Dynamic analysis of bladder diaries helps shed light on urge mechanisms

medwireNews: Dynamic analysis of individual bladder intake, voids, and sensations collated from patient diaries finds bladder filling rate (BFR) to be a key factor influencing urinary frequency and urgency and identifies potential behavioral modifications to reduce urgency episodes.

Victor Andreev (Arbor Research Collaborative for Health, Ann Arbor, Michigan, USA) and colleagues note that “commonly used metrics from [bladder diaries] ignore the timing of voids and tend to focus on summary statistics of voided volume and void frequency; however, inopportune timing of the urgent need to void can be bothersome to patients.”

Investigating Bladder Dynamics Through Patient Diaries

For the study, published in PLoS ONE in November 2023, the researchers calculated the dynamic variables of fluid intake, BFR, urge growth rate – how long it will take for a person to reach a high level of urge – and the time-dependent frequency of voiding using data from bladder diaries completed as part of the LURN study.

A total of 197 individuals (median age 61 years; 50% men) with lower urinary tract symptoms completed diaries on 3 consecutive days, recording information on the timing and volumes of fluid intake and voids, as well as bladder sensations during voiding and the types of fluids consumed. 

The patients had a physiologically plausible fluid imbalance of less than 3 L across all 3 days and 74 had at least one incontinence episode in the 3 days. Of a total 5124 voids reported, most were at an urge level of 1 (normal desire to pass urine and no urgency; 45.7%), 2 (had urgency but it passed before going to the toilet; 14.3%), or 3 (had urgency but managed to get to the toilet without leaking urine; 25.1%). A further 8.2% had urge level 4 and leaked urine.

Variability in Bladder Filling Rate and Void Volume

Time-averaged analysis showed that the dynamic variables reported were heterogenous in nature, but a general feature of the cohort was a high variability in BFR. The ratio of maximum to median filling rate ranged from a “rather low” minimum 1.6 to an “extremely high” maximum of 128.0, the team reports. For the majority (70%) of people, the ratio of maximum to median BFR was above 4.0 and for 36% it was above 8.0.

Maximum bladder void volume also showed a varied distribution, but low volume voids appeared to be prevalent, affecting 68% of individuals. Very urgent low volume voids – needing to void with urgency when only 20% or less of the bladder volume is filled with urine – were infrequent across the patients, occurring in 26%, but for some individuals, such voids happened as often as in 50% of cases, note the researchers.

“This analysis indicates that, at least for some of the individuals, the fraction of bladder volume filled with urine is not the only or even the main determinant of urinary urge,” the team observes.

Correlation Between Filling Rate and Urinary Urgency

Indeed, correlation coefficients demonstrated that voiding frequency and urge growth were only weakly associated with voided volume, whereas they were strongly and significantly correlated with BFR, and predominantly positively associated.

This suggests that “BFR rather than [voided volume] is the main determinant of urinary frequency and [urge growth rate],” say Andreev et al.

They continue: “The hypothetic mechanism is that BFR drives the urge growth rate and makes a person void when urge reaches a certain level.”

Influence of Timing and External Factors on Bladder Dynamics

Observing the intake and voiding profiles of the participants, Andreev and colleagues found that, for any given participant, the BFR could change “dramatically” during the day, peaking at 10- to 12-fold higher than the median.

The highest peaks in BFR, as well as voiding frequency and urge growth rate, occurred following the consumption of caffeine and/or alcohol, with other peaks occurring following frequent and/or high-volume drinks, they report.

Understanding Factors Influencing Urgency Episodes

Linear regression models were then created for urinary urge growth rate, based on BFR, volume of urine in the bladder, and whether the patient was awake or not. These models correctly predicted more than 90% of urgency episodes in 70% of 124 patients and were used to investigate how BFR and urine volume affect the urge growth rate.

Assessing the Impact of Different Behavioral Modifications

Comparing 106 participants who experienced at least one episode of urgency with 18 individuals without urgency, the researchers found that participants with a higher urge growth rate were more sensitive to an increase in BFR and less sensitive to increased urine volume.

Among the 106 participants who had at least one urgency episode, 17 did not consume caffeine or alcohol, 23 consumed caffeine but not alcohol, three consumed alcohol but not caffeine, and 63 consumed both caffeine and alcohol.

Simulated Exclusions and Reduction in Urgency Episodes

Modeling showed that simulated exclusion of both caffeine and alcohol in these participants had the greatest effect in reducing average urinary frequency and the average number of urgent voids by 27% and 28%, respectively, in those who consumed both.

The exclusion of alcohol alone was associated with mean reductions of 18% in both measures in the relevant participants, and the exclusion of caffeine alone with mean reductions of 15% in both measures. By comparison, reducing volume intake reduced both average frequency and number of urgent episodes by only 1–9%. 

However, they note that the most effective simulated modification for reducing the number of urgency episodes was to keep BFR and urine volume in the bladder constant and equal to median values, which reduced the rate by an average of 27% across all four groups and by 37% in patients consuming both alcohol and caffeine. 

“This result is consistent with our observation that peaks of [urge growth rate] are collocated with peaks of BFR,” they say.

Conclusion

Andreev et al conclude: “We believe that adding variables derived from the [bladder diaries] using a dynamic approach […] might improve classification and provide additional insights into the mechanism of urge in various phenotypes.”

News stories are provided by medwireNews, which is an independent medical news service provided by Springer Healthcare Ltd. © 2024 Springer Healthcare Ltd, part of the Springer Nature Group

Read the article here: PLoS One 2023; 18: e0284544

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