RESUMO
Recurrent intermittent hypoxia and subsequent increased sympathetic nervous system activity have been adopted as possible mechanisms underlying cardiac rhythm disturbances in obstructive sleep apnea syndrome [OSAS]. We analyzed nocturnal heart rate variability [HRV] in 80 patients [74 males, 6 females, mean age 47.01 +/- 10 yrs] with polysomnographically verified OSAS to assess the changes in nocturnal HRV indices, and to investigate the correlation between these changes to the severity of OSAS. The 80 patients were subdivided into 2 subgroups based upon the severity of OSAS; the first subgroup consisted of 27 patients with mild-to-moderate OSAS, while the second subgroup consisted of 53 patients with severe OSAS. For control group, 25 healthy individuals were included in the study. In time-domain analysis, the mean of the standard deviation of all RR intervals for all 5-min segments [SDNN index] was significantly different between patients with OSAS and control as well as among different stages of severity of OSAS [p = 0.02, and p = 0.046, respectively]. The standard deviation of all RR intervals [SDNN] was significantly different between patients with OSAS and control [p = 0.039]. HRV triangular index was significantly different among different stages of severity of OSAS [p = 0.023]. Frequency-domain variables namely total power, very low frequency [VLF] power, and low frequency [LF] power were significantly increased in patients with OSAS in comparison to control [p = 0.01, p = 0.024, and p = 0.018, respectively], as well as among OSAS subgroups [p = 0.01, p = 0.02, and p = 0.04, respectively]. Stepwise multiple logistic regression analysis revealed that AHI correlated positively with SDNN [r = 0.247, p = 0.036], SDNN index [r = 0.306, p = 0.009], total power [r = 0.323, p = 0.006], VLF power [r = 0.248, p = 0.037], LF power [r = 0.384, p = 0.001], and LF/HF ratio [r = 0.342, p = 0.004], but correlated negatively with RR interval [r = - 0.247, p = 0.036]. OSAS predisposes to clinically significant nocturnal impairment of the cardiac autonomic function as evidenced by nocturnal HRV analysis and this impairment was correlated to the severity of OSAS. Accordingly, HRV can serve as a simple, powerful screening tool for cases with suspected OSAS