Table 2.
Twenty-four features from the PPG signal.
| Feature | Definition |
|---|---|
| 1. Systolic Peak | The amplitude of (‘x’) from PPG waveform |
| 2. Diastolic Peak | The amplitude of (‘y’) from PPG waveform |
| 3. Height of Notch | The amplitude of (‘z’) from PPG waveform |
| 4. Systolic Peak Time | The time interval from the foot of the waveform to the systolic peak (‘t1’) |
| 5. Diastolic Peak Time | The time interval from the foot of the waveform to the height of notch (‘t2’) |
| 6. Height of Notch Time | The time interval from the foot of the waveform to the diastolic peak (‘t3’) |
| 7. ∆T | The time interval from systolic peak time to diastolic peak time |
| 8. Pulse Interval | The distance between the beginning and the end of the PPG waveform (‘tpi’) |
| 9. Peak-to-Peak Interval | The distance between two consecutive systolic peaks (tpp) |
| 10. Pulse Width | The half-height of the systolic peak |
| 11. Inflection Point Area | The waveform is first split into two parts at the notch point. The area of the first part is A1 and the area of the second part is A2. The ratio of A1 and A2 is the inflection point area (‘A1/A2 ’) |
| 12. Augmentation Index | The ratio of diastolic and systolic peak amplitude (‘y/x’) |
| 13. Alternative Augmentation Index | The difference between systolic and diastolic peak amplitude divided by systolic peak amplitude (‘(x-y)/x’) |
| 14. Systolic Peak Output Curve | The ratio of systolic peak time to systolic peak amplitude (‘t1/x’) |
| 15. Diastolic Peak Downward Curve | The ratio of diastolic peak amplitude to the differences between pulse interval and height of notch time (‘y/ tpi-t3’) |
| 16. t1/tpp | The ratio of systolic peak time to the peak-to-peak interval of the PPG waveform |
| 17. t2/tpp | The ratio of notch time to the peak-to-peak interval of the PPG waveform |
| 18. t3/tpp | The ratio of diastolic peak time to the peak-to-peak interval of the PPG waveform |
| 19. ∆T/tpp | The ratio of ∆T to the peak-to-peak interval of the PPG waveform |
| 20. z/x | The ratio of the height of notch to the systolic peak amplitude |
| 21. t2/z | The ratio of the notch time to the height of notch |
| 22. t3/y | The ratio of the diastolic peak time to the diastolic peak amplitude |
| 23. x/(tpi-t1) | The ratio of systolic peak amplitude to the difference between pulse interval and systolic peak time |
| 24. z/(tpi-t2) | The ratio of the height of notch to the difference between pulse interval and notch time |