Table 6. HRV characteristics in REM sleep according to OSA severity and MACCE.
| Controls n = 14 |
AHI <20 n = 33 |
AHI ≥20 n = 25 |
No MACCE n = 46 |
MACCE n = 12 |
|
|---|---|---|---|---|---|
| HR, 1/min | 58 (55–71) | 63 (53–76) | 64 (52–77) | 63 (52–75) | 67* (59‡-80) |
| NNI Min, ms | 850 (100) | 788 (117) | 783 (119) | 795 (118) | 752 (112) |
| NNI Max, ms | 1189 (145) | 1122 (203) | 1145 (234) | 1161 (217) | 1018 (173) ‡ |
| NNI Mean, ms | 1031 (117) | 950 (143) | 939 (143) | 960 (140) | 890 (140) * |
| NNI Dev, ms | 42 [25] | 42 [31] | 44 [33] | 45 [38] | 36 [30] |
| NNI RMSSD, ms | 21 [14] | 23 [15] | 28 [25] | 26 [25] | 18 [23] |
| NNI pNN50, % | 1.5 [5.7] | 1.8 [8.8] | 2.7 [4.6] | 2.7 [9.3] | 1.4 [4.1] ‡ |
| NNI SampEn | 1.1 (0.3) | 1.2 (0.3) | 1.1 (0.3) | 1.2 (0.3) | 1.0 (0.3) |
| NNIS Total, ms2 | 1522 [2381] | 1605 [2726] | 1714 [2842] | 1863 [3624] | 967 [1557] |
| NNIS ULF, ms2 | 126 [307] | 199 [300] | 128 [332] | 195 [312] | 86 [121] |
| NNIS VLF, ms2 | 933 [953] | 1001 [1838] | 1049 [1692] | 1172 [1838] | 525 [1144] |
| NNIS LF, ms2 | 417 [1080] | 295 [671] | 224 [461] | 276 [671] | 192 [225] * |
| NNIS HF, ms2 | 53 [140] | 85 [138] | 94 [176] | 96 [205] | 35 [86] ‡ |
| NNIS LF/HF | 10.3 [14.7] | 3.9 [4.2] * | 1.8 [3.0] † | 2.5 [3.3] † | 3.6 [3.9] |
| NNIS nLF, nu | 82 (17) | 70 (18) | 62 (18) † | 66 (17) † | 68 (22) |
| NNIS nHF, nu | 17 (16) | 27 (16) | 35 (17) † | 31 (16) † | 27 (19) |
| NNI Alpha 1 | 1.64 [0.46] | 1.18 (0.34) | 1.06 (0.37) * | 1.10 (0.32) * | 1.21 (0.48) |
Data are mean (standard deviation) or median [interquartile range] except for mean (range) for heart rate (HR). AHI = Apnea-hypopnea index, Alpha 1 = Fractal scaling exponent alpha 1, Dev = Standard deviation of NNI, HF = Power in the high frequency range (0.15–0.4 Hz), LF = Power in low frequency range 0.04–0.15 Hz), MACCE = Major adverse cardiovascular and cerebrovascular event, ms = millisecond, nHF = normalized HF ratio, nLF = normalized LF ratio, NNI = normal-to-normal interval (i.e. time between normal beats in the electrocardiogram), NNIS = NNI spectrum, pNN50 = Proportion of NNI >50 ms, RMSSD = Root mean square of the sum of successive differences (between adjacent normal-to-normal intervals, i.e. beat-to-beat variability), SampEn = Sample entropy, Total = Total power of the NNI spectrum (i.e. overall autonomic activity), ULF = Power in the ultra-low frequency range (≤0.003 Hz), VLF = Power in the very low frequency range (0.003–0.04 Hz).
*: p < 0.05 vs. controls
†: p < 0.01 vs. controls
‡: p<0.05 between patients with and without MACCE (prior to adjustment for age, body mass index, coronary artery disease and PAD history). One-way analysis of variance with Dunnett’s post hoc was used to test for differences between each patient group (with and without OSA/MACCE) vs. controls. Analysis of covariance was used to test for independent differences between patient groups (with vs. without OSA/MACCE). Non-normally distributed variables were log-transformed (natural logarithm) before the statistical analyses (non-transformed values with IQRs in square brackets shown in tables). Kruskal-Wallis’s test and Mann-Whitney’s U-test with Bonferroni’s adjustment for multiple comparisons were used to test for differences in variables that were skewed after log-transformation.