Skin sympathetic nerve activity in patients with obstructive sleep apnea.

Abstract Background Obstructive sleep apnea (OSA) is associated with increased cardiac arrhythmia and sudden cardiac death. We recently developed a new method (neuECG) to non-invasively measure electrocardiogram and skin sympathetic nerve activity (SKNA). Objectives To test the hypothesis that the SKNA measured during sleep study is higher in patients with OSA than without OSA. Methods We prospectively recorded neuECG and polysomnography in 26 patients undergoing a sleep study. Sleep stages were scored into rapid eye movement (REM), non-REM (NREM) sleep stage 1, NREM2, NREM3. Average voltage of SKNA (aSKNA) and SKNA burst area were calculated for quantification. Apnea-hypopnea index (AHI) of >5/hr was used to diagnose OSA. Results There was a positive correlation (r=0.549, p=0.018) between SKNA burst area and the arousal index in OSA but not in the control group. The average SKNA (aSKNA) during sleep was 0.61 ± 0.09 μV in OSA patients (N=18) and 0.53 ± 0.04 in control patients (N=8, p=0.025). The burst area was 3.26 [1.90-4.47] μV.s/min in OSA patients and 1.31 [0.67-1.94] μV.s/min in control (p=0.047). More apparent differences were found during NREM2, when the burst area in OSA (3.06 [1.46-5.52] μV.s/min) was much higher than that of the control (0.89 [0.79-1.65] μV.s/min, p=0.03). Conclusions OSA patients have higher SKNA activity than control patients, with the most pronounced differences observed during NREM2. Arousal at the end of apnea episodes is associated with large SKNA bursts. The overlaps of aSKNA and SKNA burst area between groups suggest that not all OSA patients have increased sympathetic tone.