End-Tidal CO2 Tension Is Predictive of Effective Nocturnal Oxygen Therapy in Patients with Chronic Heart Failure and Central Sleep Apnea

Central sleep apnea (CSA) is characterized by recurring cycles of crescendo-decrescendo ventilation during sleep, and enhances sympathetic nerve activity. Thus CSA has a prognostic impact in patients with chronic heart failure (CHF). Although nocturnal oxygen (O-2) therapy decreases frequency of CSA and improves functional exercise capacity, it is also known that some non-responders to the therapy exist. We thus aimed to identify predictors of responders to nocturnal O-2 therapy in CHF patients with CSA. In 12 CHF patients with CSA hospitalized at our department, sleep study was performed at 2 consecutive nights. Patients nasally inhaled O-2 at either the first or second night in a randomized manner. To predict the percentage reduction in apnea-hypopnea index (%Delta AHI) in response to the nocturnal O-2 therapy, we performed multiple regression analysis with a stepwise method with variables including age, brain-natriuretic peptide, circulation time, baseline AHI, hypercapnic ventilatory response and end-tidal carbon dioxide tension (PETCO2). Nocturnal O-2 therapy significantly decreasedAHl (from 32 +/- 13 /h to 12 +/- 10 /h, P < 0.0001). Among the possible predictors, PETCO2 was the only variable that is predictive of % changes in AHI. Receiver operating characteristics analysis determined 4.25% as the optimal cutoff PETCO2 level to identify responder to nocturnal O-2 therapy (> 50% reduction of AHI), with 88.9% of sensitivity and 66.7% of specificity. In conclusion, PETCO2 is useful to predict the efficacy of O-2 therapy in CHF patients with CSA, providing important information to the current nocturnal O-2 therapy.