Hypothesis / aims of study
Studies that evaluate lower urinary tract sensation during urodynamics are remarkably scarce. In the normal physiology, bladder filling is causing detrusor muscle stretch (after unfolding of the muscle from volume zero). Muscle stretch causes nerve endings firing, similar to propriocepsis in any other muscle. Mankind has learned (and every toddler learns) to perceive detrusor muscle distension as bladder filling sensation, to inhibit the innate autonomic voiding reflex and to mature to socialized voiding. Urgency is an element of the overactive bladder syndrome. Urgency is however not very specifically defined as an observation during urodynamic investigation nor patho-physiologically well explained. An earlier study with meticulous and continuous recording of sensations failed to find an association with urodynamic observations1. This specific study had included patients with detrusor overactivity only. We decided to go back to the drawing board: How does sensation relate to volume as is dictated by design of normal physiology and how is detrusor overactivity interfering with normal filling sensation? We compared the ICS filling sensation landmarks as introduced in the ICS 2002 standard of terms, and further specified for practice in the recent ICS good urodynamic practice, in a cohort of patients with and without detrusor overactivity (DO). We have evaluated the association of filled volume (detrusor distension) and sensations as well as the association between pressures and sensation, and compared those between the two cohorts.
Study design, materials and methods
This was a retrospective observational cohort study; we analyzed the urodynamic studies of female patients, without relevant neurologic pathology referred to the clinic from 2005 to October 2018 with the following study indications: stress urinary incontinence, overactive bladder syndrome or lower urinary tract symptoms, persistent to initial not invasive management. Patients with urinary tract infection or other urinary tract abnormalities were not included. Urodynamics was performed with the patients in seated position with 8F transurethral double lumen transurethral catheter and a 10F intra-rectal catheter, with fluid filled pressure tubes and external pressure sensors leveled at the height of the symphysis pubis. The bladder was filled with room temperature saline with a continuous rate of 20-40mL per minute; set on the basis of the anticipated capacity; ±10% of the maximum voided volume on bladder diary, per minute.
We analyzed the means of the variables with the t-test for independent variables and for the correlation we used Pearson correlation coefficient. Statistical assessments were considered significant when P<0.05. Statistical analyses were performed using SPSS 25.00.
Interpretation of results
Table 1 shows that patients with DO have sensations at lower volumes and higher pressures than patients without DO, as was expected. However no differences were observed when sensation was measured at percentage of capacity. Sensations with DO are at smaller volume, of a reduced total capacity, therefore at identical percentages. This may be a sign of shifting from high threshold to lower threshold sensation as is postulated on the basis of fundamental research.2 Table 2 shows that an increasing number of contractions associated with a higher pressure before contraction. In this table we see that there in not a pattern in the volume between the contractions. In table 3 is visible that most of the first contraction occur before normal desire to void, but adding up all contractions, most contractions occurred after the normal desire to void.