Conclusions: Early declines in 6MWD (within the first 6 months) predict future clinical worsening of PAH with high specificity. #x0394;6MWD may still be part of a comprehensive assessment of a patient's clinical status. However, given the poor sensitivity, a decline in 6MWD should be used with other clinical tools to make an appropriate assessment of the progression of PAH.Respiration (Source: Respiration)