Bladder sensation is measured during filling cystometry. Because sensation is inherently subjective, it requires communication between an attentive clinician and an alert, mentally competent patient [3].

While standardized ICS definitions exist for the various bladder sensations, ICS does not specify when and how these definitions should be communicated. Some clinicians simply ask the patient to report whatever they feel without any instruction. Others might instruct patients at the outset to report sensations and these sensations are described for the patients. Each clinician will communicate these definitions a little differently in order to achieve understanding among patients of different backgrounds. Due to the variability in the way information regarding bladder sensation is elicited, results can be difficult to reproduce across different laboratories.

Ideally, an ongoing conversation should be maintained between a clinician and patient throughout the study. The patient should be instructed to report when fluid in the bladder is first sensed. The patient is then asked to report occurrence of first desire to urinate followed by occurrence of strong desire to urinate. Finally, the patient should inform the clinician when restraining from urination is difficult to defer (urgency). The patient should also be queried as to what, if anything, is felt when any significant changes in detrusor pressure, like involuntary detrusor contractions, are noted. Many clinicians will provide everyday analogies in order to communicate to patients the differences among first desire, strong desire, and urgency. For example, first desire might be described as a sensation that would prompt a patient watching a good television show to go to the bathroom at the next commercial break while strong desire might prompt the patient to consider interrupting the show and walking to the bathroom and urgency is as a sensation that would prompt the patient to get up immediately and run to the bathroom.

Bladder sensation is subjective and a variety factors may affect the reliability of measurements of bladder sensation [4]. These factors may include patient anxiety, non-physiologic rate of bladder filling, and irritation from the catheter. Erdem and colleagues demonstrated the subjectivity of bladder sensation measurements by showing that a significant portion of adult men who were prepped for a urodynamics study, including catheter insertion, and told that the study had commenced reported first sensation of bladder filling (83 %), first desire to void (80 %), and strong desire to void (25 %) despite lack of bladder distension with air or fluid [5]. To investigate the impact of catheter placement on perceptions of bladder filling, another study was performed where the catheters were taped to the penile skin but not inserted [6]. Even without catheter insertion, about half of patients reported first sensation and a quarter of patients reported first desire, although no patients reported strong desire. When the catheter was then inserted but no filling occurred in the next phase of the study, a much greater portion of patients reported first sensation (87 %) and first desire (73 %), and some patients reported strong desire (18 %). This suggested that catheter placement contributes to the perception of bladder filling but other factors also play a role. The same study performed in a group of children, however, found that they were significantly less prone to reporting sensations of bladder filling without actual bladder filling [7]. Thus, sensations reported by children during urodynamic studies may be more reliable than those reported by adults. In terms of rate of bladder filling, there is conflicting data as to whether it affects bladder sensation [8–10].

One proposal to make assessment of bladder sensation more reproducible involves the use of an electronic keypad that allows patients to rate sensations of bladder filling between 0 (none) to 4 (desperate) [4]. Patients can choose their starting point and go up and down on the scale as they wish throughout the test without any prompting from the clinician. The investigators found this method promising in providing reliable and repeatable results with a statistically significant increase in bladder volume at each urge level.

Studies of normal volunteers have found a consistent pattern in patients’ reports of bladder sensations [8, 11]. These studies were performed in men and women aged 18–30. In all patients, first sensation of bladder filling was followed by first desire to void, and then followed by strong desire to void. Patients describe first sensation of filling as a vague sensation derived from fluid inflow that waxed and waned and was located in the lower pelvis. Patients did not recognize this sensation from their normal daily lives. First desire and strong desire to void were recognized as they are described by the ICS. Patients identified first desire to void as being a sensation familiar from daily life that is localized to the lower abdomen. It became gradually stronger during filling. Strong desire to void was described as a constant, almost uncomfortable sensation located in the perineal region or urethra.

Although sensation is typically part of a complete urodynamic study there has been little investigation of the clinical relevance of this information, the optimal means of eliciting the information, and the test–retest reliability of the assessments. Research has found a significant increase in volume between each sensation (see Table 13.2) [8, 11]. While volumes at which each sensation occurred varied widely among individuals and average volumes were significantly different between male and female patients, they occurred at a fairly constant percentage of total bladder volume. First sensation of bladder filling occurs at an average of 40 % of maximal cystometric capacity while strong desire to void occurs at an average 70 % of maximal cystometric capacity [12].

Cold receptors have been identified in the feline and human bladders [13]. Cold sensation is lacking in patients who have undergone cystectomy and enterocystoplasty [14]. While Bors described cold sensation as being felt in the skin rather than the bladder, other experts report the sensation as felt in the bladder rather than the urethra or skin [13]. In some laboratories, room temperature fluid is used to perform urodynamic studies instead of warmed, body temperature fluid (as a matter of convenience). While the clinical significance of intact cool sensation is currently unknown, it seems reasonable to ask if the patient feels an infusion of something cool into the bladder as another test of sensation if room temperature fluid is used.

Sensation maybe altered in a number of different conditions. The following is a list of some of these conditions: