Table 2.
Comparison of heart rate variability between the two spaceflights suggests role of brain functional network for faster adaptation to microgravity on second spaceflight.
| Unit, or frequency range (Hz) | Day time (awake) | Night time (asleep) | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| n | Mission 1 (day 18 after launch) | Mission 2 (day 21 after launch) | Paired t-test | n | Mission 1 (day 18 after launch) | Mission 2 (day 21 after launch) | Paired t-test | ||||||||
| Mean | SE | Mean | SE | t-value | p-value | Mean | SE | Mean | SE | t-value | p-value | ||||
| HR | bpm | 18 | 75.9 | 2.7 | 71.4 | 1.7 | − 1.415 | 0.1752 | 6 | 58.3 | 1.0 | 56.5 | 1.1 | − 3.277 | 0.0220 |
| NN | ms | 18 | 813.3 | 21.8 | 849.9 | 17.5 | 1.330 | 0.2012 | 6 | 1032.1 | 16.5 | 1065.3 | 19.7 | 3.100 | 0.0269 |
| β | 0.0001–0.01 | 17 | − 1.2065 | 0.0875 | − 0.9793 | 0.0465 | 1.799 | 0.0953 | 6 | − 0.7533 | 0.0732 | − 0.5400 | 0.0991 | 3.719 | 0.0137 |
| CVRR | ms | 18 | 8.08 | 0.30 | 7.40 | 0.44 | − 1.178 | 0.2549 | 6 | 5.67 | 0.30 | 5.79 | 0.28 | 0.521 | 0.6246 |
| r-MSSD | ms | 18 | 41.8 | 2.2 | 32.2 | 1.9 | − 4.697 | 0.0002 | 6 | 45.7 | 1.2 | 52.0 | 5.2 | 1.191 | 0.2869 |
| pNN50 | % | 18 | 17.7 | 1.4 | 9.2 | 1.4 | − 5.178 | 0.0001 | 6 | 20.4 | 1.0 | 15.4 | 3.4 | − 1.481 | 0.1986 |
| Length | ms | 18 | 300.2 | 12.1 | 263.6 | 8.9 | − 2.252 | 0.0378 | 6 | 302.1 | 18.6 | 305.2 | 11.9 | 0.151 | 0.8857 |
| Width | ms | 18 | 138.2 | 18.8 | 81.9 | 5.7 | − 2.965 | 0.0087 | 6 | 119.3 | 3.5 | 159.3 | 17.6 | 2.629 | 0.0466 |
| Len/Wid | – | 18 | 2.62 | 0.09 | 3.69 | 0.25 | 4.416 | 0.0004 | 6 | 2.55 | 0.09 | 2.42 | 0.31 | − 0.390 | 0.7129 |
| TF | 0.0001–0.50 | 17 | 8857.4 | 1400.4 | 5351.3 | 693.0 | − 1.871 | 0.0840 | 6 | 4238.2 | 460.1 | 4498.2 | 348.7 | 0.656 | 0.5408 |
| ULF | 0.0001–0.003 | 17 | 6227.8 | 1479.7 | 2672.4 | 583.3 | − 1.846 | 0.0878 | 6 | 1168.7 | 223.1 | 879.4 | 160.7 | − 1.961 | 0.1071 |
| VLF | 0.003–0.04 | 18 | 1566.0 | 112.6 | 1642.1 | 129.6 | 0.482 | 0.6360 | 6 | 1724.7 | 172.8 | 2083.1 | 284.0 | 1.327 | 0.2419 |
| LF | 0.04–0.15 | 18 | 920.2 | 61.1 | 872.4 | 48.5 | − 0.703 | 0.4919 | 6 | 999.7 | 142.6 | 978.2 | 108.8 | − 0.210 | 0.8422 |
| HF | 0.15–0.40 | 18 | 283.1 | 29.9 | 227.7 | 26.4 | − 2.108 | 0.0501 | 6 | 317.4 | 20.5 | 510.7 | 88.9 | 2.064 | 0.0939 |
| LF/HF | – | 18 | 3.63 | 0.20 | 4.85 | 0.29 | 4.266 | 0.0005 | 6 | 3.44 | 0.51 | 2.62 | 0.30 | − 1.236 | 0.2714 |
| LF-component | 0.05–0.15 | 18 | 783.2 | 50.9 | 747.0 | 42.3 | − 0.617 | 0.5451 | 6 | 819.3 | 113.1 | 809.2 | 104.1 | − 0.151 | 0.8859 |
| HF-component | 0.15–0.50 | 18 | 321.0 | 34.1 | 249.8 | 29.1 | − 2.479 | 0.0240 | 6 | 345.1 | 20.3 | 557.5 | 97.1 | 2.095 | 0.0903 |
| LF-band | 0.01–0.05 | 18 | 1035.6 | 86.7 | 1052.0 | 60.6 | 0.198 | 0.8453 | 6 | 1448.7 | 152.3 | 1531.0 | 187.8 | 0.402 | 0.7040 |
| MF1-band | 0.05–0.10 | 18 | 522.1 | 34.1 | 462.0 | 23.0 | − 1.623 | 0.1230 | 6 | 643.9 | 101.3 | 635.4 | 86.3 | − 0.183 | 0.8619 |
| MF2-band | 0.10–0.15 | 18 | 261.1 | 18.7 | 285.1 | 21.6 | 0.938 | 0.3612 | 6 | 175.4 | 15.5 | 173.8 | 26.7 | − 0.060 | 0.9548 |
| HF01-band | 0.15–0.20 | 18 | 111.1 | 10.9 | 95.4 | 9.0 | − 1.418 | 0.1743 | 6 | 102.5 | 10.2 | 138.3 | 17.5 | 2.256 | 0.0737 |
| HF02-band | 0.20–0.30 | 18 | 113.5 | 13.1 | 95.6 | 14.5 | − 1.415 | 0.1750 | 6 | 162.2 | 13.5 | 270.9 | 55.1 | 1.757 | 0.1392 |
| HF03-band | 0.30–0.40 | 18 | 58.5 | 6.9 | 36.7 | 5.2 | − 4.791 | 0.0002 | 6 | 52.7 | 2.1 | 101.5 | 20.8 | 2.338 | 0.0665 |
| HF04-band | 0.40–0.50 | 18 | 37.9 | 4.5 | 22.1 | 3.1 | − 5.531 | 0.0003 | 6 | 27.7 | 0.9 | 46.8 | 9.0 | 2.203 | 0.0788 |
Tests applied on hourly averages of 5-min intervals in order to eliminate or at least reduce serial correlation.
n number of hourly averages (of 5-min intervals), SE standard error.
P-values not adjusted for multiple testing; P < 0.05 after adjusting for mutiple testing highlighted in bold.