Background

The 2019 ATS/ERS spirometry standards strongly recommend the collection of the forced inspiratory vital capacity (FIVC)  immediately after the end of the forced exhalation to evaluate full inflation at the start of the FVC. A FIVC that is the greater of 5% or 0.150L (when FVC < 2L), larger than the FVC indicates the FVC started before the patient reached full inflation. 

Objective

Evaluate the utility of measuring FIVC immediately after each FVC in a clinical trial for adult DM.  

Methods

FVC and FIVC from 321 spirometry tests (160 sitting and 161 supine) from 50 patients in a clinical trial for DM were evaluated. 

Results

The FIVC was < 90% of the FVC in 52 (16.2%) tests and served no utility for evaluating full inflation. 190 (59.2%) tests started from full inflation.  The FIVC/FVC was >105% in 14 (4.4%) tests. The FIVC in these tests was 0.313L, +/- 0.166L larger than the FVC. Compared to other FVC measurements on these subjects, the FIVCs were comparable. 60 tests showed the FVC < 2L; 44 of these (73.3%) were shown to start from full inflation.  The FIVC was > 0.150L larger than the FVC in 3 (0.9%) tests. 

Conclusions

Comparing FIVC to FVC is a useful means to validate the FVC but when the FVC is used to indirectly assess respiratory muscle function and airway function is not being considered, the larger FIVC should not be used to label a test Unacceptable. Instead, the larger of FVC or FIVC should be used as 'VCmax' for each effort. Each forced exhalation followed by a forced inhalation will yield two opportunities to characterize the maximum vital capacity the patient can produce.