TABLE 1

Common cardiopulmonary exercise testing features in patients with interstitial lung disease (ILD) compared to other cardiopulmonary conditions

	ILD	COPD	CHF	PH	Deconditioning
Peak V˙_O₂	Reduced	Reduced	Reduced	Reduced	Reduced
Peak WR	Reduced	Reduced	Reduced	Reduced	Reduced
V˙_O₂ at VTh	Normal or low	Normal or low	Low (early VTh)	Low (early VTh)	Low (early VTh)
ΔV˙_O₂/ΔWR	Normal or low	Likely normal	Reduced ++	Reduced	Reduced
Maximal V˙_O₂/HR (oxygen pulse)	Likely normal	Likely normal	Reduced ++	Reduced	Reduced
Peak HR	Likely reduced	Likely reduced	Normal or low	Likely normal	Normal
ΔHR/ΔV˙_O₂	Variable	Variable	Elevated	Elevated	Elevated
BR	Reduced	Reduced	Normal	Normal	Normal
Peak f_R	Accelerated ++	Normal or accelerated	Normal or accelerated	Normal or accelerated	Normal or accelerated
Maximal V_T	Reduced	Likely reduced	Likely normal	Normal or reduced	Likely normal
V˙_E/V˙_CO₂ at VTh	Elevated ++	Variable	Elevated	Elevated ++	Normal or elevated
V˙_E/V˙_O₂ at VTh	Elevated ++	Variable	Elevated	Elevated ++	Normal or elevated
P_ETCO₂	Low	Variable, likely rising	Normal or low plateau	Low and decreasing	Normal
S_aO₂	Reduced ++	Reduced	Normal	Reduced ++	Normal
P_aO₂	Reduced ++	Reduced	Likely normal	Reduced ++	Normal
Peak P_(A-a)O₂	Widened ++	Widened	Likely normal	Widened ++	Normal
Peak V_D/V_T	High ++ sometimes not decreasing	High sometimes not decreasing	Normal or high	High ++ likely increasing	Likely normal
Other features	More severe hypoxaemia on walking than cycling	Frequent dynamic hyperinflation	Possible oscillatory breathing	Positive P_(a-ET)CO₂ during exercise	When severe, difficult to differentiate from cardiocirculatory limitation

Depending on the severity of underlying disease, pathologic features may not all be present in a given ILD patient. Conversely, associated comorbidities, obesity and/or negative inotropic drugs may result in mixed limitation pattern. ++ signs indicate potential higher variation from normal values. BR: breathing reserve; CHF: chronic heart failure; COPD: chronic obstructive pulmonary disease; f_R: respiratory frequency; HR: heart rate; P_(A-a)O₂: alveolar–arterial oxygen pressure difference; P_(a-ET)CO₂: arterial-end tidal carbon dioxide pressure difference; P_aO₂: arterial oxygen partial pressure; P_ETCO₂: end-tidal carbon dioxide partial pressure; PH: pulmonary hypertension; S_aO₂: oxygen saturation; V˙_CO₂: carbon dioxide output; V_D: dead space; V˙_E: total ventilation; V˙_O₂: oxygen uptake; V_T: tidal volume; VTh: first ventilatory threshold (anaerobic threshold); WR: work rate.