Arterial carbon dioxide tension during stay at high altitude
| Period at altitude h | Placebo kPa | Acetazolamide kPa | Theophylline kPa |
| 6 | 4.7±0.5 | 3.7±0.2** | 4.4±0.3 |
| 18 | 4.4±0.3 | 3.5±0.2** | 4.3±0.3 |
| 24 | 4.4±0.4 | 3.5±0.3** | 4.3±0.2 |
| 30 | 4.3±0.4 | 3.5±0.2** | 4.0±0.4 |
| 42 | 4.1±0.3 | 3.5±0.2** | 4.2±0.3 |
Data are presented as mean±sd
**: p<0.01 versus corresponding values in the placebo group and the theophylline group