Hypothesis / aims of study
Circadian rhythm (CR) exists in many human physical activity, which include endocrinological secretions, renal function and blood pressure. As bladder function also naturally fluctuates during the day, the state of urination also differs depending on the time of day. We previously evaluated the CR of urination in a group of hospitalized male patients with nocturia evaluated by toilet uroflowmetry over a 24-hour period and reported that voided volume (VV) was significantly higher in the nighttime than that in the daytime after adjustment for age. We also reported that the maximal flow rate (MFR) was the lowest just after waking up, and voiding time at nighttime was significantly longer than that in the morning even after adjustment for age and VV. However, because the lower urinary tract of women is anatomically different from that of men, it was speculated that urination in women, even if women had the CR as men do, may be different from that of men shown in our previous study. Unfortunately, no studies of the CR of urination in women with nocturia have been reported. Therefore, we planned a study on women using the same methodology as the study that elucidated the CR of urination in men.
Study design, materials and methods
In this retrospective study, we evaluated 2602 urinations of 58 female patients (age, 68.4 ± 15.2 years) who were hospitalized in our institution for urological disease. The number of incidents of nocturia was 2.5 ± 1.1. We assessed VV as averages of every hour by generalized linear mixed models with an identity link function to adjust for personal bias and age. MFR and voiding time were analyzed by the same method after adjustment for age, personal bias and voided volume. We also compared these CRs between women < 70 and > 70 years. Statistical analyses were performed with SPSS version 24.0 (SPSS Inc., Chicago, IL, USA).
Results
Our subjects were hospitalized for the careful examination of hematuria in 33 women, for examination of hydronephrosis in 13 women, for conservative treatment for urolithiasis in 8 women and for other reasons in 4 women. Co-morbidities were found for hypertension in 20 women, hyperlipidemia in 16 women and diabetes in 4 women. VV from 00:00-01:00 (253.8 ± 12.6 ml, P < 0.01), 02:00-3:00 (265.3 ± 13.5 ml, P < 0.01), 03:00-4:00 (250.2 ± 12.9 ml, P < 0.05) and 04:00-05:00 (256.9 ± 12.3 ml, P < 0.01) were significantly higher than that from 06:00-07:00 (205.6 ± 11.7 ml; Fig. 1A). The lowest VV was observed from 09:00-10:00 (165.7 ± 13.3 ml). MFR from 14:00-15:00 (21.3 ± 0.94 ml/s, P < 0.01), 15:00-16:00 (21.9 ± 0.95 ml/s, P < 0.01), 16:00-17:00 (22.5 ± 0.94 ml/s, P < 0.01), 17:00-18:00 (20.9 ± 0.92 ml/s, P < 0.05), 18:00-19:00 (21.8 ± 0.94 ml/s, P < 0.01) and 20:00-21:00 (21.1 ± 0.92 ml/s, P < 0.01) were significantly higher than that from 06:00-07:00 (18.8 ± 0.93 ml/s; Fig. 1B). The lowest MFR was observed from 00:00-01:00 (18.3 ± 0.97 ml/s).
Interpretation of results
Voiding time showed no statistically significant difference between the values at any time of day and that from 06:00-07:00 (Fig. 1C). We also showed that the CR of voided volume becomes less clear in the elderly women. However, no significant difference was found in the maximum flow rate and voiding time regarding the pattern of the CR between women < 70 and > 70 years old.