TABLE 1.
CPET responses in healthy individuals and how they differ in patients with ILD.
| CPET measure | Healthy individuals | ILD |
| Functional capacity | ||
| V̇O2 max, ml⋅kg–1⋅min–1 | Typically >85% predicted | Reduced, often <85% predicted |
| Peak Power Output, W | Typically >85% predicted | Reduced, often <85% predicted |
| Anaerobic Threshold, %V̇O2 max | Typically >40% of predicted V̇O2 max | Reduced, often <40% predicted V̇O2 max |
| Ventilatory and pulmonary gas exchange | ||
| fB, breaths⋅min–1 | Typically <50 breaths⋅min–1 throughout exercise | Increased for a given power output or V̇E, can be >50 breaths⋅min–1 at peak exercise |
| VT, l | Typically increases to up 50–60% VC and plateaus | Typically increases to 50–60% VC and plateaus but is reduced for any given V̇E |
| VD/VT | Decreases relative to rest, typically <0.30 at peak exercise | Minimal change from rest and can increase during exercise to >0.30 |
| V̇E/V̇CO2 | Typically <32–34 at or near anaerobic threshold and <36 at peak | Elevated throughout exercise, typically >32–34 at anaerobic threshold and >36 at peak |
| V̇E/MVV, % | Typically <85% throughout exercise | Variable, but can be >85% at peak exercise |
| SaO2 | Preserved throughout exercise, similar to resting values | Variable, but typically decrease below resting values |
| Cardiovascular | ||
| HR, % predicted maximum | Typically >90% of age predicted values at peak exercise | Variable, but will often be below age predicted values at peak exercise |
| V̇O2/HR, ml⋅beat–1 | Typically >80% of predicted at peak exercise | Reduced, usually <80% of predicted at peak exercise |
| Symptoms | ||
| Dyspnea | Increases progressively during exercise, usually >5 at peak exercise | Increased for a given power output and V̇E, usually >5 at peak exercise |
| Leg discomfort | Increases progressively during exercise, usually >5 at peak exercise | Increased for a given power output, usually >5 at peak exercise |
| Invasive measures | ||
| EMGdi, % of maximum | Increases progressively during exercise up to ∼60–70% of maximum | Increased for a given power output and V̇E, similar at peak exercise |
| PaO2, mmHg | Relatively stable during exercise, typically <10 mmHg reduction from rest | Typically drops progressively during exercise, >10 mmHg reduction from rest |
| P(A-a)O2, mmHg | Increases progressively during exercise, <25 mmHg at peak exercise | Increases progressively during exercise, often >30 mmHg at peak exercise |
| mPAP– Q̇ slope, mmHg⋅min–1⋅l–1 | <3 mmHg⋅min–1⋅l–1 | Variable, but can be >3 mmHg⋅min–1⋅l–1 |
EMGdi, diaphragm electromyography; fB, breathing frequency; HR, heart rate; mPAP, mean pulmonary artery pressure; MVV, maximal voluntary ventilation; PaO2, partial pressure of arterial oxygen; P(A-a)O2, alveolar-arterial partial pressure of oxygen gradient; Q̇, cardiac output; SaO2, arterial oxygen saturation; V̇E, minute ventilation; V̇E/V̇CO2, ventilatory equivalent for carbon dioxide; VD, dead space volume; V̇O2, oxygen uptake; VT, tidal volume.