Diurnal and nocturnal diuresis and natriuresis in obstructive sleep apnea. Effects of nasal continuous positive airway pressure therapy.

Excessive nocturnal diuresis and natriuresis have been reported in patients with sleep apnea. The mechanisms responsible for these alternations in nocturnal renal function have not been clearly identified. To gain further insight into this matter, we studied 12 patients (one woman) with a mean +/- SD age of 50 +/- 9 yr and body mass index of 36.9 +/- 8.6 kg/m2. Polysomnography showed in all a sleep apnea syndrome with an apnea-hyponea index (AHI) of 81.3 +/- 41.7. Treatment with nasal continuous positive airway pressure (nCPAP) resulted in an AHI of 19.4 +/- 13.7 and in normalization of sleep characteristics. Diurnal renal function was normal in all subjects. Although untreated, patients showed an abolition of the well-known decrease in diuresis and natriuresis during the night (diurnal and nocturnal diuresis 56.3 +/- 26.8 and 77.2 +/- 33.4 ml/h, respectively, p = NS; diurnal and nocturnal fractional urinary Na+ excretion 0.42 +/- 0.09 and 0.70 +/- 0.55 ml/100 ml glomerular filtration [GF], respectively, p = NS). Results of nocturnal studies under nCPAP therapy showed a significant decrease in diuresis and natriuresis (nocturnal diuresis before and under nCPAP, respectively: 90.4 +/- 27.3 and 70.6 +/- 25.1 ml/h, p less than 0.02; nocturnal fractional urinary sodium excretion before and under nCPAP, respectively: 0.76 +/- 0.53 and 0.44 +/- 0.37 ml/100 ml GF, p less than 0.03). Morning blood levels of renin, aldosterone, antidiuretic hormone, epinephrine, and atrial natriuretic factor showed no significant difference before and under nCPAP, whereas norepinephrine significantly decreased from 309.5 +/- 104.2 before to 230.4 +/- 88.4 pg/ml under nCPAP (p less than 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)