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

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Abstract
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, O2consumption, CO2production 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, O2consumption tended to be higher (14.2±0.6versus12.9±0.7 mL·kg−1·min−1), while maximum ventilation (46±3versus57±4 L·min−1), respiratory quotient (0.90±0.02versus1.15±0.02) and heart rate (119±4versus135±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.