Detection of a common method for undermining the evaluation of full inflation in a clinical trial for asthma

<bold>Background:</bold> Forced spirometry measurements that start below full inflation produce erroneously low results and are the greatest cause of technique-related spirometry variability. The 2019 ATS/ERS spirometry standards specify the FIVC be a vigorously coached <bold>maximal</bold> maneuver so a valid comparison of the FIVC with the FVC can be made and submaximal inhalation error (SIE) can be objectively identified. <bold>Objective:</bold> We sought to evaluate the utility of using the FIV1/FIVC ratio to detect submaximal effort in the FIVC maneuver. <bold>Methods:</bold> We examined the FIV1/FIVC ratio in 5264 acceptable measurements from 1305 subjects in a clinical trial for asthma. Random samples of 20 measurements showing FIV1/FIVC < 0.80 and another 111 showing FIV1/FIVC >0.80 were carefully inspected for evidence of submaximal inspiratory effort during the FIVC. <bold>Results:</bold> 1026 measurements (19.5%) showed FIV1/FIVC < 0.80. 101 (91.0%) of the FIV1/FIVC < 0.80 cohort showed significantly greater inspiratory flow during the IC that preceded the FVC, indicating submaximal effort. <fig><object-id>erj;64/suppl_68/PA2335/F1</object-id><object-id>F1</object-id><object-id>F1</object-id><graphic></graphic></fig> <bold>Conclusions:</bold> 1. Submaximal effort during the FIVC collection is common in clinical trials. 2. Submaximal effort during the FIVC can subvert the ability of the FIVC to detect SIE, resulting in incorrect assignment of acceptability. 3. The FIV1/FIVC ratio < 0.80 appears to have good ability to identify submaximal effort during the FIVC. 4. Further work is required.