Artefacts during uroflowmetry may arise owing to several factors, which can be broadly classified into two groups: extracorporeal and intracorporeal. Recommendations to minimise uroflowmetry artefacts include ensuring privacy, checking the report and tracing immediately, correcting artefacts manually and checking that the void was representative of normal. Initial quality checks will prevent the majority of artefacts. Artefacts may arise during the voiding phase owing to displacement of the vesical or rectal pressure transducer or inadequate pressure transmission. Artefacts are spurious and inaccurate urodynamic observations. Artefacts at uroflowmetry are minimised by checking calibration regularly and asking the patient to void normally in private. Artefacts during cystometry can be minimised by zeroing transducers to atmospheric pressure, expelling air bubbles and checking for good subtraction with cough testing before filling, at 1-minute intervals during filling and before and after voiding.

This chapter discusses the tests of urethral function. The International Continence Society (ICS) has suggested standardisation of the performance of the urethral function and defined parameters for measurements. Two tests may be included to assess urethral function specifically during filling cystometry: vesical or detrusor leak-point pressure estimation and abdominal leak-point pressure (ALPP). Tests of urethral function during voiding cystometry measure the relationship between pressure in the bladder and urine flow rate. Urethral pressure profilometry (UPP) provides a graph indicating the intraluminal pressure along the length of the urethra. Urethral retro-resistance pressure (URP) has been defined as the pressure required to achieve and maintain an open urethral sphincter. Urethral pressure reflectometry (UPR) is measured using a 5-mm diameter polyurethane bag and urethral transducer. Tests of urethral function may also be useful in identifying incompetent urethral closure mechanisms before obstructive surgery for stress urinary incontinence.

Cystometry is the measurement of pressures inside the bladder both during the storage phase and the voiding phase of urodynamics. Post-void residual urine is assessed prior to cystometry by a dedicated bladder scanner, conventional ultrasound scanner or via inserting and draining the residual urine through the urethral filling catheter. Cystometry is usually postponed if the patient has a urinary tract infection because this could influence the urodynamic findings. The bladder diary provides a good idea of the patient's normal functional bladder capacity, and is helpful in conducting the cystometrogram. Detrusor overactivity describes involuntary detrusor contractions occurring during the filling phase of cystometry. The International Continence Society defines urodynamic stress incontinence as urinary leakage seen during filling cystometry in the presence of raised abdominal pressure but in the absence of a detrusor contraction. Leakage seen during coughing while the cystometric trace shows no evidence of a detrusor contraction confirms the diagnosis.

Urodynamic investigations are used to investigate bladder function and dysfunction in women with urinary symptoms, the most common being urinary incontinence. Guidance from the National Institute for Health and Clinical Excellence covers much of when investigations should be performed. Women are often anxious and embarrassed when they attend the tests. Recognition of the artificial test conditions and the feelings of the woman are crucial to optimising the chances of reproducing symptoms. Before cystometry, written information explaining the test should be provided with the appointment letter or when the woman attends the clinic. The information should include instructions on providing a urine sample in a sterile container, bladder chart and questionnaires and advice to come with a comfortably full bladder. Women who are using drugs to treat lower urinary tract dysfunction should normally stop using the medication for an appropriate period of time before the investigation.