Table 2 The list of features extracted from HRV
No. | Name of feature | Method of extraction | Explanation |
|---|---|---|---|
1 | AVNN | Time domain | AVNN is mean of all normal sinus to normal sinus of NN intervals. \(AVNN = \frac{1}{N}\mathop \sum \limits_{j = 1}^{N} RR_{j}\) where j is interval index and N is number of total intervals |
2 | SDNN | Time domain | SDNN is the standard deviation of NN intervals \(SDNN\;\text{ = }\;\sqrt {\frac{1}{{N\;\text{ - }\;1}}\;\sum\limits_{{j\;\text{ = }\;1}}^{N} {\left( {RR_{j} \text{ - }\;\overline{{\text{RR}}} } \right)^{2} } }\) |
3 | RMSSD | Time domain | Root Mean Square of the Successive Differences (RMSSD) \(RMSSD = \sqrt {\frac{1}{N - 1}\mathop \sum \limits_{j = 1}^{N - 1} \left( {RR_{j + 1} - RR_{j} } \right)^{2} }\) |
4 | SDSD | Time domain | The standard deviation of the successive difference between adjacent R-R intervals |
5 | NN50 | Time domain | The number of pairs of adjacent NN intervals differing by more than 50 ms \(Number of \left( {RR_{j + 1} - RR_{j} } \right) > 50\) |
6 | pNN50 | Time domain | Percentage of adjacent NN intervals differing by more than 50 ms \(pNN50 = \frac{NN50}{N - 1} \times 100\) |
7 | HRV Triangular Index | Geometrical | (The total number of RR intervals)/(the height of histogram of all RR intervals with 7.8125 ms bin) |
8 | SD1 | Poincare | \(SD1^{2} = \frac{1}{2}SDSD^{2}\) where SD1 = the standard deviation of perpendicular points to the line-of-identity |
9 | SD2 | Poincare | \(SD2^{2} = 2SDNN^{2} - \frac{1}{2}SDSD^{2}\) where SD2 = the standard deviation of parallel points along the line-of-identity |
10 | SD1SD2 Ratio | Poincare | \(SD1 SD2 Ratio = \frac{SD1}{SD2}\) |
11 | S | Poincare | \(S = \pi \times {\text{SD}}1 \times {\text{SD}}2\) |
12 | TP | Frequency domain | The total power (TP) of the HRV |
13 | VLF | Frequency domain | Very low frequency (VLF) is defined as the total power (TP) ranging from 0‒0.04 Hz |
14 | LF | Frequency domain | Low frequency is defined as the total power (TP) ranging from 0.04‒0.15 Hz |
15 | HF | Frequency domain | High frequency is defined as the total power (TP) ranging from 0.15‒0.4 Hz |
16 | LFHF Ratio | Frequency domain | The ratio of LF to HF indicates the sympathovagal balance. |
17 | LFnorm | Frequency domain | \(LFnorm = \frac{LF}{TP - VLF}\) |
18 | HFnorm | Frequency domain | \(HFnorm = \frac{HF}{TP - VLF}\) |