Background: Exercise-induced pulmonary arterial hypertension (EIPAH) is associated with reduced peak exercise cardiac output (CO) and aerobic capacity (peak O(2) ). We investigated the validity of the encouraged six-minute walk test (6MWT) to identify exercise limitation and estimate aerobic capacity in subjects with EIPAH.

Methods: Seventeen subjects with EIPAH (56 ± 14 years, 15 females) and 20 healthy controls (57 ± 13 years, 19 females) 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 O(2) (1.2 ± 0.4 vs 1.7 ± 0.5, L/min, P < 0.01), six-minute walk distance (6MWD) (575 ± 86 vs 669 ± 76m, P < 0.001) and six-minute walk work (6MWW) (39 ± 11 vs 45 ± 7 km.kg, P < 0.01). In subjects with EIPAH, there was a moderate correlation between 6MWD and peak O(2) (r= 0.72, P < 0.01) and a strong correlation between 6MWW and peak O(2) (r= 0.86, P < 0.001). There were significant correlations between 6MWD and peak CO (r= 0.59, P < 0.05), and between peak O(2) and peak CO (r= 0.55, P < 0.05). Peak heart rate was similar in the CPET and 6MWT in subjects with EIPAH (133 ± 15 vs 133 ± 19 beats/minute, P= 0.8).

Conclusions: The encouraged 6MWT identifies reduced exercise capacity and provides a valid estimate of aerobic capacity in EIPAH.