should not be used. Also state
stimulator make and specifications; and stimulation parameters (pulse width,
frequency, pattern, duration, current density).
b) Other (e.g., mechanical,
chemical).
5.6.2. Definition of Sensory Thresholds. The vesical / urethral sensory threshold is defined as the least current which consistently produces a sensation perceived by the subject during stimulation at the site under investigation. However, the absolute values will vary in relation to the site of the stimulus, the characteristics of the equipment, and the stimulation parameters. Normal values should be established for each system.
6. Classification of Lower Urinary Tract Dysfunction
The lower urinary tract is composed of the bladder and urethra. They form a functional unit and their interaction cannot be ignored. Each has two functions, the bladder to store and void, the urethra to control and convey. When a reference is made to the hydrodynamic function or the whole anatomical unit as a storage organ - the vesica urinaria - the correct term is the bladder. When the smooth muscle structure known as the m.detrusor urinae is being discussed, then the correct term is detrusor. For simplicity the bladder / detrusor and the urethra will be considered separately so that a classification based on a combination of functional anomalies can be reached. Sensation cannot be precisely evaluated but must be assessed. This classification depends on the results of various objective urodynamic investigations. A complete urodynamic assessment is not necessary in all patients. However, studies of the filling and voiding phases are essential for each patient. As the bladder and urethra may behave differently during the storage and micturition phases of bladder function it is most useful to examine bladder and urethral activity separately in each phase.
Terms used should be objective and definable, and ideally should be applicable to the whole range of abnormality. When authors disagree with the classification presented below, or use terms which have not been defined here, they should ensure that the meaning of their terminology is made clear.
Assuming the absence of inflammation, infection, and neoplasm, lower urinary tract dysfunction may be caused by:
1 Disturbance
of the pertinent nervous or psychological control system.
2 Disorders
of muscle function.
3 Structural
abnormalities.
Urodynamic diagnoses based on this classification should correlate with the patient's symptoms and signs. For example, the presence of an unstable contraction in an asymptomatic continent patient does not warrant a diagnosis of detrusor overactivity during storage.
6.1. The Storage Phase
6.1.1. Bladder
Function During Storage. This may be described according to:
Detrusor activity
Bladder sensation
Bladder capacity
Compliance
6.1.2. Detrusor activity. In this context detrusor activity is interpreted from the measurement of detrusor pressure (Pdet). Detrusor activity may be:
Normal
Overactive
In normal detrusor function the bladder volume increases during the filling phase without a significant rise in pressure (accommodation). No involuntary contractions occur despite provocation. A normal detrusor so defined may be described as 'stable'.
Overactive detrusor function is characterised by involuntary detrusor contractions during the filling phase, which may be spontaneous or provoked and which the patient cannot completely suppress. Involuntary detrusor contractions may be provoked by rapid filling, alterations of posture, coughing, walking, jumping, and other triggering procedures. Various terms have been used to describe these features and they are defined as follows:
The unstable detrusor is one that is shown objectively to contract, spontaneously or on provocation, during the filling phase while the patient is attempting to inhibit micturition. Unstable detrusor contractions may be asymptomatic or may be interpreted as a normal desire to void. The presence of these contractions does not necessarily imply a neurologic disorder. Unstable contractions are usually phasic in type (Fig. 7a). A gradual increase in detrusor pressure without subsequent decrease is best regarded as a change of compliance (Fig. 7b).
Detrusor hyperreflexia is defined as overactivity due to disturbance of the nervous control mechanisms. The term 'detrusor hyperreflexia' should only be used when there is objective evidence of a relevant neurologic disorder. The use of conceptual and undefined terms such as 'hypertonic,' 'systolic,' 'uninhibited,' 'spastic,' and 'automatic' should be avoided.
6.1.3. Bladder sensation. During filling bladder sensation can be classified in qualitative terms (see Cystometry, 3.1.) and be objective measurement (see Sensory Testing, 5.6.). Sensation can be classified broadly as follows:
Normal
Increased (hypersensitive)
Reduced (hyposensitive)
Absent
6.2. Bladder capacity. (See Cystometry, 3.1.)
6.2.1. Compliance. This is defined as: D V/ D P (see Cystometry, 3.1.) compliance may change during the cystometric examination and is variably dependent upon a number of factors including:
1 Rate
of filling.
2 The part
of the cystometrogram curve used for compliance calculation.
3 The volume
interval over which compliance is calculated.
4 The geometry
(shape) of the bladder.
5 The thickness
of the bladder wall.
6 The mechanical
properties of the bladder wall.
7 The contractile/relaxant
properties of the detrusor.
During normal bladder filling little or no pressure change occurs and this is termed 'normal compliance'. However, at present there is insufficient data to define normal, high and low compliance.
When reporting compliance, specify:
1 The
rate of bladder filling.
2 The bladder
volume at which compliance is calculated.
3 The volume
increment over which compliance is calculated.
4 The part
of the cystometrogram curve used for the calculation of compliance.
6.2.2. Urethral Function During Storage. The urethral closure mechanism during storage may be:
Normal
Incompetent
The normal urethral closure mechanism maintains a positive urethral closure pressure during filling even in the presence of increased abdominal pressure. Immediately prior to micturition the normal closure pressure decreases to allow flow.
An incompetent urethral closure mechanism is defined as one which allows leakage or urine in the absence of a detrusor contraction. Leakage may occur whenever intravesical pressure exceeds intraurethral pressure (genuine stress incontinence) or when there is an involuntary fall in urethral pressure. Terms such as 'the unstable urethra' await further data and precise definition.
6.2.3. Urinary Incontinence. This is defined as involuntary loss of urine which is objectively demonstrable and a social or hygienic problem. Loss of urine through channels other than the urethra is extraurethral incontinence.
Urinary incontinence denotes:
1 A
symptom.
2 A sign.
3 A condition.
The symptom indicates the patient's statement of involuntary urine loss, the sign is the objective demonstration of urine loss, and the condition is the urodynamic demonstration of urine loss.
6.2.4. Symptoms. These can be defined as follows:
Urge incontinence - the involuntary loss of urine associated with a strong desire to void (urgency). Urgency may be associated with two types of dysfunction:
Overactive detrusor function (motor urgency)
Hypersensitivity (sensory urgency)
Stress incontinence - the symptom indicates the patient's statement of involuntary loss of urine during physical exertion.
'Unconscious' incontinence - incontinence may occur in the absence of urge and without conscious recognition of the urinary loss.
Enuresis - any involuntary loss of urine. If the term is used to denote incontinence during sleep, it should always be qualified with the adjective 'nocturnal'.
Post micturition dribble and continuous leakage - denote other symptomatic forms of incontinence.
6.2.5. Signs. The sign stress incontinence denotes the observation of loss of urine from the urethra synchronous with physical exertion (e.g., coughing). Incontinence may also be observed without physical exercise. Post-micturition dribble and continuous leakage denote other signs of incontinence. Symptoms and signs alone may not disclose the cause of urinary incontinence. Accurate diagnosis often requires urodynamic investigation in addition to careful history and physical examination.
6.2.6. Conditions. These can be defined as follows:
Genuine stress incontinence - the involuntary loss of urine occurring when, in the absence of a detrusor contraction, the intravesical pressure exceeds the maximum urethral pressure.
Reflex incontinence - loss of urine due to detrusor hyperreflexia and/or involuntary urethral relaxation in the absence of the sensation usually associated with the desire to micturate. This condition is only seen in patients with neuropathic bladder/urethral disorders.
Overflow incontinence - any involuntary loss of urine associated with overdistension of the bladder.
6.3. The Voiding Phase
6.3.1. The Detrusor During Voiding. During micturition the detrusor may be:
Acontractile
Underactive
Normal
The acontractile detrusor is one that cannot be demonstrated to contract during urodynamic studies. Detrusor areflexia is defined as acontractility due to an abnormality of nervous control and denotes the complete absence of centrally coordinated contraction. In detrusor areflexia due to a lesion of the conus medullaris or sacral nerve outflow, the detrusor should be described as decentralized - not denervated, since the peripheral neurons remain. In such bladders pressure fluctuations of low amplitude, sometimes known as 'autonomous' waves, may occasionally occur. The use of terms such as 'atonic,' 'hypotonic,' 'autonomic,' and 'flaccid' should be avoided.
Detrusor underactivity is defined as a detrusor contraction of inadequate magnitude and/or duration to effect bladder emptying with a normal time span. The term should be reserved as an expression describing detrusor activity during micturition. Patients may have underactivity during micturition and detrusor overactivity during filling.
Normal detrusor contractility. Normal voiding is achieved by a voluntarily initiated detrusor contraction that is sustained and can usually be suppressed voluntarily. A normal detrusor contraction will effect complete bladder emptying in the absence of obstruction. For a given detrusor contraction, the magnitude of the recorded pressure rise will depend on the degree of outlet resistance.
Urethral Function During Micturition. During voiding urethral function may be:
Normal
Obstructive
overactivity
mechanical
Normal. The normal
urethra opens to allow the bladder to be emptied.
Obstruction. This occurs when the urethral closure mechanism contracts against a detrusor contraction or fails to open at attempted micturition. Synchronous detrusor and urethral contraction is detrusor/urethral dyssynergia. This diagnosis should be qualified by stating the location and type of the urethral muscles (striated or smooth) which are involved. Despite the confusion surrounding 'sphincter' terminology, the use of certain terms is so widespread that they are retained and defined here. The term detrusor/external sphincter dyssynergia or detrusor-sphincter-dyssynergia (DSD) describes a detrusor contraction concurrent with an involuntary contraction of the urethral and/or periurethral striated muscle. In the adult, detrusor sphincter dyssynergia is a feature of neurologic voiding disorders. In the absence of neurologic features the validity of this diagnosis should be questioned. The term detrusor/bladder neck dyssynergia is used to denote a detrusor contraction concurrent with an objectively demonstrated failure of bladder neck opening. No parallel term has been elaborated for possible detrusor/distal urethral (smooth muscle) dyssynergia.
Overactivity of the striated urethral sphincter may occur in the absence of detrusor contraction, and may prevent voiding. This is not detrusor/sphincter dyssynergia.
Overactivity of the urethral sphincter may occur during voiding in the absence of neurologic disease and is termed dysfunctional voiding. The use of terms such as 'non-neurogenic' and 'occult neuropathic' should be avoided.
Mechanical obstruction. This is most commonly anatomical, e.g., caused by urethral stricture.
Summary
Using the characteristics of detrusor and urethral function during storage and micturition and accurate definition of lower urinary tract behaviour in each patient becomes possible.
7 Units of Measurement
In the urodynamic literature pressure is measured in centimeters of water pressure and not in millimeters of mercury. When Laplace's law is used to calculate tension in the bladder wall, it is often found that pressure is then measured in dyne/cm2. This lack of uniformity in the systems used leads to confusion when other parameters, which are a function of pressure, are computed - for instance, 'compliance', contraction force, velocity, etc. From these few examples it is evident that standardization is essential for meaningful communication. Many journals now require that the results be given in SI Units. This section is designed to give guidance in the application of the SI system to urodynamics and defines the units involved. The principal units to be used are listed in Table 1.
Table 1.. Recommended units of measurement
Quantity Acceptable
unit Symbol aThe SI
Unit is the pascal (Pa), but it is only practical at present to calibrate our
instruments in cmH2O. One centimeter of water pressure is approximately
equal to 100 pascals (1cmH2O=98.07Pa=0.098 kPa). Table 2.
List of symbols
Volume milliliter ml
Time second s
Flow rate milliliters/second ml/s
Pressure centimeters
of watera H2O
Length meters
of submultiples m, cm, mm
Velocity meters/second
or submultiples m/s, cm/s
Temperature degrees
Celsius ºC
Basic symbols Urologic
qualifiers Value
Pressure P Bladder ves Maximum max
Volume V Urethra ura Minimum min
Flow rate Q Ureter ure Average ave
Velocity v Detrusor det Isovolumetric isv
Time t Abdomen abd Isotonic ist
Temperature T External
Isobaric isb
Stream ext Isometric ism
Length l
Area A
Diameter d
Force F
Energy E
Power P
Compliance C
Work W
Energy per
unit volume e
Pdet/max = maximum
detrusor pressure
eext = kinetic
energy per unit volume in the external stream
8 Symbols
It is often helpful to use symbols in a communication. The system in Table 2 has been devised to standardise a code of symbols for use in urodynamics. The rationale of the system is to have a basic symbol representing the physical quantity with qualifying subscripts. The list of basic symbols largely conforms to international usage. The qualifying subscripts relate to the basic symbols for commonly used urodynamic parameters.
References
1. Bates P, Bradley WE, Glen E et al. First report on the standardisation of terminology of lower urinary tract function. Urinary incontinence. Procedures related to the evaluation of urine storage - cystometry, urethral closure pressure profile, units of measurement.
Br J Urol 1976; 48:39-42; Eur Urol 1976; 2:274-276; Scand J Urol Nephrol 1976; 11:193-196; Urol Int 1976; 2:81-87
2. Bates P, Glen E, Griffiths D et al. Second report on the standardisation of terminology of lower urinary tract function. Procedures related to the evaluation of micturition - flow rate, pressure measurement, symbols. Acta Urol Jpn 1977; 27:1563-1566; Br J Urol 1977; 49:207-210; Eur Urol 1977; 3:168-170; Scand J Urol Nephrol 1977; 11:197-199
3. Bates P, Bradley WE, Glen E et al. Third report on the standardization of terminology of lower urinary tract function. Procedures related to the evaluation of micturition: pressure flow relationships, residual urine. Br J Urol 1980; 52:348-350; Eur Urol 1980; 6:170-171; Acta Urol Jpn 1980; 27:1566-1568; Scand J Urol Nephrol 1980; 12:191-193
4. Bates P, Bradley WE, Glen E et al. Fourth report on the standardization of terminology of lower urinary tract function. Terminology related to neuromuscular dysfunction of lower urinary tract. Br J Urol 1981; 53:333-335; Urology 1981; 17:618-620; Scand J Urol Nephrol 1981; 15:169-171; Acta Urol Jpn 1981; 27:1568-1571
5. Abrams P, Blaivas JG, Stanton SL et al. Sixth report on the standardization of terminology of lower urinary tract function. Procedures related to neurophysiological investigations. Electromyography, nerve conduction studies, reflex latencies, evoked potentials and sensory testing. World J Urol 1986; 4:2-5; Scand J Urol Nephrol 1986; 20:161-164; Br J Urol; 59:300-307
6. Jasper HH. Report to the committee on the methods of clinical examination in electroencephalography. Electroencephalogr Clin Neurophysiol 1958; 10:370-375