Ventilatory responses to euoxic isocapnia and hyperoxic hypercapnia in young healthy (Younger), older healthy (Older) and chronic obstructive pulmonary disease (COPD) subjects
| Younger | Older | COPD | ||||
| Saline | Vitamin C | Saline | Vitamin C | Saline | Vitamin C | |
| Euoxic isocapnia | ||||||
| PETCO2 mmHg | 38.6±3.0 | 38.8±3.0 | 36.7±3.0 | 36.9±2.9 | 35.3±5.2 | 35.1±4.2 |
| SaO2 % | 97±1 | 97±1 | 96±1 | 96±1 | 94±1 | 94±1 |
| VT/tI L·s−1 | 0.57±0.13* | 0.58±0.11* | 0.46±0.08 | 0.45±0.13 | 0.66±0.12* | 0.67±0.18* |
| tI/ttot % | 42±3 | 43±3 | 41±3 | 42±5 | 35±3* | 35±3* |
| VT L per breath | 1.1±0.3 | 1.0±0.2 | 0.9±0.4 | 1.0±0.6 | 1.0±0.3 | 0.9±0.2 |
| fR breaths per min | 15±4 | 16±3 | 14±4 | 14±4 | 16±5 | 16±3 |
| V′E L·min−1 | 15.0±3.3* | 15.3±3.2* | 11.5±2.2 | 12.0±3.4 | 14.8±4.6* | 14.5±4.4 |
| Hyperoxic hypercapnia | ||||||
| PETCO2 mmHg | 44.8±3.0 | 44.9±3.1 | 42.8±4.0 | 42.8±3.1 | 42.3±4.7 | 41.9±4.0 |
| SaO2 % | 99±1 | 99±1 | 99±1 | 99±1 | 99±1 | 99±1 |
| VT/tI L·s−1 | 1.05±0.27* | 1.01±0.27* | 0.75±0.23 | 0.74±0.19 | 0.97±0.26* | 1.04±0.26*# |
| tI/ttot % | 46±4* | 46±4* | 43±3 | 43±3 | 36±3* | 36±3* |
| VT L per breath | 1.9±0.4 | 1.8±0.4 | 1.6±0.7 | 1.6±0.7 | 1.3±0.3 | 1.3±0.3 |
| fR breaths per min | 17±5 | 17±5 | 14±3 | 14±4 | 17±4* | 19±4*# |
| V′E L·min−1 | 30.9±7.9* | 29.4±8.5* | 20.3±6.1 | 20.3±6.5 | 21.8±5.8 | 23.5±6.0# |
Data are presented as mean±sd. PETCO2: end-tidal carbon dioxide tension; SaO2: arterial oxygen saturation; VT: tidal volume; tI: inspiratory time; ttot: total respiratory time; fR: respiratory frequency; V′E: minute ventilation. *: p≤0.05 versus Older under the same condition; #: p≤0.05 versus saline, within group.