Abstract Background Submaximal inhalation error (SIE) is a common spirometry error caused by starting the forced exhalation before the patient reaches full inflation and we have found it to be the major cause of excessive variability of spirometry results in clinical trials. 2019 ATS/ERS spirometry standards specifies that efforts showing FIVC - FVC 0.100 or 5% of the FVC, whichever is larger, are unacceptable. The evaluation of full inflation is rendered impossible when the FIVC inhalation is incomplete, inhaled too slowly or manually terminated before full inflation is reached. This work explores the utility of using the largest FIVC in a measurement (FIVCmax) to evaluate full inflation in efforts in the same measurement that show comparable end of forced exhalation (EOFE) conditions with the FIVCmax effort. Objective We hypothesized that the largest FIVC in the measurement could be used to evaluate full inflation in other efforts in that measurement provided that the end of forced exhalation (EOFE) conditions (time of onset of expiratory plateau or total exhalation time within 10%) were comparable to those seen in the effort providing FIVCmax. Methods A total of 2525 efforts from 478 anonymized forced spirometry measurements sessions showing FVCs 2.0L, good SOFE, a rapidly inhaled FIVC suggesting full inflation at the start of the forced exhalation and comparable EOFE with the effort showing the largest FIVC (FIVCmax) in the measurement. From these, 1065 efforts showed acceptable SOFE, comparable EOFE and a FIVC/FVC between 0.90 and 1.05, suggesting the forced exhalation started from full inflation. The FIVCmax/FVC was evaluated. Results 156 efforts showing comparable EOFE showed a FIVCmax/FVC 1.05, suggesting SIE. FIVCmax/FVC in these 156 efforts was 1.094 (+ 0.067, max 1.63). The volume below full inflation by this assessment was 0.255L (+ 0.178L, max 1.18L). The difference between the reported FVC and the FVC in these 156 efforts was 0.208L (+ 0.167L, max 0.980L). The difference between the reported FEV1 and the FEV1 in these 156 efforts was 0.112L (+ 0.123L, max 0.831L). Conclusions Evidence suggestive of SIE was found in 156 measurements (14.6% of the efforts evaluated) that the FIVC/FVC using the FIVC from the effort suggested the forced exhalation started from full inflation. The largest FIVC in a measurement (FIVCmax) appears to have utility in evaluating full inflation at the start of the forced exhalation provided the EOFE conditions are comparable. Further work in this and other cohorts is required. This abstract is funded by: None
McCarthy et al. (Fri,) studied this question.