Effect of Lateral Body Position on Heart Rate Variability in Patients with Sleep Apnea Syndrome

Abstract

Sleep apnea syndrome (SAS) can exacerbate cardiovascular disease by augmenting activity of the sympathetic nervous system. One method of treating SAS is via modulation of body posture. Therefore, the goal of the present study was to investigate whether assuming the lateral position during sleep can influence autonomic nervous system activity, as assessed by measurement of heart rate variability (HRV). Six patients with coronary artery disease (CAD) complicated by SAS underwent serial measurements of HRV and arterial blood oxygen saturation (SPO2) during sleep. Online analyses for HRV was performed using five consecutive RR intervals from electrocardiography using the modified Maximum Entropy Method. Low frequency spectra (LF, 0.04–0.15 Hz), high frequency spectra (HF, 0.15–0.40 Hz) and the ratio of low and high frequency spectra (LF/HF ratio) were continuously calculated. HRV and SPO2 measurements were performed after 30 min of sleep in different sleeping positions (supine vs. lateral) with or without supplementary oxygen administration by nasal cannula. The LF and LF/HF ratio were significantly smaller in the lateral position with and without oxygen when compared with the supine position with or without oxygen (LF: Supine to Lateral position, from 673 ± 643 ms2/Hz to 201 ± 221 ms2/Hz, P < 0.05; Supine to Lateral position with supplementary oxygen, from 617 ± 511 ms2/Hz to 288 ± 389 ms2/Hz, P < 0.05; LF/HF ratio: Supine to Lateral position, from 9.4 ± 643 to 2.9 ± 1.9, P < 0.05; Supine to Lateral position with supplementary oxygen, from 6.1 ± 3.5 to 2.3 ± 1.5, P < 0.05). Further, arterial blood oxygen saturation was higher in the lateral position than in the supine position and was higher with supplementary oxygen than without supplementary oxygen (Supine, 86.7 ± 4.3%; Lateral, 94.5 ± 0.8%; Supine + O2, 93.2 ± 4.5%; Lateral + O2, 98.2 ± 1.5%). In conclusion, the lateral position during sleep attenuated sympathetic nervous system activity and improved oxygenation in patients with concomitant CAD and SAS.