Table 2. Analysis of heart-rate variability in control, OSA−WMC, and OSA+WMC groups (selected indices with significant group differences).
| Control (n=31) | OSA−WMC (n=44) | OSA+WMC (n=60) | p‡ (ANOVA) | p§ (ANCOVA) | Subgroup analysis (no HTN or diabetes)∥ p§ (ANCOVA) | |
|---|---|---|---|---|---|---|
| Time-domain indices (ms) | ||||||
| SDNN | ||||||
| NREM sleep (N1–N2) | 43.4±23.5 | 60.7±52.5 | 85.6±104.8 | 0.038* | 0.203 | 0.130 |
| RMSSD | ||||||
| NREM sleep (N1–N2) | 37.6±29.9 | 61.3±68.1 | 105.2±134.3 | 0.005* | 0.177 | 0.117 |
| Frequency-domain indices | ||||||
| HF power (ms2) | ||||||
| NREM sleep (N1–N2) | 534.8±713.7 | 2,442.8±9,075.4 | 10,365.9±22,009.0 | 0.006*† | 0.090 | 0.181 |
| LFnu | ||||||
| Awake | 45.3±17.3 | 50.1±17.9 | 40.0±17.1 | 0.016† | 0.271 | 0.629 |
| NREM sleep (N1–N2) | 51.9±24.9 | 50.4±20.4 | 38.8±21.5 | 0.007*† | 0.065 | 0.157 |
| HFnu | ||||||
| Awake | 54.4±17.1 | 49.7±17.9 | 59.7±16.9 | 0.017† | 0.275 | 0.635 |
| NREM sleep (N1–N2) | 48.0±24.8 | 49.5±20.3 | 60.9±21.4 | 0.007*† | 0.064 | 0.160 |
| Nonlinear indices (ms) | ||||||
| Poincaré plot (SD1) | ||||||
| NREM sleep (N1–N2) | 26.6±21.2 | 43.4±48.3 | 74.5±95.2 | 0.005* | 0.177 | 0.117 |
| Poincaré ratio (SD12) | ||||||
| NREM sleep (N1–N2) | 0.52±0.32 | 0.57±0.25 | 0.72±0.30 | 0.003*† | 0.167 | 0.140 |
| REM sleep | 0.36±0.27 | 0.44±0.28 | 0.61±0.37 | 0.002*† | 0.305 | 0.479 |
| Entire sleep period | 0.44±0.18 | 0.51±0.16 | 0.60±0.19 | <0.001*† | 0.045 | 0.028 |
| Detrended fluctuation analysis 1 | ||||||
| NREM sleep (N1–N2) | 1.07±3.39 | 0.93±0.31 | 0.81±0.33 | 0.003* | 0.051 | 0.025 |
| REM sleep | 1.17±0.34 | 1.06±0.31 | 0.90±0.37 | 0.002* | 0.238 | 0.352 |
| Entire sleep period | 0.93±0.17 | 0.87±0.14 | 0.80±0.18 | 0.002* | 0.308 | 0.129 |
| ApEn | ||||||
| REM sleep | 0.90±0.22 | 0.90±0.22 | 0.78±0.27 | 0.018† | 0.234 | 0.776 |
Data are n (%) or mean±standard-deviation values.
*p<0.05 between control vs. OSA+WMC in post-hoc Turkey test, †p<0.05 between OSA−WMC vs. OSA+WMC in post-hoc Tukey test, ‡p-values calculated using ANOVA, §p-values calculated using ANCOVA with age controlled as a covariate, ∥subgroup analysis was performed in subjects who had neither hypertension nor diabetes. There were 24, 33, and 18 subjects in the control, OSA−WMC group, and OSA+WMC group, respectively.
ApEn: approximate entropy, ANCOVA: analysis of covariance, ANOVA: analysis of variance, HF: high frequency, LF: low frequency, NREM: non-rapid-eye-movement, nu: normalized unit, OSA+WMC: obstructive sleep apnea with white-matter changes, OSA−WMC: obstructive sleep apnea without white-matter changes, REM: rapid-eye-movement, RMSSD: root mean square of successive differences, SDNN: standard-deviation of normal to normal RR intervals.