Nocturnal cycler-assisted peritoneal dialysis (NPD) improves sleep apnea by augmenting middle molecule clearance and reducing upper airway edema

Abstract

We recently showed that nocturnal cycler-assisted peritoneal dialysis (NPD) may have a therapeutic edge over continuous ambulatory peritoneal dialysis (CAPD) in sleep apnea (SA) associated with renal failure. To further dissect the underlying biophysical mechanisms, we extended our investigational tools to include magnetic resonance imaging (MRI) of the upper airway and urea kinetics during sleep. In a fixed-sequence intervention study, 35 incident patients [pts (mean age: 54.5±13.4 years)] underwent one polysomnography (PSG) during mandatory NPD while awaiting CAPD training, and a second PSG after being established on stable CAPD. The prevalence of SA, defined as an apnea–hypopnea index (AHI) ≥ 15, was 17.1% during NPD and 40.0% during CAPD (p=0.008). Mean AHI increased from 7.7±2.32 during NPD to 18.9±3.77 during CAPD (p < 0.001). The central (CSA) and obstructive (OSA) forms of SA were both significantly less severe during NPD. Total body water (TBW) by bioelectrical impedance analysis was lower during NPD than during CAPD (32.6±6.77 L vs. 35.0±7.1 L, p=0.004), and NPD delivered greater reductions in TBW (–3.06±0.35 L vs. –1.07±0.31 L, p=0.015) and hydration fraction (–4.05%±0.51% vs. – 0.62%±0.44%, p=0.005) during sleep. Nightly peritoneal Kt/V (pKt/V) and creatinine clearance (pCCr) derived solely from overnight effluent were both higher during NPD than during CAPD (pKt/V: 0.29±0.06 vs. 0.063±0.027, p < 0.001; pCCr: 4.94±1.33 L vs. 1.77±0.74 L, p < 0.001). Among 10 pts who underwent MRI, pharyngeal volume and minimum pharyngeal cross-sectional area were higher (p < 0.05) and tongue volume was lower (p < 0.01) during NPD than during CAPD, signifying a more patent upper airway during NPD. Compared with CAPD, NPD may alleviate SA in pts with chronic renal failure by achieving better fluid and middle-molecule clearance during sleep, respectively resulting in less upper airway edema and hence less OSA, and less depressed respiratory drive and hence less CSA.