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Effect of continuous positive airway pressure on nocturnal urine production in patients with obstructive sleep apnea syndrome
Miyazato M, Tohyama K, Touyama M, Nakamura H, Oshiro T, Ueda S, Saito S
Commentary by Don Bliwise:
This is a study of sleep apnea patients that examined the effect of continuous positive airway pressure (CPAP) treatment on urine production. CPAP is a widely employed treatment for sleep apnea and consists of pressurized room air, usually delivered at a constant pressure (typically with a mask) as the patient sleeps. In most cases of sleep apnea, it is uniformly regarding as one of the most successful of treatments for the condition, although there can be comorbidities, e.g., heart failure, where its use may be more problematic.
Sleep apnea has been shown in observational studies to be related to nocturia and CPAP has been shown to reduce the number of nocturia episodes, but this paper is one of the first to show a decrease, not only in nocturnal voiding episodes, but also in overnight urine volumes under CPAP treatment. While total overnight urine volumes were nearly cut 50%, total 24 hr urine volume was essentially unchanged and mean voided nocturnal volume at night was unchanged. These results are consistent with treatment of sleep apnea when it occurs in the context of nocturia, perhaps even as a first line treatment. The study appeared to be well done and candidly reported (only about 75% of the patients continued to use CPAP after a period of about 3 months), but was not intended to fully elucidate the specific mechanisms by which CPAP decreases nocturnal urine production. For example, elevated atrial natriuretic peptide (ANP) accompanying sleep apnea has often been assumed to be a cause of increased urine production in these patients. The current study did not study ANP levels but did note that brain natriuretic peptide BNP, another peptide produced in the myocardium, did not change after CPAP. This at least raises the possibility that CPAP may have reduced nocturia episodes not via biochemical pathways but rather because it allowed patients to sleep more soundly without interruptions. Both animal and human (pediatric and adult) data have indicated that urine production is increased by sleep deprivation. By virtue of its ability to allow patients to sleep with less fragmentation, CPAP may be countering this effect. Although the exact mechanisms remain open to additional research, the finding is very clear: use of CPAP improves nocturia.