Table 2.
Time and Frequency Domain Features Extracted from the nSpO2 Recordings
| Feature | Description |
|---|---|
| Time domain | |
| Mt1–Mt4 | First, second, third, and fourth statistical moment of a time series |
| CTM | Central tendency measure to quantify variability |
| LZC | Lempel–Ziv complexity |
| SampEn | Sample entropy to measure irregularity |
| ODI3 | 3% oxygen desaturation index |
| Frequency domain | |
| MA | Full-spectrum amplitude maximum |
| mA | Full-spectrum amplitude minimum |
| Mf1–Mf4 | First, second, third, and fourth statistical moment of the full spectrum |
| MF | Median frequency of the full spectrum to estimate the distribution of the power of the spectrum |
| SpecEn | Spectral entropy to measure the full spectrum flatness |
| WD | Wootters’ distance to estimate the statistical distance of the full spectrum and a uniform distribution |
| MABOI* | Spectrum amplitude maximum from the band of interest* |
| mABOI | Spectrum amplitude minimum from the band of interest |
| Mf1BOI–Mf4BOI | First, second, third, and fourth statistical moment of the spectral band of interest |
Definition of abbreviation: nSpO2 = nocturnal oximetry.
*
The band of interest (BOI) was defined as the one showing the highest statistical differences among obstructive sleep apnea severity groups of the training set (21).