Fig. 2.

Primary and secondary trial outcomes. A. The primary outcome of time/day (in minutes) with CO₂ concentration > 800 ppm. Secondary outcomes: B. Time/day (in minutes) with CO₂ concentration > 1000 ppm, C. daily peak CO₂ concentration, and D. Time/day (in minutes) with CO₂ concentration > 1400 ppm. Each point represents measurements from one 24 h period (N = 77, 82, 79 and 82 days in the baseline, sham, intervention and post-intervention period, respectively). Bars represent median and interquartile range. The intervention period was compared to the baseline, sham, and post-intervention period by Kruskal-Wallis test followed by Dunn's multiple comparisons test with multiplicity-adjusted P values as indicated.