Analysis of Nocturia Determinants Using a Novel Portable Urine‐Measuring Device

ABSTRACT

Aims

To investigate the relationship between nocturia and values measured using a novel multifunctional portable urine‐measuring device.

Methods

Thirty‐five older men with nocturia and/or high‐normal or high blood pressure were enrolled to record measurements on one full day (24 h) and two nights using the portable device during urination. Participants used a semi‐conical cup with a small hole equipped with a conductivity sensor, temperature sensor, and timer to measure urine volume, salt content, urine temperature, and urination speed.

Results

Two participants were excluded owing to oliguria. The mean age of 33 participants was 75.2 ± 7.4 years (range: 55–85 years). The mean nocturnal urination frequency, including the first urination after waking, was 2.1 ± 0.6 times. Simple correlation analysis revealed that nocturnal urine frequency significantly increased with nocturnal urine volume (r = 0.65, p < 0.001) and salt content (r = 0.57, p < 0.001) but not with 24‐h urine volume and salt content. Furthermore, the frequency significantly decreased with nocturnal urine temperature (r = −0.37, p < 0.05). No significant relationship was observed between morning blood pressure and nocturnal urination frequency. A high correlation was observed between nighttime urine volume and salt content (r = 0.73, p < 0.001).

Conclusions

Nocturnal urine volume, salt content, and urine temperature are significantly correlated with nocturia. The portable urine‐measuring device could guide nocturia reduction through facilitation of the reduction of nocturnal urine volume and salt content, in addition to urine temperature monitoring.

1. Introduction

Nocturia is highly prevalent and one of the most distressing lower urinary tract symptoms among the elderly [1]. Nocturia can lead to sleep disorders [2, 3], arterial stiffness [4], elevated blood pressure [5, 6, 7, 8], falls, fractures [9, 10], and mortality [11], in addition to affecting quality of life negatively [12, 13]. Song et al. explored the influence of excessive drinking on nocturia [14], whereas Doom et al. [15] reported that a maximum voided volume, lower urinary tract symptoms, and 24‐h polyuria are key factors influencing nocturia [15].

Several studies have investigated the relationship between nocturia and salt intake, reporting a significant correlation [16, 17, 18, 19]; however, most have estimated daily salt intake using dietary surveys or spot urine tests. Since most ingested salt is excreted in urine, measuring 24‐h urinary salt (sodium chloride) excretion is the gold standard for determining dietary salt intake. However, this method is burdensome for patients, as it requires them to store urine in a container and transport it to a medical institution. Analyzing the amount of sodium and creatinine in spot urine is a simpler method to estimate salt intake, corrected by estimated creatinine based on factors, such as height, weight, age, and sex [20]. Despite its simplicity, this method lacks sufficient accuracy [21], and measuring creatinine and salt content at home presents challenges. We developed a simple self‐monitoring device that estimates salt intake by analyzing overnight urine data using an integrated calculation algorithm in collaboration with Kohno ME Laboratory (Kawasaki, Japan) [22]. This method required collecting urine in a cup, and the accuracy rated as fair [21]. Thus, a device that could measure urine and salt amounts without urine storage more accurately was required. Core body temperature is a vital sign and fever is a key indicator of disease. The gold standard for the determination of core body temperature is pulmonary artery catheter measurement, which is invasive and time‐consuming. The temperature of urine immediately after urination represents the core body temperature [23].

We considered it necessary to develop a multi‐functional urine measuring device that could measure urinary volume, salt content, and temperature immediately after urination, and the urination rate, and we propose a tool [24].

Joint research with Zeo System Co. Ltd. (Yokohama, Japan) led to the development of a device applying the principle of water clocks and Trichilly's theorem [25]. This study aimed to investigate the relationship between nocturia and values measured using a novel multifunctional portable urine‐measuring device.

2. Materials and Methods

2.1. Participants

The clinical trial was conducted from January to March 2024, at home. Owing to the design of the device, which required accurate alignment with the urination opening, the study was limited to men. A total of 35 older volunteers and patients of university hospitals who satisfied the nocturia definition, urination at least once after going to bed and before waking up and, or who had normal high or hypertension (systolic blood pressure of ≥ 130 mmHg or diastolic blood pressure of ≥ 85 mmHg).

2.2. Measuring Device and Assessment

The structure of the portable urine‐measuring device, manufactured by GEO System Co. Ltd (Yokohama, Japan), is presented in Figure 1.

Figure 1.

Novel portable urine measuring device.

The device, with built‐in temperature in the upper dish and salt sensors in the upper dish and bottom of the cup, uses a unique conical perforated cup that applies the principle of a water clock. A conductivity sensor is used to measure the salt (NaCl) concentration. The concentration of salt was adjusted by correlation formula to be between the value obtained with the ion electrode method and the value measured based on the conductivity method considering measurement based on conductivity is affected by electrolysis of some elements such as potassium [22, 26]. Before urination, participants pushed the power button.　They urinated into the opening of the cup. After urination, the urine volume, salt content, and temperature data were displayed.　The measured data and daytime in the device were transferred to a PC or tablet via Bluetooth. The data included urine volume, salt concentration, salt amount, urination time, mean urine flow rate, and urine temperature.

Measurements were recorded during urination for 4 days: one 24‐h period and two nights. Participants recorded the date and time, wake‐up time, bedtime, and urination times in a log. Blood pressure was measured twice in a sitting position using a home blood pressure monitor after waking up and urinating. A simple regression analysis was performed to examine the relationship between age, BMI, urine output, salt content, urine temperature, mean urination rate, blood pressure, and the number of nocturnal urination.

2.3. Statistical Analysis

All data were analyzed using the Bellcurve (Social Survey Research Information Co. Ltd.) in MS Excel. The data are expressed as mean ± SD. Spearman's correlation test was used to assess the relationship between the nocturnal urine frequency and variables, in addition to the relationship between urine volume and salt content. All analyses were two‐sided at the 5% significance level.

3. Results

3.1. Participant Characteristics

The participants included 15 older volunteers, 10 outpatients with renal conditions and or hypertension, and 10 outpatients with urological conditions. Two participants were excluded owing to having urine volumes of only approximately 25 mL per urination and oliguria, which is defined as < 400 mL urine output per day. The characteristics of the 33 remaining participants were as follows (Table 1).

Table 1.

Participants' characteristics.

Age (years)	75.2 ± 7.4
Body mass index (kg/ｍ2)	23.8 ± 3.2
24‐h urine volume (mL)	1586 ± 650
Nocturnal urine volume (mL)	574 ± 302
Maximum voided volume (mL)	341 ± 104
Nocturnal polyuria index (%)	36.7 ± 15.4
24‐h urinary salt excretion (g)	6.8 ± 2.7
Nocturnal urinary salt excretion (g)	2.4 ± 1.3
Daytime urine temperature (°C)	36.8 ± 0.3
Nocturnal urinary temperature (°C)	36.5 ± 0.3
Daytime Qmean (mL)	8.3 ± 3.5
Nighttime Qmean (mL)	10.2 ± 4.6
Nighttime urine frequency (No)	2.1 ± 0.6
Hypertension (%)	63.6
Mean SBP (mmHg)	138 ± 16.1
Mean DBP (mmHg)	81 ± 9.0

Abbreviations: DBP, diastolic blood pressure; Qmean, mean urinary flow rate; SBP, systolic blood pressure.

Mean age 75.2 ± 7.4 years (range: 58–88 years), BMI 23.8 ± 3.2, and the average number of urinations at night, including the number of first urinations after waking, of 2.1 ± 0.6. The daily urine output was 1586 ± 650 mL, and nocturnal urine volume after going to bed, including the number of first urinations after waking, of 574 ± 302 mL. Maximum urine volume was 341 ± 104 mL and nocturnal polyuria index was 36.7 ± 15.4%. Twenty‐one participants (63.6%), including 18 participants receiving antihypertensive drugs and 3 not taking antihypertensive drugs, had hypertension. The mean systolic and diastolic blood pressures were 138 ± 16.1 and 81 ± 9.0 mmHg, respectively. The mean urination rates during the day and night were 8.3 ± 3.5 and 10.2 ± 4.6 mL/s, respectively.

3.2. Measurement Status

The accuracy of urine volume measured using the novel device was inferior to that of the gravimetric method, although it was close (r = 0.95), and the accuracy salt concentration measured was near that of the ion electrode method (r = 0.92).

A simple correlation analysis was performed to examine the relationship between age, BMI, urine volume, salt content, urine temperature, mean urination rate, blood pressure, and number of nocturnal urinations. The findings suggested that the number of nocturnal urinations increased with an increase in urine volume (n = 33, r = 0.65, p < 0.001) (Figure 2) and nocturnal urine salt content (n = 31, r = 0.57, p < 0.001) (Figure 3), and decreased with an increase in urine temperature (n = 30, r = −0.39, p < 0.05) (Figure 4).

Figure 2.

Relationship between overnight urine volume and nighttime urine frequency.

Figure 3.

Relationship between overnight urine salt and nighttime urine frequency.

Figure 4.

Relationship between overnight urine temperature and nighttime urine frequency.

There was no significant relationship between salt concentration and nocturnal urination frequency (r = −0.19, p = 0.29). There was a high correlation between nocturnal urine volume and salt content (n = 31, r = 0.73, p < 0.001) (Figure 5), whereas there was no significant relationship between nocturnal urine volume and salt concentration (r = −0.08, p = 0.67).

Figure 5.

Relationship between overnight urine salt and overnight urine volume.

Salt and temperature measurements were missing for two and three participants, respectively, owing to wiring failure.

Although the relationship with age was not significant, a trend was observed where older individuals urinated more frequently (r = 0.32, p = 0.07). No significant relationship with BMI (r = 0.13, p = 0.46), 24‐h urine volume (r = 0.07, p = 0.73), or salt content (r = 0.041, p = 0.82) was observed. In addition, no significant relationship was observed between morning blood pressure and nocturnal urination frequency (SBP: r = −0.26, p = 0.15; DBP: r = −0.26, p = 0.15). The relationship between average urination rate and number of urinations at night was r = −0.35 (p = 0.051) and −0.17 at night (p = 0.36). The relationship between daytime urination rate and number of urinations was not significant; however, it approached significance.

4. Discussion

Using a new portable urine‐measuring device, we examined daily urine volume, urinary salt content, urine temperature immediately after urination, and urination rate in older individuals to investigate the relationships with nocturia. The trial results indicated that nocturnal urine volume, nocturnal urinary salt content, and urine temperature (corresponding to core body temperature) correlated with nocturia, whereas daily urine volume and salt content are not. Whereas daily salt intake estimated from dietary tests and spot urine analysis are reportedly related to nocturia [17, 18, 19], the present study confirmed that reducing nighttime urine volume and salt intake are effective strategies of reducing nocturia, even if daily salt intake remains at the same level. We also confirmed that nocturnal urinary salt concentration is not correlated with nocturia. We think it is reasonable, considering urinary salt concentration was not correlated with nocturnal urine volume.

An application in the device records a urination diary divided into nighttime urine and 24‐h urine. Using the data above could facilitate the reduction of nocturia. Although measurement of each urination event for 24 h may be challenging, it is relatively easy to measure urine overnight at home. Therefore, the novel device will be useful to reduce nocturnal urine volume and salt content. Daily salt intake is reportedly associated with leg edema and nocturnal urinary volume [27]. Effective strategies other than reducing salt intake include applying diuretics after breakfast, consuming potassium‐rich foods during the day, and releasing excess water and salt through daytime exercise and sweat. Avoiding salt and water intake before dinner or bedtime and extending the time between dinner and sleep could also be beneficial.

Our findings confirmed that lower urine temperature correlates with frequent nocturnal urination. We believe it could be the body's response to regulate core temperature during sleep to allow less unnecessary evaporation in people with low core body temperature. The environment potentially influences core body temperature. The present study was conducted in winter. Maintenance of a warm environment could decrease nocturia [28].

We observed no relationship between number of nighttime urinations and blood pressure upon waking. This may be attributed to the fact that over a half of the participants (18 out of 33) were on antihypertensive medication. The impact of nocturnal urination frequency is better examined through nighttime blood pressure monitoring via 24‐h measurement rather than home blood pressure measurements upon waking [5]. This may explain the lack of relationship between waking blood pressure and nocturnal urination in the present study.

However, our study had a few limitations, including restriction of the study population to men owing to the difficulty of device use in the sitting position. Further studies should be conducted to address the feasibility of using the device in a sitting position, as many men also urinate in a sitting position in western‐style toilets. This trial was conducted during the colder months from January to March; therefore, the observed effects may vary in summer.

Monitoring urine temperature could aid in the early detection of infections and heat stroke [29], and urination rate could help identify urination disorders such as prostatic hyperplasia [30].

Monaghan et al. reported that sodium restriction counseling improved nocturia in patients at a cardiology clinic [18]. However, nocturia cannot be fully diagnosed or treated by merely examining or interviewing patients at the hospital. Earlier, we developed an electronic urine salt monitoring device that was used by the patients for more than 3 weeks. During that time, the participants measured daily salt intake estimated from nighttime urine and morning blood pressure to examine their relationship and confirmed salt reduction and blood pressure lowering [22, 31].

This was an observational study that analyzed the results of patient urine measurements using a novel portable device at home. The aim of the study was to investigate the factors influencing nocturia. Using the device at home for several weeks could facilitate nocturia management by doctors and nutritionists by monitoring nighttime urinary volume amount, salt content, and temperature, as well as by enabling informed counseling related to diet, beverage intake, exercise, and sleeping environmental temperature. We intend to conduct intervention trials in the future.

5. Conclusion

Nocturnal urine volume, salt content, and urine temperature are significantly correlated with nocturia, with nocturnal salt content strongly correlated with nocturnal urine volume. The portable urine‐measuring device could facilitate nocturia management through facilitation of the reduction of nocturnal urine volume and salt content, in addition to urine temperature monitoring.

Author Contributions

Kotaro Yamasue contributed to project development, data collection, and manuscript writing. Tomohiko Kaneoka and Tomoyuki Tatenuma contributed to data collection. Masanari Umemura supervised the work.

Ethics Statement

This study was approved by the Yokohama City University Ethics Committee (approval number: F231100035). All procedures were conducted in accordance with the principles of the Declaration of Helsinki. All participants provided informed consent.

Conflicts of Interest

The authors declare no conflicts of interest.

Data Availability Statement

The data supporting the findings of this study are available from the corresponding author upon reasonable request.