Table 2. Key cardiopulmonary exercise test findings in relation to different patterns of abnormality and potential etiologies.

Pattern	Finding	Differential diagnosis
O2 delivery/utilization mismatch	⇓ peak ⩒O2 ⇓ lactate threshold	Chronic (systolic or diastolic) heart failure
	⇓ ∆⩒O2/∆WR	Pulmonary vascular disease
	⇑ ∆HR/∆⩒O2	Ischemic coronary disease
	⇓ ⩒O2/HR	Heart valve disease
	Flat or decreasing ⩒O2/HR trajectory	Severe sedentariness Peripheral muscle dysfunction
		Endocrine/metabolic disorder Anemia
Mechanical ventilatory impairment	⇓ peak ⩒O2 ⇑ peak ⩒E/MVV ⇑ peak VT/IC ⇑ peak EILV/TLC Constraint to VT expansion ⇑ peak f and f/VT Decrement in IC as ⩒E increases ⇑ dyspnea-WR and dyspnea-⩒E relationships	COPD Interstitial lung disease Other persistent airflow obstructive disorders: asthma with airway remodeling, cystic fibrosis, bronchiectasis Chest wall disease Respiratory muscle dysfunction
Impaired gas exchange/altered ventilatory control	⇓ peak ⩒O2 ⇑ ⩒E/⩒CO2 metrics Significant SpO2 decrement ⇑ dyspnea-WR but unaltered dyspnea-⩒E relationship	Chronic (systolic or diastolic) heart failure Pulmonary vascular disease Lung V/Q mismatch disorders: COPD, interstitial lung disease
Obesity	Preserved peak ⩒O2 (% of predicted)
	⇓ peak WR
	⇑ ⩒O2 and ⩒E for a given WR
	⇑ symptoms for a given WR
Dysfunctional breathing	Erratic breathing pattern: surges of ⇓ and ⇑ VT in a background of fast f
	Large fluctuations in ⩒E/⩒CO2
	⇑ ⩒E/⩒CO2 slope
	⇑ RER (usually at rest)

Peak: at peak exercise; ⩒O₂: oxygen uptake; WR: work rate; ⩒_E: minute ventilation; MVV: maximum voluntary ventilation; IC: inspiratory capacity; EILV: end-inspiratory lung volume; f: breathing frequency; ⩒CO₂: carbon dioxide output; V/Q: ventilation/perfusion; and RER: respiratory exchange ratio.