Table 2. Results of Sleep Studies in Per-Protocol Analysisa.
| Outcome | Mean (SD) | NOT vs placebo at 2048 m, mean difference (95% CI) | |||||
|---|---|---|---|---|---|---|---|
| First night at 490 m | 2048 m | ||||||
| With nocturnal placebo | With NOT | ||||||
| First night | Second night | First night | Second night | First night | Second night | ||
| Time in bed, min | 497 (29) | 486 (25) | 476 (60) | 484 (49) | 492 (25) | −2 (−23 to 20) | 16 (−5 to 37) |
| Nocturnal SpO2, % | 92 (2) | 86 (3)b | 87 (3)b | 96 (2)b | 96 (3)b | 10 (9 to 11)c | 9 (7 to 10)c |
| SpO2 <90%, % TIB | 12.5 (19.0) | 77.4 (27.7)b | 70.0 (30.5)b | 1.2 (2.8)b | 4.5 (20.6) | −76.4 (−87.5 to −65.3)c | −65.6 (−76.7 to −54.4)c |
| ODI, 1/h TIBd | 9.3 (11.7) | 40.0 (28.4)b | 34.1 (24.4)b | 4.1 (10.3) | 4.2 (11.2) | −35.9 (−44.4 to −27.5)c | −29.9 (−38.3 to −21.4)c |
| Total AHI, 1/h TIB | 19.7 (13.9) | 36.1 (27.9)b | 27.3 (22.6)b | 14.3 (16.9) | 10.4 (10.4)b | −21.7 (−29.3 to −14.3)c | −17.0 (−24.4 to −9.5)c |
| Obstructive AHI, 1/h TIB | 17.7 (13.1) | 9.3 (11.2)b | 7.6 (8.8)b | 9.0 (10.9)b | 5.5 (6.9)b | −0.3 (−3.6 to 3.0) | −2.1 (−5.4 to 1.2) |
| Central AHI, 1/h TIB | 2.1 (2.0) | 26.8 (23.9)b | 19.7 (19.5)b | 5.3 (11.4) | 4.8 (7.4) | −21.5 (−28.3 to −14.7)c | −14.9 (−21.7 to −8.1)c |
| Periodic breathing, % TIB | 0.2 (0.6) | 15.5 (16.6)b | 12.1 (13.1)b | 3.2 (8.5) | 3.1 (5.5) | −12.4 (−17.1 to −7.7)c | −9.0 (−13.7 to −4.2)c |
| TcCO2, kPa | 5.5 (0.7) | 4.8 (0.4)b | 4.8 (0.4)b | 4.9 (0.8)b | 5.3 (0.7) | 0.3 (−0.1 to 0.5) | 0.4 (0.1 to 0.8)c |
| Heart rate, bpm | 69 (10) | 76 (12)b | 74 (12)b | 68 (12) | 70 (10) | −7 (−10 to −5)c | −4 (−6 to −1)c |
| VES, 1/h TIB | 10.2 (28.3) | 14.5 (27.7) | 18.8 (44.5) | 9.7 (25.8) | 6.4 (13.7) | −4.8 (−14.9 to 8.4) | −12.3 (−22.6 to −2.1)c |
| SVES, 1/h TIB | 10.3 (18.2) | 25.4 (75.3) | 7.7 (14.7) | 15.6 (39.5) | 19.6 (44.9) | −9.8 (−27.2 to 7.6) | 12.3 (−5.3 to 29.9) |
| Total sleep time, min | 400 (61) | 349 (76)b | NA | 386 (71) | NA | 35 (9 to 61)c | NA |
| Total AHI, 1/h TST | 22.0 (15.8) | 44.0 (35.8)b | NA | 16.9 (19.7) | NA | −27.1 (−36.6 to −17.6)c | NA |
| Obstructive AHI, 1/h TST | 20.4 (15.2) | 11.6 (13.2)b | NA | 11.2 (12.5)b | NA | −0.5 (−4.7 to 3.7) | NA |
| Central AHI, 1/h TST | 1.6 (1.9) | 32.4 (32.3)b | NA | 5.7 (13.7) | NA | −26.7 (−35.2 to −18.1)c | NA |
| Nocturnal CTO, %e | 64 (6) | 59 (5)b | NA | 69 (6)b | NA | 9 (7 to 11)c | NA |
| cODI, 1/h TIBf | 0.8 (1.3) | 4.2 (5.6)b | NA | 0.6 (1.1) | NA | −3.6 (−5.8 to −1.5)c | NA |
| Sleep efficiency, % TIB | 81 (11) | 72 (15)b | NA | 78 (14) | NA | 7 (2 to 11)c | NA |
| WASO, min | 75.3 (49.3) | 116.8 (67.8)b | NA | 86.3 (62.0) | NA | −30.0 (−52.2 to −7.9)c | NA |
| Sleep latency, min | 21.2 (24.1) | 19.6 (16.0) | NA | 20.6 (15.2) | NA | 0.8 (−6.7 to 8.2) | NA |
| Arousal index, /h | 13.7 (8.8) | 18.7 (16.2)b | NA | 13.8 (9.7) | NA | −4.6 (−9.2 to 0)c | NA |
| NREM 1, % TST | 29.9 (15.0) | 33.0 (21.2) | NA | 25.5 (18.4) | NA | −7.4 (−14.0 to −0.8)c | NA |
| NREM 2, % TST | 40.6 (12.4) | 42.0 (16.8) | NA | 45.6 (13.2) | NA | 3.6 (−1.6 to 8.9) | NA |
| NREM 3 and 4, % TST | 14.1 (6.7) | 13.2 (10.1) | NA | 13.8 (8.9) | NA | 0.1 (−3.3 to 3.5) | NA |
| REM, % TST | 15.4 (4.3) | 11.9 (6.8)b | NA | 15.1 (6.8) | NA | 3.2 (0.7 to 5.7)c | NA |
Abbreviations: AHI, apnea-hypopnea index; bpm, beats per minute; CTO, cerebral tissue oxygenation; cODI, cerebral ODI; NA, not applicable; NOT, nocturnal oxygen therapy; NREM, non–rapid eye movement sleep; ODI, oxygen desaturation index; REM, rapid eye movement sleep; SpO2, mean nocturnal arterial oxygen saturation by pulse oximetry; SVES, supraventricular extra-beats; TcCO2, transcutaneous capnography; TIB, time in bed; TST, total sleep time; VES, ventricular extra-beats; WASO, wake after sleep onset.
In the first night at all locations, full polysomnography was performed; in the second night, respiratory sleep studies were performed. Thus, sleep variables are not available for second nights.
P < .05 altitude vs 490 m.
P < .05 NOT vs placebo.
ODI defined as greater than 3% dips in SpO2.
CTO measured by near-infrared spectroscopy.
cODI defined as greater than 3% dips in CTO.