Vital signs and sleep variables
| Sea level (130 m) | Moderate altitude (1300 m) | High altitude (3500 m) | High altitude %Δ from sea | p Value | |
|---|---|---|---|---|---|
| Mean daytime oxygen saturation (SpO2; %)* | 98 (98, 99) | NA | 90 (87, 91)† | −9.17 (2.1) | 0.004 |
| Mean overnight oxygen saturation (SpO2; %)* ‡ § | 97 (96, 98) | 94 (92, 97)† | 87(85, 88)† ¶ | −11.1 (2.9) | <0.0005 |
| Minimum oxygen saturation (SpO2; %)* ‡ | 92 (89, 93) | 84 (78, 94)* | 79 (76, 80)† ¶ | −14.4 (7.7) | <0.0005 |
| Number of oxygen desaturations per hour* ‡ | 0.2 (0, 1.2) | 4.9 (2, 12)* | 10.0 (4, 22)† ¶ | <0.0005 | |
| Number of central apnoeas per hour* ** | 0.2 (0, 1.2) | 1.2 (0.7, 3.2) | 3.5 (1.1, 5.7)† | 0.2 | |
| Periodic breathing (% TST)* ** | 0.0 (0, 0.3) | 0 (0, 1.2) | 0.2 (0, 1.15)† | 0.5 | |
| Daytime EtCO2 (mmHg) | 42.7 (40, 45) | NA | 36.0 (34, 38)† | −16 (5.1) | 0.004 |
| Daytime respiratory rate (breaths per min) | 21 (20, 24) | NA | 23 (22, 26)† | 8.2 (7.0) | 0.01 |
| Daytime heart rate (bpm) | 78 (72, 85) | NA | 97 (87, 109)† | 26.7 (16.3) | 0.004 |
*For the sleep and respiratory variables, transformation did not redress distributional problems, so data are presented as median and IQR (25th and 75th centiles), and were compared using Wilcoxon signed-rank test where there were no data at mid-altitude, or Friedman's ANOVA where data were available at all three altitudes, with posthoc testing using the Wilcoxon signed-rank test. p Values refer to significant change across all three altitudes.
†Significantly different from 130 m.
‡(η2) for mean overnight oxygen saturation=16.2, for minimum oxygen saturation=13.8 and for number of oxygen desaturations per hour=16.2.
§n=7 at moderate altitude.
¶Significantly different from 1300 m.
**n=3 at moderate altitude, n=8 at high altitude.
EtCO2, end-tidal pCO2; TST, total sleep time; NA, equipment failure.