For many people a recurrent strong desire to void, sometimes with incontinence, diminishes their quality of life. At present there are few insights into what underlies these problems. The condition is described as the ‘overactive bladder symptom complex’ but this definition is proving to be unhelpful. It focuses on overt bladder contractions rather than the main problem, which is altered and heightened sensation. Also, current approaches that describe bladder sensations as episodic and leading to voiding as ‘first and second sensation to void’ might also be misleading if they are taken too literally and used to suggest mechanisms. Current research is beginning to focus on the mechanisms that generate afferent information from the bladder and how it can become altered. As these views develop it is crucial that we appreciate the diversity of the bladder afferent system and distinguish between afferent and sensory information; in this review we explore this underlying complexity. The central nervous system (CNS) receives vast amounts of information from the bladder, which arises from different locations, uses different fibre types and involves different methods. The CNS is continually being bombarded with ‘afferent noise’. The challenge now is to understand the nature and components of this ‘afferent noise’ and which components are essential to sensation. The emerging picture is complex, but this complexity must not be negated or oversimplified. It must be embraced and incorporated it into thinking when designing experiments, analysing data, diagnosing patients and evaluating treatment.

AIMS The purpose of this investigation was to develop a non-invasive, objective, and unprompted method to characterize real-time bladder sensation. METHODS Volunteers with and without overactive bladder (OAB) were prospectively enrolled in a preliminary accelerated hydration study. Participants drank 2L Gatorade-G2® and recorded real-time sensation (0–100% scale) and standardized verbal sensory thresholds using a novel, touch-screen “sensation meter.” 3D bladder ultrasound images were recorded throughout fillings for a subset of participants. Sensation data were recorded for two consecutive complete fill-void cycles. RESULTS Data from 14 normal and 12 OAB participants were obtained (ICIq-OAB-5a = 0 vs. ≥3). Filling duration decreased in fill2 compared to fill1, but volume did not significantly change. In normals, adjacent verbal sensory thresholds (within fill) showed no overlap, and identical thresholds (between fill) were similar, demonstrating effective differentiation between degrees of %bladder capacity. In OAB, within-fill overlaps and between-fill differences were identified. Real-time %capacity-sensation curves left shifted from fill1 to fill2 in normals, consistent with expected viscoelastic behavior, but unexpectedly right shifted in OAB. 3D ultrasound volume data showed that fill rates started slowly and ramped up with variable end points. CONCLUSIONS This study establishes a non-invasive means to evaluate real-time bladder sensation using a two-fill accelerated hydration protocol and a sensation meter. Verbal thresholds were inconsistent in OAB, and the right shift in OAB %capacity–sensation curve suggests potential biomechanical and/or sensitization changes. This methodology could be used to gain valuable information on different forms of OAB in a completely non-invasive way.

This study suggests that FSTLP may be a more sensitive screening method than PNE to identify patients eligible for SNM therapy, warranting randomized trials.

By means of focus group research it is possible to describe the development of normal bladder sensation and to refine terminology used by healthy participants. The findings show that two types of bladder sensations are reported spontaneously by healthy uninitiated volunteers, pressure and a tingling sensation, of which the first develops in a continuous manner. The pattern in which the absolute need develops is described by the terms: no sensation, weak awareness, stronger awareness, weak need, stronger need and absolute need to void.