Abstract Body: Introduction: Supine hypertension affects most patients with autonomic failure (AF), complicates the treatment of orthostatic hypotension (OH) and induces nocturnal pressure diuresis, resulting in nocturnal volume depletion and worsening of daytime OH. We previously showed that continuous positive airway pressure (CPAP), by increasing intrathoracic pressure and reducing venous return, reduced supine blood pressure (BP), nocturia, and improved morning OH in these patients. The mechanism by which CPAP improves nocturnal diuresis in AF remains unclear, but it is explained in part by decreased pressure diuresis.
Hypothesis: We hypothesized that the CPAP-induced reduction in venous return and atrial pressure (Valsalva-like effect) would also decrease the release of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP), resulting in less diuresis.
Methods: In 8 AF patients with supine hypertension (age 70±2 yr, 6 men, 6 patients with peripheral AF and 2 with multiple system atrophy, supine systolic BP [SBP] 165±10 mmHg), we compared the effects of 2 hours of active CPAP (8-12 cm H2O as tolerated) versus sham CPAP (≤4 cm H2O) on SBP, plasma NT-proANP and NT-proBNP levels, and diuresis on two separate days in a single-blind, crossover, randomized study. Measurements were taken with patients awake and in the supine position before and at 1 h and 2 h of treatment.
Results: As expected, compared to sham, active CPAP (11±6 cm H2O) reduced supine SBP at 1 h (-7±7 mmHg vs. -19±7 mmHg, P=0.016) and 2 h (-5±8 mmHg vs. -14±7 mmHg, P=0.016). This BP reduction with CPAP was associated with a change from baseline in NT-proANP of -19±11% at 1 h (vs +27±17% with sham, P=0.009) and -17±15% at 2 h (vs +25±26% with sham, P=0.031), whereas the change in NT-proBNP did not differ significantly between groups. Urine output, however, was similar during both treatments (CPAP 273±64 vs. sham 283±86 mL, P=0.913).
Conclusion: CPAP acutely reduced supine SBP and ANP in awake AF patients with supine hypertension, whereas diuresis did not differ between treatments, likely due to the short 2 h-study. In conclusion, our findings suggest that the CPAP-induced reduction in ANP may contribute to the decrease in nocturia we previously observed with CPAP and may provide a hormonal mechanism for the nocturia in AF patients.