Tohoku J. Exp. Med., 2016 May, 239(1)

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

KOICHIRO SUGIMURA,¹ TSUYOSHI SHINOZAKI,² SHIGEFUMI FUKUI,³ HIROMASA OGAWA⁴ and HIROAKI SHIMOKAWA¹

¹Department of Cardiovascular Medicine, Tohoku University Graduate School of Medicine, Sendai, Miyagi, Japan
²Division of Cardiology, National Hospital Organization Sendai Medical Center, Sendai, Miyagi, Japan
³Pulmonary Vascular Disease Unit, National Cerebral and Cardiovascular Center Hospital, Suita, Osaka, Japan
⁴Department of Occupational Health, Tohoku University Graduate School of Medicine, Sendai, Miyagi, Japan

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 (O₂) 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 O₂ 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 O₂ at either the first or second night in a randomized manner. To predict the percentage reduction in apnea-hypopnea index (%ΔAHI) in response to the nocturnal O₂ 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 (P_ETCO₂). Nocturnal O₂ therapy significantly decreased AHI (from 32 ± 13 /h to 12 ± 10 /h, P < 0.0001). Among the possible predictors, P_ETCO₂ was the only variable that is predictive of % changes in AHI. Receiver operating characteristics analysis determined 4.25% as the optimal cutoff P_ETCO₂ level to identify responder to nocturnal O₂ therapy (> 50% reduction of AHI), with 88.9% of sensitivity and 66.7% of specificity. In conclusion, P_ETCO₂ is useful to predict the efficacy of O₂ therapy in CHF patients with CSA, providing important information to the current nocturnal O₂ therapy.

keywords —— central sleep apnea; chronic heart failure; end-tidal CO₂; oxygen therapy; sleep disordered breathing

© 2016 Tohoku University Medical Press

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Tohoku J. Exp. Med., 2016, 239, 39-45

Correspondence: Koichiro Sugimura, M.D., Ph.D., Department of Cardiovascular Medicine, Tohoku University Graduate School of Medicine, 1-1 Seiryo-machi, Aoba-ku, Sendai, Miyagi 980-8574, Japan.

e-mail: ksugimura@cardio.med.tohoku.ac.jp