Hypothesis / aims of study
It is well recognised that continence is not an automatic process but rather a learned skill under both conscious and subconscious control. Research in neuroimaging has led to evidence that no one part of the brain controls continence; several parts are involved its control and both excitatory and inhibitory signals are required in bladder function. There is some evidence that the strong desire to void may impact cognitive function. Lewis et al. used the strong desire to void as a model for pain, and found that the strong desire to void caused deterioration in cognitive performance in adults without lower urinary tract issues. (1) In addition, a study by Tuk et al. found that inhibition in visceral domains such as bladder control can lead to increased inhibition in terms of self-control for decision making. (2) This suggests that maintaining continence requires cognitive input. We hypothesise that the sensation of a strong desire to void in healthy volunteers would cause deterioration in the performance of two cognitive tests, and that this deterioration would be similar to that induced by the simultaneous performance of another cognitive task which is known to act as a source of diverted attention, the 2-back test, in which the subject is read a list of letters in a random order and indicates when the letter given is the same as the letter given 2 positions previously in the sequence.
Study design, materials and methods
Volunteers aged 18 or older recruited via posters placed around the University campus. Study participants had no significant LUTS, defined as a a score of less than four on the bladder self-control assessment questionnaire (BASQ), an absence of neurological disease that may affect cognition, no significant visual hearing or visual impairment that would prevent completion of the cognitive task, and did not use an intermittent or indwelling urinary catheter, or require dialysis. Following informed consent, participants completed two cognitive tests, the Trail Making B test (TMT-B) and a computer based test of simple reaction time (SRT).
The TMT-B is a validated test of executive function, and comprised participants linking 25 circles in alternating number-letter order (1 -> A -> 2 -> B...), while the SRT involved pressing a mouse button as quickly as possible after a visual signal was given. For the TMT-B the time taken to complete the test was recorded. For the SRT, the test was completed five times and the mean time recorded. The participants completed each test under three conditions; undistracted and with an empty bladder, distracted by simultaneously completing the n-back test, and while experiencing a strong desire to void. To reduce learning effects each participant was given two practice runs at the tests and the state under which data were collected was in a random order.
Strong desire to void was induced by drinking uncaffeinated and non-alcoholic fluids ad libitum until the participant experienced the strong desire to void. They were instructed to postpone voiding until their desire to void reached the level at which they would leave a movie theatre during the film to pass urine and were unable to "hold on" any further.
The time taken to complete each cognitive test was recorded and student's T test used to compare the undistracted state to the distracted and strong desire to void.
Results
26 participants (18 female, 8 male, mean age 22 years) were recruited and completed data collection. There were no dropouts.
Trail Making B Test
In the undistracted state, the mean time taken to complete the TMT-B was 43.3 seconds (SD 19.01). The time taken to complete the test while distracted was significantly higher at 110.6 seconds (SD 56.38), p<0.001. The time taken while experiencing a strong desire to void was 44.29s (SD 13.17), which was not significantly different to the undistracted state.
Simple Reaction Time
The mean reaction time when undistracted was 371.9ms (SD 58.04). While distracted, the reaction time was significantly higher, at 624.8ms (SD 250.8), p<0.001. When experiencing a strong desire to void, the reaction time was significantly slower than when undistracted at 421ms (SD 83.6), P<0.05
Interpretation of results
The experience of a strong desire to void induced a small but significant increase in reaction time in our group of young, healthy volunteers without lower urinary tract symptoms, which is in accordance with the findings of Lewis et al. This effect was similar but of a lesser magnitude than the reduction induced by a simultaneous distracting task, and implies that, in healthy volunteers, the strong desire to void may act as a source of diverted attention.
Concluding message
Our results suggest that the strong desire to void can impair cognitive performance even in young, healthy people. This has implications for situations in which people are undertaking tasks which rely on reaction time and when toileting facilities are not available, such as driving, and suggests that the sensation of strong desire to void affects the function of other domains of cognition.
In older adults, there is a significant association between falls and urinary urgency, and the effect on cognition via distraction has been suggested to be a possible causal factor in this association (3). Future work will investigate whether a similar or greater effect in older adults and in people with symptomatic LUTS. This work has shown that in even young, healthy people with no overt neurological or lower urinary tract dysfunction, the sensation of a strong desire to void can induce changes in cognitive performance.