Table 3. HRV characteristics in S2 sleep according to OSA severity and MACCE.
| Controls n = 15 |
AHI <20 n = 39 |
AHI ≥20 n = 32 |
No MACCE n = 51 |
MACCE n = 20 |
|
|---|---|---|---|---|---|
| HR, 1/min | 57 (52–65) | 61 (54–71) | 61 (52–72*) | 61 (53–71) | 63 (54–72) |
| NNI Min, ms | 925 (80) | 847 (149) | 833 (113) * | 844 (135) | 830 (131) |
| NNI Max, ms | 1164 (115) | 1116 (201) | 1146 (239) | 1139 (205) | 1104 (253) |
| NNI Mean, ms | 1047 (95) | 977 (173) | 980 (141) | 987 (154) | 956 (171) |
| NNI Dev, ms | 37 [18] | 40 [28] | 34 [39] | 40 [26] | 27 [35] |
| NNI RMSSD, ms | 23 [25] | 29 [23] | 26 [37] | 29 [24] | 26 [25] |
| NNI pNN50, % | 2.2 [19.0] | 5.2 [12.0] | 5.2 [14.6] | 6.2 [17.6] | 3.9 [10.4] |
| NNI SampEn | 1.5 (0.3) | 1.5 (0.3) | 1.4 (0.3) | 1.5 (0.3) | 1.4 (0.3) |
| NNIS Total, ms2 | 1209 [816] | 1306 [1789] | 981 [2988] | 1306 [2657] | 697 [2563] |
| NNIS ULF, ms2 | 29 [38] | 23 [48] | 40 [54] | 33 [42] | 39 [97] |
| NNIS VLF, ms2 | 305 [354] | 471 [1082] | 445 [1357] | 471 [1049] | 368 [1236] |
| NNIS LF, ms2 | 357 [672] | 293 [741] | 188 [645] | 387 [779] | 92 [414] |
| NNIS HF, ms2 | 100 [297] | 158 [303] | 140 [473] | 165 [462] | 87 [209] |
| NNIS LF/HF | 4.8 [7.7] | 2.5 [3.3] * | 1.9 [3.1] † | 2.4 [3.1] * | 1.5 [3.3] * |
| NNIS nLF, nu | 75 (19) | 60 (23) * | 58 (21) * | 60 (21) * | 57 (24) * |
| NNIS nHF, nu | 23 (17) | 38 (21) * | 37 (17) * | 37 (19) * | 38 (20) * |
| NNI Alpha 1 | 1.29 (0.33) | 1.05 (0.33) * | 1.00 (0.34) * | 1.04 (0.31) * | 1.00 (0.38) * |
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. 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).