Figure 1.

The arrow from top to bottom signifies the timeline over the last 40 years. The ovals linked to the timeline contain important studies on the implementation of the 6-minute-walk distance (6MWD) in respiratory medicine, especially in the field of pulmonary arterial hypertension (green), the concept of MID to address meaningful outcome measures for patients (blue), and published studies on minimal important difference of the 6MWD in patients with pulmonary arterial hypertension (purple). FDA = Food and Drug Administration; MCID = minimal clinically important difference; MID = minimal important difference; NYHA = New York Heart Association; PAH = pulmonary arterial hypertension.