Enhanced cardiorespiratory coupling in patients with obstructive sleep apnea following continuous positive airway pressure treatment

Background: Weak cardiorespiratory coupling (CRC) has been suggested in patients with obstructive sleep apnea (OSA), but the effects of continuous positive airway pressure (CPAP) on CRC remain unclear. We investigated the effects of CPAP treatment on CRC in patients with severe OSA to examine possible reversibility of altered CRC. Methods: High-resolution electrocardiograms (ECGs) and respiratory signals were simultaneously recorded for 13 never-treated OSA patients at baseline and after CPAP treatment. The analyses were performed on a 15-min daytime recording of ECG and respiration. Heart rate variability (HRV) indices were extracted from ECGs. After computing the sample entropy (SampEn) to quantify the regularity of both heart rate (SampEn(RR)) and respiration rhythm (SampEn(resp)), cross-sample entropy (cross-SampEn) was calculated to measure the interaction between the two signals. Cross-SampEn denotes asynchrony between heart rate and respiration, and thus negatively correlates with CRC. Results: Lower SampEn(RR) and higher cross-SampEn as well as a shift toward sympathetic dominance were found in OSA patients compared with age-and gender-matched controls. CPAP treatment was associated with improved sympathovagal balance, increased SampEn(RR), and enhanced CRC, corresponding to a decrease in the cross-SampEn value from 0.71 +/- 0.08 to 0.49 +/- 0.06 (P < .001). The effect sizes for the CPAP-induced changes in sympathovagal balance, SampEn(RR), and cross-SampEn were medium to large (0.54-0.90). Conclusions: The findings of our study indicate reduced CRC in untreated OSA patients and suggest that CPAP treatment may reverse this abnormality. (C) 2013 Elsevier B. V. All rights reserved.