There are five key parts of the filling and storage portion of the PFUD study that should be recorded in the final interpretation of the study. This segment of the PFUD study is sometimes referred to as “filling cystometry.” This portion commences with bladder filling and ends with the command “permission to void” [3]. The aims of this part of the study are to assess involuntary detrusor activity, bladder compliance, sensation, capacity and, in the appropriate setting, urethral function.

Contractions refer to the presence or absence of phasic (or terminal) involuntary bladder contractions with respect to detrusor function (specifically during bladder filling only) [3]. Though the actual definition of an involuntary bladder contraction is sometimes debated, the finding of the characteristic wave form, along with whether it is spontaneous or provoked, or phasic or terminal should be recorded. The pressure and volume and amplitude of such a finding may be recorded as well, although the clinical significance of such information is variable and debatable depending on the clinical circumstances of the patient under study. Nevertheless, just as importantly, the absence of such a finding should be recorded as normal.

Compliance is the relationship between the change in bladder pressure and bladder volume during bladder filling. Physiologically, compliance is determined by the innate viscoelastic properties of the bladder. Generally the rise in bladder pressure with filling, in the absence of involuntary bladder contractions, is very small, and frequently imperceptible. Compliance is calculated by dividing the change in bladder volume by the change in bladder pressure at the point in the PFUD study just prior to the command to void, and in the absence of an involuntary bladder contraction [4]. Normative values are not universally agreed upon and compliance is generally recorded as either normal or abnormal. Abnormal bladder compliance is a significant risk factor for upper urinary tract deterioration. Classically, abnormal compliance can be seen in radiation cystitis, neurogenic bladder (especially spina bifida), and denervated bladders following radical pelvic surgery.

Coarse sensation of bladder filling is quite subjective and variable due to the very artificial and non-physiological circumstances under which the PFUD study is performed. Using the term “coarse sensation,” though fairly non-descript, is pragmatic and useful. In general, the description of the sensation of bladder filling is very general and abnormalities of sensation may be described as absent, reduced, or increased [3]. Due to the need for urethral catheterization, causing some degree of urethral discomfort and/or pain, as well as the tip of the catheter within the bladder and the non-physiological filling rate, fluid and fluid temperature, the perception of bladder filling can be considerably altered. Furthermore, the patient’s ability to perceive sensation and verbally express to the examiner such sensations as the bladder fills are somewhat compromised. The volumes at which the first sensation of bladder filling, first desire to void, normal desire to void, strong desire to void, urgency, and pain are documented. It is essential to note when such sensations correlate with particular urodynamic findings such as bladder overactivity. Normative parameters and assessment methods for bladder sensation have been proposed but none are universally accepted [5].

Continence refers to the presence or absence of urinary leakage during the PFUD study. Urinary incontinence may be due to abnormalities of bladder function (involuntary detrusor contractions, or abnormal compliance), or urethral function, or a combination of both. Incontinence occurring coincident with an involuntary bladder contraction is termed detrusor overactivity incontinence [4]. Stress incontinence, due to diminished sphincter function, may be provoked with cough or Valsalva or other maneuvers. Urethral function during bladder filling may be assessed by abdominal leak point pressure or urethral pressure profilometry. Incontinence recorded during the study may reproduce the patient’s symptoms or not. For the patient without a clinical complaint of urinary incontinence, the finding of stress or detrusor overactivity incontinence is often artifactual and of little clinical significance. Alternatively, in the patient with a clinical complaint of urinary incontinence, it is important to make every effort to reproduce the incontinence during the study. For purposes of interpreting the study, it is important to record whether incontinence was noted during the study, the type of incontinence, and whether it reproduced the patient’s symptoms. Other parameters specific to the episode(s) of incontinence such as volume infused, bladder pressure, urethral pressure, and sensation at the moment of incontinence should be recorded as well.