[Association with relative nocturnal polyuria using BNP (brain natriuretic peptide) in eldely patients with nocturia].

OBJECTIVE: In addition to overactive bladder (OAB) and sleep disorders (disturbance of additional sleep induction), nocturnal polyuria has been reported as an etiology of nocturia in elderly people. To investigate the influence of heart function on nocturnal polyuria in elderly people, we examined the association with nocturnal polyuria using brain natoriuretic peptide (BNP), which are useful for evaluating the prognosis of heart failure.

PATIENTS AND METHODS: The patients were 128 patients (92 males, 36 females) who were treated for nocturia in Kohsei general hospital and other relative hospital between October 2002 and September 2005. We measured BNP levels at physical examination. Simultaneously, the patients were instructed to write a frequency volume chart (FVC) for 4 days. 24-hour urine volume, Daytime urine volume, nocturnal (sleep) urine volume, nocturnal polyuria index (NPi) were calculated from FVC. The association was examined. However, alphal-blockers or anticholinergic agents that had been prescribed to treat urination disorders were continuously administered.

RESULTS: Overall, the mean BNP level was high, 46.3+/-39.6 pg/ml. The mean 24-hour urine volume was 1,555+/- 458 ml. The mean daytime urine volume was 935+/-322 ml. The mean nocturnal urine volume was 624+/-251 ml. The mean nocturnal urine volume rate was high, 40.1 - 10.5%. However, there was a close association between BNP and the 24-hour urine volume (p = 0.0215), the daytime urine volume (p = 0.0004), the NPi (p = 0.0003). The daytime urine volume decreased with the BNP level. The NPi increased with the BNP level. Patients were divided into 2 groups, a group with a BNP level less than 50 pg/ml and a group with a BNP level of 50 pg/ml or more. In the group with a BNP level less than 50 pg/ml, the nocturnal urine volume rate was 38.14+/-10.07%. In the group with a BNP level of 50 pg/ml or more, the rate was significantly higher (43.97+/-10.48%, p<0.0029).

CONCLUSIONS: These results suggest that many elderly patients latently have mild heart failure, and that relative nocturnal polyuria reduces cardiac load. Therefore, in patients with a high BNP level, administration of antidiuretic hormone to decrease nocturnal urine volume is risky. Administration of diuretics during the afternoon or evening may be safer.