Clinically significant nocturia (≥2 nightly voids) constitutes a known putative symptom of uncontrolled hypertension. Nocturia index (Ni), the ratio of nocturnal urine volume divided by the maximum bladder capacity, has been validated as a standardized measure and as having the greatest predictive value amongst voiding diary parameters for clinically significant nocturia. However, interplay between elevated blood pressure (BP), clinically significant nocturia and Ni has not been thoroughly explored. We set out to describe this interplay within older men at a Veterans Affairs (VA) Urology clinic.

A retrospective review was conducted using data from an Institutional Review Board approved database. Demographics, in-office BP, presence of medical co-morbidities including diabetes mellitus and sleep apnea were collected on men who presented for lower urinary tract symptoms at a VA Urology clinic from 2008-2020. Elevated blood pressure was defined as ≥135 mm Hg systolic or ≥85 mm Hg diastolic. BP was measured within one month of submitted voiding diaries. Descriptive statistics as well as multivariate logistic regression including age, presence of sleep apnea and Ni were performed with moderation analysis to account for multicollinearity.

Analysis of multicollinearity with linear regression revealed a variance inflation factor (VIF) for age, systolic blood pressure, diastolic blood pressure, Ni, diabetes mellitus and sleep apnea of 1.195, 1.784, 1.886, 1.017, 1.018 and 1.046 respectively. As all values were less than the most conservative VIF cutoff of 2.5, this informed us that there were no interactions or buffer effects present amongst independent variables and supported their use in the multivariate model. Of the 280 men analyzed, 75 were found to have 0 or 1 nightly void on bladder diary and 205 men were found to have ≥ 2 nightly voids. Median age of the studied population was 68.0 (63.0, 75.0) years. On multivariate analysis of the entire patient cohort without including Ni as a covariate, elevated blood pressure was predictive of clinically significant nocturia but did not reach statistical significance (OR 1.311, 95% CI 0.754 – 2.278, p = 0.337). However, when including Ni within the model, elevated blood pressure predicted clinically significant nocturia with noted statistical significance (OR 2.459, 95% CI 1.083 – 5.584, p = 0.032). Sub-group analysis on 113 black patients (25 having 0 or 1 nightly void on bladder diary and 88 found to have ≥ 2 nightly voids) was subsequently performed. Median age was 67.0 (62.5, 74.0) and amongst this cohort on multivariate analysis without including Ni as a covariate, elevated blood pressure was predictive of clinically significant nocturia but did not reach statistical significance (OR 2.297, 95% CI 0.882 – 5.980, p = 0.089). However, when including Ni within the model, elevated blood pressure predicted clinically significant nocturia to an even greater extent with noted statistical significance (OR 6.478, 95% CI 1.263 – 33.224, p = 0.025).

The effects of elevated BP on nocturia have yet to be fully elucidated. From our analysis, we have observed a potentially synergistic relationship between a patient’s elevated in office BP and Ni on voiding diary as a strong predicator for clinically significant nocturia that is further emphasized in Black men.

More investigation is required to ascertain the physiological mechanism underlying this predictive capacity. In light of this, our findings highlight the importance of evaluating the relationship of nighttime urine volume and bladder capacity (i.e. the Ni) with elevated in-office BP.

Continence 7S1 (2023) 100925
DOI: 10.1016/j.cont.2023.100925