Physiological response to the six-minute walk test in pulmonary arterial hypertension

The 6-min walk test (6MWT) is commonly used to evaluate exercise capacity in patients with pulmonary arterial hypertension (PAH). However, little is known about the corresponding metabolic stress as measured by cardiopulmonary exercise testing. The present study, therefore, measured ventilatory variables and heart rate during the 6MWT and symptom-limited incremental maximal exercise testing in 20 patients with PAH. The distance walked in 6 min was 450+/-22 m (mean+/-se). During the 6MWT, ventilation, O2 consumption, CO2 production and heart rate increased during the first 3-4 min, and then remained stable. As compared with the maximum values measured during the cardiopulmonary exercise test, O2 consumption tended to be higher (14.2+/-0.6 versus 12.9+/-0.7 mL.kg-1.min-1), while maximum ventilation (46+/-3 versus 57+/-4 L.min-1), respiratory quotient (0.90+/-0.02 versus 1.15+/-0.02) and heart rate (119+/-4 versus 135+/-4 beats.min-1) remained lower. In conclusion, patients with pulmonary arterial hypertension exercise at higher aerobic capacity and lower metabolic stress during the 6MWT than during a cardiopulmonary exercise test.