Table 2. Heart-rate variability characteristics.
| Variable | APOE ε4-negative N = 87 | APOE ε4-positive N = 15 | F | p |
| Time Domain Measure | ||||
| Mean heart rate, beat/min | 77.9±16.0 | 80.9±16.6 | 0.454 | 0.502 |
| Standard deviation of normal interbeat intervals, ms | 70.3±32.4 | 72.1±27.8 | 0.027 | 0.871 |
| Root mean square successive difference between adjacent normal interbeat intervals, ms | 35.0±25.1 | 31.6±17.5 | 0.284 | 0.595 |
| Percentage of adjacent normal interbeat intervals that varied by greater than 50 ms, % | 12.7±18.0 | 8.0±8.8 | 0.991 | 0.322 |
| Frequency Domain Measure | ||||
| Very-low-frequency power, ln(ms2/Hz) | 7.94±0.88 | 7.88±0.93 | 0.079 | 0.779 |
| Low-frequency power, ln(ms2/Hz) | 6.41±1.07 | 6.21±0.94 | 0.491 | 0.485 |
| High-frequency power, ln(ms2/Hz) | 6.13±1.40 | 6.02±1.14 | 0.102 | 0.750 |
| Low-frequency/high-frequency power, ln(ms2/Hz) | 2.05±1.35 | 1.87±1.25 | 0.206 | 0.651 |
| Complexity Measure | ||||
| Multiscale entropy, sum of sample entropy from scale factor 1 to 20 | 28.9±5.2 | 24.6±5.5 | 9.429 | 0.003 |
Values are mean ± standard deviation unless otherwise noted.
Power spectral estimates were log transformed due to skewed distributions. F ratios from analyses of covariance, controlling for age and clinical parameters.