Test of 6-minute walking distance (6MWD)

In accordance with the American Thoracic Society guidelines (16), using a 30 meters long straight aisle with three chairs in the middle and the ends of the aisle (as a marked position or resting place for subjects), patients were asked to walk back and forth in order to record 6MWD after becoming familiar with the test environment and process. During the test procedure, the respiratory rate, heart rate, as well as blood pressure of the subjects were carefully monitored. The test was immediately terminated in the event that any symptoms of dizziness, along with anhelation and other symptoms were observed among the subjects.