Table 2.
Heart rate variability in the three positions
| Variables | Supine | Restraint | Prone |
|---|---|---|---|
| Time domain | |||
| Mean RR | 466.1 ± 167.4 | 426.8 ± 52.7 | 433.9 ± 113.8 |
| SDNN | 27.02 ± 20.56 | 24.07 ± 13.52 | 29.52 ± 28.43 |
| Mean HR | 147.2 ± 25.1 | 142.20 ± 17.9 | 140.45 ± 20.7 |
| RMSSD | 9.87 ± 9.4 | 9.81 ± 7.3 | 11.19 ± 7.7 |
| pNN50 | 0.62 ± 0.20 | 1.12 ± 4.4 | 1.45 ± 4.2 |
| Frequency domain | |||
| LF | 82.24 ± 6.7* | 80.49 ± 7.7 | 77.79 ± 9.4 |
| HF | 17.73 ± 6.7* | 19.44 ± 7.6 | 21.57 ± 9.6 |
| LF/HF | 5.68 ± 32 | 5.08 ± 2.7 | 4.49 ± 2.9 |
| Nonlinear | |||
| SD1 | 6.08 ± 3.8 | 6.98 ± 5 | 7.54 ± 5.1 |
| SD2 | 38.21 ± 28.9 | 33.41 ± 17.6 | 45.79 ± 52.9 |
| ApEn | 0.77 ± 0.28†* | 0.96 ± 0.22 | 0.86 ± 0.29 |
| SampEn | 0.63 ± 0.36†* | 0.88 ± 0.37 | 0.74 ± 0.36 |
RR - R-R interval; SDNN - mean standard deviation of all iRRs; HR - heart rate; RMSSD - root mean square of the sum of squared differences between iRRs; pNN50 - percentage of difference between adjacent normal R-R intervals greater than 50ms computed over the entire height of the histogram created by charting all R-R intervals; LF - low frequency; HF - high frequency; SD - standard deviation; ApEn - approximate entropy; SampEn: sample entropy;
*
p < 0.05 prone versus supine,
†
p < 0.05 supine versus restraint. Data are expressed as the mean and standard deviation.