Hypoxia-associated Component of RR-interval Fluctuations in Patients with Obstructive Sleep Apnea Syndrome

An RR-interval fluctuation has been used as an important clinical tool for identifying a patient at risk in cardiovascular disease. However, the role of hypoxia on RR-interval fluctuations has not been determined. Methods and Results. We performed ambulatory ECGs monitoring and measured overnight arterial oxygen saturation (SpO2) in 26 patients with obstructive sleep apnea syndrome in whom sever hypoxia occurred during sleep. By means of maximal entropy method, time series of ECG-RR intervals were transformed into frequencies. The minimal SpO2 during sleep were compared with spectrum powers of the following frequency ranges; 1) 0.0001 - 0.05 Hz, 2) 0.05 - 0.1 Hz, 3) 0.1 - 0.15 Hz, 4) 0.15 - 0.2 Hz, 5) 0.2 - 0.25 Hz, 6) 0.25 - 0.3 Hz, and 7) 0.3 - 0.5 Hz. Among the seven analyzed frequencies, the increase in the 0.05 - 0.1 Hz power of RR-interval fluctuations was linearly correlated with the minimal SpO2 during sleep (r=.80, p<.001). Conclusion. This study revealed that hypoxia contributes to 0.05 - 0.1 Hz RR-interval fluctuations in patients with obstructive sleep apnea syndrome. RR-interval fluctuations will provide important information about hypoxia.