“…Overall, the PIF measurement details, including inhalation instructions, were provided or participants were referred to patient information leaflets in 35 of the 47 studies (74.5%; Supplementary Table 1 ). 7 , 12 , 21–23 , 26 , 32–34 , 48 , 51–66 , 68 , 70–72 , 74–76 , 78 , 79 Instructions for exhalation before the inhalation maneuver were provided in 14 (29.8%) studies and included “exhale gently to FRC,” 12 , 26 , 60 , 66 “complete exhalation,” 21 , 23 , 57 , 74 “exhale to RV,” 60 , 75 “deeply exhale,” 62 “breathe out completely,” 74 and “breathe out as far as comfortable”. 70 In one study, PIF was measured after patients were asked to inhale as they normally do.…”