Table 7. HRV characteristics in S3-4 sleep according to OSA severity and MACCE.
| Controls n = 7 |
AHI <20 n = 18 |
AHI ≥20 n = 13 |
No MACCE n = 22 |
MACCE n = 9 |
|
|---|---|---|---|---|---|
| HR, 1/min | 58 (54–64) | 62 (58–69) | 59 (53–66) | 61 (54–67) | 63 (58–69) |
| NNI Min, ms | 939 (81) | 874 (156) | 910 (126) | 897 (149) | 870 (132) |
| NNI Max, ms | 1113 (84) | 1042 (173) | 1138 (174) | 1103 (187) | 1031 (148) |
| NNI Mean, ms | 1028 (80) | 963 (155) | 1020 (127) | 999 (147) | 956 (142) |
| NNI Dev, ms | 24 [12] | 23 [19] | 25 [18] | 26 [18] | 19 [14] |
| NNI RMSSD, ms | 21 [17] | 23 [15] | 23 [20] | 25 [17] | 13 [13] † |
| NNI pNN50, % | 0.8 [9.0] | 1.7 [7.8] | 1.4 [12.9] | 6.0 [16.5] | 0.8 [1.2] |
| NNI SampEn | 1.7 (0.4) | 1.6 (0.3) | 1.7 (0.1) | 1.7 (0.2) | 1.6 (0.3) |
| NNIS Total, ms2 | 454 [377] | 380 [965] | 648 [998] | 461 [940] | 292 [544] |
| NNIS ULF, ms2 | 20 [26] | 8 [17] | 17 [27] | 13 [22] | 15 [20] |
| NNIS VLF, ms2 | 181 [198] | 112 [126] | 186 [416] | 148 [138] | 167 [231] |
| NNIS LF, ms2 | 229 [219] | 69 [292] | 134 [504] | 115 [487] | 58 [214] |
| NNIS HF, ms2 | 89 [241] | 112 [148] | 153 [234] | 162 [216] | 25 [134] † |
| NNIS LF/HF | 1.5 [5.4] | 0.95 [2.5] | 1.3 [1.4] | 0.83 [0.87] | 2.3 [1.9] * |
| NNIS nLF, nu | 63 (22) | 49 (25) | 55 (16) | 46 (21) | 65 (15) * |
| NNIS nHF, nu | 35 (21) | 48 (24) | 44 (16) | 52 (21) | 33 (14) * |
| NNI Alpha 1 | 1.07 [0.66] | 0.93 (0.36) | 0.95 (0.22) | 0.88 (0.31) | 1.10 (0.26) |
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 between patients with and without MACCE
†: p<0.01 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).