Common cardiopulmonary exercise test features at peak exercise in interstitial lung disease (ILD) patients compared to healthy subjects
| Healthy subjects | ILD patients | Cause | |
| Peak V′O2 L·min−1 | ≥85% | <85% | Hypoxia, ventilatory limitation, deconditioning |
| Maximum work W | ≥85% | <85% | Hypoxia, ventilatory limitation, deconditioning |
| Heart rate beats·min−1 | ≥85% | <85% | Ventilator limitation to exercise, deconditioning |
| Oxygen saturation | Preserved | Reduced | Increased V/Q mismatch, diffusion limitation, shunt, reduced mixed venous oxygen concentration |
| Respiratory frequency breaths·min−1 | <50 | >50 | Respiratory muscle elastic loading, stimulation of peripheral mechanoreceptors |
| VT L | Increased | Reduced | Reduced lung compliance |
| V′E L·min−1 | 50–80% of MVV | >90% of MVV | Ventilator limitation to exercise |
| VD/VT | Reduced | Unchanged or increased | Increased V/Q mismatch, rapid, shallow breathing pattern |
| V′E/V′CO2 slope | 25–35 | >35 | Increased V/Q mismatch |
| Anaerobic threshold L·min−1 | >45% peak V′O2 | <45% peak V′O2 | Hypoxia, pulmonary hypertension |
Data are presented as n, unless otherwise stated. V′O2: oxygen uptake; VT: tidal volume; V′E: minute ventilation; VD: dead space volume; V′CO2: carbon dioxide production; MVV: maximal voluntary ventilation; V/Q: ventilation/perfusion.