Hypothesis / aims of study
Nocturia is defined as the number of times an individual passes urine during their main sleep period, from the time they have fallen asleep up to the intention to rise from that period. Nocturia is a prominent feature of overactive bladder syndrome. However, its association with outcomes from urodynamic testing are not well established. There is a weak but statistically significant correlation between nocturia and detrusor overactivity, urine peak flow rate and maximum cystometric capacity in men. However, there is a sparsity of data which link nocturia to urodynamic testing in women.
Our aim was to establish whether there is a link between the presence of nocturia and urodynamic findings in women.
Study design, materials and methods
A retrospective study of 3427 women from a urogynaecology clinic was performed. All women had completed a 5-day bladder diary and subsequently undergone urodynamics. Presence of nocturia was derived from the bladder diary and defined as >1 episode of interrupted sleep to pass urine in women aged up to 60 years old, >2 episodes in women aged 61-70 years and >3 episodes in women aged 71 years or over. Women with low compliance bladders and women with neurological disorders were excluded from the study. The results of the free-flow study and filling cystometry of women with nocturia and women without nocturia were compared using an independent t-test analysis. Cystometry classified patients as having: 1) Urodynamic stress incontinence; 2) Detrusor overactivity; 3) Mixed detrusor overactivity & urodynamic stress incontinence; and 4) Bladder pain. A Chi-squared test was used to compare women with the above classification between those that were adjudged to have nocturia and those that were not. The frequency of nocturia was compared with maximum bladder capacity for each of the above classifications.
Nocturia was a feature in 1452 of the 3427 women (42%) included in the study. Cystometry performed in all women classified 1454 women (42%) as having urodynamic stress incontinence; 441 women (13%) as having detrusor overactivity; and 185 women (5%) as having a mixed urodynamic stress incontinence and detrusor overactivity. The free flow study showed no differences in peak flow rate (16ml/s vs. 16ml/s, p=0.28), voided volume (188ml vs 189ml, p=0.81) or residual volumes (35ml vs 30ml, p=0.45) between women with nocturia and women without nocturia. During the filling phase, there was no difference in first desire to void (206ml vs. 209ml) or detrusor pressure at the end of filling (15cmH2O vs. 16cm H2O).
There was no significant difference between women with nocturia and women without nocturia in those classified as having urodynamic stress incontinence (43% vs 42%, p= 0.48). Maximum bladder capacity in women with urodynamic stress incontinence did not vary with increasing frequency of nocturia. There was a small but statistically significant difference between women with nocturia and women without nocturia in those classified with detrusor overactivity (15% vs 12%, p<0.05). Maximum bladder capacity in this group did not vary with increasing frequency of nocturia episodes. There was a statistically significant difference between women with nocturia and women without nocturia in the mixed incontinence group (7% vs 4%, p<0.05) and the bladder pain group (97% vs. 53%, p<0.05). Women in the bladder pain group demonstrated reduced bladder capacity with increasing frequency of nocturia (see Fig. 1).
Interpretation of results
In contrast to urodynamic studies performed in men, the presence of nocturia does not affect the peak flow rate in women. Neither does it affect the outcome of the filling phase during cystometry. Nocturia is a feature of women with detrusor overactivity and mixed incontinence but not urodynamic stress incontinence. Maximum bladder capacity remains similar in women with urodynamic stress incontinence and detrusor overactivity irrespective of voiding frequency at night. Women with nocturia were demonstrated to have a high prevalence of bladder pain during filling and were found to have reduced bladder capacity with increasing frequency of nocturia.