Table 1.
HRV time-domain measures.
| Parameter | Unit | Description |
|---|---|---|
| SDNN | ms | Standard deviation of NN intervals |
| SDRR | ms | Standard deviation of RR intervals |
| SDANN | ms | Standard deviation of the average NN intervals for each 5 min segment of a 24 h HRV recording |
| SDNN index (SDNNI) | ms | Mean of the standard deviations of all the NN intervals for each 5 min segment of a 24 h HRV recording |
| pNN50 | % | Percentage of successive RR intervals that differ by more than 50 ms |
| HR Max − HR Min | bpm | Average difference between the highest and lowest heart rates during each respiratory cycle |
| RMSSD | ms | Root mean square of successive RR interval differences |
| HRV triangular index | Integral of the density of the RR interval histogram divided by its height | |
| TINN | ms | Baseline width of the RR interval histogram |
Interbeat interval, time interval between successive heartbeats; NN intervals, interbeat intervals from which artifacts have been removed; RR intervals, interbeat intervals between all successive heartbeats.