Measurement properties of the 6-min walk test in individuals with exercise-induced pulmonary arterial hypertension

Background: Exercise-induced pulmonary arterial hypertension (EIPAH) is associated with reduced peak exercise cardiac output (CO) and aerobic capacity (peak ). We investigated the validity of the encouraged 6-min walk test (6MWT) to identify exercise limitation and estimate aerobic capacity in subjects with EIPAH. Methods: Seventeen subjects with EIPAH (56 ± 14 years, 15 women) and 20 healthy controls (57 ± 13 years, 19 women) underwent two encouraged 6MWTs and a symptom-limited cardiopulmonary exercise test (CPET). To measure central haemodynamics, subjects with EIPAH performed the CPET with a pulmonary artery catheter in situ. Results: Compared with controls, subjects with EIPAH had reduced peak (1.2 ± 0.4 vs 1.7 ± 0.5, L/min, P \u3c 0.01), 6-min walk distance (6MWD) (575 ± 86 vs 669 ± 76 m, P \u3c 0.001) and 6-min walk work (6MWW) (39 ± 11 vs 45 ± 7 km.kg, P \u3c 0.01). In subjects with EIPAH, there was a moderate correlation between 6MWD and peak (r= 0.72, P \u3c 0.01) and a strong correlation between 6MWW and peak (r= 0.86, P \u3c 0.001). There were significant correlations between 6MWD and peak CO (r= 0.59, P \u3c 0.05), and between peak and peak CO (r= 0.55, P \u3c 0.05). Peak heart rate was similar in the CPET and 6MWT in subjects with EIPAH (133 ± 15 vs 133 ± 19 beats/min, P= 0.8). Conclusions: The encouraged 6MWT identifies reduced exercise capacity and provides a valid estimate of aerobic capacity in EIPAH