Invasive test used to measure bladder sensation
Denny-Brown and Robertson were amongst the first to focus on sensation during cystometry in 1933 [
17]. It has been considered the most common tool for assessing bladder awareness, although it is invasive and requires artificial filling [
13]. Some studies have proved that cystometry is a reliable and reproducible test [
8‐
10,
18,
19]. The first was published in 1992 [
8]. Ten patients underwent the test twice in the same sitting and 95 underwent the tests 15 months apart. Patients were asked to report their bladder sensations spontaneously. The study found that 80% of the short-term participants and 73% of the long-term group had an identical pattern of filling sensation: FSF, FDV and SDV. The FSF was the most underreported sensation. Similarly, in 2002, Wyndaele and De Wachter [
19] compared the bladder sensation between two groups of volunteers who underwent cystometry 5 years apart. All participants had the same sequence of bladder sensation: FSF, FDV and SDV. In 2011, Van Meel and Wyndaele [
18] confirmed these findings. The cystometries were repeated with an interval of 7 days in 13 volunteers and 17 patients with overactive bladder (OAB). They found that all participants followed a similar pattern of sensation, with a strong correlation between the degrees of sensation during each week in all subjects (correlation coefficient
R > 0.5).
In 2004, Erdem et al. [
9] challenged the reliability of this test in 59 patients with lower urinary tract symptoms (LUTS). The cystometry comprised three phases: in phases one and three, no infusion was pumped, and in phase two, normal saline was pumped. In phase two, all patients reported sensations within the same pattern. In the phases of no infusion, 47 (79.6%) reported an FSF, 38 (64.4%) reported FDV, and 15 (25.4%) reported SDV. It does appear that the same pattern of bladder sensation is seen, even with a lack of filling. This suggests that cystometry is not reproducible and, the false sensation can be associated with having the catheter in situ rather than actual filling.
Subsequently, Erdem et al. [
20] conducted another study to investigate whether catheters had an impact on bladder sensation. Forty-five patients underwent cystometry in three phases. In the first phase the catheter was not inserted, in the second phase the catheter was inserted but no infusion was given and in the third, bladder filling was performed. In the latter, all sensations were perceived. When comparing the two first phases, none of the patients in phase one reported SDV and a higher percentage of patients felt the three sensations (FSF 86%, FDV 53% and SDV 17%) in phase two. These results were similar to the numbers found in their previous study [
9]. It does appear, therefore, that urethral catheters and bladder filling can affect patients’ sensations, as a considerable number of patients perceived FSF and FDV even without a catheter.
De Wachter et al. tested the reliability of cystometry by blinding the patients to a real and a sham bladder filling: no medium was infused [
10]. Fifty-nine patients with LUTS were recruited and, in contrast to Wyndaele’s study [
8], none had any neurogenic condition. Similar results to previous studies were obtained during a real cystometry: 88% of patients were able to identify the same pattern of bladder sensation [
10]. However, during sham cystometry, the findings differed from Erdem’s results: a small number reported sensations (5 FSF, 1 FDV), but none reported SDV. Together, these studies demonstrate that bladder filling and the presence of a catheter elicit similar sensations, but that these can be reported by patients even in the absence of infusion or a catheter. Thus, it appears that the subjective nature of these artificial definitions is open to suggestion by the environment of the test, or the staff performing it.
The publication of these studies highlights that there are conflicting data regarding the reliability of cystometry. We agree with De Wachter et al. [
10] that cystometry cannot be considered unreliable just because some sensations are reported during sham cystometry. The urinary catheter can play an important role in the perception of bladder sensation, but other factors such as memory, habituation and artificial environment can also influence it.