ICS‐SUFU standard: Theory, terms, and recommendations for pressure‐flow studies performance, analysis, and reporting. Part 1: Background theory and practice

The working group (WG) initiated by the International Continence Society Standardization Steering Committee and supported by the Society of Urodynamics, Female Pelvic Medicine and Urogenital Reconstruction has revised the (1997) ICS Standard for pressure flow studies.

recommends the term pressure-flow study 1 continue to be applied to the simultaneous recording of detrusor pressure, voided volume, and continuous voiding flow rate (voided volume differentiated with respect to time) using computerized technology.The abbreviation PFS, commonly used, is appropriate, therefore the terms PFS, PFS-graph, and PFS-analysis will be understood to indicate the conduct, reporting, and interpretation of the study.Time-based graph-analysis of a PFS voiding (pressure and uroflow rate vs. time) is reintroduced along with a (renewed) preferred ICS-PFS-plot (based on the ICS-ST97 X-Y graph 1 (see Figure 1) and explained in Part 2 for PFS-analysis.The WG continues using the word plot for the X-Y projection of pressure and flow 1 and recommends the word graph for the time-based projection.Terms and parameters specific to PFS-analysis are introduced and renewed.
The ICS-PFS22 includes clinical background and recommendations for the clinical conduct of PFS and, in the second part, recommendations for the systematic analysis of the technical quality of the test and the systematic reporting of the results.These last elements are a specific follow-up to the ICS-GUP16 but are also based on earlier ICS-terminology. 4,5ecent ICS documents 6 have discussed terms around patient perceived signs and symptoms of lower urinary tract dysfunction (LUTD) but have also included urodynamic terms.In this ICS-PFS22 document, earlier terminological imprecision regarding urodynamic studies (UDS) and pathophysiology will be corrected to ensure accurate background to the practice recommendations.
As measures of physiologic performance, uroflowmetry, (filling) cystometry, and PFS as objective indicators of hydrodynamic performance are analogous to anatomic imaging as representative for anatomical appearance.The analogy incudes also the application of statistical principles as applied in laboratory testing in objectively delineating normal from pathology.Deviations from normal anatomy on imaging are facts and deviations from normal physiology are (medical) facts also.Symptoms are the patient's report of a perception of a dysfunction and of undisputed relevance, but symptoms and how they are presented can have diverse and multiple origins.They are rarely pathognomonic of specific (patho-) physiology or (abnormal-) anatomy (or biochemistry) and diagnostic assessment may unveil unexpected results.Symptoms bear a loose correlation with UDS performance, but expert interpretation of a well-considered and conducted physiologic study is certainly valuable in explaining the signs and symptoms that the patient has expressed.This is true for cystometry and also true for PFS-analysis.Specific for PFS: the patient's experience of voiding (with or without difficulty) does not fully predict the pressure-flow regimen discovered at PFS-analysis and or the voiding efficacy.An objective grading of (dys)function is useful to put the patient's symptoms in the appropriate perspective to the expressed lower urinary tract (LUT) (dys)functions.
As for every clinical test, reliability, repeatability, representativeness, and clinical relevance are crucial to (flowrate, cystometry and) PFS analysis and interpretation.This ICS-PFS22 document discusses and makes recommendations about quality control, interpretation, and reporting of PFS, with the intention to optimize, but not determine, UDS diagnoses and or its consequences.As in every reliably performed clinical test, laboratory test, or imaging procedure, (cystometry and) PFS can also lead to clinically false positive (or irrelevant) and false negative results or can include artefacts.
The WG does not conclude or recommend in general, about the relevance and management of asymptomatic dysfunctions.The WG has not considered PFS in patients with relevant neurologic abnormalities and is not recommending for these.
The clinical management shall, as is good practice, never be based on just one parameter or an isolated UDS result, but always integrate patient history, bother, comedication, comorbidity, and accessory (objective) assessments along with the UDS diagnoses.On the other hand, after UDS, the diagnosis should only, but completely, report objectively assessed UDS related physiologic observations and parameters including a judgment of the patient's ability to cooperate and to report sensations. 2 F I G U R E 1 (Adapted form ref 1 ): PFS-graph and PFS-plots.The dotted line represents the urethral resistance relation; the pressure with corresponding flowrate during the entire voiding.In all graphs: flow begins at 1 and continues to 2, which is Q max and continues further to 3; end of voiding.The phase between 1 and 2 is the outlet distension phase; detrusor (or intravesical) pressure opens the outflow tract.Point 2 is Q max representing the maximum opening of the outflow tract and between 2 and 3 is the (elastic) collapse phase.Urethral resistance is measured through analysis of this phase (between 2 and 3) representing the lower pressure border of the urethral resistance relation.ST97 has presented the PFS plot with flowrate on the X-axis.This standard has recommended the projection with pressure on the X-axis is preferable.See part 2 of this standard for further explanations and details of analysis.PFS, pressure-flow studies.
The LUT has two but closely interrelated functional states, storage, and voiding, therefore the analysis of the voiding function should therefore also always be integrated with the analysis of the storage function (with the assessment of sensation).While focusing only on assessment of voiding, this document also augments the ICS-GUP16 recommendation that the UDS report should provide a complete and objective description of the testing and reporting should address all elements of LUT functioning, including sensation, and the dysfunctions measured and observed in every patient. 2,5ecause PFS with analysis applies only to the voiding phase of the LUT function a defined UDS demarcation between voiding and storage is necessary.7][8] In the absence of validated objective markers of the brainstem switching between storage to voiding states and back, the ICS-GUP16, 2 continued earlier definitions 4,5 that voiding, and consequently PFS begins with permission to void.Urine loss or voiding without permission to void is thus (also earlier) defined 5 as urinary incontinence and this WG keeps this dichotomy.The WG acknowledges however that this dichotomy clinically has a gray area and, that state switching may not be fully bistable.
Terminal detrusor overactivity (DO) is defined in the ICS-ST02 5 and the WG supports that permission to void can be given during (the beginning of) a terminal DO contraction and be interpreted as a (voluntary initiated) voiding.The WG further explains this, with adapted terms (par 5.1).
In general, regarding the scope or the WG's recommendations: Some patients with LUTD and relevant neurologic abnormalities (NLUTD) are (based on history) able to inhibit urine loss and void by will.Although the physiological (urodynamic) principles are not invalid in advance, PFS-analysis is not fully validated for patients with NLUTD.Furthermore, some patients (and or children) can or will not very well cooperate and or understand "permission to void" and or earlier instructions regarding bladder filling sensations and or regarding not to void.In these patients also, PFS-analysisdiagnoses should be interpreted with individualized clinical perspective, considering the individual patient's ability to comply with external requests during the test to maintain storage and voluntarily fully switch to the voiding state and the representativeness of these assessments.The WG does-within the scope of this standard-not specially recommend for the practice of PFS-analysis in case of NLUTD, mentally challenged and or not cooperating patients.
The WG retained earlier terminology for the functions of the LUT, storage and voiding. 5The WG does not recommend the words condition, disorder and disease in association with function abnormalities of LUT and recommends using the words dysfunction in the word combinations LUT-dysfunction (LUTD) for dysfunction in general, and storage dysfunction or voiding dysfunction for objectively diagnosed deviations from normal physiology, specifically related to abnormalities in one of the two specific LUT functions.

| Physiologic background of voiding
Relevant for analysis of LUT function is that the bladder outlet acts in opposition to the expulsive pressures, including those generated by the detrusor, during LUT storage function and, the opposite is true for LUT voiding function.In the situation of normal physiology, the bladder cannot fill and distend (the detrusor muscle cannot stretch) when the bladder outlet is open and, also within the normal physiology of voiding, the pelvic floor muscles (PFM) around the bladder outlet cannot distend (elongate, be opened) when the detrusor does not contract. 8,9bdominal content weight or abdominal straining during voiding can (further open the bladder outlet during voiding and) contribute to flowrate.Also "pure" Valsalva "voiding" after permission to void may result in urine loss when the abdominal pressure exceeds the urethral closure pressure, without a voiding reflex occurring.This can be seen in patients with relevant neurological abnormalities and is not representing normal voiding physiology.Pure (excessive) Valsalva voiding can however also occur in patients with an unaffected neurologic system but situational inhibition of the voiding reflex, leading to not representative voiding and this will be discussed here below and also in part 2 of this standard.
Normal and voluntary initiated voiding begins with an external urethral sphincter-PFM relaxation that evokes the involuntary autonomic reflex of voiding to begin.Synchronous with striated PFM relaxation the bladder base relaxes and funnels to allow voiding.During voiding the detrusor transfers its contraction energy to the urine, first to open the outflow tract-from proximal to distal-and subsequently to expel the urine.This is the distension phase, see Figure 1.The outflow tract determines the rate of flow in response to the head of pressure 8-10 through the flow controlling zone which is not an anatomical entity but a physiological feature (note: A-flowrate limiting urethral or bladder neck stricture is flow controlling).With normal function-physiology many anatomical points in the outflow tract are flow controlling during one single course of voiding, especially in the beginning of voiding when the outflow tract is pushed open.After maximum flowrate, the outflow tract collapses while the bladder empties and closes again by elasticity and regain of PFM tone.

| Neurophysiology and psychology of voiding
Mental stress plays a role in a medical exam, and especially in "performing" a void.The WG here adds a short explanation: Neuronal integration of the somatosensory innervated striated sphincter and PFM with autonomic voiding reflex takes place in the sacral spinal cord (Sacral intermedio-lateral nucleus and Onuf's nucleus), under guidance of a pontine nucleus, that is on its turn controllable by the frontal cortex. 6,7,11In humans, voluntary voiding after learned delay of the inborn voiding reflex, is one of the controllable autonomic (brainstem) reflexes, like coughing, eyeblinking, swallowing, and sighing, where the somatosensory system responds in conjunction with the autonomic system.The sympathetic dominance in the autonomic control to the LUT during storage phase of the LUT switches to parasympathetic dominance and stimulates (or: permits) the detrusor to contract for the voiding unconsciously, automatically, after voluntary pelvic floor relaxation. 7ocial voluntary cortical override control over the brainstem reflex is a learned behavior during maturation.The evolutionary reasons for learned continence control can only be speculated.One explanation may be that leaving traces everywhere would make pray animals as humans easily huntable and therefore evolution has taught us to void only in safe surroundings.Another evolutionary explanation may be that excretion should not contaminate areas with food or for sleeping and thus should only take place at specific places.Although these explanations are speculative it is relevant for PFS, that it is not unnatural not to be able to void in the situation of a UDS when voiding is usually possible and certainly not pathologic.Anxiety, mental stress, and or perception of unsafety, results in sympathetic dominance and this inhibits the (initiation of the) voiding reflex because parasympathetic system remains overruled.Apart from these situational neurophysiological and psychological influences, a filled rectum and or fecal urgency affect the ability to perform a voiding as usual (see ICS-GUP16 recommendations 2 ), but also the anticipation of a potential painful voiding when for example, a urethritis, vulvitis, or dermatitis exists or the sensation of the catheter in place.The WG recommends taking this human-inherent difficulty "to void at an unusual place" into account when performing and evaluating PFS.

| Practice of pressure-flow studies
Urodynamic testing is performed, and the patient is guided by a person that is trained to do so.The term and or the specific role of a urodynamicist has not been defined in earlier standardization documents.This standard will use the function designation for the person(s) that perform the UDS test, without a further definition.The WG acknowledges that every UDS laboratory has its own requirements and regulations for the level of training, knowledge, and skills of a person that has the function of urodynamicist.
For the current standard, the WG assumes that an ICS-standard PFS is performed immediately after an ICSstandard cystometry (ICS-GUP16) with a transurethral water-filled tubing system, with adequately fixed catheters, external pressure transducers, and continuous saline filling.Not continuous filling, or diuresis filling with PFS and subsequent PFS-analysis are however not excluded, and also not suprapubic catheterization.The WG also assumes (but does not require) that the PFS is element of an ICS standard UDS-test, (ICS-SUT) 2 including a (not instrumented) uroflowmetry, a cystometry and PVR measurements after both uroflowmetry tests, all performed with standard quality control 12 and with equipment that meets ICS standard criteria. 13| DEFINITIONS OF TERMS, PRESSURE-FLOW STUDIES

| Introduction and evidence base
The terms voiding and incontinence are used in earlier ICS standards, and also the term micturition was used occasionally, without precise definition but within the context of the twofold function of the LUT. 6The term emptying is, also used frequently in the medical literature, usually in the word combinations: effectivity of-or, incomplete-(bladder) emptying.The WG recommends the definition: Voiding is the intentional release of urine from the urinary bladder through the urethra to the outside of the body.For the purpose of UDS and PFS, the WG additionally defines (new) PFS-voiding as the release of urine after the urodynamicist's permission to void (the WG continues using the word urine as in earlier documents, but in case of UDS this will of course also be saline or contrast fluid).
PFS are the methods by which the relationship between pressure in the bladder and urine flow rate is measured during voiding (not changed). 2,4The intravesical and abdominal pressures are measured, from the moment of "permission to void" while uroflowmetry is performed with a transurethral (or suprapubic) catheter in place.The position of the patient, the catheter sizes and location(s) and the pressure and flow recording technique, and also corrections for any flow recording delay should be specified (not changed). 2Permission to void (not changed): The voiding phase of LUT function and the PFS starts when permission to void is given by the urodynamicist. 2,5The permission to void should always be documented on the time-based UDS graph by the urodynamicist at that same moment.The voiding phase is considered to end when the patient reports that they would end their toileting behavior associated with voiding.The urodynamicist may integrate "permission to void" with "patients" decision to void' with other signs such as patient sensations, EMG and or detrusor responses, and live imaging, when considered relevant and reliable, to modify the demarcation of the transition from storage to voiding.However, the WG does not give precise recommendations, because of lack of evidence.
The use of these signs should be specified in the test interpretation (and also in cohorts).

| Terms and units for measurement of uroflow
The WG recommends the following terms: see Appendix for earlier defined terms 2,5 and the WG's additions.The Tables 1 and 2 with symbols and qualifiers are published in ICS terms standards from its earliest versions 14,15 and not changed.Note that the WG does not define limits of normality for any of the parameters.Volumes are expressed in mL.Note that the parameters that include or refer to time are referring to the graph-display of the (UDS-) PFS.Note also that all pressures should be T A B L E 1 List of symbols.Symbols (not changed from earliest ICS standardization of terms).reported with their qualifier.The WG has added a detail for the measurement of voiding time; this is now defined as "from the first to the last drop."The WG has also added a definition for (new) time to onset of flow.

| Terms and units for measurement of pressures
The WG recommends the terms as defined earlier 2 but recommends replacing the term premicturition pressure with the pre-voiding pressure (see Appendix).

| Conclusions
Terms and definitions of earlier ICS-ST02 are not changed, apart from few additions and clarifications.Some definitions that were recently redefined are discussed and corrected.The WG has put more emphasis on the demarcation of the end of the cystometry and, on permission to void and its practical implications.

| Discussion
Permission to void was defined in ICS-ST02 and the WG has not changed this and emphasizes that the urodynamicist should always indicate the precise moment of permission to void on the UDS-graph.

| Recommendation
The WG recommends using the term voiding and putting this term for PFS into practice as: The voluntary and intentional release of urine from the urinary bladder through the urethra to the outside of the body after the urodynamicist's permission to void.The WG recommends to urodynamically demarcate voiding from the bladder storage phase with the indication permission to void in every test.
A PFS measures and reports all (physiologic) events after permission to void until the assessment of PVR.

| Introduction and evidence base
As in the ICS-GUP16, clinical history, clinical assessment, and patient information gathering should be performed before UDS is started.As per good clinical practice anatomical abnormalities or surgical alterations of the LUT and its surrounding structures should be known by the urodynamicist for all patients.This includes (estimated) prostate volume for elderly male as well as for example, parity and prolapse grade in female patients.
Many medications (also those) prescribed by other specialists, have a negative effect on for example, LUT sensations or on the contraction force of the detrusor (e.g., but not exclusively, calcium blockers, bronchodilators, antidepressants, and opiates including tramadol on peripheral or central nervous system effects or muscle effects).The WG recommends being aware of all medications present during the UDS to be able to diagnose specific dysfunctions as potentially or partially pharmacogenic (based on the known mechanism of action of the concurrent medications) [16][17][18] (note here that ICS-GUP16 does not recommend to routinely stop medication before UDS, to be able to replicate the patients daily life LUT function).
The patient should be asked whether new symptoms have arisen just before the test, including (new) symptoms of a urinary tract infection as discussed, with its consequences, in ICS-GUP16. 2,4Uro(gynaeco) logical and other LUT relevant medication use should be checked.The frequency volume chart or bladder diary (FVC-BD) providing a clue for the voided volume (s) to be expected, any earlier uroflowmetry and/or PVR volume assessments (see ICS-ST02 5 ), and other pretesting information are relevant for both the cystometry and the PFS (ICS-GUP16).It is also relevant to be aware of how much the patient has been drinking just before the test because diuresis may significantly have added to the fill volume. 19he patient should feel safe and reassured to be able to void despite the instruments and catheters and should understand the relevance of behaving as on a normal toilet.Patients have-especially for PFS-an active role in the testing and the urodynamicist has a role to communicate and cooperate in this.The WG recommends here considering also that in daily life toileting happens fairly unconscious.Especially pelvic muscle relaxation to initiate voiding happens seamlessly once on the toilet and over-concentration on functioning during the test may have an adverse effect on the voluntarystriated muscle-automatisms.
Patients must be asked for their usual voiding position and can also be asked about their usual ability to void outside their usual places.The ICS-GUP16 recommends allowing patients to void in privacy.For patients that find voiding at unusual places difficult, extra effort to help them feel comfortable is necessary, but some of these will still not be able to void in the situation of a PFS.This should lead, in combination with the pretest information, to the (new) specific diagnosis: inability to void during PFS or when this is representative for the patient as is defined in ICS-GUP16 as situational inability to void. 2 Also some patients that do not report any voiding symptom will nonetheless not be able to void during PFS.If relevant, the (new) term situational difficulty to start voiding may also be used when this observation is made (see below).Note here that (situational) inability to void (during PFS) may occur with or without (any) detrusor contraction activity (after permission to void), which should not lead to a diagnosis of underactive or acontractile detrusor; this will be further discussed in part 2.

| Conclusion
Pretest information is necessary to individualize the UDS procedure.The FVC-BD is especially relevant to estimate the expected volumes for urodynamic capacity, flow rate, and PVR.All medication used by the patient should be known because many prescriptions may affect bladder adaption to volume, (filling) sensations but especially also, the ability to start a voiding or to void with a sufficiently forceful detrusor contraction.Information is also relevant to maximally support the patients and to be aware of any patient's difficulty voiding in unusual circumstances.

| Discussion
The WG is not aware of any specific evidence for the specific relevance of clinical information before PFS and the measures taken to increases the likelihood of a representative voiding although some measures to reduce anxiety during UDS (in general) may be helpful. 20,21

| Recommendations
The WG advises that in addition to routine clinical information, the volumes from the FVC or BD and the uroflowmetry and the PVR are kept in mind by the urodynamicist, as well as the preferred voiding position for male patients or what may affect their ability to void.The WG recommends that all concurrently taken medication is known and the WG also recommends maximum mental and practical patient support for the performance of a PFS.
The WG recommends diagnosing voiding (dys) function, based on a PFS study, only with a voiding that the patient has reported to be (almost) as usual.
The WG recommends accepting that a precise PFS diagnosis cannot be made when a patient is situationally unable to void, or to void as usual.The WG has defined specific terms to describe these situations.

| Introduction and evidence base
The WG has considered the information to be provided in preparation for the PFS.Since no relevant scientific data has been published, the opinion of the WG is summarized here.
The ICS-GUP16 recommends that immediately before the test and or during the initial phase of the cystometry, it is (again) explained to the patient that they will be asked to report their bladder filling sensations throughout the study. 2,4,5The ICS-GUP16 explains how sensations should be assessed.
As a specific addition to this, related to the PFS, it can also be explained during the beginning of the cystometry that the patient will be given permission to void when they perceive a strong desire to void (SDV), or earlier, but that they must wait for this permission.However, the patients must be aware that they themselves indicate when the moment of SDV has come.It should then be explained that the urodynamic catheter will offer minimal or no restriction to the voiding flow and that the urine will pass around the urodynamic catheter, to prevent confusion especially by patients that have had earlier catheters to drain the bladder.
The WG has considered that it is acceptable to explain to the patients that the catheter only slightly obstructs the outflow channel.As the example: It can be calculated that a 7 F catheter has much smaller crosssectional area (3.8 mm 2 ) than the area of the average 20−22 F female urethra (30.5 mm 2 ) and is ≈10% of the urethral lumen.When the prostate is enlarged the flow controlling zone-area will likely be smaller but also men with prostatic enlargement are usually, very well able to void around the catheter.Certainly also for example, the sensation or awareness of the catheter being in place will have an effect on the voiding and on the ability to physically relax (PFM and or abdominal muscles), but the WG postulates that a positive and encouraging attitude of the urodynamicist towards the patient about the possibility to void will be helpful here to increase the likelihood of an (almost) representative voiding.
The ICS-GUP16 recommended letting patients urinate in their preferred position and therefore the WG considers it, based on expert opinion not illogical to allow men, who prefer to urinate in standing position (or sit only for hygienics), to stand up somewhere during cystometry (with height adjustment of external pressure sensors and funnel with flow system) before SDV for example, if they indicate normal desire to void, or earlier and, allow thus a smooth(er) transition from filling to voiding after permission.
The WG recommends urodynamicists using the results of the FVC-BD including the results of PVR assessment to prevent over or under filling (ICS-GUP16). 2Patients may be mentally (or pharmacologically) blocked and unable to adequately report filling sensations.Moreover, patients may be on nonurological medication that diminishes the ability to initiate voiding 22 (note again that discussion of patients with neurogenic LUTD is not included in this standard).The WG notes here, however that no evidence is available to determine limits of under and over-filling and, that clinical impression, proficiency, and, attentiveness of the urodynamicist during the test are relevant.
The recommendations for (not instrumented) uroflowmetry are valid for this PFS-standard and are reconfirmed by this WG.The WG considers the recommendations to instruct the patient to void as usual (by relaxation and without, extra effort) and to maximize privacy to the extent possible, to be especially relevant for PFS-test validity as well.

| Conclusions
The WG has, based on their opinion, postulated some elements of information that can be used by the urodynamicist to guide the patient through the test and to ensure a voiding that is as representative as possible.

| Recommendations
The WG recommends that the urodynamicist reiterate the filling sensation steps when the pump filling has been started and to instruct the patient early during the cystometry that they will be allowed to void when they indicate a SDV.Over-alertness for sensations and overconcentration should be prevented (ICS-GUP16).Patients should also be instructed to void as usual, without extra effort and, be prepared for the fact that voiding goes around the catheter.

| Introduction and evidence base
The WG confirms earlier recommendations for the practice of UDS in general. 1,2,4,5The WG specifically asks attention for adequate catheter fixation as described in ICS-GUP16 2 related to PFS.The high rate of expelled catheters in some earlier publications warrants attention; with adequate fixation this should easily be <1% of patients.Cough checks before and also after the voiding demonstrate uptake of pressures (or failure). 2,4The definition of expelled catheter 23 is given in ICS-GUP16 and urodynamicists should be able to (prevent this and also) check for this and decide on the necessity of immediate repetition of the test.Usually, (ICS-GUP16) PFS is performed after a cystometry where the patient is instructed to hold their urine. 2,4,5As a general standard for UDS practice, the PFS begins immediately after permission to void and ends when the detrusor pressure and or the flow rate become steady at baseline or zero and the patient considers the voiding completed. 2typical situations such as for example, intermittent voiding, 5 prolonged latency between permission and flow, loss of desire to void, and persistent sensation of PVR despite an objectively empty bladder should be reported in descriptive terms (not standardized) when they occur.A cough test to check for the catheters' position after PFS is standard. 2,4PVR is measured after PFS when voiding is considered completed.
The WG recommends considering here whether the estimated intravesical volume at the moment of permission to void is consistent with the FVC-BD.Patients may have shown DO before permission to void, and or experience SDV during a DO-contraction, that can also be the first DO contraction at a capacity "normal" for the patient.Terminal DO is defined earlier. 5A terminal DO contraction can be preceded by earlier DO at lower volumes but can also occur as an isolated (first occurring) DO contraction. 6Permission to void may be given in this situation during the building up of the contraction and all events after permission to void can be included in PFS-analysis.(Any) Detrusor activity before permission to void is defined as DO 5 (and possibly DO-urinary incontinence).A neurologically normal and cooperating person can be expected to try to prevent urine loss when asked to do so and the patient can be expected to try holding (with pelvic floor contraction).While patients recruit their PFM during cystometry as usual, they are expected to relax the PFM while voiding after permission to void as this is normal physiology.The demarcation between incontinence and voiding during cystometry with PFS is therefore the urodynamicist's permission to void-mark 2 and the voluntary (frontal-pontine-sacral-) initiation of PFM relaxation with the voiding reflex that is expected to follow.The WG recommends abandoning the earlier term uncontrollable voiding, as a variant of voiding 4,5 and use (new) terminal DO voiding, defined as voiding after permission to void, with a detrusor contraction that started during the filling phase (DO with an appropriate [compare with bladder FVC-BD] volume) and continued after permission to void.(Note that urine loss before permission to void in association with DO is unchanged: DO-incontinence).
Terminal DO-voiding can be considered appropriate for PFS-analysis when, as in every voiding, the patient considers the voiding representative of their usual behavior.The WG recommends repeating a UDS with PFS when DO incontinence of a large volume has occurred and if possible, to evaluate a PFS after permission to void, at a volume not leading to incontinence.
The WG considers without good evidence, but in agreement with accepted teaching (e.g., 24 and the ICS-GUP16, 2 ) that prolonged inhibiting of DO with a strong contraction of the PFM may have a negative effect of the ability to initiate voiding during the same test.The WG considers, without further discussing storage phase provocations, that also stress testing at or after SDV at a filled volume that is, close to the maximum of the patient's FVC-BD just before voiding may associate with (increase of mental stress and or) not representative voiding or not representative inability to start the voiding.When voiding after provocations has been abnormal (e.g., with excessive straining) or not representative, the WG recommends repeating the filling without provocations to allow a smooth transition from SDV to voiding and permit PFS-analysis of a more representative voiding or, starting with a UDS-PFS without provocations first.
For patients with a very low leak-point pressure (women, or men after radical prostatectomy) it may be difficult to fill during cystometry to a volume that allows a voiding that is representative for the situation after curing the incontinence.For women a balloon catheter can be inserted during cystometry 5:foornote30 (and removed before PFS) and penile clamp filling may be applied to make a valid PFS possible in man with urinary incontinence after radical prostatectomy. 25The WG has not further included these cystometry-techniques in this standard.
The WG is aware of the fact that many centers use two separate catheters of which the fill catheter (usually 10 F) is removed before voiding.This is not recommended ICS standard but accepted practice. 2Commonly this is done for economic reasons however the clinical disadvantage of this, potential dislocation of the pressure reading catheter while removing the filling line and, interfering with the smooth transition to voiding directly after SDV, as is advised in the ICS-GUP16. 2Referring to this and referring to what is mentioned about catheter size here above the WG suggests also considering using 2 × 5 or 6 F catheters and leave both in place for PFS of women.Especially in women leaving both catheters in place will hardly affect the "urethral lumen" during voiding, prevents dislocation and easily allows recystometry (with PFS) when needed.The WG recommends using as thin as possible catheters; double lumen or 2 in men.
The WG also recommends here to consider that PFS during video UDS (in patients without relevant neurologic abnormalities) may lead to not representative voiding when voiding position is (because of the imaging and equipment) not as usual or unnatural.Furthermore, the WG recommends considering that also privacy and the patient's relaxation are challenged (potentially and understandably) more frequently than without synchronous imaging.
The WG suggests, in agreement with the earlier standards 2,5 and also described in an explanatory narrative 26 without further explanation, for the practice of PFS: • Allow patient to take preferred position.The WG assumes on the basis of expert opinion that if situational inability to initiate voiding arises, the following measures are probably frequently applied: • Reassure the patient that nothing can go wrong; it is impossible to fail.• Display a positive, supportive attitude and help patient with mental imagination; think of being on your own toilet.
• Dim the lights and/or close doors.
• Present the sound of water running.
• Give the patient something to drink.
• Allow a woman to stand up for a while and to sit again with an immediate restart of the attempt to void.• Fill somewhat extra, especially when the "SDV sensation" is gone (but be aware of over-filling!), or remove some filling.• Ask men who have chosen to sit to stand up.
When the voiding is considered completed by the patient, and flowrate is returned to zero, the patient should be asked to cough, to check catheter position.PVR should be measured via the urodynamics catheter, which is recommended, or ultrasound (with the theoretical disadvantage of the last, that potentially contaminated fluid remains in the bladder).The WG suggests considering that it is likely that the voiding is not representative when the voiding has been with a volume that is far out of the range that the patients FVC-BD shows, especially for example, when the volume was very small with (an unexpected) large PVR and or when excessive straining is visible.

| Conclusions
The WG has postulated practical advises with the aim to maximize patient's self-confidence for the ability to void in the situation of PFS and or to support patients to void as usual, to obtain a technically and especially clinically reliable PFS from a representative voiding.
The WG has introduced the possibility of terminal DO voiding also with the aim (but without direct quantitative evidence) to ensure an as large as possible proportion of representative PFS-voidings.

| Discussion
Detrusor contraction, flow rate as well as PVR are inherently sensitive to patient cooperation and emotion and should only be clinically interpreted, and lead to a diagnosis of dysfunction, if the voiding has been representative.The recommendations may help patient cooperation and their ability to void as usual.

| Recommendations
The WG recommends urodynamicists to prepare patients during cystometry for the PFS phase of the study.
The WG recommends that the urodynamicist checks whether the patient considers the voiding (almost) as usual, and considers the necessity of repeating the test, if not.
The urodynamicist's permission to void mark should be present on the urodynamic graph and should be used as the end of UDS filling phase and the beginning of the voiding.
The WG recommends that permission to void may also be given during (the onset of) a terminal DO contraction when this occurs at a volume that is normal for the patient.
The WG recommends that a PFS voiding after permission to void during a terminal DO contraction may be considered appropriate for diagnosis when the patient considers the voiding to be as usual.
The WG has included a list of recommendations for practice of PFS based on previous standards.The WG also made recommendations for the urodynamicist's practice when situational inhibition to void occurs, based on expert consensus.

| CONCLUSIONS
This first part of the ICS-SUFU-Standard for Pressure Flow Studies has summarized basic knowledge about physiology, neurophysiology, and psychology of voiding relevant for the practice of pressure flow studies.It has introduced general terms and units and described the relevance and necessity of pretesting information.Furthermore, recommendations for explanation and communication with the patient before and during the test are given.The WG has elaborated on the relevance of the representativeness of the voiding and has also introduced terms for the inability to void.The relevance of a precise and uniform demarcation between cystometry, evaluating bladder filling phase, and pressure flow study, evaluating the voiding phase, is emphasized.The WG hopes to increase understanding as well as clinical uniformity of the practice of pressure flow studies with this standard with the aim to improve patient care.

DATA AVAILABILITY STATEMENT
Data sharing is not applicable to this article as no data sets were generated or analyzed to prepare this standard (based on published evidence only).

ORCID
14,15Qualifiers that can be used relevant to voiding.Qualifiers (not changed from earliest ICS standardization of terms).14,15 Note: Upper or lower case as used here is also part of standard notation.All physiological units are SI however p is given in cmH 2 O. Examples: maximum detrusor pressure, p det. max ; average flowrate, Q avg ; detrusor compliance, C det ; bladder pressure at 200 mL p ves200 .T A B L E 2 • (Cough) check signals and catheters fixation.• Ensure the shortest meatus to flowmeter distance.• Give permission to void: PFS starts.• Allow privacy for the patient.• Wait patient considers the voiding done.• Cough check signals after voiding.• Check representativeness of the voiding.• Consider PFS finished or consider repetition of testing.