Does Obstructive Sleep Apnea (OSA) cause Nocturnal Polyuria?

Obstructive Sleep Apnea as a Cause of Nocturnal Polyuria

Yes, obstructive sleep apnea (OSA) can cause nocturnal polyuria through several physiological mechanisms, and treatment of OSA with CPAP therapy can effectively reverse this condition. 1, 2

Pathophysiological Mechanisms

• OSA leads to nocturnal polyuria through increased secretion of atrial natriuretic peptide (ANP), which promotes sodium and water excretion by the kidneys 3
• The repeated episodes of apnea and hypoxia in OSA patients trigger ANP release, resulting in increased urine production during sleep 4, 3
• OSA increases arousals and the proportion of light sleep, raising the likelihood of waking, which then leads to urination once awake 2
• The urodynamic characteristics in OSA patients with nocturnal polyuria include weak detrusor contraction, decreased bladder compliance, and detrusor-sphincter dyssynergia 4

Clinical Evidence

• Studies have demonstrated significantly higher nocturnal urine volume, sodium excretion, and frequency of urination in OSA patients compared to healthy individuals 3, 5, 6
• More than 70% of patients with severe OSA (AHI > 50) report nocturnal micturitions more than twice a week, compared to less than 25% of healthy subjects 6
• The night-time frequency to void is significantly higher in OSA patients, with studies showing an average of 2.1 voids per night before treatment 7

Effect of CPAP Treatment

• CPAP therapy effectively reverses nocturnal polyuria in OSA patients by:
  • Significantly reducing nocturnal urine volume (from 902±297 to 447±130 ml) 3
  • Decreasing sodium excretion (from 150±33 to 89±35 mEq/12h) 3
  • Lowering ANP plasma concentrations (from 35±20 to 19±5 pg/ml) 3
  • Reducing night-time urinary frequency from 2.1 to 1.2 voids per night 7
  • Improving hours of undisturbed sleep and nocturnal polyuria index 7

Clinical Approach for Patients with Nocturia

• When evaluating patients with nocturia, screening for OSA symptoms should include questions about:
  • Gasping or stopping breathing at night
  • Daytime sleepiness
  • Non-refreshing sleep 1, 2
• Patients with nocturia who don't respond to conventional treatments should be evaluated for possible undiagnosed OSA 2
• A 72-hour bladder diary is recommended as part of the initial evaluation to document nocturia severity and overnight urine volume 1

Important Considerations

• Nocturnal polyuria in OSA patients is characterized by increased urine output, decreased osmotic pressure, and increased sodium excretion 4
• The relationship between OSA and nocturnal polyuria appears to be bidirectional - OSA can cause nocturnal polyuria, and frequent nighttime urination can disrupt sleep quality 1, 2
• Age is a confounding factor for nocturnal polyuria, but studies show that even when age-matched, OSA patients have significantly higher frequency of nocturnal micturitions compared to healthy subjects 6

By addressing the underlying OSA with CPAP therapy, clinicians can effectively manage nocturnal polyuria and improve patients' quality of life, sleep quality, and daytime functioning 7.