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

Abstract

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 (SpO 2 ) 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 SpO 2 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 SpO 2 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.