The pure effects of obstructive sleep apnea syndrome on cardiac autonomic functions: heart rate turbulence analysis.

OBJECTIVES To demonstrate the pure effect of obstructive sleep apnea syndrome (OSAS) on cardiac autonomic function (CAF) using heart rate turbulence (HRT) parameters. PATIENTS AND METHODS A total of 64 patients with OSAS and 30 age- and gender-matched healthy subjects were enrolled. All subjects had normal coronary arteries and were free from diabetes mellitus (DM) and hypertension (HT). The HRT parameters (TO, turbulence onset; TS, turbulence slope) were obtained from 24-h ambulatory electrocardiogram (ECG) recordings. HRT parameters were compared between groups, and the relationship between HRT and the apnea-hypopnea index (AHI) was examined. RESULTS No between-group differences were found in age or gender. Mean TO was significantly higher in the OSAS group than in healthy controls (0.89 ± 0.5, -0.08 ± 0.26; p < 0.001; respectively). The mean TS did not differ between the two groups (2.81 ± 3.06 versus 3.14 ± 2.33; p = 0.212). The AHI was positively correlated with TO (r = 0.845, p < 0.001). The multiple logistic regression analysis revealed that after adjustment for other variables, TO was a significant and independent predictor of AHI, OR 2.394 (95% CI: 1.596-3.591). CONCLUSIONS HRT (TO in particular) is correlated with AHI. Thus, impaired HRT may be an important factor underlying the occurrence of arrhythmia and sudden cardiac death in patients with OSAS.