高齢者夜間頻尿における脳性ナトリウム利尿ペプチド(BNP)と相対的夜間多尿の関連  [in Japanese] ASSOCIATION WITH RELATIVE NOCTURNAL POLYURIA USING BNP (BRAIN NATRIURETIC PEPTIDE) IN ELDELY PATIENTS WITH NOCTURIA  [in Japanese]

(目的)高齢者の夜間頻尿の原因として過活動膀胱(Overactive bladder : OAB),睡眠障害(再入眠障害)とともに問題となっているのが夜間多尿である.高齢者の夜間多尿に高血圧をはじめとする循環器障害がどの程度影響しているかをみるため,心不全の予後評価に有用とされている脳性ナトリウム利尿ペプチド(Brain natoriuretic peptide : BNP)を用いて1日尿量,昼間尿量,夜間(睡眠中)尿量,夜間尿量率(NPi)との関連性を検討した.(対象と方法)対象は2002年10月から2005年9月の間に1晩に1回以上の夜間頻尿を主訴に外来を受診した128例(男92例, 女36例)である.方法は外来受診時BNPの測定を行い,同時に排尿チャート(Frequency volume chart : FVC)を4日間以上記載してもらった.FVCより1日尿量,昼間尿量,夜間(睡眠中)尿量,夜間尿量率(NPi)を算出し,関連性について検討した.除外対象を血清クレアチニン値1.2mg/dlを越える腎機能低下症例,明らかな心疾患(慢性心不全,心筋梗塞,来治療の狭心症,心房細動などの不整脈など)を有する症例,排尿日誌を正確に記入できない症例とした.なお,排尿障害の治療として使用していたα1-blockerや坑コリン剤は継続投与のままとした.(結果)全症例のBNP値は46.3±39.6pg/mlと高値であった.全症例の1日尿量は1,555±458ml,昼間尿量は935±322ml,夜間尿量は624±251mlで,NPiは40.1±10.5%と高値であった.BNPは1日尿量(p=0.0215)と昼間尿量(p=0.0004)との間に有意な負の相関があり,NPiとの間には有意な正の相関(p=0.003)が認められた.BNPを潜在性心疾患の可能性があるといわれている50pg/ml未満と以上で分けてみると,NPiは50pg/ml未満群では38.14±10.07%であるのに対し,50pg/ml以上群では43.97±10.48%と有意に高値を示した(p<0.0029).(結論)高齢者では潜在的に軽度の心不全を持っている症例が多く,昼間に尿量減少を示す傾向かあり,昼間に生じた軽度のうっ血状態を改善するために相対的に夜間尿量が増加し,心負荷を軽減している可能性が示唆された.夜間多尿による夜間頻尿症例のなかには少なからず潜在性心不全による多尿患者が含まれている可能性があり,バゾプレッシン製剤を眠前に使用するか,利尿剤を昼間に使用して相対的に夜間尿量を減少させるのかの指針にBNPが有効であると思われた.

(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, α1-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.