Table 2.

Basic patterns of exercise limitation

Variable	Pattern of Limitation
	Cardiac	Ventilatory	Pulmonary Vascular/Interstitial Lung Disease
Ventilatory threshold	Present	Absent	Present
PaCO2 or PetCO2 at end-exercise	Decreased	Unchanged or increased	Decreased
PaO2 at end-exercise	Stable	Decreased	Decreased
Dead-space fraction	Decreased	Unchanged or decreased	Unchanged or increased
Metabolic acidosis at end-exercise	Present	Absent	Present
Reason for stopping test	Leg fatigue	Dyspnea	Dyspnea and/or leg fatigue

Definition of abbreviation: Pet_CO2 = end-tidal (partial) carbon dioxide pressure.

Note: This table summarizes the most common patterns seen in cardiac, ventilatory, and pulmonary vascular limitations to exercise.