The association between muscle strength and functional exercise capacity is well-known in pulmonary arterial hypertension (PAH) patients. Assessment of muscle strength and functional capacity are important for quality of life. However, in clinical practice, objective measurements of respiratory and peripheral muscle strength take time and require special equipment unlike the six-minute walk test (6MWT). A distance more than 380 m on therapy is associated with improved survival in PAH. The aim was to determine the discriminant validity utilization of the 6-minute walk distance (6MWD) for comparison of peripheral and respiratory muscle weakness in PAH patients.
In total, 24 PAH patients including 11 patients with >380 m on 6MWT and 13 with <380 m were included. Mean pulmonary arterial pressure (MPAP) was measured by heart catheterisation. Exercise capacity was assessed by the 6MWT. Respiratory muscle strength was assessed by maximal inspiratory and expiratory pressures (MIP-MEP). Peripheral muscle strength (knee extension, shoulder flexion, shoulder abduction, elbow flexion and grip strength) was measured with hand-held and handgrip dynamometer.
There were no significant differences in MPAP between two groups (p>0.05). The patients with <380 m on the 6MWD had significantly less MIP (p=0.002), shoulder flexion strength (p=0.016), shoulder abduction strength (p=0.019), elbow flexion strength (p=0.004), grip strength (p<0.001), and the knee strength (p=0.037) than the other group.
The results of this study suggest that the 6MWD can discriminate the patients with PAH with impaired peripheral and respiratory muscle strength.