Secondly, among children with moderate SDB, the pattern of HRV indices shift across sleep stages is similar to that of the no SDB group, except for the LF/HF ratio, which did not decrease until the SWS stage (it actually increased significantly in Stage 2 (1.46, SE?=?0.15) compared to wake (1.04, SE?=?0.18), P?=?0.05). Furthermore, in Fig.?1 we calculated and presented percentage differences in HRV indices contrasting SWS and REM in the moderate SDB and no SDB groups. It is evident from this figure that in both groups HF, RMSSD and SDNN decreased, and LF increased, from SWS to REM sleep. The SWS?CREM changes were more pronounced in moderate SDB children, and the between-group INK-128 differences for HF [?24% (SE?=?7) in moderate SDB versus ?10% (SE?=?1) in no SDB] and RMSSD [?27% (SE?=?5) versus ?12% (SE?=?2)] were significant (P?<?0.05). The LF/HF ratio increased by 298% and 410% from SW to REM, respectively, for the no SDB and moderate SDB group, although the between-group difference was not statistically significant (data not shown in Fig.?1). These data suggest a greater decrease in parasympathetic modulation from SWS to REM sleep in the moderate SDB group. Thirdly, in children with moderate SDB, the mean levels of stage-specific selleck inhibitor HRV indices are generally lower than those in the no SDB group, with the statistical comparisons shown in column ??P-2?? in Table?2. For instance, REM stages HF and LF are significantly lower in moderate SDB group compared to the no SDB group [mean (SE) of HF: 4.49 (0.43) versus 5.80 (0.05) ms2, respectively, P?<?0.05, mean (SE) of LF: 4.74 (0.36) versus 5.36 (0.05), respectively, P?=?0.05]. However, some of the statistical comparisons (column labeled ??P-2?? in Table?2) did not reach the traditional P????0.05 statistical significance level because of the small sample size, and a population-based young children sample was analyzed, hence a sample (n?=?7) of relatively less severe and shorter duration of SDB compared to clinical samples. The lower HRV values in the moderate SDB group imply that the impaired stage-specific 5?min HRV indices in this group are indicative of the autonomic balance BKM120 in vitro of less parasympathetic modulation. Lastly, the HRV indices shift across sleep stages among the mild SDB group are in a similar pattern and direction as that of the no SDB group and unexpectedly, as shown in Table?2, the mild SDB group had a statistically better HRV profile than the no SDB group in all HRV indices during REM sleep; but significant differences in HRV indices between the mild SDB and the no SDB group were sparse or absent in other stages. Specifically, the mild SDB group had higher REM stage HF, LF, SDNN, RMSSD values and lower LF/HF ratio and HR values than those of the REM stage values in the no SDB group, indicated by P-values in the ??P-2?? column.