Table 2. Heart rate and time-domain HRV parameters in the cool condition (TN-2°C), at thermoneutrality (TN) and in the warm condition (TN+2°C) during active sleep (AS) and quiet sleep (QS).
| TN-2°C | TN | TN+2°C | Thermal condition Effect | Sleep stage effect | ||||
| AS | QS | AS | QS | AS | QS | |||
| HR (bpm) | 148.0±10.2 | 144.3±12.0 | 148.8±8.0 | 144.0±10.2 | 152.2±9.4 | 150.5±10.4 | P = 0.0023 | P<0.001 |
| SDNN (ms) | 26.0±10.7 | 20.2±8.7 | 20.6±6.0 | 15.3±7.5 | 18.6±6.3 | 15.4±8.4 | P<0.001 | P = 0.0025 |
| r-MSSD (ms) | 11.8±5.8 | 12.7±7.0 | 10.7±5.6 | 9.4±5.2 | 8.6±4.5 | 7.3±4.0 | P = 0.005 | NS |
| pNN25 (%) | 7.2±9.5 | 8.7±10.3 | 6.7±9.3 | 3.9±5.7 | 3.4±5.4 | 2.3±3.5 | P = 0.0178 | NS |
Values are quoted as the mean ± standard deviation. NS: non-significant in an analysis of variance with repeated measures.